From the Guidelines
Arrhythmias following acute myocardial infarction (MI) require prompt recognition and management, with continuous cardiac monitoring for at least 24-48 hours post-MI being essential for all patients, as recommended by the American Heart Association 1. The most common arrhythmias to recognize include ventricular tachycardia, ventricular fibrillation, atrial fibrillation, and bradyarrhythmias.
- For ventricular arrhythmias, look for wide-complex tachycardias, particularly in the first 48 hours when the risk is highest.
- Sustained ventricular tachycardia requires immediate treatment with amiodarone 150 mg IV over 10 minutes, followed by 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours.
- For hemodynamically unstable patients, immediate electrical cardioversion at 120-200 joules (biphasic) is indicated.
- New-onset atrial fibrillation presents with irregular rhythm and absent P waves and may require rate control with metoprolol 5 mg IV every 5 minutes up to 15 mg, or diltiazem 0.25 mg/kg IV over 2 minutes.
- Bradyarrhythmias, particularly high-degree AV blocks, may require temporary pacing, especially with inferior wall MIs. These arrhythmias occur due to myocardial ischemia, autonomic dysfunction, electrolyte abnormalities, and structural remodeling following infarction. Maintaining normal electrolyte levels (potassium >4.0 mEq/L, magnesium >2.0 mg/dL) and optimizing beta-blocker therapy can help prevent arrhythmias in the post-MI setting, as supported by the European Society of Cardiology 1 and the American College of Cardiology/American Heart Association task force 1.
From the Research
Arrhythmia Recognition Following Acute MI
- The incidence of arrhythmia after myocardial infarction has declined since the introduction of reperfusion techniques, but ischemic arrhythmias are still associated with increased morbidity and mortality, particularly in the first 48 hours after hospital admission 2.
- Factors influencing mortality and morbidity rates include the type of arrhythmia, heart rate, and level of dissociation between atrial and ventricular rhythm, as well as patient characteristics such as age, sex, and history of smoking or cardiac surgery 3.
- Common arrhythmias associated with acute myocardial infarction include bradycardia, supraventricular and ventricular tachycardia, with optimal treatment approaches based on the pathophysiology of the infarct and contributing medical factors 4.
- Ventricular tachyarrhythmias are a common cause of sudden death in acute MI, and the presence of these arrhythmias can independently influence mortality in patients recovering from MI 5.
Predictors of In-Hospital Lethal Arrhythmia
- Independent predictors of in-hospital ventricular tachycardia and fibrillation (VT/VF) after acute myocardial infarction include extensive myocardial damage, cardiogenic shock, lower grade initial Thrombolysis in Myocardial Infarction (TIMI) flow on coronary angiography, and concomitant chronic kidney disease (CKD) 6.
- Other factors that may increase the risk of arrhythmia and mortality after acute MI include old age, advanced heart disease, diabetes mellitus, and history of smoking 3.
- The type of arrhythmia, such as sinus arrhythmia, atrioventricular (AV) nodal blocks, and ventricular tachycardia, can also impact outcomes, with sinus arrhythmia having the best survival rates and AV nodal blocks and ventricular tachycardia having the worst outcomes 3.