Abnormal Q waves in Wolff-Parkinson-White syndrome. Incidence and clinical significance.

Between January 1970 and January 1975 the diagnosis of Wolff-Parkinson-White syndrome was entertained in 44 patients. Thirty-one (70%) of these patients had negative sigma-deflections (Q waves) on one or more electrocardiographic leads, thereby simulating a pattern of myocardial infarction (Mi). Fifteen patients (34%) were initially referred with an erroneous diagnosis of Mi based on the presence of Q waves. In nine of these 15 patients, the referring diagnosis was Mi plus ventricular preexcitation; in six, the diagnosis of ventricular preexcitation was overlooked entirely. The incidence of misdiagnosis (34%) was exactly the same as that reportly by Wolff and White approximately 30 years ago. Erroneous diagnosis of Mi can be virtually eliminated by normalizing the QRS complex by premature stimulation of the atrium during the effective refractory period of the accessory pathway.