Determinants of exercise intolerance in patients with heart failure and reduced or preserved ejection fraction

Insights Into the Role of Obesity in Heart Failure With Preserved Ejection Fraction Pathophysiology and Management

Heart failure (HF) is a significant global health issue, categorized by left ventricular ejection fraction, being either reduced (HFrEF < 0.40) or preserved (HFpEF > 0.50), or in the middle of this range. Although the overall incidence of HF remains stable, HFpEF cases are increasing, representing about 50% of all HF cases. Outcomes for HFpEF are similar to those for HFrEF, leading to substantial health-care resource use. Despite extensive research over the past 2 decades, the prognosis and mortality rates for HFpEF remain high. A key feature of HFpEF is exercise intolerance, characterized by severe exertional dyspnea and fatigue, which significantly impacts quality of life. The underlying mechanisms of exercise intolerance are not fully understood due to the complex pathophysiology and multisystem involvement. Obesity is a common comorbidity in HFpEF, especially in North America, leading to worsening symptoms, hemodynamics, and mortality rates. Increased adiposity leads to inflammation, hypertension, dyslipidemia, and insulin resistance, and impairing cardiac, vascular, pulmonary, and skeletal muscle function. Therefore, managing obesity is crucial in treating HFpEF. In this review we explore the pathophysiologic mechanisms of HFpEF, emphasizing obesity's role, and we discuss current management strategies while identifying areas needing further research.

Mitochondrial Dysfunction in Cardiovascular Diseases

Mitochondrial dysfunction is increasingly recognized as a central contributor to the pathogenesis of cardiovascular diseases (CVDs), including heart failure, ischemic heart disease, hypertension, and cardiomyopathy. Mitochondria, known as the powerhouses of the cell, play a vital role in maintaining cardiac energy homeostasis, regulating reactive oxygen species (ROS) production and controlling cell death pathways. Dysregulated mitochondrial function results in impaired adenosine triphosphate (ATP) production, excessive ROS generation, and activation of apoptotic and necrotic pathways, collectively driving the progression of CVDs. This review provides a detailed examination of the molecular mechanisms underlying mitochondrial dysfunction in CVDs, including mutations in mitochondrial DNA (mtDNA), defects in oxidative phosphorylation (OXPHOS), and alterations in mitochondrial dynamics (fusion, fission, and mitophagy). Additionally, the role of mitochondrial dysfunction in specific cardiovascular conditions is explored, highlighting its impact on endothelial dysfunction, myocardial remodeling, and arrhythmias. Emerging therapeutic strategies targeting mitochondrial dysfunction, such as mitochondrial antioxidants, metabolic modulators, and gene therapy, are also discussed. By synthesizing recent advances in mitochondrial biology and cardiovascular research, this review aims to enhance understanding of the role of mitochondria in CVDs and identify potential therapeutic targets to improve cardiovascular outcomes.

Effects of concentric and eccentric exercise regimens on bioenergetic efficiency of lymphocytes in sedentary males

Eccentric exercise training (EET) increases physical performance while having lower metabolic demand than concentric exercise training (CET). Whether EET influences bioenergetic efficiency in peripheral blood mononuclear cells (PBMCs) remains unclear. This study investigates the effects of EET and CET on PBMC phenotypes and mitochondrial functions in blood. Thirty three sedentary healthy males were randomly assigned to either EET (n = 11) or CET (n = 11) that performed at progressively increased from 60% to 80% of maximal absolute workload for 30 min/day, 5 days/week for 6 weeks, or a control group (n = 11) that did not receive any exercise intervention. A graded exercise stress test (GXT) was performed before and after the intervention. PBMC phenotypes and mitochondrial respiratory capacity were analyzed using flowcytometry and high-resolution respirometry, respectively. In the same absolute workload, EET elicited lower heart rate and rating of perceived exertion than CET. However, EET as CET increased the VO2 level at the ventilatory threshold. Notably, both EET and CET increased central memory (CD45RO+/CD62+/CD3+) T cells and decreased effector memory T cells reexpressing CD45RA (CD45RA+/CD62-/CD3+). Moreover, the two exercise regimens diminished the loss of mitochondrial membrane potential (ΔΨm) caused by GXT, increased maximal/reserve O2 consumption rates (OCR), and bioenergetic health index in intact PBMCs and enhanced complex I-/II-related OCR in PBMCs with a substrate-rich environment. EET improves aerobic fitness with a lower cardiovascular response to exercise than CET. Moreover, EET as CET reduces senescent T-cell distribution in blood and improves PBMC bioenergetic efficiency by stabilizing ΔΨm and increasing capacity of oxidative phosphorylation.

Characterization of a novel ovine model of hypertensive heart failure with preserved ejection fraction

The lack of animal models that accurately represent heart failure with preserved ejection fraction (HFpEF) has been a major barrier to the mechanistic understanding and development of effective therapies for this prevalent and debilitating syndrome characterized by multisystem impairments. Herein, we describe the development and characterization of a novel large animal model of HFpEF in older, female sheep with chronic 2-kidney, 1-clip hypertension. At 6-wk post unilateral renal artery clipping, hypertensive HFpEF sheep had higher mean arterial pressure compared with similarly aged ewes without unilateral renal artery clipping (mean arterial pressure = 112.7 ± 15.9 vs. 76.0 ± 10.1 mmHg, P < 0.0001). The hypertensive HFpEF sheep were characterized by 1) echocardiographic evidence of diastolic dysfunction (lateral e' = 0.11 ± 0.02 vs. 0.14 ± 0.04 m/s, P = 0.011; lateral E/e' = 4.25 ± 0.77 vs. 3.63 ± 0.54, P = 0.028) and concentric left ventricular hypertrophy without overt systolic impairment, 2) elevated directly measured left ventricular end-diastolic pressure (13 ± 5 vs. 0.5 ± 1 mmHg, P = 2.1 × 10-6), and 3) normal directly measured cardiac output. Crucially, these hypertensive HFpEF sheep had impaired exercise capacity as demonstrated by their 1) attenuated cardiac output (P = 0.001), 2) augmented pulmonary capillary wedge pressure (P = 0.026), and 3) attenuated hindlimb blood flow (P = 3.4 × 10-4) responses, during graded treadmill exercise testing. In addition, exercise renal blood flow responses were also altered. Collectively, our data indicates that this novel ovine model of HFpEF may be a useful translational research tool because it exhibits similar and clinically relevant impairments as that of patients with HFpEF.NEW & NOTEWORTHY We show that older, female sheep with chronic 2-kidney, 1-clip hypertension have similar cardiac and noncardiac exercise hemodynamic abnormalities as patients with HFpEF. This clinically relevant, translatable, and novel large animal model of HFpEF may be useful for elucidating mechanisms and developing treatments for this increasingly common syndrome with few clinically impactful therapies.

Identifying the Mechanisms of a Peripherally Limited Exercise Phenotype in Patients With Heart Failure With Preserved Ejection Fraction

BACKGROUND

We identified peripherally limited patients using cardiopulmonary exercise testing and measured skeletal muscle oxygen transport and utilization during invasive single leg exercise testing to identify the mechanisms of the peripheral limitation.

METHODS

Forty-five patients with heart failure with preserved ejection fraction (70±7 years, 27 females) completed seated upright cardiopulmonary exercise testing and were defined as having a (1) peripheral limitation to exercise if cardiac output/oxygen consumption (VO2) was elevated (≥6) or 5 to 6 with a stroke volume reserve >50% (n=31) or (2) a central limitation to exercise if cardiac output/VO2 slope was ≤5 or 5 to 6 with stroke volume reserve <50% (n=14). Single leg knee extension exercise was used to quantify peak leg blood flow (Doppler ultrasound), arterial-to-venous oxygen content difference (femoral venous catheter), leg VO2, and muscle oxygen diffusive conductance. In a subset of participants (n=36), phosphocreatine recovery time was measured by magnetic resonance spectroscopy to determine skeletal muscle oxidative capacity.

RESULTS

Peak VO2 during cardiopulmonary exercise testing was not different between groups (central: 13.9±5.7 versus peripheral: 12.0±3.1 mL/min per kg; P=0.135); however, the peripheral group had a lower peak arterial-to-venous oxygen content difference (central: 13.5±2.0 versus peripheral: 11.1±1.6 mLO2/dL blood; P<0.001). During single leg knee extension, there was no difference in peak leg VO2 (P=0.306), but the peripherally limited group had greater blood flow/VO2 ratio (P=0.024), lower arterial-to-venous oxygen content difference (central: 12.3±2.5 versus peripheral: 10.3±2.2 mLO2/dL blood; P=0.013), and lower muscle oxygen diffusive conductance (P=0.021). A difference in magnetic resonance spectroscopy-derived phosphocreatine recovery time was not detected (P=0.199).

CONCLUSIONS

Peripherally limited patients with heart failure with preserved ejection fraction identified by cardiopulmonary exercise testing have impairments in oxygen transport and utilization at the level of the skeletal muscle quantified by invasive knee extension exercise testing, which includes an increased blood flow/V̇O2 ratio and poor muscle diffusive capacity.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04068844.

