Syncope has been related to atrial or ventricular tachyarrhythmias or bradyarrhythmias, heart block, obstruction to left ventricular outflow, diastolic dysfunction, altered baroreflex mechanisms, and myocardial ischemia. Factors limiting functional class include myocardial ischemia and left ventricular systolic dysfunction, two major determinants of prognosis in hypertrophic cardiomyopathy. Finally, multiple-repetitive or prolonged bursts of nonsustained ventricular tachycardia on ambulatory Holter ECG have been associated with an increased incidence of sudden cardiac death.
This study has several limitations. (1) Most (85%) of the study patients were referred from outlying hospitals. Despite the fact that referral was exclusively based on disease diagnosis, the possibility of selection bias influencing the results cannot be excluded. However, it is reasonable to assume that selection bias in the hospital setting would have resulted in a rapid rate of progression and not in the benign clinical course observed in this study. (2) The disease-causing genes, which appear to have different prognostic impact, were not assessed. However, detailed analysis of disease-causing genes in large populations is not yet available, restricting prospective mortality studies. For this reason, we believe that it is useful to assess data related to the natural history and prognosis of patients with hypertrophic cardiomyopathy from representative patient populations as in the present study. my canadian pharmacy