A 47-year-old man develops sudden-onset midsternal chest pain and diaphoresis during a meeting in his office. He has a history of diet-controlled type 2 diabetes mellitus, hypertension, and hyperlipidemia. While waiting for emergency medical services (EMS), the patient suddenly becomes unresponsive and pulseless. His coworkers begin cardiopulmonary resuscitation. EMS workers quickly arrive and the patient is successfully resuscitated. In the emergency department, blood pressure is 142/88 mm Hg and pulse is 92/min. ECG shows normal sinus rhythm with occasional premature ventricular contractions and 3 mm of ST-segment elevation in leads V1-V3. What is the most likely source of this patient's out-of-hospital cardiac arrest?
This patient with midsternal chest pain and contiguous ST-segment elevation on ECG has experienced an acute myocardial infarction (MI). Ventricular arrhythmias, including premature ventricular contractions, nonsustained or sustained ventricular tachycardia, and ventricular fibrillation, frequently occur in acute MI. These arrhythmias likely result from increased automaticity and a propensity for the development of reentrant circuits in the ischemic myocardium, as well as increased sympathetic tone in the setting of acute MI. Ventricular fibrillation is the most common underlying arrhythmia responsible for sudden cardiac arrest (SCA) in acute MI and is the most common cause of acute MI-related death. Most episodes of ventricular fibrillation in acute MI occur within the first hour of symptom onset, but patients remain at acutely elevated risk for arrhythmia for at least 48 hours.
(Choices A and D) Pulseless electrical activity (PEA) refers to a cardiac rhythm that is usually perfusing (eg, sinus tachycardia, sinus bradycardia) but cannot generate sufficient cardiac output to create a measurable blood pressure or palpable pulse. An underlying mechanical issue (eg, severe hypovolemia, massive pulmonary embolism, markedly impaired left ventricular contractility) or other potentially reversible cause (eg, hypoxia, severe electrolyte abnormality) is typically responsible. PEA often degenerates into asystole, which involves the complete absence of cardiac electrical activity. Both PEA and asystole are managed the same per advanced cardiac life support protocol. Acute MI (especially a massive MI) may occasionally produce PEA, but ventricular fibrillation is far more common.
(Choice B) Atrial fibrillation occasionally occurs during the first few hours of acute MI, likely triggered by atrial stretch and increased sympathetic tone. However, atrial fibrillation is only rarely a primary cause of SCA.
(Choice C) Atrioventricular conduction block can occur in patients with acute MI, typically in those with an inferior wall MI (this patient's ST-segment elevation in V1-V3 is consistent with an anteroseptal MI) Atrioventricular block associated with acute MI is usually transient and rarely leads to SCA.
Educational objective:
Ventricular arrhythmias (eg, premature ventricular contractions, nonsustained or sustained ventricular tachycardia, ventricular fibrillation) frequently occur with acute myocardial infarction (MI). Ventricular fibrillation is the most common cause of sudden cardiac arrest in acute MI and is the most common cause of acute MI-related death.