During atrial overdrive pacing at a cycle length of 420 ms, the following EKG was recorded (Fig. 1). What is the mechanism for the progressive widening of QRS complexes and for the normal narrow ...

Methods:Of 668 consecutive patients with symptomatic type II second- or third-degree AV block, 2:1 AV block, atrial ... rhythm has wide QRS and rate ≥40 beats/min Atrial fibrillation and ...