A 21-year-old man comes to the office due to recurrent heart palpitations that start and stop abruptly. After initial workup, the physician suspects that there is an abnormal conduction pathway in this patient's heart that bypasses the atrioventricular node. Assuming the diagnosis is correct, which part of the patient's ECG is most likely to be affected during normal sinus rhythm?

Question

A 21-year-old man comes to the office due to recurrent heart palpitations that start and stop abruptly.  After initial workup, the physician suspects that there is an abnormal conduction pathway in this patient's heart that bypasses the atrioventricular node.  Assuming the diagnosis is correct, which part of the patient's ECG is most likely to be affected during normal sinus rhythm?

Quizplus · Accepted Answer

11ec160b_3aa7_8134_9249_21653a44acc8_MD0001_00 This young patient's repeated episodes of palpitations are suggestive of paroxysmal supraventricular tachycardia, and the physician suspects Wolff-Parkinson-White (WPW) syndrome. WPW syndrome is caused by an accessory conduction pathway (bundle of Kent) that allows electrical conduction impulses to bypass the atrioventricular node and cause preexcitation of the ventricles. This preexcitation leads to characteristic findings on baseline ECG, including a shortened PR interval (often <0.12 seconds), early upslope of the QRS complex (delta wave), and a widened QRS complex. Many patients with an accessory conduction pathway can be asymptomatic and are diagnosed only when a WPW pattern is incidentally recognized on ECG. However, some patients will develop symptomatic arrhythmias. Atrioventricular reentry 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 and a racing heart. (Choice A) Except during periods of paroxysmal supraventricular tachycardia, a patient with an accessory conduction pathway should have a normal P wave on ECG. (Choice C) The S wave 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, respectively, of the ventricular cardiomyocyte action potential. Due to changes in the normal geographic sequence of ventricular depolarization and repolarization as a result of preexcitation, there may be variable ST-segment/T-wave abnormalities. 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: Wolff-Parkinson-White syndrome is characterized by symptomatic paroxysmal supraventricular tachycardia (eg, atrioventricular reentrant tachycardia) due to the presence of an accessory conduction pathway. During normal sinus rhythm, the presence of this accessory pathway causes ventricular preexcitation, which can be identified on ECG by the triad of a shortened PR interval, early upslope of the QRS complex (delta wave), and a widened QRS interval.

A 21-Year-Old Man Comes to the Office Due to Recurrent