Elevated sympathetic-mediated vasoconstriction at rest but intact functional sympatholysis during exercise in heart failure with reduced ejection fraction

Patients with heart failure with reduced ejection fraction (HFrEF) have exaggerated sympathoexcitation and impaired peripheral vascular conductance. Evidence demonstrating consequent impaired functional sympatholysis is limited in HFrEF. This study aimed to determine the magnitude of reduced limb vascular conductance during sympathoexcitation and whether functional sympatholysis would abolish such reductions in HFrEF. Twenty patients with HFrEF and 22 age-matched controls performed the cold pressor test (CPT) [left foot 2-min in -0.5 (1)°C water] alone and with right handgrip exercise (EX + CPT). Right forearm vascular conductance (FVC), forearm blood flow (FBF), and mean arterial pressure (MAP) were measured. Patients with HFrEF had greater decreases in %ΔFVC and %ΔFBF during CPT (both P < 0.0001) but not EX + CPT (P = 0.449, P = 0.199) compared with controls, respectively. %ΔFVC and %ΔFBF decreased from CPT to EX + CPT in patients with HFrEF (both P < 0.0001) and controls (P = 0.018, P = 0.015), respectively. MAP increased during CPT and EX + CPT in both groups (all P < 0.0001). MAP was greater in controls than in patients with HFrEF during EX + CPT (P = 0.025) but not CPT (P = 0.209). In conclusion, acute sympathoexcitation caused exaggerated peripheral vasoconstriction and reduced peripheral blood flow in patients with HFrEF. Handgrip exercise abolished sympathoexcitatory-mediated peripheral vasoconstriction and normalized peripheral blood flow in patients with HFrEF. These novel data reveal intact functional sympatholysis in the upper limb and suggest that exercise-mediated, local control of blood flow is preserved when cardiac limitations that are cardinal to HFrEF are evaded with dynamic handgrip exercise.NEW & NOTEWORTHY Patients with HFrEF demonstrate impaired peripheral blood flow regulation, evidenced by heightened peripheral vasoconstriction that reduces limb blood flow in response to physiological sympathoexcitation (cold pressor test). Despite evidence of exaggerated sympathetic vasoconstriction, patients with HFrEF demonstrate a normal hyperemic response to moderate-intensity handgrip exercise. Most importantly, acute, simultaneous handgrip exercise restores normal limb vasomotor control and vascular conductance during acute sympathoexcitation (cold pressor test), suggesting intact functional sympatholysis in patients with HFrEF.

α-Adrenergic regulation of skeletal muscle blood flow during exercise in patients with heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) has been characterized by lower blood flow to exercising limbs and lower peak oxygen utilization (V ̇ O 2 ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ ), possibly associated with disease-related changes in sympathetic (α-adrenergic) signaling. Thus, in seven patients with HFpEF (70 ± 6 years, 3 female/4 male) and seven controls (CON) (66 ± 3 years, 3 female/4 male), we examined changes (%Δ) in leg blood flow (LBF, Doppler ultrasound) and legV ̇ O 2 ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ to intra-arterial infusion of phentolamine (PHEN, α-adrenergic antagonist) or phenylephrine (PE, α1-adrenergic agonist) at rest and during single-leg knee-extension exercise (0, 5 and 10 W). At rest, the PHEN-induced increase in LBF was not different between groups, but PE-induced reductions in LBF were lower in HFpEF (-16% ± 4% vs. -26% ± 5%, HFpEF vs. CON; P < 0.05). During exercise, the PHEN-induced increase in LBF was greater in HFpEF at 10 W (16% ± 8% vs. 8% ± 5%; P < 0.05). PHEN increased legV ̇ O 2 ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ in HFpEF (10% ± 3%, 11% ± 6%, 15% ± 7% at 0, 5 and 10 W; P < 0.05) but not in controls (-1% ± 9%, -4% ± 2%, -1% ± 5%; P = 0.24). The 'magnitude of sympatholysis' (PE-induced %Δ LBF at rest - PE-induced %Δ LBF during exercise) was lower in patients with HFpEF (-6% ± 4%, -6% ± 6%, -7% ± 5% vs. -13% ± 6%, -17% ± 5%, -20% ± 5% at 0, 5 and 10 W; P < 0.05) and was positively related to LBF, leg oxygen delivery, legV ̇ O 2 ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ , and the PHEN-induced increase in LBF (P < 0.05). Together, these data indicate that excessive α-adrenergic vasoconstriction restrains blood flow and limitsV ̇ O 2 ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ of the exercising leg in patients with HFpEF, and is related to impaired functional sympatholysis in this patient group. KEY POINTS: Sympathetic (α-adrenergic)-mediated vasoconstriction is exaggerated during exercise in patients with heart failure with preserved ejection fraction (HFpEF), which may contribute to limitations of blood flow, oxygen delivery and oxygen utilization in the exercising muscle. The ability to adequately attenuate α1-adrenergic vasoconstriction (i.e. functional sympatholysis) within the vasculature of the exercising muscle is impaired in patients with HFpEF. These observations extend our current understanding of HFpEF pathophysiology by implicating excessive α-adrenergic restraint and impaired functional sympatholysis as important contributors to disease-related impairments in exercising muscle blood flow and oxygen utilization in these patients.

Association of chronotropic incompetence with reduced cardiorespiratory fitness in older adults with HIV

OBJECTIVE

Understanding the physiological drivers of reduced cardiorespiratory fitness in people with HIV (PWH) will inform strategies to optimize healthspan. Chronotropic incompetence is common in heart failure and associated with low cardiorespiratory fitness yet is understudied in PWH. The objective was to determine the prevalence of chronotropic incompetence and its relationship with cardiorespiratory fitness.

DESIGN

Participants were PWH at least 50 years of age with no prior history of heart failure or coronary heart disease who were enrolled in a randomized exercise trial. Baseline cardiopulmonary exercise testing (CPET) was used to measure cardiorespiratory fitness as peak oxygen consumption (VO2peak) and calculate the chronotropic index from heart rate values. Chronotropic incompetence was defined as an index less than 80%.

RESULTS

The 74 participants were on average 61 years old, 80% Black or African American, and 93% men. Chronotropic incompetence was present in 31.1%. VO2peak was significantly lower among participants with chronotropic incompetence compared with participants without chronotropic incompetence [mean (SD) ml/min/kg: 20.9 (5.1) vs. 25.0 (4.5), P = 0.001]. Linear regression showed that chronotropic incompetence and age were independent predictors of VO2peak, but smoking and comorbidity were not. The chronotropic index correlated with VO2peak (r = 0.48, P < 0.001).

CONCLUSION

Among older PWH without heart failure or coronary heart disease, chronotropic incompetence was present in approximately one-third of individuals and was associated with clinically relevant impaired cardiorespiratory fitness. Investigation of chronotropic incompetence in large cohorts which includes PWH and heart failure may contribute to strategies that promote healthy aging with HIV infection and offer a preclinical window for intervention.

Leucine Supplementation Prevents the Development of Skeletal Muscle Dysfunction in a Rat Model of HFpEF

Heart failure with preserved ejection fraction (HFpEF) is associated with exercise intolerance due to alterations in the skeletal muscle (SKM). Leucine supplementation is known to alter the anabolic/catabolic balance and to improve mitochondrial function. Thus, we investigated the effect of leucine supplementation in both a primary and a secondary prevention approach on SKM function and factors modulating muscle function in an established HFpEF rat model. Female ZSF1 obese rats were randomized to an untreated, a primary prevention, and a secondary prevention group. For primary prevention, leucine supplementation was started before the onset of HFpEF (8 weeks of age) and for secondary prevention, leucine supplementation was started after the onset of HFpEF (20 weeks of age). SKM function was assessed at an age of 32 weeks, and SKM tissue was collected for the assessment of mitochondrial function and histological and molecular analyses. Leucine supplementation prevented the development of SKM dysfunction whereas it could not reverse it. In the primary prevention group, mitochondrial function improved and higher expressions of mitofilin, Mfn-2, Fis1, and miCK were evident in SKM. The expression of UCP3 was reduced whereas the mitochondrial content and markers for catabolism (MuRF1, MAFBx), muscle cross-sectional area, and SKM mass did not change. Our data show that leucine supplementation prevented the development of skeletal muscle dysfunction in a rat model of HFpEF, which may be mediated by improving mitochondrial function through modulating energy transfer.

Testosterone and the heart: friend or foe?

Cardiovascular disease (CVD) is the leading cause of death in women aged 65 years and older. Sex hormones have been implicated as having a critical role in the evolution of CVD, with the focus mainly on estrogens in women. Available data also indicate that low testosterone blood levels may be detrimental to cardiovascular function in women. At blood concentrations considered normal for premenopausal women, testosterone has favorable effects on blood vessel function (relaxation and contraction), much of which is determined by the endothelial cells that line the inside of blood vessels. Testosterone enhances endothelium-dependent and independent brachial artery vasodilation and has an acute systolic blood pressure-lowering effect in postmenopausal women. Advantageous effects of testosterone in animal models have been seen for myocardial function and cardiac electrical signaling. Human data are mainly limited to observational and mechanistic studies, which mostly demonstrate beneficial effects of testosterone on cardiovascular health. Few studies of testosterone use in women, with cardiovascular endpoints as primary outcomes, have been published.

Circulating Growth Differentiation Factors 11 and 8, Their Antagonists Follistatin and Follistatin-Like-3, and Risk of Heart Failure in Elders

BACKGROUND

Heterochronic parabiosis has identified growth differentiation factor (GDF)-11 as a potential means of cardiac rejuvenation, but findings have been inconsistent. A major barrier has been lack of assay specificity for GDF-11 and its homolog GDF-8.

METHODS

We tested the hypothesis that GDF-11 and GDF-8, and their major antagonists follistatin and follistatin-like (FSTL)-3, are associated with incident heart failure (HF) and its subtypes in elders. Based on validation experiments, we used liquid chromatography-tandem mass spectrometry to measure total serum GDF-11 and GDF-8, along with follistatin and FSTL-3 by immunoassay, in 2 longitudinal cohorts of older adults.

