Is sublingual Isosorbide Dinitrate (Isosorbide Dinitrate) safe to administer in a patient with an inferior wall myocardial infarction (MI)?

Sublingual Isosorbide Dinitrate in Inferior Wall MI: Contraindicated

Sublingual isosorbide dinitrate should NOT be administered to patients with inferior wall myocardial infarction due to the high risk of precipitating severe hypotension and worsening outcomes. 1

Pathophysiology and Risk

Inferior wall MIs have a critical association with right ventricular (RV) involvement that makes nitrate administration particularly dangerous:

• 10-15% of inferior MIs show classical hemodynamic abnormalities of RV infarction 1
• Up to 50% of inferior MIs demonstrate some degree of RV ischemia 1
• RV infarction creates a state where cardiac output becomes highly preload-dependent

When RV infarction is present, the following pathophysiological changes occur:

• Reduced RV contractility
• Increased dependence on adequate preload (right atrial filling pressure)
• Shifting of interventricular septum toward left ventricle
• Reliance on the pressure gradient between right and left atria for pulmonary perfusion

Specific Contraindication

The ACC/AHA guidelines explicitly state that nitrates, including isosorbide dinitrate:

1. Should be "carefully titrated in patients with inferior wall MI because of its frequent association with RV infarction" 1
2. Are specifically contraindicated "in patients with right ventricular infarction" 1
3. Should be avoided in inferior wall STEMI patients until RV infarction has been ruled out 1

Diagnostic Approach

Before considering nitrate therapy in inferior MI:

1. Perform right-sided ECG (especially lead V4R) to assess for RV involvement

   • ST elevation ≥1mm in V4R is the single most predictive finding for RV ischemia 1
   • This finding may be transient and disappear within 10 hours of symptom onset

2. Assess for clinical triad suggestive of RV involvement:

   • Hypotension
   • Clear lung fields
   • Elevated jugular venous pressure

Hemodynamic Consequences

Administration of sublingual isosorbide dinitrate in inferior MI with RV involvement can lead to:

• Profound hypotension due to reduced preload
• Decreased cardiac output
• Reflex tachycardia
• Worsening myocardial ischemia
• Potential cardiovascular collapse

Alternative Management for Inferior MI with RV Involvement

Instead of nitrates, the recommended approach includes:

1. Maintain right ventricular preload:

   • IV normal saline volume loading 1
   • Explicitly avoid nitrates and diuretics 1

2. Maintain AV synchrony:

   • AV sequential pacing for symptomatic high-degree heart block 1
   • Prompt cardioversion for hemodynamically significant SVT 1

3. Consider inotropic support if cardiac output fails to increase after volume loading:

   • Dobutamine 1

4. Focus on reperfusion strategies:

   • Thrombolytic agents
   • Primary PCI
   • CABG in selected patients with multivessel disease 1

Summary

Sublingual isosorbide dinitrate is contraindicated in inferior wall MI due to the high risk of RV involvement, which creates a preload-dependent state where nitrate-induced venodilation can cause severe hemodynamic compromise. Always perform right-sided ECG leads to rule out RV infarction before considering nitrate therapy in inferior MI patients.