Sex-Specific Aspects in the Pathophysiology and Imaging of Coronary Macro- and Microvascular Disease

Sexually dimorphic mechanisms of H2O2-mediated dilation in porcine coronary arterioles with ischemia and endurance exercise training

We determined the impact of sex on H2O2-mediated dilation in coronary arterioles and the contribution of K+ channels after exercise training in ischemic heart disease. We hypothesized that arterioles from male and female swine would similarly display impaired H2O2-induced dilation after chronic occlusion that would be corrected by exercise training. Yucatan miniswine were surgically instrumented with an ameroid constrictor around the proximal left circumflex artery, gradually inducing occlusion and a collateral-dependent myocardium. Arterioles from the left anterior descending artery myocardial region served as nonoccluded controls. Eight weeks postoperatively, swine of each sex were separated into sedentary and exercise-trained (progressive treadmill regimen; 5 days/wk for 14 wk) groups. Collateral-dependent arterioles of sedentary female pigs displayed impaired sensitivity to H2O2 that was reversed with exercise training. In contrast, male pigs exhibited enhanced sensitivity to H2O2 in collateral-dependent versus nonoccluded arterioles in both sedentary and exercise-trained groups. Large-conductance, calcium-dependent K+ (BKCa) and 4-aminopyridine (AP)-sensitive voltage-gated K+ (Kv) channels contributed to H2O2-mediated dilation in nonoccluded and collateral-dependent arterioles of exercise-trained females, but not in arterioles of sedentary female or sedentary or exercise-trained male swine. BKCa channel, protein kinase A (PKA), and protein kinase G (PKG) protein levels were not significantly different between groups, nor were kinase enzymatic activities. Taken together, our studies suggest that in female swine, exercise training stimulates the coupling of H2O2 signaling with BKCa and 4-AP-sensitive Kv channels, compensating for impaired dilation in collateral-dependent arterioles. Interestingly, coronary arterioles from neither sedentary female or male swine, regardless of training status, depended upon BKCa or 4-AP-sensitive Kv channels for H2O2-mediated dilation.NEW & NOTEWORTHY The current studies reveal sexually dimorphic adaptations to H2O2-mediated dilation, and unique contributions of K+ channels, in coronary arterioles from swine subjected to chronic ischemia and exercise training; findings important for development of therapeutic strategies. In female swine, chronic ischemia attenuates dilation, which is reversed by exercise training via BKCa and Kv channel stimulation. In male swine, ischemia enhances dilation to H2O2, which is further augmented by exercise training and independent of BKCa and Kv channels.

Myocardial blood flow reference values for 13N-ammonia PET myocardial perfusion imaging in patients without flow-limiting coronary artery disease

PURPOSE

To determine the most important patient factors influencing quantitative MBF and to report the lower (LRL) and upper (URL) reference limits for 13N-ammonia positron emission tomography (PET) myocardial perfusion imaging (MPI).

METHODS

Patients who underwent 13N-ammonia PET-MPI were screened, and those with evidence of myocardial ischemia or scar, known cardiomyopathy, impaired left ventricular function, non-response to vasodilators, and those who underwent a stress-rest protocol were excluded. Multiple linear regression analyses were performed to identify independent predictors of rest MBF (rMBF), stress MBF (sMBF), and myocardial flow reserve (MFR), and predictor importance was calculated. Finally, median, LRL, and URL for rMBF, sMBF, and MFR were calculated based on the presence of predictors.

RESULTS

Among 784 patients with a median coronary artery calcium score (CACS) of 69, median rMBF was 0.75mL∙min- 1∙g- 1 (LRL = 0.49 mL∙min- 1∙g- 1; URL = 1.33 mL∙min- 1∙g- 1), median sMBF was 2.41mL∙min- 1∙g- 1 (LRL = 1.42 mL∙min- 1∙g- 1; URL = 3.73 mL∙min- 1∙g- 1), and median MFR was 3.09 (LRL = 2.11; URL = 4.65). The body mass index (BMI) was the single most important independent predictor of rMBF, sMBF, and MFR (predictor importance of 72%, 87%, and 41%, respectively; standardized β=-0.434, -0.566 and - 0.174, respectively). Additional predictors were sex and hypertension for rMBF, sex for sMBF, and hypertension and CACS for MFR.

