Abstract 3764: Women Do More With Less: Sex Differences in Myocardial Contraction Fraction, a Volumetric Measure of Myocardial Function
INTRODUCTION Ejection fraction (EF) is commonly used to summarize left ventricular (LV) systolic performance, but compensatory changes in LV geometry, e.g. concentric LV hypertrophy, allow preservation of EF despite LV dysfunction at the level of myofibrillar contraction. In contrast to EF, myocardial contraction fraction (MCF, the ratio of stroke volume to myocardial volume) is independent of “endocardial surface function.” MCF is a volumetric measure of total myocardial systolic performance and is the 3D extension of the 1D/2D midwall shortening fraction. Prior reports suggest sex-specific differences in LV EF, but sex- and age-specific differences in MCF are unknown.
METHODS Adults from the Framingham Heart Study Offspring cohort underwent cardiac MRI on a 1.5-T Philips scanner. Contiguous-slice SSFP breathold cine acquisitions were performed to obtain volumetric datasets with 1.56x1.92x10.0 mm3 voxels. LV borders were manually traced and LV stroke and myocardial volumes were determined using summation of slices to calculate MCF. We analyzed all participants (N=606) who were free of any history of hypertension at this and all prior examinations (no SBP>140 or DBP>90 mmHg, no antihypertensive medication). Results are summarized as mean±SD. Gender differences were assessed using 2-tailed unpaired t tests, p<0.05 was considered significant.
RESULTS Overall, women had greater MCF than men (0.93±0.12 vs. 0.80±0.14, p<0.0001), and this difference was consistent when considering subjects partitioned by quartiles of ages. There were no significant gender differences in age: N=239 men, 60.9±7.9y vs N=367 women, 61.3±8.5y, p=0.53. Correlations of MCF with age in men and women were similar, but a significant non-zero correlation was found only in women (r=−0.17, p=0.001) and not in men (r=−0.09, p=0.18, NS).
CONCLUSIONS MCF is significantly greater in women than men across all ages, suggesting that each gram of female myocardium is proportionally able to eject a greater volume of blood than each gram of male myocardium. MCF may prove to be useful for early identification of patients with heart failure despite preserved EF, a population in which women are over represented. For studies employing MCF, reference and partition values should be sex-specific.