A 25-year-old man comes to the emergency department due to chest heaviness and palpitations for the last 3 hours. Over the past year, he has had similar episodes that resolved with deep breathing, but none lasted as long as this one. The patient has no chronic medical conditions and takes no medications. He does not use tobacco, alcohol, caffeine, or illicit drugs. Blood pressure is 100/70 mm Hg, and pulse is 160/min and regular. The neck is supple, the thyroid is normal, and there is no lymphadenopathy. The lungs are clear to auscultation. ECG is shown in the exhibit. Which of the following is the most likely cause of this patient's symptoms?

Question

A 25-year-old man comes to the emergency department due to chest heaviness and palpitations for the last 3 hours.  Over the past year, he has had similar episodes that resolved with deep breathing, but none lasted as long as this one.  The patient has no chronic medical conditions and takes no medications.  He does not use tobacco, alcohol, caffeine, or illicit drugs.  Blood pressure is 100/70 mm Hg, and pulse is 160/min and regular.  The neck is supple, the thyroid is normal, and there is no lymphadenopathy.  The lungs are clear to auscultation.  ECG is shown in the exhibit.  Which of the following is the most likely cause of this patient's symptoms?

Quizplus · Accepted Answer

11ec160b_3aa0_070f_9249_e72990dd9ba4_MD0001_00 This patient's ECG reveals a narrow QRS complex tachycardia with a regular rhythm and nonvisible P waves. These findings are consistent with paroxysmal supraventricular tachycardia (PSVT), an episodic cardiac arrhythmia that originates at or above the atrioventricular (AV) node. The most common type of PSVT is AV nodal reentrant tachycardia (AVNRT), which usually affects young patients (eg, age <40) with an otherwise normal heart. Patients with AVNRT have 2 distinct AV nodal conduction pathways: a fast pathway with a long refractory period and a slow pathway with a short refractory period. During normal conduction, an impulse from the atria travels down both the fast and slow pathways, and the impulse from the slow pathway is blocked by the long refractory period of the fast pathway, allowing organized conduction of one impulse to the ventricles. On occasion, an impulse from the atria (eg, premature atrial contraction) occurs while the fast pathway is still refractory, traveling down only the slow pathway. If the fast pathway is no longer refractory by the time the impulse reaches the bottom of the slow pathway, the impulse may travel back up the fast pathway, creating a reentrant circuit with rapid conduction of impulses to the ventricles. On ECG, retrograde conduction up the fast pathway creates a retrograde P wave; however, because this conduction is usually simultaneous with anterograde conduction to the ventricles, the P wave is often buried within the QRS complex and is not visible. (Choice A) Abnormal conduction in areas of ischemic ventricular scarring is a common cause of monomorphic ventricular tachycardia. ECG shows a regular rhythm, but with wide QRS complexes because the arrhythmia originates below the AV node. (Choice C) Atrial remodeling with ectopic foci in the pulmonary vein ostia is the typical cause of atrial fibrillation. ECG shows an irregular rhythm and no P waves (P waves are truly absent because no organized atrial depolarization occurs). The QRS complexes are narrow. (Choice D) Degeneration of the sinoatrial node can lead to sick sinus syndrome, usually in patients age >65. ECG can show sinus bradycardia with sinus pauses and sinus arrest. Patients may sometimes develop episodes of sinus tachycardia, which can appear similar to PSVT but with normal P waves present. (Choice E) Delayed repolarization of ventricular cardiomyocytes can lead to torsade de pointes, a form of polymorphic ventricular tachycardia. ECG shows wide QRS complexes that oscillate in height and position. Educational objective: Atrioventricular nodal reentrant tachycardia is the most common type of paroxysmal supraventricular tachycardia, resulting from abnormal conduction through 2 distinct atrioventricular nodal pathways. ECG typically demonstrates a narrow QRS complex tachycardia with a regular rhythm and buried (not visible) P waves.

A 25-Year-Old Man Comes to the Emergency Department Due to Chest