CONCLUSION

In patients without flow-limiting CAD, MBF is strongly influenced by the patient's habitus, whereby median and reference limits for sMBF and rMBF decrease with increasing BMI. Consequently, MFR exhibits stable lower reference limits across a wide range of BMI and may be considered the most robust quantitative parameter derived from 13N-ammonia PET-MPI.

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.

Traditional Cardiovascular Risk Factors and Coronary Microvascular Dysfunction in Women and Men: A Single-Center Study

INTRODUCTION

Coronary microvascular dysfunction (CMD) is common in patients with and without obstructive epicardial coronary artery disease (CAD). Risk factors for the development of CMD have not been fully elucidated, and data regarding sex-associated differences in traditional cardiovascular risk factors for obstructive CAD in patients with CMD are lacking.

METHODS

In this single-center, prospective registry, we enrolled patients with nonobstructive CAD undergoing clinically indicated invasive assessment of coronary microvascular function between November 2019 and March 2023. Associations between coronary microvascular dysfunction, traditional cardiovascular risk factors, and sex were assessed using univariate and multivariate regression models.

RESULTS

Overall, 245 patients with nonobstructive CAD were included in the analysis (62.9% female; median age 68 (interquartile range: 59, 75). Microvascular dysfunction was diagnosed in 141 patients (57.5%). The prevalence of microvascular dysfunction was similar in women and men (59.0% vs. 57.0%; p = 0.77). No association was found between traditional risk factors for coronary atherosclerosis and CMD regardless of whether CMD was structural or functional. In women, but not in men, older age and the presence of previous ischemic heart disease were associated with lower coronary flow reserve (β = -0.29; p < 0.01 and β = -0.15; p = 0.05, respectively) and lower resistive reserve ratio (β = -0.28; p < 0.01 and β = -0.17; p = 0.04, respectively).

CONCLUSION

For the entire population, no association was found between coronary microvascular dysfunction and traditional risk factors for coronary atherosclerosis. In women only, older age and previous ischemic heart disease were associated with coronary microvascular dysfunction. Larger studies are needed to elucidate risk factors for CMD.

Sex differences in the genetic and molecular mechanisms of coronary artery disease

Sex differences in coronary artery disease (CAD) presentation, risk factors and prognosis have been widely studied. Similarly, studies on atherosclerosis have shown prominent sex differences in plaque biology. Our understanding of the underlying genetic and molecular mechanisms that drive these differences remains fragmented and largely understudied. Through reviewing genetic and epigenetic studies, we identified more than 40 sex-differential candidate genes (13 within known CAD loci) that may explain, at least in part, sex differences in vascular remodeling, lipid metabolism and endothelial dysfunction. Studies with transcriptomic and single-cell RNA sequencing data from atherosclerotic plaques highlight potential sex differences in smooth muscle cell and endothelial cell biology. Especially, phenotypic switching of smooth muscle cells seems to play a crucial role in female atherosclerosis. This matches the known sex differences in atherosclerotic phenotypes, with men being more prone to lipid-rich plaques, while women are more likely to develop fibrous plaques with endothelial dysfunction. To unravel the complex mechanisms that drive sex differences in CAD, increased statistical power and adjustments to study designs and analysis strategies are required. This entails increasing inclusion rates of women, performing well-defined sex-stratified analyses and the integration of multi-omics data.

Sex differences in contributors to coronary microvascular dysfunction

Background

Coronary microvascular dysfunction (CMD) has differences in prevalence and presentation between women and men; however, we have limited understanding about underlying contributors to sex differences in CMD. Myocardial perfusion reserve index (MPRI), as semi-quantitative measure of myocardial perfusion derived from cardiac magnetic resonance (CMR) imaging has been validated as a measure of CMD. We sought to understand the sex differences in the relations between the MPRI and traditional measures of cardiovascular disease by CMR.

