A 16-year-old previously healthy boy is brought to the office due to palpitations. He was watching a documentary at a movie theater when his heart suddenly began to race and he became lightheaded. The patient says that he has felt "rapid heartbeats" in the past and thought that they were due to stress from school exams, but he has never had associated lightheadedness before. He has no chest pain or dyspnea. Physical examination is within normal limits. ECG strip is shown in the exhibit. Which of the following is most likely to be seen in this patient?

Question

A 16-year-old previously healthy boy is brought to the office due to palpitations.  He was watching a documentary at a movie theater when his heart suddenly began to race and he became lightheaded.  The patient says that he has felt "rapid heartbeats" in the past and thought that they were due to stress from school exams, but he has never had associated lightheadedness before.  He has no chest pain or dyspnea.  Physical examination is within normal limits.  ECG strip is shown in the exhibit.  Which of the following is most likely to be seen in this patient?

Quizplus · Accepted Answer

11ec160b_3aa7_f665_9249_2314cd03f6ce_MD0001_00 This patient's ECG demonstrates Wolff-Parkinson-White (WPW) pattern. The pattern is caused by an accessory conduction pathway (also known as an accessory bypass tract or a bundle of Kent) that directly connects the atria to the ventricles and allows electrical impulses to bypass the atrioventricular node, causing preexcitation (early excitation) of the ventricles. This preexcitation creates the characteristic triad of ECG findings that constitutes WPW pattern: Many patients with WPW pattern on ECG are asymptomatic; however, some develop symptomatic cardiac arrhythmias. WPW syndrome is the combination of WPW pattern on ECG and the presence of symptomatic arrhythmia. Atrioventricular reentrant tachycardia (AVRT), a type of paroxysmal supraventricular tachycardia that occurs due to reentry of electrical impulses through the accessory conduction pathway, is the most common associated arrhythmia and can manifest with intermittent palpitations, sensation of a racing heart, and lightheadedness or syncope. (Choice B) Cardiac myocyte degeneration below the level of the atrioventricular node leads to variable degrees of conduction block and presents with slow heart rate. (Choice C) Patients with wandering atrial pacemaker or ectopic atrial rhythm have ectopic atrial foci that replace the sinus node as the dominant pacemaker; P waves of varying morphology are seen on ECG. This patient has normal, uniform P waves suggesting normal sinus node function. (Choice D) Long QT syndrome (LQTS) is a disorder of ventricular repolarization characterized by a prolonged QT interval on ECG. Congenital LQTS is due to a mutation in the genes encoding for cardiac sodium or potassium channels. (Choice E) Atrial fibrillation is most often triggered by rapid electrical impulses originating in the pulmonary veins, and is characterized by an irregularly irregular rhythm and the absence of P waves. Educational objective: Wolff-Parkinson-White (WPW) pattern is characterized by a shortened PR interval, widening of the QRS complex, and slurred initial upstroke of the QRS complex (delta wave). It is caused by an accessory pathway that bypasses the atrioventricular node, causing preexcitation of the ventricles. Patients with WPW pattern can develop symptomatic arrhythmia (eg, atrioventricular reentrant tachycardia) due to reentry of electrical impulses through the accessory conduction pathway.

A 16-Year-Old Previously Healthy Boy Is Brought to the Office