Myocardial Flow Reserve, an Independent Prognostic Marker of All-Cause Mortality Assessed by 82Rb PET Myocardial Perfusion Imaging: A Danish Multicenter Study

Sex differences in myocardial flow reserve among individuals with type 2 diabetes: insights from the DiaHeart study

BACKGROUND

Type 2 diabetes is a stronger risk factor for cardiovascular disease (CVD) in women compared with men possibly due to higher susceptibility to develop myocardial microvascular dysfunction. We investigated sex-dependent effects of risk factors on myocardial blood flow (MBF) and myocardial flow reserve (MFR) in individuals with type 2 diabetes without overt CVD.

METHODS

Cross-sectional analysis of a prospective study including 901 individuals recruited between 2020 and 2023. All participants underwent a cardiac 82-Rubidium positron emission tomography/computed tomography scan to quantify MBF at rest and during pharmacologically induced stress, allowing for calculation of MFR. Linear regression, with/without interaction terms for sex, was used to test whether sex modified the association between MFR/MBF and risk factors.

RESULTS

Mean (SD) age was 65 (8.9) years, diabetes duration was 14 (8.4) years, and 266 (29.5%) were women. Women had higher MBF at rest and stress but had lower MFR (mean (SD) 2.44 (0.67) vs. 2.59 (0.77), p = 0.003) than men. A similar proportion of men and women (21.1% vs. 23.7%) had an MFR < 2. The decline in predicted MFR with age differed between sexes. At age 55, women had a mean MFR that was 0.29 lower than men (95% CI: - 0.44 to - 0.14), but by age 75, this difference had nearly disappeared (- 0.04, 95% CI: - 0.19 to 0.11). However, after adjustment for other risk factors, the interaction between sex and age was not statistically significant (p = 0.057). No other risk factors exhibited significant sex-dependent interactions.

CONCLUSIONS

In individuals with type 2 diabetes without overt CVD, women exhibited lower MFR than men, primarily due to higher MBF at rest, suggesting sex-related differences. While MFR declined in both sexes, the sex difference was more pronounced in younger individuals and diminished over time. These findings underscore the need for further research into sex-specific thresholds for MFR in cardiovascular risk stratification.

PET myocardial perfusion imaging: Trends, challenges, and opportunities

Various non-invasive images are used in clinical practice for the diagnosis and prognostication of chronic coronary syndromes. Notably, quantitative myocardial perfusion imaging (MPI) through positron emission tomography (PET) has seen significant technical advancements and a substantial increase in its use over the past two decades. This progress has generated an unprecedented wealth of clinical information, which, when properly applied, can diagnose and fine-tune the management of patients with different types of ischemic syndromes. This state-of-art review focuses on quantitative PET MPI, its integration into clinical practice, and how it holds up at the eyes of modern cardiac imaging and revascularization clinical trials, along with future perspectives.

Myocardial ischemia in patients with mild-to-moderate aortic stenosis: Interaction with cardiac remodeling and adverse events

BACKGROUND

The association between aortic valve stenosis (AVS) and myocardial perfusion abnormalities has been incompletely characterized. We sought to assess the predictors of myocardial ischemia in patients with mild-to-moderate AVS, and its relationship with long-term prognosis.

METHODS

Eighty-nine patients with mild-to-moderate AVS (peak velocity between 2.6 and 4.0 m/second and aortic valve area > .6 cm2/m2), preserved left ventricular (LV) function, and either normal coronary arteries (28 patients) or non-obstructive coronary artery disease (<50% stenosis; 61 patients) were individuated. Myocardial perfusion imaging was performed using a cadmium-zinc-telluride camera, and the summed difference score (SDS) was computed. The presence of either LV hypertrophy (LVH) (LV mass index [LVMI] > 115 g/m2 [males] or 95 g/m2 [females]) or concentric LV remodeling (relative wall thickness: >.42) was determined at two-dimensional echocardiography.

