Non-obstructive hypertrophic cardiomyopathy exhibit subclinical abnormalities in systolic and diastolic ventricular kinetic energy and systolic haemodynamic forces on 4D flow CMR
Authors: Pola K , Ashkir Z , Arheden H , Watkins H , Neubauer S , Arvidsson P M , Raman B 
Published: November 2023

Abstract

Background
Patients with non-obstructive hypertrophic cardiomyopathy (nHCM) exhibit a range of anatomical variations including septal, reverse septal, apical, and concentric hypertrophy. Cardiovascular magnetic resonance imaging (CMR) with 4D flow permits assessment of haemodynamic forces (HDF) and kinetic energy (KE) of intraventricular blood flow (1,2). These parameters may indicate subclinical flow inefficiencies which may not be detectable on routine transthoracic echocardiography (3,4). The aim of this study was therefore to investigate if left ventricular (LV) HDF and KE differ between nHCM and controls, and between subgroups of nHCM.

Methods
Patients with nHCM (n=71) and age- and sex-matched controls (n=20) underwent CMR at 3T (Trio, Siemens) (Table 1). Patients were categorised as phenotype positive (P+) based on presence of hypertrophy (maximum wall thickness ≥15mm, or ≥13mm with a positive family history), and as phenotype negative (P-) referring to pre-hypertrophic sarcomeric variant carriers. Patients with P+ nHCM were classified into subgroups based on the pattern of hypertrophy. Left ventricular HDF and KE were computed over the cardiac cycle using validated modules (1) (Figure 1). Measurements of HDF were based on the Navier-Stokes equations (1), and analysed in three orthogonal directions as root mean square and peak values for systole and diastole. Force ratio was calculated as the sum of the two transverse components divided by the longitudinal component. The Mann-Whitney U test was used for group comparisons, Pearson analysis for correlations, and Fisher’s exact test for binary categorical data.

Results
P+, P- patients and controls had comparable LV ejection fraction from CMR, LV outflow tract pressure gradients, and diastolic parameters on echocardiography (Table 1). Systolic HDF and force ratio were increased, primarily in the lateral wall-septum direction in septal and reverse septal P+ patients compared to controls, but did not differ in any other directions in P+ compared to P- patients and to controls (Table 1, Figure 1). Diastolic HDF and force ratio did not differ between groups.
Systolic KE was increased in P+ patients compared to P- and to controls (Table 1, Figure 1), mainly through increased KE in patients with septal and reverse septal hypertrophy. P+ patients also had increased late diastolic (A-wave) KE relative to P- patients and to controls (Table 1).
Both systolic KE and force ratio correlated with maximum wall thickness in patients (r=0.31, p=0.005; r=0.43, p&lt;0.0001).

Conclusion
In non-obstructive hypertrophic cardiomyopathy, left ventricular HDF and KE analysis from 4D flow CMR detect subclinical flow abnormalities. Increased systolic HDF and KE are linked to the extent and pattern of hypertrophy. Late diastolic A-wave KE was also abnormal in P+ patients despite normal diastolic velocities on echocardiography.Table 1Figure 1