Adenosine-Responsive wide QRS complex tachycardia: what is the mechanism?

A 45-year-old man presented with an acute anterior wall myocardial infarction and underwent successful percutaneous transluminal angioplasty of the left anterior descending coronary artery. Twenty-four hours later, a wide QRS tachycardia at a rate of 108 beats/min that had a QRS duration of 150 msec was noted by telemetric monitoring. There were no symptoms associated with the tachycardia. A 12-lead ECG was recorded (Fig. I). The tachycardia terminated after infusion of 12 mg of adenosine (Fig. 2). What is the mechanism of this adenosineresponsive wide QRS complex tachycardia?