Why are nitrates (vasodilators) avoided in right ventricular (RV) infarction?

Nitrates Are Avoided in RV Infarction Due to Preload Reduction and Risk of Hemodynamic Collapse

Nitrates are contraindicated in right ventricular (RV) infarction because they reduce preload, which can cause profound hypotension and hemodynamic collapse in patients who are dependent on adequate RV filling pressures to maintain cardiac output. 1

Pathophysiology of RV Infarction

• RV infarction typically occurs with inferior myocardial infarctions, most commonly due to occlusion of the right coronary artery proximal to the RV branches 1
• When the right ventricle becomes ischemic, it acutely dilates, resulting in:
  • Reduced RV systolic pressure and output
  • Decreased LV preload
  • Reduced LV end-diastolic dimension and stroke volume
  • Shifting of the interventricular septum toward the left ventricle 1
• In RV infarction, the right ventricle becomes stiff, dilated, and critically dependent on adequate preload to maintain cardiac output 2

Hemodynamic Consequences of Nitrates in RV Infarction

• In RV infarction, the pressure gradient between right and left atria becomes a crucial driving force for pulmonary perfusion 1
• Nitrates cause venodilation, which reduces preload to both ventricles 1
• This preload reduction is particularly detrimental in RV infarction because:
  • The ischemic RV is already struggling to generate adequate cardiac output
  • The RV becomes preload-dependent to maintain forward flow
  • Reduced preload further compromises an already dysfunctional RV 1

Clinical Evidence and Guidelines

• ACC/AHA guidelines explicitly recommend avoiding nitrates in patients with RV infarction 1
• In patients with inferior MI and RV involvement, nitrate administration can cause a marked hypotensive response (>30 mmHg decrease in systolic blood pressure with symptoms) 3
• Studies have shown that 75% of patients with documented RV involvement in inferior MI developed significant hypotension in response to nitrates 3
• The clinical triad of hypotension, clear lung fields, and elevated jugular venous pressure in the setting of an inferior MI is characteristic of RV ischemia 1

Management Approach for RV Infarction

• Treatment strategy for RV infarction prioritizes maintaining adequate RV preload:
  • Volume loading with IV normal saline is first-line therapy for hypotension 1
  • Avoid nitrates and diuretics which reduce preload 1
  • Maintain atrioventricular synchrony 1
  • Consider inotropic support with dobutamine if cardiac output fails to increase after volume loading 1
  • Pursue reperfusion strategies (thrombolytics, primary PCI, or CABG) 1

Recent Developments and Controversies

• A 2023 systematic review and meta-analysis challenged the absolute contraindication of nitrates in RV infarction, suggesting the risk may be overstated 4
• However, this review acknowledged key limitations including:
  • All studies had concomitant inferior and RV MI (not isolated RV infarction)
  • Very low certainty of evidence
  • Did not evaluate beneficial effects 4
• Despite this recent challenge, the established guidelines and pathophysiological principles still support avoiding nitrates in RV infarction due to the potential for serious hemodynamic compromise 1

Common Pitfalls and Caveats

• RV infarction may not be immediately apparent without specific diagnostic approaches:
  • Look for ST elevation in right precordial lead V4R (most predictive ECG finding) 1
  • Be aware this finding may be transient (resolving within 10 hours of symptom onset) 1
• Hypotension from nitrates in RV infarction may be mistakenly attributed to other causes, leading to inappropriate management 3
• Signs of RV involvement may be masked by volume depletion and only become evident after adequate volume loading 1
• Patients with RV infarction have significantly higher mortality (25-30%) compared to those with inferior MI without RV involvement (6%) 1