When to Initiate Antiarrhythmic Therapy

This decision must be approached individually for each case, however some general guidelines include:

1. If the patient is symptomatic due to the dysrhythmia (syncopal or weak or in heart failure due to the fast heart rate)
2. If you believe the patient’s rhythm is in imminent danger of degenerating to ventricular fibrillation
3. If you believe the patient is at risk of sudden death (either due to severity of the arrhythmia or the presence of underlying structural heart diseases associated with sudden death, like DCM in Dobermans or ARVC in Boxers)

There is often little difficulty in determining if condition #1 is present. Determining if condition #2 or 3 is present is more challenging. In determining the significance of ventricular arrhythmias, heart rate is likely one of the more important criteria. If VPCs occur at a fast heart rate (i.e. >170 bpm), this potentially represents a more clinically significant condition, whereas if they occur at a more normal heart rate, this situation may not represent as significant of a risk. The definitive importance of heart rate in the presence of VPCs remains to be determined.

Why not institute anti-arrhythmic therapy in any case just to be safe? The issue isthat all anti-arrhythmics have the potential to be pro-arrhythmic, some more than others. Therefore, follow-up to assess efficacy is critical in any patient in which anti-arrhythmic therapy is initiated.