Electrophysiological alterations in heart failure.

Electrophysiological defects are common and diverse features of heart failure. Cardiac arrhythmias may be precipitated by mechanical factors, catecholamine release, ischaemia drug therapy or drug-induced hypokalaemia. There is a high prevalence of ventricular and supraventricular arrhythmias, and chronic atrial fibrillation is also common. Ventricular arrhythmias are characterized by multiform, bigeminal and paired beats. There is also a high incidence of non-sustained ventricular tachycardia. These abnormalities are particularly prevalent amongst patients in New York Heart Association (NYHA) functional class IV. Although the presence of complex ventricular arrhythmias and non-sustained ventricular tachycardia are regarded as prognostic markers, their role in the initiation of sudden death has yet to be proven. The results of a recent placebo-controlled clinical trial have indicated that combined therapy with isosorbide dinitrate and hydralazine can reduce mortality due to sudden death or pump failure, and is superior in this respect to prazosin. In another key study, enalapril was superior to placebo at lowering mortality caused by pump failure, but did not reduce the incidence of sudden death. These findings point to new directions of investigation which might clarify the importance of arrhythmias in heart failure, and reveal improved ways of controlling cardiac rhythm and improving prognosis.