A 36-year-old man comes to the emergency department due to loss of consciousness. He was standing in a crowded subway station when he felt lightheaded, had a pounding sensation in his chest, and passed out. On awakening, he felt short of breath for a little while and then was "completely fine." He has had no similar episodes, nor chest pain, confusion, tongue biting, or urinary incontinence. The night before, he was at a party with friends and consumed alcohol. Later he was nauseated and had 3 episodes of vomiting and one episode of diarrhea. In the emergency department, blood pressure is 124/68 mm Hg and pulse is 80/min. There is a small laceration above his right eyebrow. Cardiac examination shows normal heart sounds with regular rhythm. The lungs are clear to auscultation. Neurologic examination shows no abnormalities. ECG is shown in the exhibit.
Which of the following is the most likely cause of this patient's syncope?

Question

A 36-year-old man comes to the emergency department due to loss of consciousness.  He was standing in a crowded subway station when he felt lightheaded, had a pounding sensation in his chest, and passed out.  On awakening, he felt short of breath for a little while and then was "completely fine."  He has had no similar episodes, nor chest pain, confusion, tongue biting, or urinary incontinence.  The night before, he was at a party with friends and consumed alcohol.  Later he was nauseated and had 3 episodes of vomiting and one episode of diarrhea.  In the emergency department, blood pressure is 124/68 mm Hg and pulse is 80/min.  There is a small laceration above his right eyebrow.  Cardiac examination shows normal heart sounds with regular rhythm.  The lungs are clear to auscultation.  Neurologic examination shows no abnormalities.  ECG is shown in the exhibit. 
Which of the following is the most likely cause of this patient's syncope?

Quizplus · Accepted Answer

Explanation: 11ec2b69_be68_274d_8f63_cda118551577_MD0005_00 This patient's ECG shows a Wolff-Parkinson-White (WPW) pattern, a type of cardiac preexcitation caused by an accessory pathway. Normal electrical impulses pass from the atria to the ventricles via the atrioventricular (AV) node/His-Purkinje system; however, in patients with WPW there is an extra conduction pathway (accessory pathway) that directly connects the atria to the ventricles and bypasses the AV junction. The accessory pathway conducts faster than the AV node and excites the ventricles prematurely, manifesting on resting ECG as a short PR interval with a characteristic delta wave and widened QRS complex (>0.12 sec). ECG Although patients with a WPW pattern on ECG can be asymptomatic, some develop tachyarrhythmias; the combination of WPW findings on ECG and symptomatic tachyarrhythmia constitutes WPW syndrome. Paroxysmal supraventricular tachycardia is the most common arrhythmia; it is usually a regular, narrow complex tachycardia. If patients with WPW develop atrial fibrillation, they can conduct down the accessory pathway from the atria to the ventricles at a very fast rate, commonly resulting in syncope. This patient's ingestion of alcohol, a known precipitant of atrial fibrillation, likely placed him at risk for such a scenario. (Choice A) Acute coronary syndrome can sometimes present with nausea, vomiting, palpitations, or syncope, rather than chest pain. However, it is unlikely in this young patient with no significant risk factors for coronary artery disease and ECG showing no ST segment elevation/depression to suggest myocardial ischemia. (Choice B) Bradyarrhythmias generally arise from sinoatrial node dysfunction or AV nodal conduction block, and typically present with syncope or presyncope. However, this patient's WPW pattern on ECG and palpitations before passing out make a tachyarrhythmia more likely. (Choice C) Orthostatic hypotension is defined as a decrease in systolic blood pressure ?20 mm Hg with change in position from supine to standing; it can be due to an inadequate autonomic response or volume depletion. Although this patient may be hypovolemic from vomiting and diarrhea, his presentation is more consistent with WPW syndrome given the palpitations and classic ECG findings. (Choice E) Vasovagal (neurocardiogenic) syncope can have many triggering factors (eg, stress, pain) and is caused by decreased sympathetic drive (causing vasodilation) combined with increased parasympathetic response (causing bradycardia). The ECG findings in this patient make cardiogenic syncope due to WPW more likely. Educational objective: The classic Wolff-Parkinson-White pattern on ECG consists of short PR interval, delta wave, and wide QRS complex. Some patients can become symptomatic with tachyarrhythmias, and syncope can result. References: WPW and preexcitation syndromes (http://www.ncbi.nlm.nih.gov/pubmed/18368860)

A 36-Year-Old Man Comes to the Emergency Department Due to Loss