An inferior myocardial infarction results from occlusion of the right coronary artery (RCA). This can cause a ST elevation myocardial infarction or a non-ST segment elevation myocardial infarction. The mechanism is usually plaque rupture causing thrombus, however plaque erosion or progressive hemodynamic stenosis can contribute as well. Some rare causes of inferior myocardial infarctions exist and include ascending aortic dissection when the right coronary ostium is involved.
The ECG findings of an inferior ST segment elevation myocardial infarction include:
ST segment elevation in the inferior leads (II, III, and aVF) of at least 1 mm.
Reciprocal ST segment depression in the lateral and/or high lateral leads (I, aVL, V5 and V6).
Note: If the reciprocal ST depressions are not present, consider alternative causes of ST segment elevation such as pericarditis.
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Inferior myocardial infarctions have multiple potential complications and can be fatal. See the review on ST elevation myocardial infarction for more detail on complications of an inferior myocardial infarction and a detailed discussion on treatment.
Briefly, complications include ventricular tachycardia or ventricular fibrillation, cardiogenic shock, acute mitral valve regurgitation, acute ventricular septal defect, bradycardia, left ventricular aneurysm formation and right ventricular infarction. Treatment is emergent percutaneous coronary intervention (PCI) depending on the clinical presentation (ST elevation versus non-ST elevation myocardial infarction and high versus low risk features). Medical therapy includes