Myocardial contraction fraction and mortality in cardiac amyloidosis: a prospective single-center cohort study

Left ventricular ejection fraction (LVEF) often remains normal in cardiac amyloidosis (CA) because declines in stroke volume (SV) parallel reductions in end-diastolic volume. The myocardial contraction fraction (MCF), the ratio of SV to myocardial volume, has been proposed as superior to LVEF in predicting mortality in CA.

Thirty patients with confirmed CA underwent echocardiography and were followed for a mean of 18.2 ± 5.8 months. MCF was calculated from standard two-dimensional echocardiographic measurements. Cox proportional hazards modeling with Lasso-penalized selection was used to evaluate the association of MCF with all-cause mortality.

Mean age was 70.1 ± 8.6 years; 76.7% were male. Thirteen patients (43.3%) died. MCF was lower among those who died compared with survivors (21.9% vs 38.2%; p < 0.0001); 87.5% of patients with MCF ≤ 25% died, compared with 27.3% of those with MCF > 25%. MCF ≤ 25% was independently associated with mortality (HR: 5.456; 95% CI: 1.628-18.29; p = 0.006); modeled as a continuous variable, each 5-percentage-point increase in MCF was associated with lower mortality (HR: 0.57; p = 0.002), while MAPSE < 10 mm and grade 3 diastolic dysfunction were retained in the multivariable model but did not reach significance after penalization.

MCF ≤ 25% demonstrated numerically greater discriminative ability for all-cause mortality compared with LVEF (C-statistic 0.83 vs 0.71) and was the only echocardiographic parameter to remain an independent predictor after Lasso-penalized multivariable adjustment. These hypothesis-generating findings, from a small single-centre cohort, require validation in larger, subtype-specific studies.