A 47-year-old man develops sudden onset of mid-sternal chest pain and diaphoresis during a meeting in his office. While waiting for emergency medical personnel to arrive, he complains of dizziness and becomes unresponsive. His coworkers perform cardiopulmonary resuscitation and he regains consciousness after 60 seconds. The patient has a history of diet-controlled type 2 diabetes mellitus, hypertension, and hyperlipidemia. In the emergency department, his blood pressure is 142/88 mm Hg and pulse is 92/min. Electrocardiogram shows normal sinus rhythm, ventricular premature complexes, and a 3-mm ST-segment elevation in leads V1-V3. What is the most likely primary pathophysiologic mechanism responsible for this patient's syncopal episode?

Question

A 47-year-old man develops sudden onset of mid-sternal chest pain and diaphoresis during a meeting in his office.  While waiting for emergency medical personnel to arrive, he complains of dizziness and becomes unresponsive.  His coworkers perform cardiopulmonary resuscitation and he regains consciousness after 60 seconds.  The patient has a history of diet-controlled type 2 diabetes mellitus, hypertension, and hyperlipidemia.  In the emergency department, his blood pressure is 142/88 mm Hg and pulse is 92/min.  Electrocardiogram shows normal sinus rhythm, ventricular premature complexes, and a 3-mm ST-segment elevation in leads V1-V3.  What is the most likely primary pathophysiologic mechanism responsible for this patient's syncopal episode?

Quizplus · Accepted Answer

Ventricular arrhythmias, including ventricular premature beats, nonsustained or sustained ventricular tachycardia, and ventricular fibrillation, are quite common in the immediate post-myocardial infarction (MI) period. Ventricular fibrillation is the most frequent underlying arrhythmia responsible for sudden cardiac arrest in the setting of acute MI; more than 50% occur within the first hour of symptom onset. Reentry is the predominant mechanism responsible for ventricular arrhythmias in the immediate post-infarction period. The underlying mechanism responsible for periinfarction ventricular arrhythmias varies according to the time elapsed since the onset of MI. Arrhythmias occurring within 10 minutes of coronary occlusion are known as "immediate" or phase 1a ventricular arrhythmias. Acute ischemia causes heterogeneity of conduction with areas of marked conduction slowing and delayed activation, which in turn predisposes to reentrant arrhythmias. On the contrary, "delayed" or phase 1b arrhythmias occur about 10-60 minutes after acute infarction and are thought to result from abnormal automaticity. (Choices A and E) Pulseless electrical activity is defined as the presence of electrocardiographic rhythm in the absence of adequate cardiac mechanical contraction to generate a palpable pulse. Asystole is the complete absence of electrical and mechanical cardiac activity. Patients with prolonged duration of cardiac arrest can degenerate into pulseless electrical activity or asystole, which usually signifies the presence of severe and irreversible myocardial damage. (Choice C) Atrio-ventricular conduction block can occur in patients with acute MI, especially those with inferior wall MI. It is usually transient and resolves after successful reperfusion with thrombolytics or primary percutaneous coronary intervention. (Choices B and D) Supraventricular tachycardias other than atrial fibrillation or flutter are uncommon in the periinfarction period. Even atrial fibrillation occurs rarely (about 3%) during the first 3 hours of acute MI; if it does occur, it rarely presents with syncope. Educational objective: Reentrant ventricular arrhythmias (eg, ventricular fibrillation) are the most common cause of sudden cardiac arrest in the immediate post-infarction period in patients with acute myocardial infarction. References: Sustained ventricular arrhythmias in patients receiving thrombolytic therapy: incidence and outcomes. The GUSTO investigators. (http://www.ncbi.nlm.nih.gov/pubmed/9843464)

A 47-Year-Old Man Develops Sudden Onset of Mid-Sternal Chest Pain