Redistribution of cardiac output during exercise by functional mitral regurgitation in heart failure: compensatory O2 peripheral uptake to delivery failure

Limits to Submaximal and Maximal Exercise in Patients with Hypertrophic Cardiomyopathy

BACKGROUND

Patients with hypertrophic cardiomyopathy (HCM) often have reduced exercise capacity, and it is unclear whether cardiovascular regulation during exercise is intact in these patients. We aimed to determine the relationship between cardiac output (Q̇_c) and oxygen uptake (V̇O₂), and stroke volume (SV) reserve in HCMcompared to healthy participants and participants with left ventricular hypertrophy (LVH) but not HCM.

METHODS

Sixteen patients with HCM (48±7 years, 44% female), 16 participants with LVH (49±5 years, 44% female), and 61 healthy controls (CON: 52±5 years, 52% female) completed submaximal steady-state treadmill exercise followed by a maximal exercise test. V̇O₂, Q̇_c,SV and arterio-venous oxygen difference were measured during rest and exercise, and Q̇_c/V̇O₂ slopes were constructed.

RESULTS

The Q̇_c/V̇O₂ slopewas blunted in HCM compared to CON and LVH (HCM 4.9±0.7 vs. CON 5.5± 1.0 [P = 0.027], vs LVH 6.0±1.0AU [P = 0.002]) and participants with HCM had a lower SV reserve (HCM 53±33%, controls 83±33%, LVH 82±22%; HCM vs. controls P = 0.002; HCM vs. LVH P = 0.015). Despite a blunted Q̇_c/V̇O₂ slope, 75% of patients with HCM achieved ≥80% predicted V̇O₂max by augmenting a-vO₂ difference at maximal exercise (16.0±0.8 mL/100mL vs 13.8±2.7 mL/100mL, P = 0.021).

CONCLUSIONS

Patients with HCM do not appropriately match Q̇_c to metabolic demand, primarily due to inadequate stroke volume augmentation. Despite this central limitation, many patients achieve normal exercise capacities by significantly increasing peripheral oxygen extraction.

Cardiac Imaging for the Assessment of Left Atrial Mechanics Across Heart Failure Stages

The left atrium (LA) is emerging as a key element in the pathophysiology of several cardiac diseases due to having an active role in contrasting heart failure (HF) progression. Its morphological and functional remodeling occurs progressively according to pressure or volume overload generated by the underlying disease, and its ability of adaptation contributes to avoid pulmonary circulation congestion and to postpone HF symptoms. Moreover, early signs of LA dysfunction can anticipate and predict the clinical course of HF diseases before the symptom onset which, particularly, also applies to patients with increased risk of HF with still normal cardiac structure (stage A HF). The study of LA mechanics (chamber morphology and function) is moving from a research interest to a clinical application thanks to a great clinical, prognostic, and pathophysiological significance. This process is promoted by the technological progress of cardiac imaging which increases the availability of easy-to-use tools for clinicians and HF specialists. Two-dimensional (2D) speckle tracking echocardiography and feature tracking cardiac magnetic resonance are becoming essential for daily practice. In this context, a deep understanding of LA mechanics, its prognostic significance, and the available approaches are essential to improve clinical practice. The present review will focus on LA mechanics, discussing atrial physiology and pathophysiology of main cardiac diseases across the HF stages with specific attention to the prognostic significance. Imaging techniques for LA mechanics assessment will be discussed with an overlook on the dynamic (under stress) evaluation of the chamber.

Combined use of stress echocardiography and cardiopulmonary exercise testing to assess exercise intolerance in patients treated for acute myocardial infarction

Exercise intolerance after acute myocardial infarction (AMI) is a predictor of worse prognosis, but its causes are complex and poorly studied. This study assessed the determinants of exercise intolerance using combined stress echocardiography and cardiopulmonary exercise testing (CPET-SE) in patients treated for AMI. We prospectively enrolled patients with left ventricular ejection fraction (LV EF) ≥40% for more than 4 weeks after the first AMI. Stroke volume, heart rate, and arteriovenous oxygen difference (A-VO2Diff) were assessed during symptom-limited CPET-SE. Patients were divided into four groups according to the percentage of predicted oxygen uptake (VO2) (Group 1, <50%; Group 2, 50-74%; Group 3, 75-99%; and Group 4, ≥100%). Among 81 patients (70% male, mean age 58 ± 11 years, 47% ST-segment elevation AMI) mean peak VO2 was 19.5 ± 5.4 mL/kg/min. A better exercise capacity was related to a higher percent predicted heart rate (Group 2 vs. Group 4, p <0.01), higher peak A-VO2Diff (Group 1 vs. Group 3, p <0.01) but without differences in stroke volume. Peak VO2 and percent predicted VO2 had a significant positive correlation with percent predicted heart rate at peak exercise (r = 0.28, p = 0.01 and r = 0.46, p < 0.001) and peak A-VO2Diff (r = 0.68, p <0.001 and r = 0.36, p = 0.001) but not with peak stroke volume. Exercise capacity in patients treated for AMI with LV EF ≥40% is related to heart rate response during exercise and peak peripheral oxygen extraction. CPET-SE enables non-invasive assessment of the mechanisms of exercise intolerance.

Exercise-induced mitral regurgitation and right ventricle to pulmonary circulation uncoupling across the heart failure phenotypes

Exercise-induced mitral regurgitation (Ex-MR) is one of the mechanisms that contribute to reduced functional capacity in heart failure (HF). Its prevalence is not well defined across different HF subtypes. The aim of the present study was to describe functional phenotypes and cardiac response to exercise in HFrEF, HFmrEF, and HFpEF, according to Ex-MR prevalence. A total of 218 patients with HF [146 men, 68 (59-78) yr], 137 HFrEF, 41 HFmrEF, 40 HFpEF, and 23 controls were tested with cardiopulmonary exercise test combined with exercise echocardiography. Ex-MR was defined as development of at least moderate (≥2+/4+) regurgitation during exercise. Ex-MR was highly prevalent in the overall population (52%) although differed in the subgroups as follows: 82/137 (60%) in HFrEF, 17/41 (41%) in HFmrEF, and 14/40 (35%) in HFpEF (P < 0.05). Ex-MR was associated with a high rate of ventilation (VE) to carbon dioxide production (VCO₂) in all HF subtypes [31.2 (26.6-35.6) vs. 33.4 (29.6-40.5), P = 0.004; 28.1 (24.5-31.9) vs. 34.4 (28.2-36.7), P = 0.01; 28.8 (26.6-32.4) vs. 32.2 (29.2-36.7), P = 0.01] and with lower peak VO₂ in HFrEF and HFmrEF. Exercise right ventricle to pulmonary circulation (RV-PC) uncoupling was observed in HFrEF and HFpEF patients with Ex-MR [peak TAPSE/SPAP: HFrEF 0.40 (0.30-0.57) vs. 0.29 (0.23-0.39), P = 0.006; HFpEF 0.44 (0.28-0.62) vs. 0.31 (0.27-0.33), P = 0.05]. HFpEF with Ex-MR showed a distinct phenotype characterized by better chronotropic reserve and peripheral O₂ extraction.NEW & NOTEWORTHY Ex-MR is a common mechanism across the spectrum of HF subtypes and combines with ventilatory inefficiency and RV-PC uncoupling. Interestingly, in HFpEF, Ex-MR emerged as unexpectedly prevalent and peculiarly associated with increased chronotropic response and peripheral O₂ extraction as potential adaptive mechanisms to backward flow redistribution.