Asymmetric hypertrophic cardiomyopathy

Last revised by Joachim Feger on 9 Sep 2023

Asymmetric hypertrophic cardiomyopathy is the most common morphological variant or phenotype of hypertrophic cardiomyopathy (HCM).

Approximately 60-70% of cases with hypertrophic cardiomyopathy make up for the asymmetric phenotype 1-3.

Asymmetric hypertrophic cardiomyopathy might be associated with the following 1-4:

The clinical presentation of asymmetric hypertrophic cardiomyopathy does not differ significantly from other types of hypertrophic cardiomyopathy. Patients might present with a performance deficit, dyspnea, angina, presyncope, syncope on exertion or might be entirely asymptomatic 2.

Complications of asymmetric hypertrophic cardiomyopathy include 2-4:

Asymmetric hypertrophic cardiomyopathy features an asymmetric disproportionally increased myocardial wall thickness. The interventricular septum or more precisely the anteroseptal segments of the myocardium are most frequently affected but other segments might also be involved 1,2.  A wall thickness of ≥15 mm or z-score ≥2 and a ratio of >1.5 compared to non-hypertrophied normal segments is considered diagnostic 1.

The following subtypes of asymmetric septal hypertrophic cardiomyopathy can be distinguished 1:

  • basal septum hypertrophic cardiomyopathy
  • diffuse septum hypertrophic cardiomyopathy
  • mid septum hypertrophic cardiomyopathy
  • free-wall hypertrophic cardiomyopathy

Microscopically hypertrophic cardiomyopathy is characterized by the following features 2,5:

  • cardiac myocyte hypertrophy
  • cardiac myocyte disarray
  • interstitial or replacement fibrosis
  • bizarre enlarged nuclei with nuclear hyperchromasia and pleomorphism

Asymmetric septal hypertrophic cardiomyopathy has been defined by the following imaging criteria 1-4:

  • basal septal thickness ≥15 mm in adults
  • a wall-thickness ratio of the septum versus the inferior wall >1.5 
  • in children z-score≥2

Echocardiography can visualize asymmetric hypertrophy and can provide additional information on cardiac function including cardiac strain.

Cardiac MRI can demonstrate asymmetric hypertrophy and can assess cardiac function including cardiac volumes and cardiac strain. It can provide additional prognostic information concerning associated myocardial fibrosis and potential differential diagnosis.

The radiological report should include a description of the following:

Besides medical treatment patients with asymmetric hypertrophic cardiomyopathy might benefit from interventions as myomectomy or septal ablation especially if in association with left ventricular obstruction and higher gradients (e.g. ≥50 mmHg) 3,4. Patients with a history of cardiac arrest, significant arrhythmias or first-degree family history of sudden cardiac death, as well as massive hypertrophy (myocardial wall thickness ≥30 mm), should be considered for an implantable cardioverter-defibrillator 3.

Conditions that might mimic the clinical presentation or imaging appearance of asymmetric hypertrophic cardiomyopathy include 3,4,6:

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