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.