Proarrhythmic effects of antiarrhythmic drugs: evolving concepts.

Although antiarrhythmic drugs are prescribed to reduce an arrhythmia, they may have the paradoxic effect of actually exacerbating that arrhythmia or causing new or more serious forms. This effect is known as "proarrhythmia." Proarrhythmic events may be segregated into those that occur "early" after therapy (within 30 days) and those that occur "late," after many months of therapy and manifesting as a fatal event (an increased risk of sudden cardiac death). The ability of the physician to predict drug proarrhythmia and its severity depends on the class of antiarrhythmic drug chosen, the type of ventricular arrhythmia to be treated, and the severity of the patient's underlying left ventricular dysfunction. Before the start of antiarrhythmic therapy, the physician must be able to quantitate the degree of proarrhythmic risk so that the benefit/risk ratio of such drug use can be determined.