P200 - SEX-DIFFERENCES IN CARDIAC PERFORMANCE AND THE RELATIVE INFLUENCE OF HEART RATE AND STROKE VOLUME ON CARDIAC INDEX: A MAGNETIC RESONANCE IMAGING STUDY

Background: Cardiac index (CI) standardizes cardiac output (CO) to body surface area (BSA). This study examines sex differences in the contributions of stroke volume (SV), heart rate (HR), and BSA to CI in individuals with normal left ventricular ejection fractions (LVEF) using cardiac magnetic resonance imaging (CMR).

METHODS AND RESULTS: This prospective cohort study utilized data from the Courtois Cardiovascular Signature Program (CCVS). Participants aged 34 to 80 with a normal LVEF (≥ 50%) and not on beta or calcium channel blockers were included. CI was categorized as normal (≥ 2.5 L/min/m2) or low ( < 2.5 L/min/m2). Left ventricular end-diastolic volume (EDV) served as a surrogate for SV. Pearson correlation analysis assessed linear relationships between HR, EDV, and BSA with CI. A sex-stratified regression analysis adjusted for age determined the strength of each predictor’s (HR, EDV, or BSA) association with CI.

Among 1,074 participants (618 females, 58%, mean age: 55 ± 11 years), 33% of both sexes had a low CI with a normal LVEF. Comparing males vs females, in low CI states, EDV was the strongest predictor of CI for both sexes (β = 0.95 vs β = 0.86; p < 0.001), though its influence on CI was 11% stronger in males. Conversely, HR had a 16% greater influence in females (β = 0.59 vs β = 0.69; p < 0.001). These sex differences were further reflected in the proportion of CI variance explained by EDV and HR: EDV accounted for 41% in males compared to 37% in females, while HR contributed 26% in males compared to 33% in females. BSA negatively correlated with CI only in females in this group (r = -0.05, p = 0.51 vs r = -0.15, p = 0.03). In normal CI states, HR dominated in males (β = 0.87 vs β = 0.77; p < 0.001), while EDV influenced the CI in females more (β = 0.74 vs β = 0.86; p < 0.001). BSA retained a stronger negative association in females despite nonsignificant correlations.

Conclusion: Sex-specific hemodynamic adaptations to CI are context-dependent. Females rely more on HR than males in low CI states, while SV (represented by EDV) is the primary driver in males. In normal CI states, males depend more on HR and females on preload. Body habitus more negatively impacts females across all CI ranges. These findings suggest that therapies targeting HR or preload may have sex-specific treatment efficacies and warrant further investigation.