Discussion
The typical form of AVNRT uses the slow pathway as the anterograde limb and the fast pathway as the retrograde limb with perinodal atrial tissue bridging the fast to the slow pathways. The ECG of typical AVNRT shows a short R-P or simultaneous R-P during tachycardia with pseudo R’ in V1. However, this finding needs to be differentiated from JT as the ECG of JT may resemble typical AVNRT, especially when the tachycardia is relatively slow. In these tachycardias, a patient may be significantly symptomatic even when in slow heart rate given the simultaneous atrial and ventricular activation, which generates atrial contraction during mitral and tricuspid valves closure resulting in palpitation, heart pounding, fatigue, or poor exercise tolerance.
While the usual heart rates of typical AVNRT during tachycardia range from 150/min to 220/min, some patients present with slow AVNRT if the conduction time of the slow pathway is long and its effective refractory period is short (compared to fast pathway). This type of slow typical AVNRT mimics JT and sometimes may be mistakenly treated as JT as described in Case 4. These slow tachycardias should be distinguished from JT with appropriate pacing maneuvers so that appropriate ablation treatment can be performed.