RESULTS

In 2 599 participants (age 75.2 ± 4.3) followed for 10.8 ± 5.6 years, 721 HF events occurred. After adjustment, neither GDF-11 (HR per doubling: 0.93 [0.67, 1.30]) nor GDF-8 (HR: 1.02 per doubling [0.83, 1.27]) was associated with incident HF or its subtypes. Positive associations with HF were detected for follistatin (HR: 1.15 [1.00, 1.32]) and FLST-3 (HR: 1.38 [1.03, 1.85]), and with HF with preserved ejection fraction for FSTL-3 (HR: 1.77 [1.03, 3.02]). (All HRs per doubling of biomarker.) FSTL-3 associations with HF appeared stronger at higher follistatin levels and vice versa, and also for men, Blacks, and lower kidney function.

CONCLUSIONS

Among older adults, serum follistatin and FSTL-3, but not GDF-11 or GDF-8, were associated with incident HF. These findings do not support the concept that low serum levels of total GDF-11 or GDF-8 contribute to HF late in life, but do implicate transforming growth factor-β superfamily pathways as potential therapeutic targets.

Role of exercise therapy and cardiac rehabilitation in heart failure

Heart failure (HF) is a common cause of hospitalization and death, and the hallmark symptoms of HF, including dyspnea, fatigue, and exercise intolerance, contribute to poor patient quality of life (QoL). Cardiac rehabilitation (CR) is a comprehensive disease management program incorporating exercise training, cardiovascular risk factor management, and psychosocial support. CR has been demonstrated to effectively improve patient functional status and QoL among patients with HF. However, CR participation among patients with HF is poor. This review details the mechanisms of dyspnea and exercise intolerance among patients with HF, the physiologic and clinical improvements observed with CR, and the key components of a CR program for patients with HF. Furthermore, unmet needs and future strategies to improve patient participation and engagement in CR for HF are reviewed.

The inorganic NItrate and eXercise performance in Heart Failure (iNIX-HF) phase II clinical trial: Rationale and study design

Background

Heart failure (HF) is a debilitating and often fatal disease that affects millions of people worldwide. Diminished nitric oxide synthesis, signaling, and bioavailability are believed to contribute to poor skeletal muscle function and aerobic capacity. The aim of this clinical trial (iNIX-HF) is to determine the acute and longer-term effectiveness of inorganic nitrate supplementation on exercise performance in patients with HF with reduced ejection fraction (HFrEF).

Methods

This clinical trial is a double-blind, placebo-controlled, randomized, parallel-arm design study in which patients with HFrEF (n = 75) are randomized to receive 10 mmol potassium nitrate (KNO3) or a placebo capsule daily for 6 wk. Primary outcome measures are muscle power determined by isokinetic dynamometry and peak aerobic capacity (VO2peak) determined during an incremental treadmill exercise test. Endpoints include the acute effects of a single dose of KNO3 and longer-term effects of 6 wk of KNO3. The study is adequately powered to detect expected increases in these outcomes at P < 0.05 with 1-β>0.80.

Discussion

The iNIX-HF phase II clinical trial will evaluate the effectiveness of inorganic nitrate supplements as a new treatment to ameliorate poor exercise capacity in HFrEF. This study also will provide critical preliminary data for a future 'pivotal', phase III, multi-center trial of the effectiveness of nitrate supplements not only for improving exercise performance, but also for improving symptoms and decreasing other major cardiovascular endpoints. The potential public health impact of identifying a new, relatively inexpensive, safe, and effective treatment that improves overall exercise performance in patients with HFrEF is significant.

Neural control of the circulation during exercise in heart failure with reduced and preserved ejection fraction

Patients with heart failure with reduced (HFrEF) and preserved ejection fraction (HFpEF) exhibit severe exercise intolerance that may be due, in part, to inappropriate cardiovascular and hemodynamic adjustments to exercise. Several neural mechanisms and locally released vasoactive substances work in concert through complex interactions to ensure proper adjustments to meet the metabolic demands of the contracting skeletal muscle. Specifically, accumulating evidence suggests that disease-related alterations in neural mechanisms (e.g., central command, exercise pressor reflex, arterial baroreflex, and cardiopulmonary baroreflex) contribute to heightened sympathetic activation and impaired ability to attenuate sympathetic vasoconstrictor responsiveness that may contribute to reduced skeletal muscle blood flow and severe exercise intolerance in patients with HFrEF. In contrast, little is known regarding these important aspects of physiology in patients with HFpEF, though emerging data reveal heightened sympathetic activation and attenuated skeletal muscle blood flow during exercise in this patient population that may be attributable to dysregulated neural control of the circulation. The overall goal of this review is to provide a brief overview of the current understanding of disease-related alterations in the integrative neural cardiovascular responses to exercise in both HFrEF and HFpEF phenotypes, with a focus on sympathetic nervous system regulation during exercise.

Exercise Rehabilitation for People With End-Stage Kidney Disease: Who Will Fill the Gaps?

Exercise rehabilitation is a well established therapy for reducing morbidity and mortality and improving quality of life and function across chronic conditions. People with dialysis-dependent kidney failure have a high burden of comorbidity and symptoms, commonly characterised as fatigue, dyspnoea, and the inability to complete daily activities. Despite more than 30 years of exercise research in people with kidney disease and its established benefit in other chronic diseases, exercise programs are rare in kidney care and are not incorporated into routine management at any stage. In this review, we describe the mechanisms contributing to exercise intolerance in those with end-stage kidney disease and outline the role of exercise rehabilitation in addressing the major challenges to kidney care: cardiovascular disease, symptom burden, and physical frailty. We also draw on existing models of exercise rehabilitation from other chronic conditions to inform the way forward and challenge the status quo of exercise rehabilitation in both practice and research.

Energetics of collective movement in vertebrates

The collective directional movement of animals occurs over both short distances and longer migrations, and is a critical aspect of feeding, reproduction and the ecology of many species. Despite the implications of collective motion for lifetime fitness, we know remarkably little about its energetics. It is commonly thought that collective animal motion saves energy: moving alone against fluid flow is expected to be more energetically expensive than moving in a group. Energetic conservation resulting from collective movement is most often inferred from kinematic metrics or from computational models. However, the direct measurement of total metabolic energy savings during collective motion compared with solitary movement over a range of speeds has yet to be documented. In particular, longer duration and higher speed collective motion must involve both aerobic and non-aerobic (high-energy phosphate stores and substrate-level phosphorylation) metabolic energy contributions, and yet no study to date has quantified both types of metabolic contribution in comparison to locomotion by solitary individuals. There are multiple challenging questions regarding the energetics of collective motion in aquatic, aerial and terrestrial environments that remain to be answered. We focus on aquatic locomotion as a model system to demonstrate that understanding the energetics and total cost of collective movement requires the integration of biomechanics, fluid dynamics and bioenergetics to unveil the hydrodynamic and physiological phenomena involved and their underlying mechanisms.

Evidence of impaired functional sympatholysis in patients with heart failure with preserved ejection fraction

Exercising muscle blood flow is reduced in patients with heart failure with a preserved ejection fraction (HFpEF), which may be related to disease-related changes in the ability to overcome sympathetic nervous system (SNS)-mediated vasoconstriction during exercise, (i.e., "functional sympatholysis"). Thus, in 12 patients with HFpEF (69 ± 7 yr) and 11 healthy controls (Con, 69 ± 4 yr), we examined forearm blood flow (FBF), mean arterial pressure (MAP), and forearm vascular conductance (FVC) during rhythmic handgrip exercise (HG) at 30% of maximum voluntary contraction with or without lower-body negative pressure (LBNP, -20 mmHg) to increase SNS activity and elicit peripheral vasoconstriction. SNS-mediated vasoconstrictor responses were determined as LBNP-induced changes (%Δ) in FVC, and the "magnitude of sympatholysis" was calculated as the difference between responses at rest and during exercise. At rest, the LBNP-induced change in FVC was significantly lesser in HFpEF compared with Con (HFpEF: -9.5 ± 5.5 vs. Con: -21.0 ± 8.0%; P < 0.01). During exercise, LBNP-induced %ΔFVC was significantly attenuated in Con compared with rest (HG: -5.8 ± 6.0%; P < 0.05) but not in HFpEF (HG: -9.9 ± 2.5%; P = 0.88). Thus, the magnitude of sympatholysis was lesser in HFpEF compared with Con (HFpEF: 0.4 ± 4.7 vs. Con: -15.2 ± 11.8%; P < 0.01). These data demonstrate a diminished ability to attenuate SNS-mediated vasoconstriction in HFpEF and provide new evidence suggesting impaired functional sympatholysis in this patient group.NEW & NOTEWORTHY Data from the current study suggest that functional sympatholysis, or the ability to adequately attenuate sympathetic nervous system (SNS)-mediated vasoconstriction during exercise, is impaired in patients with heart failure with preserved ejection fraction (HFpEF). These observations extend the current understanding of HFpEF pathophysiology by implicating inadequate functional sympatholysis as an important contributor to reduced exercising muscle blood flow in this patient group.

