Aggravation of arrhythmia: a complication of antiarrhythmic drug therapy

Aggravation of arrhythmia is a complication of antiarrhythmic drug therapy that is not uncommon. It may represent a worsening of an existing arrhythmia or a new arrhythmia not previously experienced by the patient. When non-invasive methods are used to evaluate drug effects, the overall incidence of aggravation is 9% while with electrophysiologic testing, it is 18%. While aggravation of arrhythmia may occur when the blood level of the drug is in the toxic range, most often this complication is observed when blood levels are in the defined therapeutic range. It is not associated with drug dose, baseline ECG intervals, changes in these intervals during therapy, the nature of the heart disease or other clinical parameters. However, it is more common in patients with a history of sustained ventricular tachycardia or ventricular fibrillation and in those with reduced left ventricular function and a history of congestive heart failure. Aggravation with one drug does not predict this complication with another agent, even if both are in the same subclass. Worsening of arrhythmia may often be precipitated by exercise testing, even when arrhythmia is suppressed on ambulatory monitoring. The frequency, unpredictability and seriousness of this side-effect demands the cautious use of antiarrhythmic drugs.