What is the likely affected vessel and potential complications in an inferior myocardial infarction (MI)?

Inferior Myocardial Infarction: Affected Vessel and Potential Complications

In inferior myocardial infarction (MI), the right coronary artery (RCA) is most commonly the culprit vessel, typically occluded proximally to the major right ventricular branches, with right ventricular infarction being the most significant potential complication that can lead to increased morbidity and mortality.

Culprit Vessel in Inferior MI

• The right coronary artery (RCA) is the infarct-related artery in approximately 80% of inferior MIs, while the left circumflex coronary artery (LCx) accounts for the remaining 20% 1, 2
• Occlusion of the RCA proximal to the right ventricular branches leads to more severe hemodynamic consequences compared to distal RCA or LCx occlusions 2
• Electrocardiographic criteria can help differentiate between RCA and LCx occlusion:
  • ST elevation greater in lead III than in lead II suggests RCA occlusion 3
  • ST depression in lead I is more common with RCA occlusion 3
  • The ratio of ST depression in lead V3 to ST elevation in lead III (V3/III ratio) <0.5 identifies proximal RCA occlusion with 91% sensitivity and 91% specificity 2

Right Ventricular Infarction

• Right ventricular (RV) ischemia/infarction occurs in up to 50% of inferior MIs, although only 10-15% of patients show classical hemodynamic abnormalities 4
• RV infarction significantly increases mortality in inferior MI patients (25-30% vs. 6% without RV involvement), identifying a high-risk subgroup 4
• Most patients with RV infarction demonstrate return of normal RV function over weeks to months, suggesting RV stunning rather than irreversible necrosis 4

Clinical Presentation of RV Infarction

• The clinical triad of hypotension, clear lung fields, and elevated jugular venous pressure in the setting of inferior MI is characteristic of RV ischemia (though sensitivity is less than 25%) 4
• Distended neck veins alone or the presence of Kussmaul's sign may also indicate RV involvement 4
• Electrocardiographic finding of 1mm ST-segment elevation in right precordial lead V4R is the single most predictive finding for RV ischemia (may be transient, resolving within 10 hours of symptom onset) 4
• Hemodynamic finding of right atrial pressure ≥10 mmHg and >80% of pulmonary wedge pressure is a relatively sensitive and specific finding 4

Complications of Inferior MI

Right Ventricular Dysfunction

• RV dysfunction can lead to reduced cardiac output, hypotension, and cardiogenic shock in 25-50% of patients with RV infarction 4
• The presence of RV dysfunction is associated with significantly increased short-term morbidity and mortality and may influence long-term outcomes 4
• Patients with RV infarction have a greater burden of arrhythmias, contributing to mortality 4

Conduction Abnormalities

• Inferior MI is frequently associated with atrioventricular (AV) blocks due to involvement of the AV node, which is typically supplied by the RCA 4
• High-degree or third-degree heart block may complicate inferior MI, especially with RCA occlusion 4
• When AV block complicates inferior MI, the prognosis is related primarily to the extent of myocardial injury rather than the AV block itself 4

Other Complications

• Arrhythmias: Both atrial and ventricular arrhythmias may occur, with atrial fibrillation being particularly problematic in RV infarction as it reduces the atrial contribution to RV filling 4
• Mechanical complications: Inferior wall rupture, although less common than anterior wall rupture, can occur 4
• Ischemic mitral regurgitation due to papillary muscle dysfunction 4

Management Considerations for RV Infarction

• Maintain RV preload:
  • Volume loading with IV normal saline is essential when hypotension is present 4
  • Avoid nitrates and diuretics which can reduce preload and worsen hypotension 4
• Maintain AV synchrony:
  • Prompt cardioversion for hemodynamically significant supraventricular tachyarrhythmias 4
  • AV sequential pacing for symptomatic high-degree heart block unresponsive to atropine 4
• Provide inotropic support:
  • Dobutamine if cardiac output fails to increase after volume loading 4
• Early reperfusion:
  • Patients with RV infarction are high-priority candidates for reperfusion therapy 4
  • Primary percutaneous coronary intervention (PCI) is preferred as it may result in rapid hemodynamic improvement 4

Prognosis

• One-year mortality after RV infarction is approximately 18% in patients with isolated RCA lesions compared to 27% in those with combined right and left coronary artery disease 4
• Long-term mortality beyond the first year remains at an additional 2-3% per year through year 10 4
• Most patients recover RV function within days to weeks after the infarct, suggesting that RV stunning rather than permanent damage has occurred 4