Myocardial Contraction Fraction in Outcomes in Transthyretin Amyloidosis

Abstract

Introduction Myocardial contraction fraction (MCF), the ratio of stroke volume to myocardial volume, is a novel index of myocardial function that is a volumetric measure of myocardial shortening, highly correlated with global longitudinal strain. Previous studies have demonstrated that MCF can distinguish between physiological and pathological causes of hypertrophy and is superior to ejection fraction (EF) in predicting mortality in transthyretin cardiac amyloidosis (ATTR-CA). The association of MCF on major adverse cardiac events (MACE) in ATTR-CA while on disease modifying therapy has not yet been defined. Hypothesis MCF will predict MACE while EF will not in patients taking tafamidis. Methods Clinical and demographic characteristics of patients initiated on tafamidis were measured. Estimates of end systolic, diastolic volumes, left ventricular mass and volume from M-Mode echocardiography were used to calculate EF and MCF. Subjects were divided according to median values for MCF and EF and followed for at least 12 months to assess MACE, defined as unplanned cardiovascular hospitalization or all-cause mortality. Kaplan-Meier curves compared event rates above and below median MCF and EF, with log-rank testing performed. Results There were 65 subjects initiated on Tafamidis. Median age was 77 years, with 78% male, 50 with wild-type, 15 with mutations (13 V122I, 2 Thr60Ala). Median MCF and EF were 16% and 52% respectively. Subjects below MCF 16% experienced more MACE at 15 month follow-up than above 16% (log-rank p = 0.041), while no difference was observed above or below median EF 52% (log-rank = 0.766). Conclusion MCF of 16% is better able to discriminate risk for unplanned cardiovascular hospitalization than EF of 52%.