Hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is defined as the unexplained, asymmetical or concentric hypertrophy of the undilated left ventricle. There is also hypertrophy of the right ventricle.

It may be inherited as an autosomal dominant condition, but at least half of cases may be the result of sporadic mutation.

Summary points:

• most common genetic cardiac disease (1)
  • approximate prevalence of 1:500 (2)
  • note that although the estimated prevalence of HOCM in adults is 1 in 500 - in children, the prevalence is much lower (4)
• characterised by marked and asymmetric left ventricular hypertrophy, a non-dilated left ventricular cavity, diastolic impairment, generally systolic function is preserved
• left ventricular outflow obstruction at rest caused by mitral-septal contact during systole occurs in in about 20% of patients
• diagnostic features:
  • LV wall thickness >= 13mm on echocardiography in the absence of a well recognised. physiological cause (2)
• in many cases patients remain asymptomatic throughout life. However in other cases patients develop heart failure or atrial fibrillation, and some die suddenly, often at a young age without previous symptoms
  • typically develops in adolescence but late onset well recognised
    • 40-50% have left ventricular outflow tract obstruction with associated systolic murmur. Symptoms include chest pain, dyspnoea, palpitations, syncope. Minority at risk of SCD, stroke or heart failure (2)
• commonest cause of sudden cardiac death in young people and athletes
• cardioverter defibrillator is the only effective treatment for the prevention of sudden death
• medical treatment with blockers or verapamil has been shown to improve symptoms of heart failure - however medical treatment has not been shown to modify the clinical course
• if outflow obstruction and severe symptoms unresponsive to medical therapy represent then these patients are candidates for surgical myectomy or alcohol septal ablation to relieve the outflow obstruction
• the minority of adult patients will develop proxysmal or chronic atrial fibrillation
• annual mortality related to HOCM is 1-2% in most studies with contemporary management strategies, and may be as low as 0.5% (4)
  • most HCM-related deaths at age <= 60 years occur suddenly, while older patients die more often of stroke or heart failure
  • sudden cardiac death is often related to ventricular arrhythmias, which can be a consequence of ischaemia, left ventricle outflow tract (LVOT) obstruction, or supraventricular arrhythmias

Exercise and HOCM

• one of the major determinants of exercise intolerance and limiting symptoms among patients with obstructive hypertrophic cardiomyopathy (HCM) is an elevated intracardiac pressure resulting from left ventricular outflow tract obstruction (5)
• HOCM is the most frequently cited cause of exercise-related sudden cardiac death (SCD) in young individuals and has claimed the lives of some high-profile athletes (6)
  • the circumstantial link between exercise and SCD from HOCM has resulted in conservative exercise recommendations which focus on activities that should be avoided rather than the minimal amount of physical activity required to reap the multiple rewards of exercise
  • consequently, most patients with HOCM are confined to a sedentary lifestyle through fear of SCD, with accruing risk factors such as obesity and low cardiorespiratory fitness that confer a worse prognosis.
  • evidence has shown that recent exercise programmes in asymptomatic and symptomatic individuals with HOCM have shown that mild and moderate exercise is safe and accompanied by increased functional capacity and improved quality of life
    • population studies also reveal that individuals with HCM in the higher quartiles of self-reported physical activity have lower total cardiovascular mortality compared with those in the lower quartiles
  • the impact of vigorous exercise on the natural history of HOCM is unknown, although current experience suggests that affected adults with mild morphology and absence of high-risk factors may partake in such activity without adverse events
  • evidence has shown that, among patients with symptomatic obstructive HCM, treatment with aficamten (mong patients with symptomatic obstructive HCM, treatment with aficamten resulted in a significantly greater improvement in peak oxygen uptake than placebo) resulted in a significantly greater improvement in peak oxygen uptake than placebo (5)

Reference:

1. BMJ 2006;332:1251-1255.
2. Factfile (5/09).Inherited cardiovascular disease. British Heart Foundation.
3. Factfile (5/97). Hypertrophic cardiomyopathy. British Heart Foundation.
4. 2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: Developed by the task force for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death of the European Society of Cardiology (ESC) Endorsed by the Association for European Paediatric and Congenital Cardiology (AEPC), European Heart Journal, 2022;, ehac262, https://doi.org/10.1093/eurheartj/ehac262
5. Maron MS et al. Aficamten for Symptomatic Obstructive Hypertrophic Cardiomyopathy. NEJM May 13th 2024
6. Gati S, Sharma S.Exercise prescription in individuals with hypertrophic cardiomyopathy: what clinicians need to know.Heart Published Online First: 23 February 2022. doi: 10.1136/heartjnl-2021-319861