What are the contraindications to nitrate administration in a patient with possible ST-Elevation Myocardial Infarction (STEMI) and ongoing chest discomfort?

Contraindications to Nitrate Administration in Patients with Suspected STEMI

Nitrates should not be administered to patients with suspected STEMI who have systolic blood pressure less than 90 mmHg or ≥30 mmHg below baseline, severe bradycardia (<50 beats per minute), tachycardia (>100 beats per minute) without symptomatic heart failure, right ventricular infarction, or recent use of phosphodiesterase inhibitors for erectile dysfunction. 1, 2

Absolute Contraindications

1. Hemodynamic Instability:

   • Hypotension: SBP <90 mmHg or ≥30 mmHg below baseline 1
   • Severe bradycardia: Heart rate <50 beats per minute 1
   • Tachycardia: Heart rate >100 beats per minute without symptomatic heart failure 1

2. Right Ventricular Infarction:

   • Patients with right ventricular involvement should not receive nitrates as this can dramatically reduce preload and cause profound hypotension 2
   • This is particularly important in inferior wall MIs, which commonly involve the right ventricle 3

3. Medication Interactions:

   • Recent use of phosphodiesterase-5 inhibitors for erectile dysfunction 1, 2:
     • Within 24 hours of sildenafil use
     • Within 48 hours of tadalafil use
     • Timing after vardenafil use not clearly determined, but similar precautions apply

Clinical Implications and Management

When evaluating a patient with suspected STEMI and ongoing chest discomfort:

1. Before administering nitrates:

   • Check vital signs, particularly blood pressure and heart rate
   • Obtain a 12-lead ECG to identify location of infarct (especially to rule out right ventricular involvement)
   • Ask specifically about use of medications for erectile dysfunction
   • Establish IV access before nitrate administration, particularly in patients with inferior MI 2

2. Monitoring during nitrate administration:

   • Monitor blood pressure after each dose
   • Discontinue nitrates if systolic BP drops below 90 mmHg or 30 mmHg below baseline 2
   • Have patients sit down when taking nitrates to prevent falls from lightheadedness 2

Special Considerations

While traditional teaching has emphasized avoiding nitrates in inferior MIs due to potential right ventricular involvement, recent research suggests this may be overstated:

• A 2016 study found no significant difference in hypotension rates between inferior and non-inferior STEMI patients receiving nitrates (8.2% vs. 8.9%) 4
• However, caution is still warranted as severe hypotension can occur in patients with right ventricular infarction 3

Alternative Approaches for Pain Management

If nitrates are contraindicated but the patient has ongoing chest discomfort:

• Morphine sulfate (2-4 mg IV with increments of 2-8 mg repeated at 5-15 minute intervals) may be considered 2
• Focus on rapid reperfusion strategies as the definitive treatment for ongoing ischemia
• Beta blockers may be appropriate if no contraindications exist

Common Pitfalls to Avoid

1. Failing to ask about PDE-5 inhibitor use before administering nitrates
2. Not recognizing right ventricular involvement in inferior wall MIs
3. Continuing nitrate therapy despite significant drops in blood pressure
4. Using nitrates as the sole therapy rather than focusing on definitive reperfusion strategies

By carefully screening for these contraindications before administering nitrates, clinicians can avoid potentially dangerous complications while effectively managing chest discomfort in patients with suspected STEMI.