A wide QRS tachycardia followed by alternating bundle branch block

A 72-year-old man presented to the emergency department with palpitations and dizziness. His history revealed myocardial infarction 4 years ago. Figure  1 shows the electrocardiogram (ECG) on admission. The lower panel is the continuation of the upper panel.
Source: Heart Rhythm - Category: Cardiology Authors: Tags: Josephson and Wellens ECG Lessons: A Monthly Visit to the 12 Lead ECG Source Type: research