As already stated, the initial arrhythmia is a supraventricular tachycardia (narrow QRS complex tachycardia) in which the P wave is most likely to be found immediately following the QRS complex (see the inferior leads and lead aVL). In that case the most likely diagnosis is AV nodal reentrant tachycardia (AVNRT). The efficacy of adenosine to terminate the tachycardia (Fig. 2) fits this diagnosis. An alternative diagnosis would be AV re-entrant tachycardia, using a bypass tract. The P wave is then to be expected at least 80 msec from the QRS complex. In any case, termination of the tachycardia occurs suddenly and is followed by an irregular wide complex tachycardia (14 complexes) without discernable P waves (Fig. 2, terminal part of upper strip and initial part of lower strip). In the middle part of the lower strip (Fig. 2) sinus rhythm with 1:1 conduction to the ventricle resumes.
Fig. 2
Monitor strip during termination of the tachycardia
