From the Guidelines
Nitroglycerin should be avoided in patients with posterior myocardial infarction (MI) because it can cause dangerous hypotension and worsen the patient's condition. Posterior MIs typically involve the right ventricle, which is preload-dependent, meaning it relies heavily on adequate blood return to function properly. Nitroglycerin works as a vasodilator that reduces preload by dilating veins, decreasing blood return to the heart. In posterior MI patients, this reduction in preload can severely compromise right ventricular filling, leading to profound hypotension, decreased cardiac output, and potentially cardiogenic shock. According to the most recent guidelines, such as those outlined in 1, the routine use of nitroglycerin in patients with acute myocardial infarction is not supported by conclusive evidence, and its use should be carefully considered, especially in patients with low blood pressure.
Instead of nitroglycerin, management should focus on:
- Maintaining adequate preload with IV fluids
- Treating arrhythmias
- Providing oxygen if needed
- Considering early reperfusion therapy If a patient with posterior MI develops hypotension after receiving nitroglycerin, immediate fluid resuscitation is necessary to restore preload and blood pressure. This is why obtaining a right-sided ECG is important when inferior MI is suspected, as it helps identify right ventricular involvement and guides appropriate treatment decisions, as noted in earlier guidelines 1 and 1.
From the Research
Nitroglycerin Use in Myocardial Infarction
- Nitroglycerin is a first-line treatment for angina pectoris and acute myocardial infarction (MI), achieving its benefit through vasodilation and increased blood flow to the myocardium 2.
- However, continuous delivery of nitroglycerin results in tolerance, limiting its use, and sustained treatment can negatively affect cardiomyocyte viability following ischemia, resulting in increased infarct size 2.
Posterior Myocardial Infarction
- Posterior wall MI involves occlusion of either the left circumflex or the right coronary artery and can occur along with acute inferior or lateral MI, or as an isolated event 3.
- Electrocardiographic abnormalities suggestive of acute posterior wall MI include horizontal ST segment depression, a tall, upright T wave, a tall, wide R wave, and an R/S wave ratio greater than 1.0 in lead V2 3.
Pharmacologic Management Post-MI
- The pharmacologic management of post-MI patients aims to prevent subsequent events, including death, reinfarction, and rehospitalization, and to minimize left ventricular remodeling and prevent progression to heart failure 4.
- Recommended treatments include angiotensin-converting enzyme (ACE) inhibitors, antiplatelet therapy, beta blockers, and aldosterone blockade for patients with low ejection fractions and heart failure 4.
- There is no specific mention of nitroglycerin use in posterior MI in the provided studies, suggesting that its use may not be recommended or may be contraindicated in this specific context 2, 4, 5, 6, 3.