CMR FEATURE TRACKING GLOBAL LONGLUTONAL STRAIN: A Novel Tool to Refine Sudden Cardiac Death Risk Prediction in Hypertrophic Cardiomomply

Hypertrophic cardiomyopathy (HCM) stands as one of the most common inherited cardiac disorders, characterized by abnormal thickening of the heart muscle, particularly the left ventricular (LV) myocardium, in the absence of other identifiable causes such as hypertension or aortic stenosis. First described in the mid-20th century, HCM has since been recognized as a heterogeneous condition with a broad spectrum of clinical presentations, ranging from asymptomatic individuals to those experiencing severe symptoms like heart failure, arrhythmias, and sudden cardiac death (SCD). The prevalence of HCM is estimated at approximately 1 in 500 individuals in the general population, though recent genetic and imaging studies suggest it may be as high as 1 in 200 when including subclinical cases. This makes HCM not only a significant public health concern but also a leading cause of SCD in young adults and athletes. Genetically, HCM is primarily an autosomal dominant disorder, with mutations in genes encoding sarcomeric proteins—such as myosin heavy chain (MYH7), myosin-binding protein C (MYBPC3), and troponin T (TNNT2)—accounting for the majority of cases. These mutations disrupt the normal architecture and function of cardiac myocytes, leading to myocardial hypertrophy, disarray, and fibrosis. The hypertrophy is often asymmetric, most commonly affecting the interventricular septum, but it can involve other regions like the apex or be concentric in nature. This structural remodeling impairs diastolic relaxation, increases LV outflow tract (LVOT) obstruction in a subset of patients (obstructive HCM), and predisposes the heart to electrical instability. Clinically, patients with HCM may present with symptoms such as dyspnea, chest pain, syncope, or palpitations, often exacerbated by exercise. However, a substantial proportion remain asymptomatic until a catastrophic event occurs. Diagnosis typically involves a combination of family history, electrocardiography (ECG) showing LV hypertrophy patterns, and imaging modalities like echocardiography, which reveals wall thickness greater than 15 mm in adults (or 13 mm in those with a family history). Cardiac magnetic resonance (CMR) imaging has become indispensable for detailed tissue characterization, identifying fibrosis via late gadolinium enhancement (LGE), which is a hallmark of adverse remodeling. Despite advances in management, including beta-blockers, calcium channel blockers, septal myectomy, alcohol septal ablation, and implantable cardioverter-defibrillators (ICDs), the unpredictable nature of SCD remains a central challenge in HCM care. SCD, often due to ventricular arrhythmias like ventricular tachycardia or fibrillation, accounts for up to 1% annual mortality in HCM cohorts, with higher rates in younger patients. Identifying those at highest risk is crucial to guide preventive therapies, yet current strategies fall short in precision.