Which types of myocardial infarction (MI) require caution with nitrates?

From the Guidelines

Caution should be exercised when using nitrates in patients with right ventricular infarction (RV MI) and inferior wall myocardial infarction, as well as those with hypotension, marked bradycardia or tachycardia, or recent use of phosphodiesterase-5 inhibitors. These patients are particularly vulnerable to the hypotensive effects of nitrates because their cardiac output is highly dependent on adequate preload (venous return to the heart) 1. Nitrates cause venodilation, which reduces preload by pooling blood in the peripheral veins. In right ventricular infarction, the damaged right ventricle already struggles to pump blood effectively, and further reduction in preload from nitrates can precipitate profound hypotension and cardiovascular collapse. Similarly, patients with inferior wall MI often have associated right ventricular involvement. If nitrates must be used in these patients, start with very low doses, monitor blood pressure continuously, and have IV fluids readily available to counteract hypotension 1. Patients should be positioned supine rather than sitting or standing to minimize venous pooling. The risk is highest within the first 24-48 hours after the infarction when hemodynamic instability is most pronounced.

Some key considerations when using nitrates in these patients include:

• Avoiding nitrates in patients with hypotension or those who have recently received a phosphodiesterase inhibitor 1
• Using nitrates with caution in patients with right ventricular infarction or inferior wall MI 1
• Monitoring blood pressure closely and having IV fluids available to counteract hypotension 1
• Positioning patients supine to minimize venous pooling 1

It's also important to note that the use of nitrates should not preclude the use of other proven mortality-reducing interventions, such as beta blockers 1. Overall, the decision to administer nitrates should be made on a case-by-case basis, taking into account the individual patient's clinical presentation and medical history 1.

From the FDA Drug Label

Nitrate therapy may aggravate the angina caused by hypertrophic cardiomyopathy The FDA drug label does not answer the question about which types of myocardial infarction (MI) to exert caution for with nitrates, but it does mention that hypertrophic cardiomyopathy may be aggravated by nitrate therapy.

• Key points to consider when using nitrates:
  • Use with caution in patients who may be volume-depleted or already hypotensive 2
  • May cause severe hypotension, particularly with upright posture 2
  • Concomitant use with certain medications, such as soluble guanylate cyclase stimulators, is contraindicated 2 However, the label does not provide direct information about types of MI to exert caution for with nitrates.

From the Research

Types of Myocardial Infarction (MI) Requiring Caution with Nitrates

• Right ventricular myocardial infarction (RVMI): Although the American Heart Association (AHA) and European Society of Cardiology (ESC) recommend caution with nitrates in RVMI due to the risk of decreasing preload and reducing cardiac output 3, recent studies suggest that this risk may be lower than previously thought 3.
• Hypovolaemic patients or patients with right heart infarction: These patients may be especially susceptible to hypotension caused by nitrates 4.
• Patients with left ventricular failure: While nitrates can be beneficial in patients with left ventricular failure, high doses (larger than 100 micrograms/min) may cause a paradoxical increase in the ischemic condition 4.
• Patients with severe angina or unstable angina: Nitrates can be used to relieve chest pain, but caution should be observed if the patient is sweating or hypotensive 5.

Key Considerations

• Nitrates should be used with caution in patients with myocardial infarction, especially in those with RVMI, hypovolaemia, or right heart infarction.
• The dose of nitrates should be carefully titrated to avoid hypotension and other adverse effects.
• The benefits and risks of nitrate administration should be carefully weighed, taking into account the individual patient's condition and medical history 6, 7.