RESULTS

Forty (45%) and 49 (55%) patients had mild and moderate AVS, respectively. Fifty (56%), 17 (19%), and 22 (25%) patients had normal LV geometry, concentric LV remodeling, and LVH, respectively. An interaction between LV remodeling and inducible ischemia was revealed with progressively higher values of SDS in patients with normal LV geometry (3 ± 3), concentric remodeling (4 ± 2), and LVH (7 ± 2) (P < .001). Accordingly, a moderate correlation existed between LVMI and SDS values (R: .67; P < .001). After a median follow-up of 84 ± 47 months, 27 adverse events were recorded, including 19 AV replacements and 8 deaths. On multivariable analysis, the presence of LVH (hazard ratio [HR]: 6.46; 95% confidence interval [CI]: 2.09-20.00; P = .001) and a higher SDS (HR: 1.41; 95% CI: 1.15-1.75; P = .001) were the two independent predictors of AE.

CONCLUSIONS

In patients with mild-to-moderate AVS, myocardial ischemia correlates with the severity of adverse LV remodeling. Patients with LVH and ischemia are at increased risk of AE.

Links Between Obstructive Sleep Apnea and Myocardial Blood Flow Changes Impacting Adverse Cardiovascular Disease-related Outcomes

PURPOSE OF REVIEW

Recent studies have demonstrated an association between obstructive sleep apnea (OSA) and abnormal myocardial blood flow (MBF), myocardial flow reserve (MFR), and coronary microvascular dysfunction (CMD). Here, we review the evidence and describe the potential underlying mechanisms linking OSA to abnormal MBF. Examining relevant studies, we assess the impact of OSA-specific therapy, such as continuous positive airway pressure (CPAP), on MBF.

RECENT FINDINGS

Recent studies suggest an association between moderate to severe OSA and abnormal MBF/MFR. OSA promotes functional and structural abnormalities of the coronary microcirculation. OSA also promotes the uncoupling of MBF to cardiac work. In a handful of studies with small sample sizes, CPAP therapy improved MBF/MFR. Moderate to severe OSA is associated with abnormal MFR, suggesting an association with CMD. Evidence suggests that CPAP therapy improves MBF. Future studies must determine the clinical impact of improved MBF with CPAP.

Age- and Sex-Specific Myocardial Blood Flow Values in Patients Without Coronary Atherosclerosis on Rb-82 PET Myocardial Perfusion Imaging

BACKGROUND

Quantitative myocardial blood flow (MBF) on positron-emission tomography myocardial perfusion imaging is a measure of the overall health of the coronary circulation. The ability to adequately augment blood flow, measured by myocardial blood flow reserve (MBFR), is associated with lower major adverse cardiovascular events and all-cause mortality. The age-specific ranges of MBFR in patients without demonstrable coronary artery disease have not been well established. We aimed to determine the effect of age and sex on MBF in a cohort of patients without demonstrable coronary artery disease.

METHODS

Patients who underwent positron-emission tomography myocardial perfusion imaging studies from 2012 to 2022 on positron-emission tomography/computed tomography cameras were included if the summed stress score was 0, the coronary calcium score was 0, and the left ventricular ejection fraction was ≥50%. Those with known coronary artery disease, prior history of coronary intervention, diabetes, heart/kidney/liver transplant, cirrhosis, or chronic kidney disease stage IV+ were excluded. MBF was calculated using a net retention model (ImagenQ, Cardiovascular Imaging Technologies, Kansas City), and quantile regression models were developed to predict MBF.

RESULTS

Among 2789 patients (age 59.9±13.0 years, 76.4% females), median rest MBF was 0.73 (0.60-0.91) mL/min·g, stress MBF was 1.72 (1.41-2.10) mL/min·g, and MBFR was 2.31 (1.96-2.74). Across all ages, males augmented MBF in response to vasodilator stress to a greater degree than females but achieved lower absolute stress MBF. Younger males in particular achieved a higher MBFR than their female counterparts, and this gap narrowed with increasing age. Predicted MBFR for a 20-year-old male was 3.18 and female was 2.50, while predicted MBFR for an 80-year-old male was 2.17 and female was 2.02.

