We prospectively recruited 118 consecutive HCM patients and 35 age- and sex-matched controls, who were referred for CMR examination from January 2018 to June 2019. HCM was diagnosed by CMR with the following criteria: unexplained LV wall thickness ≥ 15 mm (or ≥ 13 mm with a clear family history of HCM) in adult patients without any other systemic disease or cardiac diseases that could be responsible for myocardial hypertrophy . The preserved EF was defined as LVEF ≥ 50% by CMR or echocardiography. All HCM patients with evidence of coronary heart disease with significant stenosis ≥ 50% were excluded by computed tomography or invasive coronary angiography. Additionally, patients with evidence of ischemic cardiomyopathy or with a history of invasive cardiac procedure, such as alcohol septal ablation, septal myectomy or heart transplantation, were also excluded. The exclusion criteria for all subjects included renal dysfunction (glomerular filtration rate (eGFR) < 30 mL/min/1.73 m2) and any CMR contraindications, such as claustrophobia or inner device implantation. According the above criteria, 19 HCM patients and 2 healthy controls had a LVEF < 50%, 5 patients lacked LGE images because they had renal dysfunction, 4 patients had a history of severe coronary artery disease and 4 patients had a history of cardiac surgery. Thus, 86 HCM patients and 33 healthy controls were eventually enrolled in the present study. This study was approved by the ethics committee of Tongji Medical College, Huazhong University of Science and Technology, and all participants in the study signed informed consent forms autonomously and voluntarily prior to participation.
The biochemical indices included the serum Nt-proBNP, hs-cTnI, creatine kinase (CK), creatine kinase-MB (CK-MB), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) levels, which were obtained for clinical evaluation purposes. Peripheral venous blood samples were collected from all HCM patients at the morning of CMR examination. Blood samples were centrifuged at 3000 rpm for 15 min, and plasma was stored at −80∘C for further analysis. An electrochemiluminescent immunoassay assay (Roche Diagnostics, Mannheim, Germany) was performed for measurement of plasma Nt-proBNP levels. The analytical range was 5 to 35000 pg/mL and the normal reference range was ≤ 100 pg/mL. The inter-assay and intra-assay coefficients of variation were < 4.7% and < 5.8%, respectively. Serum levels of hs-cTnI were measured using the Abbott Architect high-sensitivity cTnI assay (Abbott Diagnostics, Abbott Park, USA). The lower limit of detection was 1.2 ng/L; the 99th percentile cutoff value was 26 ng/L; and the coefficient of variation was < 10%. Serum CK, CK-MB, AST and LDH levels were determined using an automatic particle chemiluminescence immunoassay (Abbott Aeroset, Minnesota) with the use of commercial kits (Abbott). The normal reference ranges of the assays were the following: 38 to 174 U/L for CK, < 6.6 ng/mL for CK-MB, 8 to 40 U/L for AST and 109 to 245 U/L for LDH.
CMR examination protocol
All CMR examinations were performed with a 1.5 T system (MAGNETOM Aera, Siemens Healthineers, Erlangen, Germany). The LV long-axis (4-, 3-, 2-chamber) and short -axis (covering all basal to apex segments) cine images were acquired using a balanced steady state free precession (bSSFP) sequence. The parameters were as follows: field of view (FOV): 360 mm × 270 mm, matrix: 256 × 192, repetition time/echo time (TR/TE): 2.9 ms/1.2 ms, flip angle: 80°, and slice thickness: 6 mm. LGE images of the LV long-axis (4-, 3-, 2-chamber) planes and whole LV short-axis slices were performed 10 to 15 minutes after the cubital intravenous administration of a bolus of gadolinium-diethylenetriamine pentaacetic acid (DTPA) (0.2 mmol/kg, Magnevist, Bayer Healthcare, Berlin, Germany) using a phase-sensitive inversion recovery (PSIR) sequence. The parameters were as follows: FOV: 360 mm × 270 mm, matrix: 256 ×192, TR/TE: 12.44 ms/1.19 ms, inversion recovery time: 300 ms; flip angle: 40°, and slice thickness: 8 mm.
CMR image analysis
All CMR image analyses were semi-quantitatively performed using the commercial post-processing software (Cvi42, Circle Cardiovascular imaging, Calgary, AB, Canada).
For the quantification of LV volume and function, we imported all short-axis cines into the software and then manually delineated the LV endocardial and epicardial contours. All cardiac functional parameters were indexed to the body surface area (BSA) in this study. The LVEF, end-diastolic volume index (EDVI), end-systolic volume index (ESVI), stroke volume index (SVI), cardiac index and end-diastolic myocardial mass (MI) were acquired. Additionally, the LV end-diastolic maximum wall thickness (MWT) was defined as the greatest segments of the 16-segment model of the American Heart Association (AHA). For the quantification of LV myocardial strain, we imported all LV long- and short-axis cines into the software. Then, we manually delineated the LV endocardial and epicardial contours of all the above images in the end diastole stage. Then, the LV 3D global peak systolic longitudinal strain (GLS), circumferential strain (GCS) and radial strain (GRS) were semi-quantitatively calculated using the tissue feature tracking method (Fig. 1).
For the quantification of the extent of LGE, we imported the whole LV short-axis slices of the LGE images into the software and manually delineated the LV endocardial and epicardial contours. A semi-quantitative grey-scale threshold method was used to calculate the extent of LGE. The enhanced myocardium was defined as a signal intensity threshold of > 6 SD above the mean signal intensity of the normal myocardium [23, 24]. The previous studies demonstrated that the 6SD is the most optimal threshold especially for quantitative LGE in patients with HCM, as it is most strongly correlated with histopathology , as well as manual measurements . Then, the total LV enhanced volume and mass were calculated, and the extent of LGE was expressed as the percentage of the total myocardial mass (%LGE) (Fig. 2). The HCM patients were divided into two subgroups based on the presence or absence of LGE. All papillary muscles and trabeculae were excluded from the LV myocardium during the LV function, deformation and LGE analyses.
The Kolmogorov–Smirnov test was used to check normality. Data are expressed as the mean ± SD or number (percentage) for all continuous and categorical variables. Differences between two groups were assessed using an independent-sample Student’s t test or the Mann-Whitney test. Comparisons between three groups were analyzed using one-way ANOVA or the Kruskal-Wallis test, and the Bonferroni correction was selected as the post hoc test when appropriate. The chi-square test or Fisher’s exact test was used for the comparison of all categorical variables. Pearson’s or Spearman’s correlation test was applied for the assessment of the LGE% and all candidate variables, as appropriate. Univariate and multivariate linear regression analyses were utilized to assess the associations between the LGE% and all candidate variables. Receiver operating characteristic (ROC) curve analysis was applied for the detection of the diagnostic performance of the presence of LGE. The highest Youden’s index values were used to calculate the optimal cut-off values of the candidate variables. The sensitivity, specificity, optimal cut-off value, positive predictive value (PPV) and negative predictive value (NPV) were calculated and expressed with the corresponding 95% confidence intervals (CI). An intra-class correlation coefficient (ICC) with 95% CI was used for the assessment of the intra- and inter-observer agreement. A two-sided p value < 0.05 was considered statistically significant. Analyses were performed using SPSS Statistics (SPSS, version 21, IBM, Chicago, IL, USA) and MedCalc 16.2.0 (MedCalc Software, Mariakerke, Belgium).