Development of heart failure in bradycardic sick sinus syndrome

Mounting evidence shows that elevated resting sinus rate is an independent predictor of cardiovascular morbidity and mortality in the general population, in elderly subjects, and in patients with myocardial infarction or hypertension. Therefore, a rather slow sinus rate appears to be a protecting factor acting through several mechanisms. The present contribution focuses on the relationship between sinus rate and heart failure. Its major objectives are to discuss whether in patients with heart failure a rather slow heart rate is advisable and whether a sinus bradycardia secondary to sinus node dysfunction can facilitate the development of heart failure. It has been reported that among patients with left ventricular dysfunction, increased sinus rate was a predictor of cardiovascular death at univariate analysis; however, a multivariate analysis to verify whether sinus rate was an independent predictor of mortality was not performed. Randomized trials carried out by utilizing beta-blockers or amiodarone in patients with heart failure showed that heart rate reduction by these drugs was a marker of their ability to reduce mortality. However, beta-blockers and amiodarone have additional pharmacological effects which interfere with the disease substrate. So, at present, though the results of these trials show that a rather slow sinus rate is advisable, we do not know whether in patients with heart failure sinus rate represents an independent predictor of mortality as in patients with myocardial infarction or hypertension and whether the reduction of sinus rate per se is beneficial. The results of the recent randomized THEOPACE trial showed, for the first time, that in a patient population with symptomatic sinus bradycardia (sinus rate < 50 b/min), an increase in heart rate, induced by DDD pacing or oral theophylline, reduced the incidence of overt heart failure. Therefore, sinus bradycardia seems to play a role in the genesis of heart failure. In a post-hoc analysis of the results of this trial it emerged that in the control (not treated) group, the subjects with sinus bradycardia more prone to develop heart failure were those of old age, about 80 years, with organic heart disease and severe chronotropic incompetence. However, this conclusion needs further validation.