CONCLUSIONS

In patients without demonstrable coronary artery disease, MBFR is higher in younger males than younger females and decreases with age in both sexes. Age- and sex-specific MBFR may be important in risk prediction and guidance for revascularization and warrant further study.

82-rubidium positron emission tomography determined myocardial flow reserve and outcomes following cardiac revascularisation - A multicentre registry study

BACKGROUND

Finding patients with chronic coronary syndromes (CCS) whom revascularization could benefit, is complicated. Myocardial flow reserve (MFR), a measurement of myocardial perfusion, has proven prognostic value on survival and risk of major adverse cardiac events (MACE). We investigated if MFR identifies who may benefit from revascularization.

METHODS

Among 7462 patients from Danish hospitals examined with 82Rb PET between January 2018 and August 2020, patients with ≥5% reversible perfusion defects were followed for MACE and all-cause mortality. Associations between revascularisation (within 90 days) and outcomes according to MFR (< and ≥ 2) was assessed by Cox regression adjusted by inverse probability weighting for demographics, cardiovascular risk factors, comorbidities, and 82Rb PET variables.

RESULTS

Of 1806 patients with ≥5% reversible perfusion defect, 893 (49%) had MFR < 2 and 491 underwent revascularisation (36.6% in MFR < 2 versus 17.9% MFR ≥ 2, p < 0.001). During a median follow-up of 37.0 [31.0-45.8 IQR] months, 251 experienced a MACE and 173 died. Revascularisation was associated with lower adjusted risk of all-cause mortality (hazard ratio [HR], 0.51 [95% CI, 0.30-0.88], p = 0.015) and MACE (HR, 0.54 [0.33-0.87], p = 0.012) in patients with MFR < 2 but not MFR ≥ 2 for all-cause mortality (HR 1.33 [0.52-3.40], p = 0.542) and MACE (HR 1.50 [0.79-2.84], p = 0.211). MFR significantly modified the association between revascularisation and MACE, but not all-cause mortality (interaction p-value 0.021 and 0.094, respectively).

CONCLUSIONS

Revascularization was associated with improved prognosis among patients with impaired MFR. No association was seen in patients with normal MFR. In patients with regional ischemia, MFR may identify patients with a prognostic benefit from revascularization.

Prognostic value of positron emission tomography derived myocardial flow reserve: A systematic review and meta-analysis

BACKGROUND AND AIMS

Positron Emission Tomography (PET)-derived myocardial flow reserve (MFR) has been shown to have a role in the diagnosis and prognosis of patients with coronary artery disease (CAD). We performed a systematic review and meta-analysis to summarize the body of literature and synthesize the evidence on the prognostic role of PET-derived MFR in patients with known or suspected CAD.

METHODS

A comprehensive literature search of the Medline database from its inception to August 2023, in humans, in any language, was conducted for clinical studies examining the prognostic value of PET imaging in patients of any age, sex, and CAD status. Systematic screening and data extraction of the identified studies were followed by quantitative meta-analysis of PET-MFR's role in predicting adverse clinical events using random effect model. Studies were appraised using the modified Newcastle-Ottawa tool.

RESULTS

A total of 21 studies assessing the prognostic role of PET derived MFR in 46,815 patients with known and/or suspected CAD were included (mean (SD) age 66 (4) years, 48% women). The mean follow-up duration was 36 months (range 10-96). Cardiovascular risk factors were prevalent (73% hypertension, 35% diabetes and 67% dyslipidemia). The definition of the composite outcome varied between studies, with various combinations of mortality, non-fatal myocardial infarction, hospitalization, and coronary revascularization. Pooled impaired MFR was significantly associated with an increased risk of adverse outcomes (RR = 2.94, 95% CI 2.42-3.56, p < 0.001). Results were similar in a subgroup of patients with suspected CAD.

CONCLUSIONS

The available body of evidence shows that impaired PET-derived MFR measured using different tracers and PET systems is strongly associated with an increased risk of adverse cardiovascular events. Limitations of this review include observational nature of studies, marked heterogeneity in patient populations, inconsistency in thresholds to define abnormal MFR, and differing components for the composite outcome.