Is moderate asymmetric septal hypertrophy considered Hypertrophic Cardiomyopathy (HCM)?

From the Guidelines

Moderate asymmetric septal hypertrophy can be considered a form of hypertrophic cardiomyopathy (HCM) if it meets specific diagnostic criteria and is accompanied by other supporting features. The diagnosis of HCM is established most easily and reliably with two-dimensional echocardiography by demonstrating left ventricular hypertrophy (LVH) (typically asymmetric in distribution, and showing virtually any diffuse or segmental pattern of left ventricular [LV] wall thickening) 1. HCM is typically diagnosed when there is unexplained left ventricular wall thickness ≥15 mm in any myocardial segment, with asymmetric septal hypertrophy being the most common pattern. However, milder forms of septal thickening (11-14 mm) may represent early or less severe manifestations of HCM, especially when accompanied by other supporting features such as family history of HCM, ECG abnormalities, or genetic testing positive for HCM-associated mutations 1. Some key points to consider in the diagnosis of HCM include:

• The presence of unexplained left ventricular wall thickness ≥15 mm in any myocardial segment
• Asymmetric septal hypertrophy as the most common pattern
• Milder forms of septal thickening (11-14 mm) may represent early or less severe manifestations of HCM
• The importance of distinguishing pathological septal hypertrophy from physiological adaptations seen in athletes or secondary hypertrophy due to conditions like hypertension or aortic stenosis
• The clinical significance of moderate asymmetric septal hypertrophy depends on whether it causes functional abnormalities like left ventricular outflow tract obstruction, diastolic dysfunction, or arrhythmias
• Patients with moderate asymmetric septal hypertrophy should undergo comprehensive cardiac evaluation including echocardiography, possibly cardiac MRI, ECG, and in some cases genetic testing to determine if they truly have HCM requiring monitoring or treatment 1. It's also important to note that the natural history of HCM can be altered by a number of therapeutic interventions, including ICDs for secondary or primary prevention of sudden death, drugs to control heart failure symptoms, surgical septal myectomy or alcohol septal ablation for progressive and drug-refractory heart failure caused by LVOT obstruction, and heart transplantation for systolic or diastolic dysfunction associated with severe unrelenting symptoms 1.

From the Research

Definition of Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a genetic cardiac disorder characterized by unexplained left ventricular hypertrophy in the absence of other cardiac or systemic etiologies 2.

Asymmetric Septal Hypertrophy

Asymmetric septal hypertrophic cardiomyopathy (ASH) is the common phenotype of HCM, and it can be classified into different subtypes based on magnetic resonance imaging (MRI) findings 3.

Classification of Septal Morphology

Septal morphologies in HCM can be categorized into four patterns of hypertrophy: catenoid, simple sigmoid, neutral, and apical 4.

Moderate Asymmetric Septal Hypertrophy

While there is no direct evidence in the provided studies that specifically defines moderate asymmetric septal hypertrophy as HCM, the studies suggest that asymmetric septal hypertrophy is a common phenotype of HCM 3.

• The presence of septal hypertrophy in HCM is common, and it can be classified into different subtypes based on MRI findings 4, 3.
• The classification of septal morphology in HCM is associated with significant differences in clinical, haemodynamic, and myocardial characteristics 4.
• ASH can be classified into three subtypes using MRI: contiguous, sigmoid, and reverse-curve subtypes, which might be related to the presence of risk factors 3.

Treatment of Hypertrophic Cardiomyopathy

The treatment of HCM typically involves medical management with β-blockers or verapamil, and disopyramide may be used in patients who are persistently symptomatic despite β-blockers or verapamil and have evidence of left ventricular outflow tract obstruction 5, 6, 2.

• Disopyramide is a safe and effective medication that reduces heart failure symptoms and left ventricular outflow tract gradient and delays the need for invasive therapy in patients with obstructive HCM 6, 2.
• The pharmacologic rationale for use of disopyramide is largely based on its strong negative inotropic property 2.