Left atrial ejection force assessed by 4D flow CMR identifies early hemodynamic decompensation in HCM patients

Background In Hypertrophic cardiomyopathy (HCM) is accompanied with impaired left ventricular (LV) filling and stiff ventricle. Left atrial contractile function may increase to compensate at early stage and decompensate at advanced stage. Purpose To develop a novel index of LA contractile function in terms of LA ejection force from 4D flow CMR, and hypothesize LA ejection force can differentiate hemodynamic compensation from decompensation in a cohort of HCM. Methods Patients with HCM (n=60) and 20 healthy volunteers with similar age underwent 4D flow CMR were analyzed. Through-plane flow multiplanar reconstruction across the mitral orifice was generated using the four-chamber long-axis view as anatomical guidance, and mitral orifice contours were delineated throughout the cardiac cycle. The mitral orifice area (MOA) and blood velocity across mitral orifice were derived (Fig. 1). LA ejection force during atrial systole was calculated as ρ*(peak A-wave velocity)2 *MOA, where ρ = 1.06g/cm3, peak A-wave velocity was identified as the maximal value during late diastole from the blood velocity curve. Compensated hemodynamics in HCM is defined as: preserved or hyperdynamic LVEF (>60%), impaired relaxation but manageable filling pressure (PCWP <18 mmHg), where PCWP was calculated using formula: PCWP = 6.1352 + 0.07204*maximal LA volume + 0.02256*LV mass. Results Compensated (n = 30) and decompensated HCM (n = 30) cohorts were comparable in age (mean 51 years), body surface area, and heart rate. Decompensated HCM exhibited significantly increased left ventricular and left atrial volumes, with concomitant reductions in LV and LA ejection fractions, indicative of advanced hemodynamic impairment. Compared with controls, HCM patients exhibited significantly reduced LA ejection force (1.79 ± 1.08 vs 3.87 ± 0.99 kdyn, P < 0.001), with further reduction in decompensated HCM compared to compensated HCM (1.32 ± 0.80 vs 2.25 ± 1.14 kdyn, P = 0.001). The relation between disease progression and LA ejection force is presented in Fig. 2. Using a threshold of 2.88 kdyn (mean – 1 SD of the normal range) identified 100 % of decompensated HCM patients, whereas a more stringent threshold of 1.93 kdyn (mean – 1.96 SD) identified 23 of 30 decompensated HCM cases. Conclusions 4D flow CMR derived LA ejection force is significantly reduced in HCM, particularly in decompensated patients. Thresholds derived from normal reference values effectively identify decompensated HCM, highlighting LA ejection force as a sensitive marker of atrial dysfunction and disease progression.