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Hypertrophic obstructive cardiomyopathy

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Hypertrophic obstructive cardiomyopathy (HOCM) is a genetically determined disease of the heart muscle. It is caused by a mutation in about 60 to 70% of cases, affecting 1 out of 200 adults in the general population. [1]

The mutation involves one of several sarcomere genes which are responsible for coding components of the contractile apparatus of the heart and is inherited in an autosomal dominant fashion. The major causes of death in HOCM are sudden cardiac death (SCD), heart failure, and stroke. [2] [3]

Diagnosis

HOCM typically manifests during adolescence but can also develop during infancy, childhood, and adulthood (ages 20 to 50 years). [4] HOCM patients who are identified late in life (age >60 years) are at low risk for HOCM-related death or adverse events compared with early-onset disease.

The main characteristic feature of HOCM is left ventricular hypertrophy (LVH). In most patients with HOCM, the LV wall thickness typically does not change once early adulthood is reached. LVH can be associated with a wide range of clinical manifestations and haemodynamic abnormalities. In most patients with HOCM, the LVH is not progressive, and HOCM is compatible with normal longevity in the vast majority with an annual mortality rate of 1% or less among non-referral-based cohorts.

A clinical diagnosis of HOCM is confirmed by any of the following: [5]

  • Unexplained increased LV wall thickness ≥15mm is imaged anywhere in the LV wall
  • A wall thickness of ≥13mm, especially if identified in a patient who has an affected family member with HOCM.

Newer techniques (genetic testing, cardiac MRI) have increased recognition of the HOCM phenotype and improved clinical diagnosis. [6] [7]

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Complications

People with HOCM can develop abnormalities with the heart’s ability to pump effectively. This includes left ventricular outflow obstruction and diastolic dysfunction. Myocardial ischaemia and mitral regurgitation can also develop, depending on where the hypertrophy is situated. Heart failure is the most common presentation in patients with HOCM, occurring in >90% of symptomatic patients. [8]

Other complications include chest pain, arrhythmias, syncope, acute haemodynamic collapse, and end-stage disease.

Progression of HOCM

Treatment

A number of treatment interventions should be considered which may prolong life for some HOCM patients. These include:

  • Medical therapy
  • Non-pharmacological therapies (septal reduction therapy; catheter ablation)
  • Implantable cardioverter-defibrillator (ICD)
  • Heart transplant

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Primary prevention ICD is for HOCM patients with ≥1 major risk factor. Major risk factors include: sudden death in one or more first-degree relatives; maximal LV wall thickness ≥30 mm; or a recent and unexplained syncopal event. [9] Secondary prevention ICD is for HOCM patients who have survived cardiac arrest due to ventricular tachycardia or ventricular fibrillation and are at an increased risk for recurrent events. [10]

Genotype positive/phenotype negative patients

This refers to family members who carry a disease-causing sarcomere mutation but without LVH. Approximately 50% of these individuals have an abnormal ECG. Despite not having increased wall thickness yet, their myocardium may still not be structurally normal.

The risk of developing clinical evidence of HOCM with LVH in family members who have a HOCM-related mutation is not clear. An annual phenotypic conversion rate has been estimated to be <1-5% per annum. [11] Studies suggest that it is possible for many genotype-positive, phenotype-negative patients to achieve normal longevity without developing LVH or incurring HOCM-related complications.

The risk of sudden death in gene carriers is also unknown but considered to be very low, and therefore consideration for prophylactic ICD should be resolved on an individual case basis. However, current society guidelines do not recommend excluding genotype positive/phenotype negative HOCM family members from participating in organized competitive sports. [12] [13] [14]

Underwriting considerations

HOCM can now be considered a disease compatible with normal life expectancy for many patients with this disease. Younger age of onset is associated with increased mortality risk compared to the general population. [15]

Author

Dr Monique Esterhuizen

Chief Medical Officer and Head of Medical & Health Services

Hannover Life Re of Australasia

November 2023

References

  1. Semsarian C, Ingles J, Maron MS, Maron BJ. New perspectives on the prevalence of hypertrophic cardiomyopathy. J Am Coll Cardiol 2015; 65:1249.
  2. Elliott PM, Gimeno JR, Thaman R, et al. Historical trends in reported survival rates in patients with hypertrophic cardiomyopathy. Heart 2006; 92:785.
  3. Maron BJ, Olivotto I, Spirito P, et al. Epidemiology of hypertrophic cardiomyopathy-related death: revisited in a large non-referral-based patient population. Circulation 2000; 102:858
  4. Maron BJ. Hypertrophic cardiomyopathy: a systematic review. JAMA 2002; 287:1308
  5. Gersh BJ, Maron BJ, Bonow RO, et al. 2011 ACCF/AHA guideline for the diagnosis and treatment of hypertrophic cardiomyopathy: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation 2011; 124:2761
  6. Maron BJ, Semsarian C. Emergence of gene mutation carriers and the expanding disease spectrum of hypertrophic cardiomyopathy. Eur Heart J 2010; 31:1551
  7. Maron MS, Maron BJ, Harrigan C, et al. Hypertrophic cardiomyopathy phenotype revisited after 50 years with cardiovascular magnetic resonance. J Am Coll Cardiol 2009; 54:220
  8. Wigle ED, Rakowski H, Kimball BP, Williams WG. Hypertrophic cardiomyopathy. Clinical spectrum and treatment. Circulation 1995; 92:1680.
  9. Trivedi A, Knight BP. ICD Therapy for Primary Prevention in Hypertrophic Cardiomyopathy. Arrhythm Electrophysiol Rev. 2016;5(3):188-196. doi: 10.15420/aer.2016:30:2. PMID: 28116084; PMCID: PMC5248664.
  10. Elliott PM, Sharma S, Varnava A, et al. Survival after cardiac arrest or sustained ventricular tachycardia in patients with hypertrophic cardiomyopathy. J Am Coll Cardiol 1999; 33:1596.
  11. Maurizi N, Michels M, Rowin EJ, et al. Clinical Course and Significance of Hypertrophic Cardiomyopathy Without Left Ventricular Hypertrophy. Circulation 2019; 139:830
  12. Maron BJ, Yeates L, Semsarian C. Clinical challenges of genotype positive (+)-phenotype negative (-) family members in hypertrophic cardiomyopathy. Am J Cardiol 2011; 107:604.
  13. Caselli S, Pelliccia A. The electrocardiogram and the phenotypic expression of hypertrophic cardiomyopathy. Eur Heart J 2019; 40:982
  14. Maron BJ, Udelson JE, Bonow RO, et al. Eligibility and Disqualification Recommendations for Competitive Athletes With Cardiovascular Abnormalities: Task Force 3: Hypertrophic Cardiomyopathy, Arrhythmogenic Right Ventricular Cardiomyopathy and Other Cardiomyopathies, and Myocarditis: A Scientific Statement From the American Heart Association and American College of Cardiology. Circulation 2015; 132:e273.
  15. Maron BJ, Casey SA, Poliac LC, et al. Clinical course of hypertrophic cardiomyopathy in a regional United States cohort. JAMA 1999; 281:650.

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