A 32-year-old woman is brought to the emergency department after she passed out at a local bank. The patient had been standing in line for a long time when she felt warm and nauseated and then lost consciousness for a few seconds. She quickly returned to normal. Her friend, who witnessed the episode, saw no abnormal, jerky movements of the extremities. Toward the end of her usual 5-mile run earlier this morning, the patient felt slightly light-headed. She has no known medical conditions. Family history is significant for a paternal uncle who died from a "heart attack" at age 55. Supine blood pressure is 110/70 mm Hg and pulse is 75/min. Two minutes after the patient stands, blood pressure is 108/70 mm Hg and pulse is 88/min. No jugular venous distension is noted. There are no heart murmurs. An S3 is present. Peripheral pulses are full and symmetric. ECG shows normal sinus rhythm with T-wave inversion in lead V₁. Chest x-ray reveals a normal heart size. Which of the following is most closely associated with this patient's likely cause of syncope?

Question

Quizplus · Accepted Answer

Explanation: 11ec2b69_c11f_3140_8f63_6d81dcbf5666_MD0005_00 This patient most likely experienced vasovagal syncope, a type of reflex syncope. Clinical features characteristic of vasovagal syncope in this patient include the presence of a vasovagal trigger (eg, prolonged standing) and an autonomic prodrome (eg, warmth, nausea) prior to the syncopal event. Neurologic signal initiation in vasovagal syncope is thought to be triggered in the cerebral cortex or within various baroreceptors or mechanoreceptors (eg, cardiopulmonary). The signal is then sent via afferent neuronal pathways to the brainstem's cardioregulatory center, where some combination of cardioinhibitoryresponse (ie, increased parasympathetic stimulation) and vasodepressorresponse (ie, decreased sympathetic stimulation) occurs. This leads to decreased heart rate and contractility with peripheral vasodilation, which, in turn, leads to hypotension, decreased cerebral perfusion, and syncope. The classic prodromal symptoms (eg, warmth, nausea, diaphoresis) in vasovagal syncope likely represent early physiologic manifestations of altered autonomic activity. afferent neuronal pathways (Choice A) The sudden, unexpected death of a young relative (eg, age <40) raises concern for an inherited arrhythmia-inducing syndrome (eg, long QT syndrome), but such an event in an older relative is less suspicious because myocardial infarction-induced sudden cardiac death becomes more common with age. Arrhythmia-inducing syndromes can present with syncope, but the syncope typically has no autonomic prodrome. (Choice B) Exertional light-headedness (eg, while running) raises suspicion for left ventricular (LV) outflow obstruction (eg, aortic stenosis, hypertrophic cardiomyopathy), which may cause exertional syncope but usually not at rest. This patient has no murmur to suggest LV outflow obstruction, and her slight light-headedness while running is likely best explained by dehydration. (Choice C) An S3 is a low-frequency heart sound that may be heard during LV diastolic filling. It commonly indicates ventricular enlargement and heart failure (eg, dilated cardiomyopathy), which increase the risk of cardiac syncope. However, an S3 is frequently a normal finding in those age <40, especially in the absence of other signs of heart failure (eg, cardiac enlargement, jugular venous distension). S3 (Choice D) T-wave inversions are nonspecific ECG findings possibly suggesting ventricular pathology that would predispose to cardiac syncope (eg, myocardial ischemia); however, isolated T-wave inversions in lead V₁ are considered normal. Educational objective: Vasovagal syncope, a type of reflex syncope, involves a combined cardioinhibitory and vasodepressor response driven by the autonomic nervous system. Patients typically have an identifiable trigger (eg, prolonged standing) and experience an autonomic prodrome (eg, nausea, warmth) prior to losing consciousness. References: Guidelines for the diagnosis and management of syncope (version 2009). (http://www.ncbi.nlm.nih.gov/pubmed/19713422) Syncope: epidemiology, etiology, and prognosis. (http://www.ncbi.nlm.nih.gov/pubmed/25538626)

A 32-Year-Old Woman Is Brought to the Emergency Department After