Methods

A retrospective analysis of a single-center cohort of patients receiving clinical stress CMR from 2015 to 2022 was performed. Patients with calculated MPRI and no visible perfusion defects consistent with obstructive epicardial coronary disease were included. We compared associations between MPRI versus traditional cardiovascular risk factors and markers of cardiac structure/function in sex-stratified populations using univariable and multivariable regression models.

Results

A total of 229 patients [193 female, 36 male, median age 57 (47-67) years] were included in the analysis. In the female population, no traditional cardiovascular risk factors were associated with MPRI, whereas in the male population, diabetes (β: -0.80, p = 0.03) and hyperlipidemia (β: -0.76, p = 0.006) were both associated with reduced MPRI in multivariable models. Multivariable models revealed significant associations between reduced MPRI and increased ascending aortic diameter (β: -0.42, p = 0.005) and T1 times (β: -0.0056, p = 0.03) in the male population, and increased T1 times (β: -0.0037, p = 0.006) and LVMI (β: -0.022, p = 0.0003) in the female population.

Conclusion

The findings suggest different underlying pathophysiology of CMD in men versus women, with lower MPRI in male patients fitting a more "traditional" atherosclerotic profile.

A Practical Approach to Invasive Testing in Ischemia with No Obstructive Coronary Arteries (INOCA)

Up to 65% of women and approximately 30% of men have ischemia with no obstructive coronary artery disease (CAD; commonly known as INOCA) on invasive coronary angiography performed for stable angina. INOCA can be due to coronary microvascular dysfunction or coronary vasospasm. Despite the absence of obstructive CAD, those with INOCA have an increased risk of all-cause mortality and adverse outcomes, including recurrent angina and cardiovascular events. These patients often undergo repeat testing, including cardiac catheterization, resulting in lifetime healthcare costs that rival those for obstructive CAD. Patients with INOCA often remain undiagnosed and untreated. This review discusses the symptoms and prognosis of INOCA, offers a systematic approach to the diagnostic evaluation of these patients, and summarizes therapeutic management, including tailored therapy according to underlying pathophysiological mechanisms.

Sex-Specific Associations of Risks and Cardiac Structure and Function With Microalbumin/Creatinine Ratio in Diastolic Heart Failure

Background: Heart failure with preserved ejection fraction (HFpEF) affects women more frequently than men. However, data on sex-specific associations of adverse health outcomes and left ventricular structure and function and with microalbuminuria in patients with HFpEF are scarce. Methods: In 1,334 participants enrolled in the Treatment of Preserved Cardiac Function Heart Failure with an Aldosterone Antagonist (TOPCAT) Trial, we estimated the sex-specific multivariable-adjusted risk and LV traits with urine microalbumin/creatine ratio (ACR), using Cox or linear regression. Results: In total, 604 (45.3%) were women. In multivariable-adjusted analyses, a doubling of ACR in both men and women was associated with higher posterior (+0.014 cm, p = 0.012/+0.012 cm, p = 0.033) wall thickness and left ventricular mass index (+2.55 mg/m2, p = 0.004/+2.45 mg/m2, p = 0.009), whereas was also associated with higher septal (+0.018 cm, p = 0.002) and left atrial volume index (+1.44 mL/m2, p = 0.001) in men. ACR was a key predictor of all-cause (HR, 1.11; p = 0.006) and cardiovascular (HR, 1.17; p = 0.002) death in women, whereas in men ACR was associated with HF hospitalization (HR, 1.23; p < 0.001), any hospitalization (HR, 1.06; p = 0.006), and myocardial infarction (HR, 1.19; p = 0.017). The interactions of sex with ACR were significant for hospitalization for heart failure and any hospitalization (p ≤ 0.034). Conclusions: Outcomes and cardiac structure and function in patients with HFpEF appear to be influenced by ACR that vary according to sex. In men, ACR was significant associated with LV diastolic function, hospitalization, and myocardial infarction, whereas in women was associated with mortality.