The group-beating

What is the rhythm?

Figure 1

This is a regularly irregular wide QRS rhythm. There is left axis deviation, rS in II, III and aVF, qR in aVL (left anterior fascicular block) and poor R wave progression. P waves are difficult to see in limb leads but better appreciated in lead V1 (Figure 2). The PP interval is about 440 ms (11 small squares) or an atrial rate of 136 bpm (sinus tachycardia vs. atrial tachycardia). The initial PRI is about 240 ms (first degree AV block). There is a group-beating of 2 and 3 QRS. Thus, this is sinus tachycardia or atrial tachycardia, first degree AV block, 3:2 and 4:3 Wenckebach cycles, left anterior fascicular block, intraventricular conduction delay (because of a widened QRS that do not fit either left/right bundle branch block criteria).

Figure 2

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