Revisiting cardiac output estimated noninvasively from oxygen uptake during exercise: an exploratory hypothesis-generating replication study

Stringer et al. [J Appl Physiol (1985) 82: 908-912, 1997] developed a method from invasive data to estimate cardiac output during incremental exercise testing based on Fick's principle. The authors proposed that the arterio-mixed venous oxygen content difference increases linearly with percentage of maximal O2 consumption. We hypothesized an S-shaped pattern in the published data and calculated the inflection point of this curve and of the standard resting oxygen dissociation curve. Using a partial F test, we compared the linear model with a third-order polynomial model, which showed a better fit to the data [F(2,101) = 9.5, P < 0.001]. This finding was reproduced in a dataset published by Åstrand et al. in 1964 [F(2, 122) = 10.6, P < 0.001]. The inflection point of the curve coincided with the lactate acidosis threshold [first ventilatory threshold (VT1)] as measured by Stringer et al. (VT1 at 50% and inflection point at 56% [95% CI, 52.9 to 60.7] of maximal O2 consumption). The inflection point of the standard resting oxygen dissociation curve was calculated at a partial pressure of 21.5 mmHg and a saturation of 36%, matching the "critical capillary Po2" concept of Stringer et al. (21.2 mmHg). We conclude that the arterio-mixed venous oxygen content difference increases in an S-shaped manner with percentage of maximal oxygen consumption and that the inflection point of this curve may correspond to VT1 and that of the in vivo oxygen dissociation curve. Further research is needed to confirm these findings and improve the method.NEW & NOTEWORTHY In 1997, Stringer, Hansen, and Wasserman developed a method for estimating cardiac output during incremental exercise testing. They observed that the arterio-mixed venous oxygen content difference increases linearly with the percentage of maximal O2 consumption. This increase may be better modelled by an S-shaped function, the inflection point of which may be related to the first ventilatory threshold and the inflection point of the oxygen dissociation curve. This finding may help to improve the method.

Effects of Whey Protein Isolate on Body Composition, Muscle Mass, and Strength of Chronic Heart Failure Patients: A Randomized Clinical Trial

Heart failure (HF) is associated with a reduction of skeletal muscle mass. Whey protein isolate (WPI) has been beneficial in increasing muscle mass and strength, in addition to improving body composition. The goal of this research was to evaluate the effect of WPI on the body composition, muscle mass, and strength of chronic HF patients. For this purpose, twenty-five patients of both genders with predominantly NYHA I functional class and a median age of 65.5 (60.5-71.0) years were used to conduct a randomized, single-blind, placebo-controlled clinical trial and received 30 g per day of WPI for 12 weeks. Anthropometric measurements, body composition analysis, and biochemical exams were performed at the beginning and end of the study. An increase in skeletal muscle mass was observed in the intervention group after 12 weeks. A reduction in waist circumference, body fat percentage, and an increase in skeletal muscle index was observed when compared to the placebo group. No significant effect on muscle strength was observed after 12 weeks of intervention. These data demonstrate that WPI consumption contributed to the increase of skeletal muscle mass, strength, and reduction of body fat in HF patients.

Obesity, Preserved Ejection Fraction Heart Failure, and Left Ventricular Remodeling

Owing to the overwhelming obesity epidemic, preserved ejection fraction heart failure commonly ensues in patients with severe obesity and the obese phenotype of preserved ejection fraction heart failure is now commonplace in clinical practice. Severe obesity and preserved ejection fraction heart failure share congruent cardiovascular, immune, and renal derangements that make it difficult to ascertain whether the obese phenotype of preserved ejection fraction heart failure is the convergence of two highly prevalent conditions or severe obesity enables the development and progression of the syndrome of preserved ejection fraction heart failure. Nevertheless, the obese phenotype of preserved ejection fraction heart failure provides a unique opportunity to assess whether sustained and sizeable loss of excess body weight via metabolic bariatric surgery reverses the concentric left ventricular remodeling that patients with preserved ejection fraction heart failure commonly display.

Supervised Exercise Training for Chronic Heart Failure With Preserved Ejection Fraction: A Scientific Statement From the American Heart Association and American College of Cardiology

Heart failure with preserved ejection fraction (HFpEF) is one of the most common forms of heart failure; its prevalence is increasing, and outcomes are worsening. Affected patients often experience severe exertional dyspnea and debilitating fatigue, as well as poor quality of life, frequent hospitalizations, and a high mortality rate. Until recently, most pharmacological intervention trials for HFpEF yielded neutral primary outcomes. In contrast, trials of exercise-based interventions have consistently demonstrated large, significant, clinically meaningful improvements in symptoms, objectively determined exercise capacity, and usually quality of life. This success may be attributed, at least in part, to the pleiotropic effects of exercise, which may favorably affect the full range of abnormalities-peripheral vascular, skeletal muscle, and cardiovascular-that contribute to exercise intolerance in HFpEF. Accordingly, this scientific statement critically examines the currently available literature on the effects of exercise-based therapies for chronic stable HFpEF, potential mechanisms for improvement of exercise capacity and symptoms, and how these data compare with exercise therapy for other cardiovascular conditions. Specifically, data reviewed herein demonstrate a comparable or larger magnitude of improvement in exercise capacity from supervised exercise training in patients with chronic HFpEF compared with those with heart failure with reduced ejection fraction, although Medicare reimbursement is available only for the latter group. Finally, critical gaps in implementation of exercise-based therapies for patients with HFpEF, including exercise setting, training modalities, combinations with other strategies such as diet and medications, long-term adherence, incorporation of innovative and more accessible delivery methods, and management of recently hospitalized patients are highlighted to provide guidance for future research.

Supervised Exercise Training for Chronic Heart Failure With Preserved Ejection Fraction: A Scientific Statement From the American Heart Association and American College of Cardiology

Heart failure with preserved ejection fraction (HFpEF) is one of the most common forms of heart failure; its prevalence is increasing, and outcomes are worsening. Affected patients often experience severe exertional dyspnea and debilitating fatigue, as well as poor quality of life, frequent hospitalizations, and a high mortality rate. Until recently, most pharmacological intervention trials for HFpEF yielded neutral primary outcomes. In contrast, trials of exercise-based interventions have consistently demonstrated large, significant, clinically meaningful improvements in symptoms, objectively determined exercise capacity, and usually quality of life. This success may be attributed, at least in part, to the pleiotropic effects of exercise, which may favorably affect the full range of abnormalities-peripheral vascular, skeletal muscle, and cardiovascular-that contribute to exercise intolerance in HFpEF. Accordingly, this scientific statement critically examines the currently available literature on the effects of exercise-based therapies for chronic stable HFpEF, potential mechanisms for improvement of exercise capacity and symptoms, and how these data compare with exercise therapy for other cardiovascular conditions. Specifically, data reviewed herein demonstrate a comparable or larger magnitude of improvement in exercise capacity from supervised exercise training in patients with chronic HFpEF compared with those with heart failure with reduced ejection fraction, although Medicare reimbursement is available only for the latter group. Finally, critical gaps in implementation of exercise-based therapies for patients with HFpEF, including exercise setting, training modalities, combinations with other strategies such as diet and medications, long-term adherence, incorporation of innovative and more accessible delivery methods, and management of recently hospitalized patients are highlighted to provide guidance for future research.

Factors contributing to exercise tolerance in patients with coronary artery disease undergoing percutaneous coronary intervention

BACKGROUND

Exercise tolerance plays a vital role in the process of cardiac rehabilitation in patients undergoing percutaneous coronary intervention (PCI). The study sought to determine the characteristics, risks and correlates of post-PCI exercise tolerance in patients with coronary artery disease (CAD).

METHODS

We analyzed clinical data of 299 CAD patients undergoing elective PCI and completing cardiopulmonary exercise testing (CPET). According to the Weber classification, post-PCI exercise tolerance was evaluated by peak oxygen uptake (VO₂ peak). We assessed the impact of 34 predefined clinical features, cardiac functional parameters, and blood biochemistry data on exercise tolerance by univariate analysis and logistics regression analysis.

RESULTS

Of 299 patients, 74.92% were men and average age was 60.90 ± 10.68 years. VO₂ peak in the entire population was 17.54 ± 3.38 ml/kg/min, and 24.41% (n = 73) were less than 16 ml/kg/min, who were considered to have exercise intolerance. Multivariate logistics regression results showed that sex, diabetes mellitus, number of stents, left atrial diameter (LAD), end-diastolic volume (EDV), and hemoglobin influenced the peak oxygen uptake of CAD patients undergoing elective PCI. (All p < 0.05).

CONCLUSIONS

Nearly one quarter of CAD patients have exercise intolerance in the early post-PCI period. Female, diabetes mellitus, number of stents, LAD, EDV might negatively impacted post-PCI exercise tolerance, which need further warrant by large scale cohort study.

Impact of the Insoluble Gas Concentration on Measured Stroke Volume at Rest and Submaximal Exercise Using the Innocor Device

INTRODUCTION

The Innocor® device uses an insoluble gas (SF 6 ) to estimate lung volume and the rate of disappearance of a soluble gas (nitrous oxide) to measure pulmonary blood flow (PBF), which approximates cardiac output assuming no shunt. We sought to identify error in the measurement of the insoluble gas in an effort to reduce variation in Innocor® measurement.

METHODS

We enrolled 28 participants from the Dallas Heart Study (mean age, 63 yr; 57% men; 43% White). Stroke volume was measured at rest and at submaximal (20 and 40 W) exercise using both echocardiography (Philips iE33) and the Innocor® device. We defined a priori peak and equilibrium SF 6 measurement errors as greater or less than 20% of the mean observed value. Three Innocor measurements were obtained at rest ( n = 27) for a total of 81 measurements. Of these, 22% had SF 6 measurements that fell outside of the a priori range.

RESULTS

Resting Innocor® stroke volume measures with peak SF 6 measured above a priori range (>0.12%) was associated with larger stroke volumes compared with stroke volume measures without peak SF 6 error (101.4 [26.8] vs 64.9 [8.7] mL; P = 0.006) and overestimated stroke volume when compared with stroke volume by echo (101.4 [26.8] vs 59.9 [16.3] mL; P = 0.017). A similar pattern was observed at submaximal exercise. In contrast, there was no consistent association between variation in equilibrium SF 6 concentrations and measured stroke volume.

CONCLUSIONS

Variability in peak SF 6 concentration is common while using the Innocor® device and results in overestimated stroke volume. These findings have implications for research protocols using this device.

