A 21-year-old man comes to the office due to recurrent heart palpitations that start and stop abruptly. Further evaluation is indicative of an abnormal conduction pathway in the patient's heart that bypasses the atrioventricular node. Which of the following portions of this patient's ECG is most likely to be affected during normal sinus rhythm?
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This young patient has paroxysmal supraventricular tachycardia (eg, repeated palpitation episodes) due to Wolff-Parkinson-White (WPW) syndrome. WPW syndrome is caused by an accessory pathway (bundle of Kent) that allows electrical impulses to bypass the atrioventricular node and cause preexcitation of the ventricles. This preexcitation leads to characteristic findings on baseline ECG during sinus rhythm, including a shortened PR interval (often <120 msec), slurred upslope of the QRS complex (delta wave), and a widened QRS complex.
Many patients with an accessory conduction pathway are asymptomatic and diagnosed only when a WPW pattern is incidentally recognized on ECG. However, some patients will develop symptomatic arrhythmias. Atrioventricular reentrant tachycardia (AVRT), a type of paroxysmal supraventricular tachycardia, is the most common arrhythmia that occurs with WPW. AVRT results from a rapid reentrant circuit that typically travels down the AV node to the ventricles and back up the accessory pathway, with patients often experiencing palpitations or a feeling of a racing heart.
(Choice A) When in sinus rhythm, a patient with an accessory conduction pathway should have a normal P wave on ECG.
(Choice C) The terminal portion of the QRS complex on ECG is typically unaffected in patients with an accessory conduction pathway.
(Choices D and E) The ST segment and T wave roughly correspond to the plateau and repolarization phases of the ventricular cardiomyocyte action potential, respectively. Because preexcitation causes abnormal ventricular depolarization, it follows that repolarization changes may be present as well, manifesting as alterations in the ST segment and T wave. However, these findings are less common than the usual WPW triad of ECG abnormalities and, when present, are nonspecific for diagnosing an accessory conduction pathway.
Educational objective:
An accessory atrioventricular conduction pathway causes ventricular preexcitation that manifests on ECG with a Wolff-Parkinson-White (WPW) pattern, consisting of a shortened PR interval, slurred upslope of the QRS complex (delta wave), and a widened QRS interval. Some patients with an accessory conduction pathway develop paroxysmal tachyarrhythmias, most commonly atrioventricular reentrant tachycardia, which constitutes WPW syndrome.