A 28-year-old woman comes to the emergency department due to palpitations and a feeling of her heart racing for the past 3 hours. Over the past year, she has had similar episodes that resolved with deep breathing, but this episode has lasted longer. The patient has no chronic medical conditions and takes no medications. She does not use tobacco, alcohol, caffeine, or illicit drugs. Blood pressure is 100/68 mm Hg, and pulse is 164/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 28-year-old woman comes to the emergency department due to palpitations and a feeling of her heart racing for the past 3 hours.  Over the past year, she has had similar episodes that resolved with deep breathing, but this episode has lasted longer.  The patient has no chronic medical conditions and takes no medications.  She does not use tobacco, alcohol, caffeine, or illicit drugs.  Blood pressure is 100/68 mm Hg, and pulse is 164/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

Explanation: 11ec25c8_d18b_0afe_bc81_eb27d16e5000_MD0003_00 This patient's ECG reveals a narrow QRS complex tachycardia with a regular rhythm and P waves obscured by the QRS complexes. These findings are consistent with paroxysmal supraventricular tachycardia (PSVT), an episodic cardiac arrhythmia that originates above the ventricles (ie, 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. ECG AVNRT is caused by 2 distinct conduction pathways through the AV node: a fast pathway with a long refractory period a slow pathway with a short refractory period. Initiation of the reentry circuit is triggered when an impulse (eg, premature atrial contraction) cannot proceed normally down the fast pathway due to the pathway's long refractory period; instead, the signal travels down the slow pathway. After reaching the final common pathway (ie, where the pathways meet), the impulse travels in a retrograde direction up the fast pathway because the pathway is no longer in the refractory period. Retrograde atrial depolarization then occurs simultaneously with anterograde ventricular depolarization, causing characteristic buried P waves within QRS complexes on ECG (P waves are present but not visible). Continuous activation of this accessory circuit leads to sustained tachycardia. reentry circuit Less common types of PSVT include atrioventricular reentry tachycardia, which results from an accessory pathway outside the AV node (ie, Wolff-Parkinson-White syndrome). Wolff-Parkinson-White syndrome (Choices A and B) Monomorphic ventricular tachycardia can occur due to abnormal electrical activity around ischemic scar tissue or abnormal automaticity of the ventricular conduction system (eg, in the setting of dilated cardiomyopathy). ECG shows wide QRS complexes because the arrhythmia originates below the AV node. Monomorphic ventricular tachycardia (Choice C) Atrial fibrillation results from atrial remodeling leading to disorganized atrial electrical activity, often originating in the pulmonary vein ostia. ECG shows an irregular rhythm with narrow QRS complexes and truly absent P waves. Atrial fibrillation 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 28-Year-Old Woman Comes to the Emergency Department Due to Palpitations