Ascending aorta flow derangement is a marker of outflow obstruction in hypertrophic cardiomyopathy

Abstract

Background Alterations in systolic blood flow are a characteristic finding in patients with obstructive hypertrophic cardiomyopathy (HCM). Echocardiography is the gold standard for hemodynamic assessment in HCM, but this technique is generally limited to measurement of the left ventricular outflow tract (LVOT) pressure gradient and may not provide a complete description of the hemodynamic impact of the disease. In this study, we sought to employ time-resolved, three-dimensional phase contrast (4D flow) MRI to visualize and quantify 3D blood flow patterns in the LVOT and ascending aorta (AAo) in patients with obstructive and nonobstructive HCM. Methods Obstructive (n = 12) and non-obstructive (n = 18) HCM patients as well as 10 normal volunteers were included in this IRB-approved study. Obstruction was defined as LVOT pressure gradient > 30 mmHg on patients’ most recent echocardiography study (ΔPecho). Septal thickness, LVOT diameter and septum/free wall ratio were measured on SSFP cine MRI. 4D flow MRI data analysis included correction for eddy currents and velocity aliasing, followed by flow visualization and quantification in dedicated software (EnSight, CEI, Apex, NC). 3D blood flow patterns within the LVOT and AAo were graded for the presence of helical flow (absent = 0, mild/moderate = 1, severe = 2) by two observers blinded to diagnosis, and the results were averaged. MRI-measured pressure gradient (ΔPMRI) was calculated from the peak systolic 3D blood velocity profile within the LVOT using the simplified Bernoulli equation. (Figure 1) The Mann-Whitney U test was used to compare groups and Spearman’ s( rS) or Pearson’s (r) correlations were used as appropriate. Results