Coronary artery bypass graft surgery (CABG) can be used in acute myocardial infarction as both primary and secondary therapy. Patients with recurrent ischemia uncontrolled by medical therapy who are ineligible for PTCA may require emergent CABG. Operative mortality is increased in the peri-infarction period, primarily in patients with poor hemodynamics, congestive heart failure, and advanced age.
What arrhythmias occur in acute myocardial infarction?
Both supraventricular and ventricular arrhythmias are seen in acute myocardial infarction. Of supraventricular arrhythmias, sinus bradycardia is present most commonly with inferior infarction and suggests a better prognosis. Sinus tachycardia (heart rate 100 bpm) in acute myocardial infarction may be caused by pain, anxiety, left ventricular dysfunction, hypovolemia, pericarditis, or atrial infarction; it is a marker of poor prognosis because it generally signals a significant amount of left ventricular dysfunction. Premature atrial contractions (PACs) are also common and may result from increased atrial pressure with congestive heart failure. Atrial fibrillation occurs in 15% of infarctions and is a marker of poor prognosis. Other supraventricular tachycardias are infrequent in myocardial infarction but should be treated promptly if symptomatic.
Ventricular arrhythmias are the leading cause of prehospital mortality in acute myocardial infarction. Ventricular fibrillation (VF) is believed to be responsible for 60% of infarction-related prehospital mortality and occurs predominantly in the first 12 hours. Primary VF (without heart failure) should be distinguished from secondary VF (with significant heart failure). Primary VF occurs predominantly in the first few hours after myocardial infarction and rarely results in death if the patient is hospitalized and defibrillation is available early. Secondary VF may occur at any time during the hospitalization, and defibrillation is not always successful. Premature ventricular beats (PVCs) occur in 90% of patients with acute myocardial infarction and do not predict VF. However, in the immediate postinfarction period, PVCs that occur frequently or in pairs or groups of three do predict risk of VF.
Although prophylactic lidocaine is no longer recommended for all patients with acute infarction, it may be indicated in those with very frequent or complex ectopy in the first 24 hours post infarction. Treatment of chronic but asymptomatic PVCs with antiarrhythmic drugs in the late postinfarction period leads to higher mortality and is not recommended. Accelerated idioventricular rhythm is a nonspecific marker for myocardial reperfusion and should not be treated unless symptoms exist.
How is the risk for sudden death assessed in postinfarction patients?
The signal-averaged ECG may be useful in predicting risk for sudden death in postinfarction patients as well as for guiding medical management or placement of an automatic implantable defibrillator. Electrophysiologic studies may be useful in assessing risk of late sudden death postinfarction and are usually performed if the patient has an episode of ventricular tachycardia or ventricular fibrillation after the first 48 hours of infarction or if the signal-averaged ECG is positive in patients with complex ventricular ectopy.