This is a recording from a patient being treated for a wide complex tachycardia . The recording could be sinus with a first degree block (plus a partial right bundle branch block or possibly RVH). It is to be noted though that a sinus rate of 100/min seems some what fast for a patient on nadolol and that the rhythm is irregular. On the other hand, the more likely rhyhtm is SVT (or slow atrial flutter at a rate of 200/min) with variable block though mostly 2:1 block. This is an atrial rate similar to that of the wide complex tachycardia, and if one looks in lead I and lead V1 there does appear to be atrial activity at twice the ventricular rate.