Similar QRS morphology in sinus rhythm and ventricular tachycardia

A 74-year-old man with coronary artery disease and bifascicular block suffered recurrent tachycardia. Although the similarity of QRS morphology in tachycardia and sinus rhythm suggested a supraventricular origin, His bundle electrocardiography and programmed stimulation showed a ventricular origin. Digitalis toxicity was not an etiological factor and there was no evidence to suggest a His bundle tachycardia. The case illustrates that in occasional circumstances the onset of ventricular tachycardia may produce no change in QRS morphology thus making the diagnosis by conventional electrocardiographic criteria difficult.