[Arrhythmias in hypertrophic cardiomyopathy. Significance and therapeutic consequences].

The natural history of the patient with hypertrophic cardiomyopathy is characterized by slow progression of symptoms and left ventricular hypertrophy; severe functional limitation is unusual and encountered only in about 20%. Most of the deaths are sudden and occur irrespective of the functional status of the patient and there are no routine electrocardiographic or hemodynamic measurements indicative of poor prognosis. Sudden death may be associated with syncope and young age at diagnosis as well as with a family history of sudden death. The mechanisms underlying the cause of sudden death have not been clearly elucidated. Although complete heart block may complicate myotomy or myectomy, the development, in an unoperated patient, of symptomatic conduction disease is uncommon. Preexcitation syndromes may be present in a small subpopulation (about 2%), but this appears seldom responsible for sudden death. Outflow tract spasm has also been postulated as a causal factor but the fact that proportionately an equal number of patients with and without ventricular outflow gradients die suddenly, suggests that other mechanisms must be important. Further hypotheses, currently however, without substantiation, have implicated acute changes in diastolic filling or acute myocardial ischemia as causes of sudden death. Recently published studies have stressed the importance of ventricular arrhythmias as a cause of sudden death. Ventricular tachycardia occurs in about 30% of such patients and can be found significantly more frequent in adult patients who die suddenly. In children and adolescents, since they have a lesser incidence of ventricular tachycardia, possibly, other mechanisms are involved. In general, episodes of ventricular tachycardia are asymptomatic and self-limited; the main ventricular rate recorded during 135 episodes in 30 of our patients was 142 beats per minute with an average duration of eight beats. Variable QRS morphology suggests different sites of origin. Due to the marked spontaneous variability, the probability of missing ventricular tachycardia with a single 24-hour continuous ambulatory ECG is 54%; on 96 hours of continuous ECG monitoring the probability can be reduced to 8%. Accordingly, continuous ambulatory ECG monitoring should be carried out for at least 48 to 72 hours. At the time of diagnosis, approximately 7% of the patients have atrial fibrillation. On three days of continuous 24-hour ECG monitoring, about 40% will be found to have atrial fibrillation or supraventricular arrhythmias. The correlation between supraventricular arrhythmias and sudden death is weaker than that of the latter with ventricular arrhythmias.(ABSTRACT TRUNCATED AT 400 WORDS)