The recording is interesting as the patient goes from sinus rhythm to at first a wide complex tachycardia at about 130/min. The wide QRS though disappears after nine complexes and is replaced by narrow complexes at a slightly slower rate. No p wave activity is seen. This a supraventricular tachycardia with a from of abberancy. In this case we are probably seeing a rate dependent left bundle branch block or the effect of a left bundle branch block which persists for the nine complexes because of continued block in the left bundle from the depolarizations from the intact right bundle.