Accelerated idioventricular rhythm (AIVR), also known as slow VT, is related to increased automaticity. The ECG shows 3 - 10 consecutive QRS complexes originating from the ventricles, with a heart rate typically between 60 - 110 bpm. The onset and termination of tachycardia are gradual, often following a ventricular premature beat or when the ventricular pacemaker accelerates beyond the sinus rate. Fusion beats are common at the onset and termination of the arrhythmia, and ventricular capture is frequent. It often occurs in patients with organic heart disease, particularly during reperfusion after acute myocardial infarction, cardiac surgery, cardiomyopathy, rheumatic fever, and digitalis toxicity. The episodes are brief or intermittent, and do not affect prognosis. Patients are generally asymptomatic, requiring no antiarrhythmic treatment.
Figure 1 Accelerated idioventricular rhythm
In lead II, a series of wide, abnormal QRS complexes can be seen, with a ventricular rate of 79 - 88 bpm. Sinus P waves gradually overlap with the QRS complexes (indicated by arrows, showing AV dissociation).