Myocardial Infarction with Nonobstructive Coronary Arteries

Myocardial infarction with nonobstructive coronary arteries (MINOCA) is an important subtype of myocardial infarction (MI) that occurs in approximately 6-8% of patients with spontaneous MI who are referred for coronary angiography. MINOCA disproportionately affects women, but men are also affected. Pathogenesis is more variable than in MI with obstructive coronary artery disease (MI-CAD). Dominant mechanisms include atherosclerosis, thrombosis, and coronary artery spasm. Management of MINOCA varies based on the underlying mechanism of infarction. Therefore, systematic approaches to diagnosis are recommended. The combination of invasive coronary angiography, multivessel intracoronary imaging, provocative testing for coronary spasm, and cardiac magnetic resonance imaging provides the greatest diagnostic yield. Current clinical practice guidelines for the secondary prevention of MI are based largely on data from patients with MI-CAD. Thus, optimal medications after MINOCA are uncertain. Clinical trials focused on the treatment of patients with MINOCA are urgently needed to define optimal care.

Exercise Mode in Heart Failure: A Systematic Review and Meta-Analysis

BACKGROUND

Optimising exercise prescription in heart failure (HF) with a preserved (HFpEF) or reduced (HFrEF) ejection fraction is clinically important. As such, the aim of this meta-analysis was to compare traditional moderate intensity training (MIT) against combined aerobic and resistance training (CT) and high-intensity interval training (HIIT) for improving aerobic capacity (VO₂), as well as other clinically relevant parameters.

METHODS

A comprehensive systematic search was performed to identify randomised controlled trials published between 1990 and May 2021. Research trials reporting the effects of MIT against CT or HIIT on peak VO₂ in HFpEF or HFrEF were considered. Left-ventricular ejection fraction (LVEF) and various markers of diastolic function were also analysed.

RESULTS

Seventeen studies were included in the final analysis, 4 of which compared MIT against CT and 13 compared MIT against HIIT. There were no significant differences between MIT and CT for peak VO₂ (weighted mean difference [WMD]: 0.521 ml min^-1 kg^-1, [95% CI] =  - 0.7 to 1.8, P_fixed = 0.412) or LVEF (WMD: - 1.129%, [95% CI] =  - 3.8 to 1.5, P_fixed = 0.408). However, HIIT was significantly more effective than MIT at improving peak VO₂ (WMD: 1.62 ml min^-1 kg^-1, [95% CI] = 0.6-2.6, P_random = 0.002) and LVEF (WMD: 3.24%, [95% CI] = 1.7-4.8, P_random < 0.001) in HF patients. When dichotomized by HF phenotype, HIIT remained significantly more effective than MIT in all analyses except for peak VO₂ in HFpEF.

CONCLUSIONS

HIIT is significantly more effective than MIT for improving peak VO₂ and LVEF in HF patients. With the exception of peak VO₂ in HFpEF, these findings remain consistent in both phenotypes. Separately, there is no difference in peak VO₂ and LVEF change following MIT or CT, suggesting that the addition of resistance exercise does not inhibit aerobic adaptations in HF.

Sympathetic and hemodynamic responses to exercise in heart failure with preserved ejection fraction

Excessive sympathetic activity during exercise causes heightened peripheral vasoconstriction, which can reduce oxygen delivery to active muscles, resulting in exercise intolerance. Although both patients suffering from heart failure with preserved and reduced ejection fraction (HFpEF and HFrEF, respectively) exhibit reduced exercise capacity, accumulating evidence suggests that the underlying pathophysiology may be different between these two conditions. Unlike HFrEF, which is characterized by cardiac dysfunction with lower peak oxygen uptake, exercise intolerance in HFpEF appears to be predominantly attributed to peripheral limitations involving inadequate vasoconstriction rather than cardiac limitations. However, the relationship between systemic hemodynamics and the sympathetic neural response during exercise in HFpEF is less clear. This mini review summarizes the current knowledge on the sympathetic (i.e., muscle sympathetic nerve activity, plasma norepinephrine concentration) and hemodynamic (i.e., blood pressure, limb blood flow) responses to dynamic and static exercise in HFpEF compared to HFrEF, as well as non-HF controls. We also discuss the potential of a relationship between sympathetic over-activation and vasoconstriction leading to exercise intolerance in HFpEF. The limited body of literature indicates that higher peripheral vascular resistance, perhaps secondary to excessive sympathetically mediated vasoconstrictor discharge compared to non-HF and HFrEF, drives exercise in HFpEF. Excessive vasoconstriction also may primarily account for over elevations in blood pressure and concomitant limitations in skeletal muscle blood flow during dynamic exercise, resulting in exercise intolerance. Conversely, during static exercise, HFpEF exhibit relatively normal sympathetic neural reactivity compared to non-HF, suggesting that other mechanisms beyond sympathetic vasoconstriction dictate exercise intolerance in HFpEF.

Single-leg cycling to maintain and improve function in healthy and clinical populations

Exercise with reduced muscle mass facilitates greater muscle-specific adaptations than training with larger muscle mass. The smaller active muscle mass can demand a greater portion of cardiac output which allows muscle(s) to perform greater work and subsequently elicit robust physiological adaptations that improve health and fitness. One reduced active muscle mass exercise that can promote greater positive physiological adaptations is single-leg cycling (SLC). Specifically, SLC confines the cycling exercise to a smaller muscle mass resulting in greater limb specific blood flow (i.e., blood flow is no longer "shared" by both legs) which allows the individual to exercise at a greater limb specific intensity or for a longer duration. Numerous reports describing the use of SLC have established cardiovascular and/or metabolic benefits of this exercise modality for healthy adults, athletes, and individuals living with chronic diseases. SLC has served as a valuable research tool for understanding central and peripheral factors to phenomena such as oxygen uptake and exercise tolerance (i.e., V̇O_2peak and V̇O₂ slow component). Together, these examples highlight the breadth of applications of SLC to promote, maintain, and study health. Accordingly, the purpose of this review was to describe: 1) acute physiological responses to SLC, 2) long-term adaptations to SLC in populations ranging from endurance athletes to middle aged adults, to individuals living with chronic disease (COPD, heart failure, organ transplant), and 3) various methods utilized to safely perform SLC. A discussion is also included on clinical application and exercise prescription of SLC for the maintenance and/or improvement of health.

Current Approach to the Diagnosis of Sarcopenia in Heart Failure: A Narrative Review on the Role of Clinical and Imaging Assessments

Sarcopenia has been established as a predictor of poor outcomes in various clinical settings. It is particularly prevalent in heart failure, a clinical syndrome that poses significant challenges to health care worldwide. Despite this, sarcopenia remains overlooked and undertreated in cardiology practice. Understanding the currently proposed diagnostic process is paramount for the early detection and treatment of sarcopenia to mitigate downstream adverse health outcomes.

Sarcopenic Obesity Is Associated With Reduced Cardiorespiratory Fitness Compared With Nonsarcopenic Obesity in Patients With Heart Failure With Reduced Ejection Fraction

BACKGROUND

Sarcopenia impairs cardiorespiratory fitness (CRF) in patients with heart failure with reduced ejection fraction (HFrEF). Obesity has also been shown to impair CRF; however, the effects of sarcopenia on CRF in patients with obesity and HFrEF are unknown. The aim of this analysis was to examine differences in CRF between patients with sarcopenic obesity (SO) and non-SO (NSO) with HFrEF. We also assessed associations between skeletal muscle mass index (SMMI) and CRF.

METHODS

Forty patients with HFrEF and obesity underwent cardiopulmonary exercise testing to collect measures of CRF including peak oxygen consumption (VO2), circulatory power, oxygen uptake efficiency slope, O2 pulse, and exercise time. Body composition was performed in all patients using bioelectrical impedance analysis to quantify fat mass index and divide patients into SO and NSO based on SMMI cutoffs. Results are presented as mean (SD) or median [interquartile range] as appropriate.

RESULTS

Nearly half (43% [n=17]) of patients had SO. Patients with SO had a lower SMMI than those with NSO, and no differences in fat mass index were observed between groups. Those with SO achieved a lower absolute peak VO2 (NSO, 1.62±0.53 L·min-1 versus SO, 1.27±0.44 L·min-1, P=0.035), oxygen uptake efficiency slope (NSO, 1.92±0.59 versus SO, 1.54±0.48, P=0.036), and exercise time (NSO, 549±198 seconds versus SO, 413±140 seconds, P=0.021) compared to those with NSO. On multivariate analysis, SMMI remained a significant predictor of absolute peak VO2 when adjusted for age, sex, adiposity, and HF severity.

CONCLUSIONS

In patients with HFrEF and obesity, sarcopenia, defined as low SMMI, is associated with a clinically significant reduction in CRF, independent of adiposity.

Empagliflozin Preserves Skeletal Muscle Function in a HFpEF Rat Model

Besides structural alterations in the myocardium, heart failure with preserved ejection fraction (HFpEF) is also associated with molecular and physiological alterations of the peripheral skeletal muscles (SKM) contributing to exercise intolerance often seen in HFpEF patients. Recently, the use of Sodium-Glucose-Transporter 2 inhibitors (SGLT2i) in clinical studies provided evidence for a significant reduction in the combined risk of cardiovascular death or hospitalization for HFpEF. The present study aimed to further elucidate the impact of Empagliflozin (Empa) on: (1) SKM function and metabolism and (2) mitochondrial function in an established HFpEF rat model. At the age of 24 weeks, obese ZSF1 rats were randomized either receiving standard care or Empa in the drinking water. ZSF1 lean animals served as healthy controls. After 8 weeks of treatment, echocardiography and SKM contractility were performed. Mitochondrial function was assessed in saponin skinned fibers and SKM tissue was snap frozen for molecular analyses. HFpEF was evident in the obese animals when compared to lean—increased E/é and preserved left ventricular ejection fraction. Empa treatment significantly improved E/é and resulted in improved SKM contractility with reduced intramuscular lipid content. Better mitochondrial function (mainly in complex IV) with only minor modulation of atrophy-related proteins was seen after Empa treatment. The results clearly documented a beneficial effect of Empa on SKM function in the present HFpEF model. These effects were accompanied by positive effects on mitochondrial function possibly modulating SKM function.

