Inferior STEMI ECG recognition: leads II, III, and aVF
Inferior STEMI presents with ST elevation in leads II, III, and aVF — reflecting occlusion of the right coronary artery (RCA) in ~80% of patients, or the left circumflex artery (LCx) in the remaining 20%. The inferior wall of the left ventricle is the territory at risk.
Reciprocal ST depression: reciprocal depression in lead aVL (and often lead I) is the most reliable confirmatory sign of inferior STEMI. Reciprocal changes increase diagnostic specificity substantially and should be actively sought on every inferior STEMI evaluation. Lead aVL reciprocal depression occurring alongside inferior ST elevation warrants STEMI protocol activation even before troponin results.
ST elevation magnitude: lead III typically shows more ST elevation than lead II in inferior STEMI. If lead II > lead III, consider pericarditis, benign early repolarization, or non-ischemic causes in the differential.
Right ventricular involvement: V4R assessment and nitrate contraindication
Right ventricular infarction complicates inferior STEMI in approximately 30–40% of cases. Assessment is MANDATORY in all inferior STEMIs before administering nitrates.
Right-sided leads (V4R): apply right-sided lead V4R (mirror position of V4 on the right chest). ST elevation ≥ 1mm in V4R confirms right ventricular involvement. This single finding changes management.
Nitrate contraindication: NEVER give nitroglycerin to a patient with inferior STEMI and right ventricular involvement. RV infarction requires preload to maintain right ventricular output. Nitroglycerin drops venous return (preload), causing precipitous hypotension in the preload-dependent RV — potentially fatal. IV fluid challenge (NS 500mL) is the correct hemodynamic support for RV infarction. Atropine for bradycardia (inferior STEMI commonly involves the AV node).