Natural history of hypertrophic cardiomyopathy: Japanese experience

Most patients with hypertrophic cardiomyopathy (HCM) remain clinically stable for long periods of time, whereas some patients progress to severe systolic dysfunction. Therefore, the natural history of HCM is largely unknown.

The present study followed up 59 patients with HCM (32 males, 27 females, mean age 38.6 +/- 13.6 years) for 10 years or more (mean 16.0 +/- 4.7 years) after the initial diagnosis.

Eight of 17 patients who showed abnormal Q-waves at the initial examination had lost Q-waves, suggesting remodeling from asymmetric to generalized hypertrophy. The thickness of the interventricular septum showed remarkable changes, increasing by > or = 5 mm in 7 patients and decreasing by > or = 5 mm in 21. These observations indicate that ventricular remodeling occurs in patients with HCM. Follow-up electrocardiography demonstrated new Q-waves in 10 patients and bundle branch blocks or intraventricular conduction disturbances in 13. Left ventricular end-diastolic diameter increased from 41.6 to 48.1 mm, associated with a decrease in fractional shortening from 40.6% to 34.0%. Left ventricular systolic dysfunction, defined as left ventricular end-diastolic diameter > 55 mm or fractional shortening < 25%, developed in 13 patients. These observations indicate that myocardial disease including the conduction system is progressive in patients with HCM and finally deteriorates to systolic dysfunction. Left ventricular outflow obstruction also presented evolutional changes. At the initial study, 23 patients showed systolic anterior motion of the mitral valves. Systolic anterior motion disappeared in 13 patients, reduced in 2, increased in 2, and remained stable in only 6. One patient without systolic anterior motion at the initial study developed new systolic anterior motion. Impaired left ventricular filling increased left atrial diameter from 35.5 to 46.9 mm and atrial fibrillation frequently developed (24 patients).

These findings suggest that HCM is a slowly progressive disease which develops evolutional remodeling of left ventricular hypertrophy and outflow obstruction, eventually progressing to systolic dysfunction with cavity dilation and wall thinning.