A total of 96 unrelated HCM patients who were diagnosed in our hospital from March 2016 to April 2019 were selected for gene detection, and 45 HCM patients who were carrying sarcomere gene mutations were selected as the gene positive/phenotype positive (G+/P+) group. Gene detection and conventional echocardiography were performed on the first-degree relatives of 45 unrelated patients (i.e., parents, children, siblings of the same parent). According to the examination results, 40 patients with HCM sarcomere mutation genes but no ventricular wall hypertrophy were selected as the gene positive phenotype negative (G+/P-) group. At the same time, 48 healthy volunteers without gene mutations were selected as normal controls.
The diagnostic criterion of HCM is that the thickness of the left ventricular wall in one or more myocardial segments is greater than or equal to 15 mm. It was necessary to exclude myocardial hypertrophy due to athletics, metabolic diseases, congenital heart diseases and other systemic diseases. In patients with a clear family history, an unexplained left ventricular wall thickness of one or more myocardial segments ≥ 13 mm was observed.
All G+/P+ individuals had interventricular septum thickening, with or without other left ventricular wall thickening. Before examination, β-blockers, calcium antagonists and angiotensin-converting enzyme inhibitors were stopped for at least 24 hours. The exclusion criteria were as follows: 1) patients with ventricular wall hypertrophy caused by hypertension, coronary heart disease, diabetes mellitus, valvular disease, congenital heart disease, pulmonary heart disease, metabolic disease or other factors, as well as athletes with cardiac hypertrophy, were excluded after obtaining a medical history and performing a physical examination, ECG and echocardiography; 2) patients with HCM whose left ventricular ejection fraction was less than 50%; 3) accepted patients with HCM who underwent percutaneous septal myocardial ablation, surgical septal myomectomy or permanent pacemaker implantation or experienced atrial fibrillation.
The inclusion criteria for the G+/P- group were as follows: 1) carrier of a sarcomere mutation gene verified by gene generation; 2) maximum left ventricular wall thickness (LVMWT) less than 13 mm detected by echocardiography. The exclusion criteria were as follows: 1) diabetes mellitus and hypertension; 2) cardiac muscle noncompaction and amyloidosis; 3) metabolic diseases and other systemic diseases; 4) significant pulmonary lesions; 5) treadmill test, coronary angiography or coronary artery computed tomography (CT) results indicating coronary heart disease, which was definitively diagnosed by imaging; 6) congenital heart disease; 7) moderate and severe valve stenosis and regurgitation detected by echocardiography.
Thirty first-degree relatives (parents, children, siblings of the same parent) of 45 unrelated patients were examined by gene testing and routine echocardiography. According to the results of the examination, 40 patients with HCM sarcomere mutation genes but no ventricular wall hypertrophy were selected as the positive gene group, and 48 healthy volunteers without gene mutations were selected as the normal control (G-/P-) group.
This cross-sectional study was conducted with the permission of the Institutional Ethics Committe. All subjects provided written informed consent.
For the ECG recordings, all subjects laid on their left side. Three short-axis views (mitral valve level, papillary muscle level and apical level) and three long-axis views (apical three-chamber view, apical two-chamber view and apical four-chamber view) of the LV were obtained on a Siemens S2000 ultrasound system (Axius, Siemens Medical Solutions, Malvern, PA, USA) with a 4Px probe (2.75–4.25 MHz). All images and clips were stored on the echocardiographic machine for analysis.
The interventricular septal thickness in diastole (IVSD) and left atrial diameter (LAD) were detected in the parasternal long-axis view. The LVMWT was measured in diastole in the basal, mid and apical short-axis views and in the apical long-axis view.
The left atrial volume (LAV), left ventricular end-diastolic volume (LVEDV) and left ventricular end-systolic volume (LVESV) were measured by the Simpson biplane method in the apical two-chamber and four-chamber views. The left atrial volume index (LAVI) was calculated as LAVI = LAV/body surface area (BSA).
The left ventricular outflow tract pressure gradient (LVOT-PG) was measured by continuous-wave Doppler (CW), and the sampling line was placed at the stenosis of the left ventricular outflow tract. In the apical four-chamber view, E/A was measured by pulsed-wave Doppler (PW). The ejection fraction (EF) was estimated using the Simpson biplane method.
All recordings were performed by professional sonographers. All conventional echocardiography parameters were read offline.
Velocity vector imaging echocardiography
Movie clips were recorded in 3 cardiac cycles and stored, and three apical views of the LV were analyzed offline using VVI software (Axius, Siemens Medical Solutions). A line was fitted along the internal surface of the LV endocardium at end-diastole. We used a frame-by-frame image tracking mode to estimate the movement of the myocardium. The acoustic marker of the myocardium was accurately identified and automatically tracked during several consecutive frames.
The longitudinal strain, circumferential strain, and radial strain curves were measured for each LV segment using long-axis and short-axis views according to the 16-segment model of the American Society of Echocardiography [8,9]. In this model, we placed a sampling point on each segment to record the strain experienced during 3 cardiac cycles. The mean value of each measurement was calculated for further analysis.
The global longitudinal strain (GLS), circumferential strain (GCS),and radial strain (GRS) were obtained by averaging all the segment strain values.
The displacement angle of the left ventricle was defined as the left ventricular rotation, with the clockwise direction rotation being positive and the counterclockwise direction rotation being negative. The Peak basilar rotation angle (PBr), the Peak mid rotation angle (PMr) and the peak apex rotation angle(PAr) were measured.The peak left ventricular twist (Ptw) angle was the pure difference in left ventricular rotation angle between the apex and the base, Ptw = PBr-PAr.
Fasting blood samples were collected from each patient within 24 hours after enrollment. Blood sampling was standardized without tourniquet and immediately centrifuged twice. NT-pro-BNP was analyzed on a Modular E 170 (Roche Diagnostics, Mannheim, Germany).
Interobserver and Intraobserver Variability
To assess the interobserver variability, which was expressed as the coefficient of variation (CV), 2 independent investigators who were blinded to each other’s results analyzed 30 randomly selected VVI movie clips. For intraobserver variability, 30 VVI movie clips were analyzed 3 times within an interval of 2 weeks by one investigator who was blinded to the previous results.
Data and Statistical analysis
All measurement data are expressed as the mean ± standard deviation (SD) and were analyzed using the SPSS 17.0 statistical software package (IBM Corp., Chicago, IL, USA). Significant differences between the two groups were analyzed by one-way ANOVA, and comparisons between the two groups were conducted using independent sample t tests. Pearson’s correlation analysis was used if the independent variables and dependent variables were normally distributed. The plasma concentration of NT- pro- BNP was logarithmically converted to log NT- pro- BNP, and the normal distribution was analyzed by analysis of variance. P < 0.05 and P < 0.01 indicated significant differences. Correlations between VVI parameters and NT- pro- BNP levels were analyzed by linear regression.