Cardiovascular Mechanisms of Exercise Intolerance in Older Patients with Heart Failure

Exercise intolerance, measured by peak oxygen consumption (V̇O2), is a hallmark feature of heart failure (HF). The effect is compounded in the elderly HF patient by aging-associated changes such as a reduction in lean muscle mass, an increase in adiposity, and a reduction in maximal heart rate and peripheral blood flow with exercise. There is a non-linear reduction in peak V̇O2 with age that accelerates in the later decades of life. Peak V̇O2 is further reduced due to central and peripheral maladaptation from HF. Central mechanisms include impaired peak heart rate, stroke volume, contractility, increased filling pressures, and a blunted vasodilatory response. Peripheral mechanisms include endothelial dysfunction, reduced blood flow to muscles, and impaired skeletal muscle oxidative capacity. This review presents a focused update on mechanisms leading to impaired aerobic capacity in older HF patients.

Heart Failure in Cardiac Rehabilitation: A REVIEW AND PRACTICAL CONSIDERATIONS

PURPOSE

Exercise cardiac rehabilitation (CR) represents an evidence-based therapy for patients with heart failure with reduced ejection fraction (HFrEF) and this article provides a concise review of the relevant exercise testing and CR literature, including aspects unique to their care.

CLINICAL CONSIDERATIONS

A hallmark feature of HFrEF is exercise intolerance (eg, early-onset fatigue). Drug therapies for HFrEF target neurohormonal pathways to blunt negative remodeling of the cardiac architecture and restore favorable loading conditions. Guideline drug therapy includes β-adrenergic blocking agents; blockade of the renin-angiotensin system; aldosterone antagonism; sodium-glucose cotransport inhibition; and diuretics, as needed.

EXERCISE TESTING AND TRAINING

Various assessments are used to quantify exercise capacity in patients with HFrEF, including peak oxygen uptake measured during an exercise test and 6-min walk distance. The mechanisms responsible for the exercise intolerance include abnormalities in ( a ) central transport (chronotropic response, stroke volume) and ( b ) the diffusion/utilization of oxygen in skeletal muscles. Cardiac rehabilitation improves exercise capacity, intermediate physiologic measures (eg, endothelial function and sympathetic nervous system activity), health-related quality of life (HRQoL), and likely clinical outcomes. The prescription of exercise in patients with HFrEF is generally similar to that for other patients with cardiovascular disease; however, patients having undergone an advanced surgical therapy do present with features that require attention.

SUMMARY

Few patients with HFrEF enroll in CR and as such, many miss the derived benefits, including improved exercise capacity, a likely reduction in risk for subsequent clinical events (eg, rehospitalization), improved HRQoL, and adoption of disease management strategies.

Could SGLT2 Inhibitors Improve Exercise Intolerance in Chronic Heart Failure?

Despite the constant improvement of therapeutical options, heart failure (HF) remains associated with high mortality and morbidity. While new developments in guideline-recommended therapies can prolong survival and postpone HF hospitalizations, impaired exercise capacity remains one of the most debilitating symptoms of HF. Exercise intolerance in HF is multifactorial in origin, as the underlying cardiovascular pathology and reactive changes in skeletal muscle composition and metabolism both contribute. Recently, sodium-related glucose transporter 2 (SGLT2) inhibitors were found to improve cardiovascular outcomes significantly. Whilst much effort has been devoted to untangling the mechanisms responsible for these cardiovascular benefits of SGLT2 inhibitors, little is known about the effect of SGLT2 inhibitors on exercise performance in HF. This review provides an overview of the pathophysiological mechanisms that are responsible for exercise intolerance in HF, elaborates on the potential SGLT2-inhibitor-mediated effects on these phenomena, and provides an up-to-date overview of existing studies on the effect of SGLT2 inhibitors on clinical outcome parameters that are relevant to the assessment of exercise capacity. Finally, current gaps in the evidence and potential future perspectives on the effects of SGLT2 inhibitors on exercise intolerance in chronic HF are discussed.

Matching of O2 Utilization and O2 Delivery in Contracting Skeletal Muscle in Health, Aging, and Heart Failure

Skeletal muscle is one of the most dynamic metabolic organs as evidenced by increases in metabolic rate of >150-fold from rest to maximal contractile activity. Because of limited intracellular stores of ATP, activation of metabolic pathways is required to maintain the necessary rates of ATP re-synthesis during sustained contractions. During the very early phase, phosphocreatine hydrolysis and anaerobic glycolysis prevails but as activity extends beyond ∼1 min, oxidative phosphorylation becomes the major ATP-generating pathway. Oxidative metabolism of macronutrients is highly dependent on the cardiovascular system to deliver O₂ to the contracting muscle fibres, which is ensured through a tight coupling between skeletal muscle O₂ utilization and O₂ delivery. However, to what extent O₂ delivery is ideal in terms of enabling optimal metabolic and contractile function is context-dependent and determined by a complex interaction of several regulatory systems. The first part of the review focuses on local and systemic mechanisms involved in the regulation of O₂ delivery and how integration of these influences the matching of skeletal muscle O₂ demand and O₂ delivery. In the second part, alterations in cardiovascular function and structure associated with aging and heart failure, and how these impact metabolic and contractile function, will be addressed. Where applicable, the potential of exercise training to offset/reverse age- and disease-related cardiovascular declines will be highlighted in the context of skeletal muscle metabolic function. The review focuses on human data but also covers animal observations.

Validity of Estimated Cardiorespiratory Fitness in Patients With Primary Breast Cancer

Background

Estimated peak oxygen consumption (Vo₂peak) is widely used in oncology; however, estimated Vo₂peak equations were developed in noncancer settings.

Objectives

The aim of this study was to evaluate the validity of estimated Vo₂peak in women with primary breast cancer and to develop oncology-specific estimated Vo₂peak equations.

Methods

Vo₂peak was directly measured (TrueOne 2400, Parvo Medics) during 380 cardiopulmonary exercise tests in women previously treated for breast cancer (mean age: 59 ± 10 years; 3.1 ± 1.2 years post-therapy). The American College of Sports Medicine (ACSM), the Fitness Registry and the Importance of Exercise National Database (FRIEND), and heart failure (HF)-FRIEND equations were used to estimate Vo₂peak. New equations were developed using patient and peak (Onc_peak) or submaximal (Onc_sub) exercise test characteristics.

Results

The median differences between measured and estimated Vo₂peak were 7.0 mL O₂·kg⁻¹·min⁻¹, 3.9 mL O₂·kg⁻¹·min⁻¹, and −0.2 mL O₂·kg⁻¹·min⁻¹ for ACSM, FRIEND, and HF-FRIEND, respectively. The number of estimated Vo₂peak values within ±3.5 mL O₂·kg⁻¹·min⁻¹ of the measured values was 70 (18%), 164 (43%), and 306 (81%) for ACSM, FRIEND, and HF-FRIEND, respectively. The Onc_peak and Onc_Sub models included body mass index, age, a history of chemotherapy or radiation, the peak measured heart rate, and the treadmill grade and/or speed. The median differences between measured and estimated Vo₂peak were 0.02 mL O₂·kg⁻¹·min⁻¹ (Onc_peak) and −0.2 mL O₂·kg⁻¹·min⁻¹ (Onc_sub). Eighty-six percent (n = 325) and 76% (n = 283) estimated Vo₂peak values were within ±3.5 mL O₂·kg⁻¹·min⁻¹ of the measured Vo₂peak values for Onc_peak and Onc_sub, respectively.

Conclusions

HF-FRIEND or oncology-specific equations could be applied to estimate Vo₂peak in patients previously treated for breast cancer in settings where cardiopulmonary exercise tests are not available. (Trial Comparing the Effects of Linear Versus Nonlinear Aerobic Training in Women With Operable Breast Cancer [EXCITE]; NCT01186367

Exercise Training in Heart Failure With Reduced Ejection Fraction and Permanent Atrial Fibrillation: A Randomized Clinical Trial

BACKGROUND

Heart failure (HF) associated with atrial fibrillation (AF) increases patients' physical inactivity, worsening their clinical condition and mortality. Exercise training is safe and has clear benefits in HF. However, little is known about the effects of exercise training on heart failure patients with reduced ejection fraction and permanent atrial fibrillation (HFAF).

OBJECTIVE

To test the hypothesis that exercise training improves functional capacity, cardiac function, and quality of life in patients with HFAF.

METHODS

This randomized clinical trial was conducted at the Heart Institute. Patients with HFAF, LVEF ≤40% and resting HR ≤80 bpm were included in the study. Cardiopulmonary testing, echocardiography, autonomic, and quality of life assessment were performed before and after the 12-week protocol period.

RESULTS

Twenty-six patients, 58±1 years, were randomized to exercise training (HFAF-trained, n=13) or no training (HFAF-untrained, n=13). At baseline, no differences between groups were found. Exercise improved VO₂ peak, slope VE/VCO₂, and quality of life. HFAF-trained significantly decreased resting HR (from 73±2 to 69±2 bpm, P=.02) and recovery HR (from 148±11 to 128±9 bpm, P=.001). Concomitantly, LVEF increased (from 31±1 to 36±0.9 %, P=.01), LA decreased (from 52±1.2 to 47±1mm, P=.03), and LV-ESV and LV-EDV deceased (from 69±2 to 64±1.8 mL/m², and 99±2.1 to 91±2, P<.05, respectively). No changes were observed in the untrained group.

