Hypertrophic cardiomyopathy classification

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Editors-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Soroush Seifirad, M.D.[2]

Overview

There are two variants of hypertrophic cardiomyopathy: an obstructive variant, and a non-obstructive variant. About 25% of individuals with hypertrophic cardiomyopathy (HCM) demonstrate an obstruction to the outflow of blood from the left ventricle during rest. In other individuals, obstruction only occurs under certain conditions. This is known as dynamic outflow obstruction because the degree of obstruction is variable and is dependent on the amount of blood in the ventricle immediately before ventricle systole (contraction). If left ventricular outflow obstruction is present, then this syndrome has been known as wide variety of terms including: hypertrophic cardiomyopathy or HCM, asymmetric septal hypertrophy or ASH, hypertrophic obstructive cardiomyopathy, HOCM, idiopathic hypertrophic subaortic stenosis or IHSS.

A non-obstructive variant of HCM is known as apical hypertrophic cardiomyopathy , which is also known as nonobstructive hypertrophic cardiomyopathy and Japanese variant hypertrophic cardiomyopathy or the Yamaguchi variant (since the first cases described were all in individuals of Japanese descent), also known as apical hypertrophic cardiomyopathy (ApHCM) or Yamaguchi syndrome.

Obstructive Variant

About 25% of individuals with hypertrophic cardiomyopathy (HCM) demonstrate an obstruction to the outflow of blood from the left ventricle during rest. In other individuals, obstruction only occurs under certain conditions. This is known as dynamic outflow obstruction because the degree of obstruction is variable and is dependent on the amount of blood in the ventricle immediately before ventricle systole (contraction). If left ventricular outflow obstruction is present, then this syndrome has been known as wide variety of terms including: hypertrophic cardiomyopathy or HCM, asymmetric septal hypertrophy or ASH, hypertrophic obstructive cardiomyopathy, HOCM, idiopathic hypertrophic subaortic stenosis or IHSS, familial isolated hypertrophic obstructive cardiomyopathy, familial isolated hypertrophic subaortic stenosis, familial or idiopathic hypertrophic subaortic stenosis, familial or idiopathic hypertrophic obstructive cardiomyopathy, primitive hypertrophic obstructive cardiomyopathy, primitive hypertrophic subaortic stenosis.

Obstructive HCM Schematic view. Please note the interventricular wall thickness. Authors own work.
Schematic view of Yamaguchi syndrome (apical hypertrophy): Please note the ace of spade appearance of the ventricles. Authors own work.
Normal heart Schematic view. Authors own work.

Non-Obstructive Variant

A non-obstructive variant of HCM is known as apical hypertrophic cardiomyopathy [1], which is also known as nonobstructive hypertrophic cardiomyopathy and Japanese variant hypertrophic cardiomyopathy or the Yamaguchi variant (since the first cases described were all in individuals of Japanese descent), also known as apical hypertrophic cardiomyopathy (ApHCM) or Yamaguchi syndrome.

  • Ace of spade observation in echocardiography is pathognomonic of apical hypertrophy.
  • Nevertheless, hypertrophic non-obstructive cardiomyopathy can either be familial or sporadic. It has been shown that a number of chronic medical conditions might be contributed to HNCM development such as thyroid disease, diabetes, and obesity.
  • Mutations in several genes (MYH7, MYBPC3, TNNT2, and TNNI3 genes) cause the inherited form of hypertrophic cardiomyopathy.
  • This is an autosomal dominant familial disorder.
  • HNCM can potentially evolve into:
  • Hypertrophic obstructive cardiomyopathy
  • Heart valve regurgitation
  • Aberrant heartbeats (arrhythmia)
  • Sudden cardiac arrest
  • Dilated cardiomyopathy


References

  1. Rivera-Diaz J, Moosvi AR. Apical hypertrophic cardiomyopathy. South Med J. 1996 Jul; 89(7):711-3. (Medline abstract; Full text)

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