II, III and aVF inferior; V1 to V4 anterior; I, aVL, V5 and V6 lateral
Mnemonic
Group the leads and the artery follows:
| Territory | Leads | Artery |
|---|---|---|
| Inferior | II, III, aVF | Right coronary |
| Anteroseptal | V1 to V4 | Left anterior descending |
| Lateral | I, aVL, V5, V6 | Left circumflex |
| Posterior | Reciprocal in V1 to V3 | Right coronary or circumflex |
“I saw a very large lateral wall” places I, aVL, V5, V6 together, and “the inferior leads all have F or numerals: II, III, aVF”.
Posterior infarction has no direct leads, so it shows as its mirror image in V1 to V3: ST depression, tall R waves and upright T waves. Confirm with posterior leads V7 to V9.
Always do right sided leads (V4R) in inferior infarction, because up to 40 per cent involve the right ventricle, and those patients are preload dependent so nitrates and diuretics can cause profound hypotension.
Expansion
| Territory | Leads | Usual artery |
|---|---|---|
| Inferior | II, III, aVF | Right coronary |
| Anteroseptal | V1 to V2 | Left anterior descending |
| Anterior | V3 to V4 | Left anterior descending |
| Lateral | I, aVL, V5, V6 | Circumflex |
| Posterior | Reciprocal changes in V1 to V3 | Right coronary or circumflex |
Posterior infarction has no direct lead, so it appears as a mirror image: tall R waves and ST depression in V1 to V3, confirmed with posterior leads V7 to V9.
Two clinical corollaries: an inferior infarct should prompt a right-sided ECG, because right ventricular involvement makes the patient preload dependent and nitrate sensitive; and aVR, often ignored, shows ST elevation in left main stem or severe three-vessel disease.