[Secondary atypical hypertrophy: hypertrophic cardiomyopathy with acquired risk factors (author's transl)].

New clinical concept of "secondary atypical hypertrophy" was proposed for hypertrophic cardiomyopathy (HCM) associated with an acquired risk factors such as hypertension, strenuous exercise, etc, based on the following findings. 1) Case-control study suggested that history of hypertension, physical labor and weight gain were thought to be risk factors of apical hypertrophy. History of hypertension was also demonstrated in 55% of older cases of HCM (greater than 35 yrs) with asymmetric septal hypertrophy, and this figure was appreciably higher than that in general population (around 26% in our population survey). Thus hypertension was suggested to have a causal relationship to HCM as an important risk factor in older cases. 2) Even in cases without hypertension, 29% of non-obstructive HCM exhibited a marked increase in systolic blood pressure on bicycle ergometer stress test, suggesting an important of transient hypertension during exercise as a risk factor of unusual hypertrophy. 3) The cases of HCM with definite family history and the cases of HCM with secondary atypical hypertrophy, with acquired risk factors such as hypertension, presented different clinical features. The latter is older and predominant in males. In the former, QRS pattern was les distorted, suggesting milder congenital defect of the myocardium. Left ventricular function was less impaired in cases with secondary atypical hypertrophy if judged from diastolic descent rate of the mitral valve, left ventricular enddiastolic pressure and functional aerobic impairment (FAI). On the other hand, no differences were observed between cases with ventricular septal hypertrophy and left ventricular outflow obstruction. 4) Follow-up study demonstrated rather favorable prognosis in cases with secondary atypical hypertrophy because of the absence of sudden death despite of their older age. These distinctive difference in clinical features, prognosis and then management in cases with HCM with acquired risk factors suggested a validity of the concept of secondary atypical hypertrophy in clinical practice.