Flow inefficiencies in non-obstructive HCM revealed by left ventricular kinetic energy and hemodynamic force analysis from 4D flow CMR

Patients with non-obstructive hypertrophic cardiomyopathy (HCM) exhibit myocardial changes which may cause flow inefficiencies not detectable on echocardiogram. We investigated whether left ventricular (LV) kinetic energy (KE) and hemodynamic forces (HDF) on 4D-flow CMR provide more sensitive measures of flow in non-obstructive HCM. 90 participants (70 non-obstructive HCM and 20 healthy controls) underwent 4D-flow CMR. Patients were categorized as phenotype positive (P+) based on maximum wall thickness (MWT) ≥15mm or ≥13mm for familial HCM, or pre-hypertrophic sarcomeric variant carriers (P-). LV KE and HDF were computed from 4D-flow CMR. Stroke work was computed using a previously valdated non-invasive method. P+, P- and controls had comparable diastolic velocities and LV outflow gradients on echocardiography, LV ejection fraction and stroke volume on CMR. P+ had greater stroke work than P-, higher systolic KE compared to controls (5.8vs4.1mJ, p=0.0009), and higher late diastolic KE relative to P- and controls (2.6vs1.4vs1.9 mJ, p<0.0001 respectively). MWT was associated with systolic KE (r=0.5, p<0.0001) and diastolic KE (r=0.4, p=0.005), which also correlated with stroke work. Systolic HDF ratio was increased in P+ compared to controls (1.0vs0.8, p=0.03) and correlated with MWT (r=0.3, p=0.004). Diastolic HDF was similar between groups. Sarcomeric variant status was not associated with KE or HDF. Despite normal flow velocities on echocardiography, non-obstructive HCM exhibited greater stroke work, systolic KE and HDF ratio, and late diastolic KE relative to controls. 4D-flow CMR provides more sensitive measures of hemodynamic inefficiencies in HCM, holding promise for clinical trials of novel therapies and clinical surveillance of non-obstructive HCM.