Phenotyping Hypertophic Cardiomyopathy with Cardiac MRI – Insights into Tissue characterization and SCD Risk Stratification

The role of cardiac magnetic resonance imaging (MRI) in the clinical management of patients with hypertrophic cardiomyopathy (HCM) is increasingly important, as reflected in recent guideline updates. Sudden cardiac death (SCD) risk stratification poses a significant challenge to clinicians and remains a topic of debate among international cardiology societies. Although cardiac MRI tissue parameters were initially excluded from endorsed SCD risk stratification strategies, studies have shown their utility in improving risk assessment, which is mirrored in their inclusion in recent guideline updates. This study examines the phenotype of HCM patients using cardiac MRI and evaluates its potential in refining SCD risk stratification.

This monocentric cross-sectional longitudinal study recruited patients who visited the cardiomyopathy outpatient clinic at University Hospital Heidelberg and underwent cardiac MRI examinations. Secondary causes of left ventricular hypertrophy and HCM phenocopies were excluded through comprehensive clinical testing, including extended family history, physical examinations, ECG, echocardiography, coronary angiography, genetic testing, and cardiac MRI. Follow-up visits and unplanned admissions were recorded over a 10-year period. Cardiac dimensions and volumetric analyses were performed using short-axis steady-state free precession (SSFP) cine sequences. Tissue characterization was assessed using T1- and T2-weighted fast spin-echo (FSE) sequences and late gadolinium enhancement (LGE) sequences.

A total of 198 HCM patients were recruited, the majority of whom were male (73.7%) and had no clinically relevant left ventricular outflow obstruction (69.1%). The mean left ventricular ejection fraction was 63.9% ± 8.86%, and the median maximum left ventricular wall thickness was 19 mm (IQR 16-24mm). LGE was present in most cases, with a mean LV-LGE mass of 7.1% ± 6.8%. Genotype-positive HCM patients had a higher mean LGE (8.8% ± 7.8%) compared to genotype-negative patients (5.6% ± 6.6%). The median T1 relaxation time was slightly elevated (1058 ms; IQR 1009-1077ms), while the T2 relaxation time was normal (50 ms ± 3.5 ms). Over a follow-up period of 10 years, 12 patients suffered SCD. Patients with an LGE mass of 10% or more had a significantly higher risk for SCD (hazard ratio = 3.46; p = 0.037) (Fig. 1).

This study characterizes the phenotype of HCM patients using cardiac MRI. Genotype-positive HCM patients presented with more severe left ventricular hypertrophy and a higher percentage of myocardial fibrosis. Cardiac MRI not only aids in differentiating the diverse causes of left ventricular hypertrophy but also serves as an additional tool for SCD risk stratification. LGE sequences enable the identification of myocardial fibrosis, which is associated with poor outcomes.