Predictors of atrial emptying function in patients with hypertrophic cardiomyopathy: insights from cardiovascular magnetic resonance

Abstract

Background: Atrial function is an integral part of cardiac function that is often neglected. Previous studies have shown that the left atrium (LA) is dilated and its contractile capacity is reduced in HCM patients. Whether this is related to pathophysiological aspects of HCM such as the degree of left ventricular (LV) hypertrophy, myocardial fibrosis or diastolic dysfunction remains to be established. Methods: 56 patients with HCM (44M/12F, mean age 55(plus or minus)14 years) and 50 normal controls (35M/15F, mean age 52(plus or minus)11 years) underwent CMR (Siemens Avanto 1.5T). HCM patients with reduced ejection fraction (EF<55%), known coronary artery disease, atrial fibrillation, hypertension, and moderate or severe valve disease were excluded. The imaging protocol included standard long and short-axis SSFP cines and late gadolinium enhancement (LGE) imaging. In addition to standard LV measurements (volumes, ejection fraction, mass), atrial volumes (max, min volume indexed for BSA) were measured using biplane-length-area method in 2 orthogonal planes (HLA and VLA SSFP retro-gated cine sequences). Diastolic function parameters (peak flow rate, time-to-peakflow, deceleration time) were assessed using manual tracing of endocardial border across all temporal phases of the short axis stack and corrected for end-diastolic volume and RR interval respectively. Ventricular fibrosis was calculated using a full-width at half-maximum algorithm and expressed as LV mass percentage. Results: Maximum LA volume was increased (63.3(plus or minus)16.6 vs 50.8 (plus or minus)14.5 ml/ m2; p<0.001) and LA ejection fraction (LAEF) was significantly reduced (54.1(plus or minus)11.2% vs 63.9(plus or minus)4.8%; p<0.001) in HCM patients compared to normal (Figure presented) controls, respectively (Figure). HCM patients had increased ejection fraction (76(plus or minus)6 vs 71(plus or minus)5%, p<0.001) and mass index (88(plus or minus)24 vs 57(plus or minus)12 g/ m2, p<0.001) compared to normals. The average amount of fibrosis in HCM patients was 11(plus or minus)7%. Univariate and multivariate analysis for LAEF in HCM patients are summarised in table 1. Age, LV mass index, LV wall thickness, and myocardial fibrosis showed significant bivariate correlations with LAEF. To analyse the relation between LAEF and ventricular parameters we performed linear regression analysis. This showed that LAEF is predicted independently by 4 variables in a backward selection model (R2=0.415): age, LV mass index, extent of myocardial fibrosis, and the LV time to peak flow. Conclusions: Atrial size is increased and function is impaired in HCM. This process is related to parameters characterizing other pathophysiological aspects of HCM including myocardial fibrosis, degree of LV hypertrophy, and LV diastolic dysfunction. In addition, age is an important contributor to LA emptying function. (Table presented).