CONCLUSION

Exercise training can improve exercise capacity, quality of life, and cardiac function in patients with heart failure with reduced ejection fraction and permanent atrial fibrillation.

Coronary Arterial Function and Disease in Women With No Obstructive Coronary Arteries

Ischemic heart disease (IHD) is the leading cause of mortality in women. While traditional cardiovascular risk factors play an important role in the development of IHD in women, women may experience sex-specific IHD risk factors and pathophysiology, and thus female-specific risk stratification is needed for IHD prevention, diagnosis, and treatment. Emerging data from the past 2 decades have significantly improved the understanding of IHD in women, including mechanisms of ischemia with no obstructive coronary arteries and myocardial infarction with no obstructive coronary arteries. Despite this progress, sex differences in IHD outcomes persist, particularly in young women. This review highlights the contemporary understanding of coronary arterial function and disease in women with no obstructive coronary arteries, including coronary anatomy and physiology, mechanisms of ischemia with no obstructive coronary arteries and myocardial infarction with no obstructive coronary arteries, noninvasive and invasive diagnostic strategies, and management of IHD.

Body Composition and Incident Heart Failure in Older Adults: Results From 2 Prospective Cohorts

Background Aging is associated with central fat redistribution and skeletal muscle decline, yet the relationships of tissue compartments with heart failure (HF) remain incompletely characterized. We assessed the contribution of body composition to incident HF in elders. Methods and Results Participants from 2 older cohorts who completed dual-energy X-ray absorptiometry (DEXA) and, in one cohort, computed tomography were included. We evaluated associations with incident HF for DEXA principal components (PCs) and total lean, appendicular lean, total fat and trunk fat mass; and for computed tomography measures of abdominal visceral and subcutaneous fat, thigh muscle, intermuscular fat area and thigh muscle density. DEXA analysis included 3621, and computed tomography analysis 2332 participants. During median follow-up of 11.8 years, 927 participants developed HF. DEXA principal components showed no relationship with HF. After adjustment for height, weight, and cardiovascular risk factors, total lean mass was near significantly associated with higher HF (hazard ratio [HR], 1.25 per SD [1.00-1.56]), whereas total fat mass and thigh muscle density were significantly related to lower HF (HR, 0.82 [0.68-0.99] and HR, 0.87 [0.78-0.97], respectively). Patterns were similar for HF subtypes. The relationships with HF for total lean and fat mass were attenuated after adjusting for intercurrent atrial fibrillation or excluding high natriuretic peptide levels. Conclusions Total lean mass was positively associated, while total fat mass and thigh muscle density were inversely associated, with incident HF. These findings highlight the limitations of DEXA for assessment of HF risk in elders and support the preeminence of computed tomography-measured skeletal muscle quality over mass as a determinant of HF incidence.

Comparison of Cardiorespiratory Fitness in Black or African American Versus Caucasian Patients With Heart Failure

PURPOSE

Cardiopulmonary exercise testing (CPX) is a well-established assessment with important insight into prognosis and therapeutic efficacy in patients with heart failure (HF). Prior studies have identified several clinical differences between Black or African American (B-AA) and Caucasian patients with HF. Differences in key CPX responses between these two groups require further investigation.

METHODS

Using a database consisting of subjects with symptomatic HF who had undergone CPX for inclusion in various prospective randomized clinical trials, we identified 198 (n = 94 [47%] B-AA; n = 105 [53%] Caucasian) patients with a qualifying baseline CPX. Significant univariate predictors of peak oxygen uptake (V˙o2peak) were included in a multivariate linear regression model.

RESULTS

When compared with Caucasian patients, B-AA were younger (mean ± SD = 54.8 ± 10.0 vs 57.9 ± 9.6 yr, P = .03), had higher C-reactive protein (CRP) (median [IQR] = 4.9 [2.3, 8.8] vs 1.9 [0.6, 5.5] mg/L, P < .0001), lower hemoglobin (13.0 ± 1.8 vs 13.8 ± 1.6 g/dL, P = .003), and lower left ventricular ejection fraction (LVEF) (40 [32, 51] vs 53 [43, 59]%, P < .00010). During CPX, B-AA patients also had lower V˙o2peak (14.6 ± 3.9 vs 17.6 ± 4.8 mL·kg-1·min-1, P < .0001). No differences were observed between B-AA and Caucasian in the minute ventilation/carbon dioxide production (V˙e/V˙co2) slope (P = .14). The difference in V˙o2peak between B-AA and Caucasian was largely attenuated after adjusting for age, body mass index, CRP, N-terminal pro-brain natriuretic peptide, hemoglobin, LVEF, and peak HR (14.1: 95% CI, 13.2-14.9 vs 15.6: 95% CI, 14.4-16.8 mL·kg-1·min-1, P = .053).

CONCLUSIONS

Directly measured V˙o2peak was significantly lower in B-AA than in Caucasians with HF. This is largely explained by differences in clinical characteristics, whereas no significant differences were observed in the V˙e/V˙co2 slope.

Exercise training and inflammatory markers in coronary artery disease patients

Aim. To evaluate the influence of exercise training on inflammatory markers and exercise tolerance in coronary artery disease (CAD) patients. Patients and methods. A total of 54 subjects were enrolled in the present study, including 34 CAD patients (CAD group: 59.2 ± 8.2 years) and 20 healthy controls (C group: 54.2 ± 8.0 years). C reactive protein (CRP), erythrocyte sedimentation rate (ESR), white blood cell (WBC), and placental growth factor (PIGF) were determined, and an exercise test was performed in both groups at baseline and once again in CAD group after the supervised 3 weeks of aerobic exercise training. Results. At baseline, CRP, ESR and PIGF were significantly higher in the CAD group compared to the C group (p = 0.038, p = 0.019 and p = 0.002), while exercise capacity was significantly higher in the C group (p ˂ 0.01). After 3 weeks of exercise training, CRP, ESR, WBC count and PIGF significantly decreased (p = 0.048, p ˂ 0.001, p = 0.002 and p ˂ 0.001 respectively), while exercise capacity significantly increased (p ˂ 0.001) in the CAD group. In the CAD group, CRP decrease significantly correlated with WBC and PIGF decrease (r = 0.816, p = 0.002 and r = 0.988, p ˂ 0.001), as well as with exercise capacity increase (r = 0.834, p ˂ 0.001). Also, WBC decrease significantly correlated both with PIGF decrease (r = 0.768, p ˂ 0.001) and exercise capacity increase (r = 0.548, p = 0.012), while PIGF decrease significantly correlated with exercise capacity increase (r = 0.548, p = 0.013). Conclusion. Residential exercise training in CAD patients reduces inflammation, expressed through a significant decrease in CRP, ESR, WBC count and PIGF levels. Those positive changes in inflammatory markers are associated with significant improvement in exercise capacity.

Exercise: a molecular tool to boost muscle growth and mitochondrial performance in heart failure?

Impaired exercise capacity is the key symptom of heart failure (HF) and is associated with reduced quality of life and higher mortality rates. Unfortunately, current therapies, although generally lifesaving, have only small or marginal effects on exercise capacity. Specific strategies to alleviate exercise intolerance may improve quality of life, while possibly improving prognosis as well. There is overwhelming evidence that physical exercise improves performance in cardiac and skeletal muscles in health and disease. Unravelling the mechanistic underpinnings of exercise‐induced improvements in muscle function could provide targets that will allow us to boost exercise performance in HF. With the current review we discuss: (i) recently discovered signalling pathways that govern physiological muscle growth as well as mitochondrial quality control mechanisms that underlie metabolic adaptations to exercise; (ii) the mechanistic underpinnings of exercise intolerance in HF and the benefits of exercise in HF patients on molecular, functional and prognostic levels; and (iii) potential molecular therapeutics to improve exercise performance in HF. We propose that novel molecular therapies to boost adaptive muscle growth and mitochondrial quality control in HF should always be combined with some form of exercise training.

Mechanism of Dyspnea during Exercise in Children with Corrected Congenital Heart Disease

This study will evaluate cardiorespiratory and peripheral muscle function and their relationship with subjective dyspnea threshold after the surgical correction of congenital heart disease in children. Thirteen children with surgically repaired congenital heart disease were recruited. Each participant performed an incremental exercise test on a cycle ergometer until exhaustion. Gas exchanges were continuously sampled to measure the maximal aerobic parameters and ventilatory thresholds. The functional capacity of the subjects was assessed with a 6 min walk test. At the end of the exercise test, isokinetic Cybex Norm was used to evaluate the strength and endurance of the knee extensor muscle in the leg. Dyspnea was subjectively scored with a visual analog scale during the last 15 s of each exercise step. Oxygen consumption measured at the dyspnea score/VO₂ relationship located at the dyspnea threshold, at which dyspnea suddenly increased. Results: The maximal and submaximal values of the parameters describing the exercise and the peripheral muscular performances were: VO₂ Peak: 33.8 ± 8.9 mL·min^-1·kg^-1; HR: 174 ± 9 b·min^-1; VEmax: 65.68 ± 15.9 L·min^-1; P max: 117 ± 27 W; maximal voluntary isometric force MVIF: 120.8 ± 41.9 N/m; and time to exhaustion Tlim: 53 ± 21 s. Oxygen consumption measured at the dyspnea threshold was related to VO₂ Peak (R² = 0.74; p < 0.01), Tlim (R² = 0.78; p < 0.01), and the distance achieved during the 6MWT (R² = 0.57; p < 0.05). Compared to the theoretical maximal values for the power output, VO₂, and HR, the surgical correction did not repair the exercise performance. After the surgical correction of congenital heart disease, exercise performance was impeded by alterations of the cardiorespiratory function and peripheral local factors. A subjective evaluation of the dyspnea threshold is a reliable criterion that allows the prediction of exercise capacity in subjects suffering from congenital heart disease.

