What is the role of nitrates in right myocardial infarction (MI)?

From the Guidelines

Nitrates should be avoided in patients with right ventricular myocardial infarction (RV MI) due to the risk of severe hypotension and worsening of the patient's condition. The use of nitrates in RV MI can lead to a decrease in preload, which is essential for maintaining cardiac output in these patients, as the right ventricle becomes stiff and unable to fill properly 1. According to the ACC/AHA guidelines, nitrates should not be administered to patients with suspected RV infarction, as they can cause a significant drop in blood pressure, leading to further complications 1.

Key Considerations

• In right ventricular infarction, the heart is dependent on adequate preload to maintain cardiac output, and nitrates can reduce venous return, leading to hypotension 1.
• Alternative medications, such as morphine (used cautiously) or careful fluid administration, should be considered for patients with suspected right MI who require treatment for chest pain or pulmonary congestion 1.
• If nitrates have already been given and hypotension occurs, immediate fluid resuscitation with normal saline (500-1000 mL bolus) should be administered to restore preload 1.
• Diagnosis of right ventricular involvement should be confirmed with a right-sided ECG (V3R-V6R leads) showing ST elevation, particularly in V4R, in patients with inferior MI 1.

Management Strategies

• Maintain right ventricular preload with volume loading (IV normal saline) in patients with hypotension and right ventricular ischemia/infarction 1.
• Avoid the use of nitrates and diuretics in patients with right ventricular ischemia/infarction 1.
• Consider inotropic support, such as dobutamine, if cardiac output fails to increase after volume loading 1.
• Reduce right ventricular afterload with left ventricular dysfunction using arterial vasodilators, such as sodium nitroprusside or hydralazine 1.

From the FDA Drug Label

CLINICAL PHARMACOLOGY The principal pharmacological action of Nitroglycerin Injection is relaxation of vascular smooth muscle and consequent dilatation of peripheral arteries and veins, especially the latter Dilatation of the veins promotes peripheral pooling of blood and decreases venous return to the heart, thereby reducing left ventricular end-diastolic pressure and pulmonary capillary wedge pressure (preload).

PRECAUTIONS General: Severe hypotension and shock may occur with even small doses of nitroglycerin. This drug should therefore be used with caution in patients who may be volume depleted or who, for whatever reason, are already hypotensive.

The use of nitrates in right myocardial infarction (MI) should be approached with caution. Nitrates can cause severe hypotension and shock, especially in patients who are volume depleted or hypotensive. In the context of right MI, where patients may already have compromised right ventricular function, the use of nitrates may exacerbate hypotension and worsen cardiac output. Therefore, close monitoring of blood pressure and cardiac function is essential when using nitrates in patients with right MI 2, 2, 2.

From the Research

Nitrates in Right Myocardial Infarction

• The use of nitrates in right myocardial infarction (MI) is a topic of debate, with some studies suggesting that they may be harmful due to the risk of decreasing preload and reducing cardiac output 3.
• However, a systematic review and meta-analysis found that the administration of nitrates during right ventricular MI did not significantly increase the risk of adverse events, such as hypotension, syncope, or death 3.
• The American Heart Association (AHA) and European Society of Cardiology (ESC) recommend avoiding nitrates in patients with right ventricular MI due to the risk of reducing cardiac output and precipitating hypotension 3.
• Other studies suggest that nitrates may be beneficial in certain cases, such as when used in combination with other therapies, like positive inotropic agents and early coronary reperfusion 4, 5.
• The pathophysiology of right ventricular MI is complex, and the clinical sequelae can vary from no hemodynamic compromise to severe hypotension and cardiogenic shock 6, 4, 5.
• Diagnosis of right ventricular MI is based on physical examination, electrocardiography, echocardiography, and coronary angiography, and treatment should be tailored to the individual patient's needs 6, 4, 5.

Key Findings

• A study published in 1987 found that nitrates can relieve symptoms and improve left ventricular hemodynamics during acute myocardial ischemia, but may not be beneficial in right ventricular MI 7.
• A study published in 2010 found that right ventricular involvement in inferior MI is associated with a worse prognosis and increased in-hospital morbidity and mortality 6.
• A systematic review and meta-analysis published in 2023 found that the administration of nitrates during right ventricular MI did not significantly increase the risk of adverse events 3.
• Studies published in 2013 and 2021 found that right ventricular MI is associated with high rates of in-hospital morbidity and mortality, and that early identification and treatment are crucial to improving patient outcomes 4, 5.