Lateral infarction

ECG: Sinus rhythm, normal PR interval; discrete elevation in the high lateral territory (leads I, aVL) with minimal reciprocal depression in lead III; in this patient with many risk factors and with typical chest pain, emergency coronary angiography was proposed in spite of limited electrocardiographic changes; this examination revealed an occlusion of a dominant circumflex artery;

Patient 2: 78-year-old man with no prior history, hospitalized for chest pain at H + 5;

ECG: Sinus rhythm, normal PR interval; poor R wave progression from V1 to V4 with Q-wave in leads I, aVL; wide amplitude elevation in the anterior territory (V2 to V5) and lateral territory (leads I, aVL); anterolateral infarction corresponding to a proximal LAD thrombosis;

Comments: The left ventricular lateral wall is supplied by branches from the LAD and circumflex arteries. On the ECG, a lateral infarction can be analyzed from the high lateral (leads I, aVL) and low lateral leads (V5-V6). There are generally three types of lateral infarctions:

1. The anterolateral infarction (patient 2) related to a LAD occlusion; the elevation is present in both the lateral (leads I, aVL) and anterior leads (often with a maximum amplitude from V2 to V4); there is a reciprocal depression in the inferior leads; the extension to the lateral wall suggests the presence of a proximal LAD thrombosis and massive infarction;
2. The posterolateral infarction is generally related to an occlusion of the left circumflex artery; the elevation is observed in the inferior (leads II, III and aVF) and lateral leads (leads I, V5, V6); a reciprocal depression is preferentially found in the septal leads (V1 to V3); the presence of large amplitude R waves in V1-V2 suggests the presence of a concomitant posterior infarction; a posterolateral infarction also suggests an extensive infarction secondary to a thrombosis of the proximal circumflex artery;
3. The isolated lateral infarction related to an occlusion of a smaller-sized artery (dominant circumflex, first diagonal branch, marginal branch from the circumflex); this type of localization is much rarer than the above two categories; as in patient 1, electrocardiographic diagnosis can be difficult with a modest elevation observed in leads I, aVL and may often be absent despite a coronary occlusion, resulting in a delay in diagnosis and treatment. The isolated lateral infarction probably corresponds to the configuration with the highest diagnostic and therapeutic delay. The presence of typical chest pain associated with even limited electrocardiographic changes in this area should evoke an acute coronary syndrome and warrant performing an emergency diagnostic coronary angiography. The reciprocal depression generally observed in the inferior leads can also be of modest amplitude. When the first diagonal branch of the LAD is the culprit artery, a depression is commonly observed in septal leads (V1 to V3).

Take-home message: The diagnosis of lateral infarction is straightforward when it is part of an extensive myocardial disease (anterolateral or posterolateral) but can be much more difficult when isolated with often an elevation of very low amplitude in leads I and aVL.