Bigeminal rhythm VII.

Figure 1. Electrocardiogram recorded 14 hours after admission. See text for explication. An earlier electrocardiogram recorded immediately after admission had a sinus rate of 92 beats/min and Wolff-Parkinson-White type preexcitation on all beats. A 57-year-old woman with a history of high blood pressure and dyslipidemia presented to the emergency department with chest pain, palpitations, dyspnea, diaphoresis, nausea, and vomiting that awakened her at night and lasted several hours. It was the fourth such episode in 2 years, but no arrhythmia had been documented. On the current admission, laboratory studies, including troponin I, were normal. An exercise echocardiographic study showed a normal hypercontractile left ventricular response and failed to induce chest pain. An electrocardiogram recorded 14 hours after admission (Figure 1) showed sinus rhythm at a rate of 90 beats/min with normal P-R intervals and QRS complexes alternating with short P-R intervals followed by wide QRSs with delta waves—i.e., the Wolff-Parkinson-White pattern of ven-tricular preexcitation. That the pattern occurred only with every other complex indicates 2:1 block in the accessory pathway. The Wolff-Parkinson-White pattern of preexcitation is seen in the electrocardiograms of approximately 0.3% of the population and is more common in males (2, 3). Intermittent preexcitation is noted in 7% to 90% of these persons, depending on how vigorously it is pursued (1, 4). Episodes of tachyarrhythmia, usually orthodromic atrioventricular reciprocating tachycardia, occur in 25% to 50% of persons with the Wolff-Parkinson-White pattern of ventricular preexcitation (1–3). We speculated that the current patient's episodes of palpitation were due to such an arrhythmia, but it had never been documented electrocardiographically, nor could it be induced at electrophysiologic study. During