Preservation of Cardiac Reserve and Cardiorespiratory Fitness in Patients With Acute De Novo Versus Acute on Chronic Heart Failure With Reduced Ejection Fraction

There is limited understanding on the potential differences in the pathophysiology between de novo heart failure with reduced ejection fraction (HFrEF) and acute on chronic HFrEF. The aim of this study was to assess differences in cardiorespiratory fitness (CRF) parameters between de novo heart failure and acute on chronic HFrEF using cardiopulmonary exercise testing (CPX). We retrospectively analyzed CPX data measured within 2 weeks of discharge following acute hospitalization for HFrEF. Data are reported as median and interquartile range or frequency and percentage (%). We included 102 patients: 32 (31%) women, 81 (79%) black, 57 (51 to 64) years of age, BMI of 34 (29 to 39) Kg/m². Of these, 26 (25%) had de novo HFrEF and 76 (75%) had acute on chronic HFrEF. When compared with acute on chronic, patients with de novo HFrEF had a significantly higher peak oxygen consumption (VO₂) (16.5 [12.2 to 19.4] vs 12.8 [10.1 to 15.3] ml·kg^-1·min^-1, p <0.001), %-predicted peak VO₂ (58% [51 to 75] vs 49% [42 to 59]) p = 0.012), peak heart rate (134 [117 to 147] vs 117 [104 to 136] beats/min, p = 0.004), peak oxygen pulse (12.2 [10.5 to 15.5] vs 9.9 [8.0 to 13.1] ml/beat, p = 0.022) and circulatory power (2,823 [1,973 to 3,299] vs 1,902 [1,372 to 2,512] mm Hg·ml·kg^-1·min^-1, p = 0.002). No significant difference in resting left ventricular ejection fraction was found between groups. In conclusion, patients with de novo HFrEF have better CRF parameters than those with acute on chronic HFrEF. These differences are not explained by resting left ventricular systolic function but may be related to greater preservation in cardiac reserve during exercise in de novo HFrEF patients.

Effect of early cardiac rehabilitation on prognosis in patients with heart failure following acute myocardial infarction

Objective

The purpose of this retrospective study is to evaluate the effectiveness of early cardiac rehabilitation on patients with heart failure following acute myocardial infarction.

Methods

Two hundred and thirty-two patients who developed heart failure following acute myocardial infarction were enrolled in this study. Patients were divided into heart failure with reduced ejection fraction group (n = 54) and heart failure with mid-range ejection fraction group (n = 178). Seventy-eight patients who accepted a two-week cardiac rehabilitation were further divided into two subgroups based on major adverse cardiovascular events. Key cardio-pulmonary exercise testing indicators that may affect the prognosis were identified among the cardiac rehabilitation patients.

Results

Early cardiac rehabilitation significantly reduced cardiac death and re-hospitalization in patients. There was more incidence of diabetes, hyperkalemia and low P_ETCO₂ in the cardiac rehabilitation group who developed re-hospitalization. Low P_ETCO₂ at anaerobic threshold (≤ 33.5 mmHg) was an independent risk factor for re-hospitalization.

Conclusions

Early cardiac rehabilitation reduced major cardiac events in patients with heart failure following acute myocardial infarction. The lower P_ETCO₂ at anaerobic threshold is an independent risk factor for re-hospitalization, and could be used as a evaluating hallmark for early cardiac rehabilitation.

Cardiac rehabilitation in heart failure: Indications for exercise training based on heart failure phenotype

Exercise intolerance with dyspnea and fatigue is pervasive amongst individuals with heart failure (HF) due to both central and peripheral mechanisms. Cardiac rehabilitation (CR) is a cornerstone therapy for numerous cardiovascular disease (CVD) processes, and it's use in HF with reduced ejection fraction (HFrEF) has shown significant benefit in improved mortality and quality of life (QoL). Less is known about the benefit of CR in the setting of HF with preserved ejection fraction (HFpEF), and optimal exercise therapy (ET) may vary based on underlying disease phenotype. Here we offer review of existing data for ET in both HFrEF and HFpEF with proposed exercise treatment modalities based on underlying comorbidities and variable phenotypes.

High-intensity interval training versus progressive high-intensity circuit resistance training on endothelial function and cardiorespiratory fitness in heart failure: A preliminary randomized controlled trial

INTRODUCTION

Exercise training is strongly recommended as a therapeutic approach to treat individuals with heart failure. High-intensity exercise training modalities still controversial in this population. The study aims to preliminary assess the consequences of high-intensity exercise training modalities, aerobic interval training (HIIT) and progressive high circuit-resistance training (CRT), on primarily endothelial function and cardiorespiratory fitness, and secondly on muscle strength and physical performance in heart failure patients.

METHODS

This preliminary multicentric randomized controlled trial comprised 23 heart failure patients, aged 56 ± 10 years old, mainly New York Heart Association classification I and II (%), hemodynamically stable, who compromise at least 36 exercise sessions of a randomly assigned intervention (HIIT, CRT or control group). Endothelial function, cardiopulmonary exercise testing, muscle strength and physical performance were completed at baseline and post-intervention.

RESULTS

Although no effects on endothelial function; both HIIT and CRT modalities were able to produce a positive effect on [Formula: see text] peak (HIIT = +2.1±6.5, CRT = +3.0±4.2 and control group = -0.1± 5.3 mL/kg/min, time*group p-value<0,05) and METs (HIIT = +0.6±1.8, CRT = +0.9±1.2 and control group = 0±1.6, time*group p-value<0,05). Only HIIT increased isokinetic torque peak (HIIT = +8.8±55.8, CRT = 0.0±60.7 and control group = 1.6±57.6 Nm) matched p-value<0,05. Regarding the physical performance, the CRT modality reduced chair stand test completion time (HIIT = -0.7±3.1, CRT = -3.3±3.2 and control group = -0.3±2.5 s, matched p-value<0,05 and HIIT improved global physical performance(time*group p<0,05).

CONCLUSION

This preliminary study trends to indicate for the first time that high-intensity interval training promotes a jointly superior effect compared to progressive high intensity circuit-resistance training by improving cardiorespiratory fitness, muscular strength, and physical performance. Further research with larger cohort is necessary.

CLINICAL TRIAL REGISTRATION NUMBER

ReBEC RBR-668c8v.

Exercise Intolerance in Older Adults With Heart Failure With Preserved Ejection Fraction: JACC State-of-the-Art Review

Exercise intolerance (EI) is the primary manifestation of chronic heart failure with preserved ejection fraction (HFpEF), the most common form of heart failure among older individuals. The recent recognition that HFpEF is likely a systemic, multiorgan disorder that shares characteristics with other common, difficult-to-treat, aging-related disorders suggests that novel insights may be gained from combining knowledge and concepts from aging and cardiovascular disease disciplines. This state-of-the-art review is based on the outcomes of a National Institute of Aging-sponsored working group meeting on aging and EI in HFpEF. We discuss aging-related and extracardiac contributors to EI in HFpEF and provide the rationale for a transdisciplinary, "gero-centric" approach to advance our understanding of EI in HFpEF and identify promising new therapeutic targets. We also provide a framework for prioritizing future research, including developing a uniform, comprehensive approach to phenotypic characterization of HFpEF, elucidating key geroscience targets for treatment, and conducting proof-of-concept trials to modify these targets.

Hemodynamic Determinants of Activity Measured by Accelerometer in Patients With Stable Heart Failure

OBJECTIVES

This study examined the link between accelerometer recordings and cardiac pathophysiology measured with right heart cauterization at rest and with exercise in patients with HFrEF.

BACKGROUND

Patient-worn accelerometers are increasingly being used in patients with heart failure with reduced ejection fraction (HFrEF) to assess activity and serve as surrogate endpoints in heart failure trials.

METHODS

Physical average daily activity (PADA) and total average daily activity according to accelerometer units were assessed in 63 patients (mean age 58 ± 10 years; mean ejection fraction 26% ± 4%). Patients underwent hemodynamic exercise testing and accelerometry. Patients were divided according to PADA in PADA_Low and PADA_High activity level groups based on median counts per minute of physical activity.

RESULTS

Patients in the PADA_Low group were older and more frequently treated with diuretics. At rest, the PADA_Low group was characterized by a lower cardiac index (2.2 ± 0.4 L/min/m² vs 2.4 ± 0.4 L/min/m²; P = 0.01) and stroke volume (70 ± 19 mL vs 81 ± 17 mL; P = 0.02) but not pulmonary capillary wedge pressure (12 ± 5 mm Hg vs 11 ± 5 mm Hg; P = 0.3). The PADA_Low group reached a lower cardiac index (4.8 ± 1.7 L/min/m² vs 6.6 ± 1.7 L/min/m²; P < 0.001) but not in pulmonary capillary wedge pressure (31 ± 12 mm Hg vs 27 ± 8 mm Hg; P = 0.2) at peak exercise. The attenuated increase was associated with an attenuated increase in stroke volume (94 ± 32 mL vs 121 ± 29 mL; P < 0.001) rather than a reduced increase in heart rate (42 ± 23 beats/min vs 52 ± 21 beats/min; P = 0.07). PADA and total average daily accelerometer units were associated with patient-reported functional impairment according to the Kansas City Cardiomyopathy Questionnaire but not with New York Heart Association functional class.

CONCLUSIONS

Among stable ambulatory patients with HFrEF, lower daily activity is associated with poorer cardiac index reserve and reduced cardiac index during exercise. (Empagliflozin in Heart Failure Patients With Reduced Ejection Fraction; NCT03198585).