Inferior, posterior and lateral wall myocardial infarction

Inferior, posterior and lateral wall myocardial infarction

Inferior, posterior and lateral wall myocardial infarction
Inferior, posterior and lateral wall myocardial infarction

ST segment elevation and T wave inversion are present in II, III and aVF, the inferior leads. The ST segment is coved and T waves are inverted in V5 and V6, the lateral leads. Minimal ST segment depression is seen in lead I and aVL, which can be taken as reciprocal to the ST segment elevation in inferior leads. There are tall R waves in V1 and V2 with R/S ratio more than 1, and ST segment depression with upright T waves. These feature are suggestive of posterior wall infarction, being the inverse of Q wave, ST elevation and T wave inversion which would have been recorded in a posterior lead. There is also loss of r wave amplitude in V5, V6. Together with the changes in inferior and lateral leads, the full diagnosis is inferior, posterior and lateral wall infarction. This combination can occur in occlusion of a dominant left circumflex coronary artery which supplies the inferior, posterior and lateral walls of the left ventricle. A distal occlusion of a dominant right coronary artery can also cause this pattern. A more proximal occlusion of right coronary artery would produce right ventricular infarction and null out the ST segment depression in anterior leads seen in true posterior wall infarction. The term true posterior wall infarction is sometimes used as inferior wall infarction was called posterior wall infarction earlier.

Detailed evaluation of ECG in myocardial infarction is relevant even in this era of early coronary angiography and primary angioplasty. Sometimes it may be difficult to find the culprit lesion after coronary angiography when multivessel disease is found. Correlation with ECG is useful then [1]. Sometimes complete occlusion of side branches at bifurcation can be completely missed during the evaluation of a coronary angiogram. But if preceding ECG data has suggested an occlusion in the territory, a careful inspection of the angiogram often brings out the occlusion missed at one look [1].

It may be noted that while angiography identifies the anatomy, ECG suggests the physiology of myocardium during acute ischemia, an information which is hard to get from angiography [1]. Of course, a no-reflow or slow flow of an open coronary artery can be visualized on angiography. But ECG gives more information in the form of persisting ST elevation after apparent reperfusion on angiography which may indicate ongoing ischemia.

Correlation of electrocardiographic and pathological information in posterolateral infarction has been published as early as 1949 [2]. A new revised terminology based on magnetic resonance imaging studies by a committee appointed by the International Society for Holter and Noninvasive Electrocardiography has suggested that the term posterior wall infarction should be abandoned [3]. They suggested that the term inferior should be applied to the entire left ventricular wall that lies on the diaphragm. Overall, the terms for 6 locations of myocardial infarctions suggested by the committee are septal, mid-anterior, apical-anterior, extensive anterior, lateral and inferior.

References

  1. Birnbaum Y, Drew BJ. The electrocardiogram in ST elevation acute myocardial infarction: correlation with coronary anatomy and prognosis. Postgrad Med J. 2003 Sep;79(935):490-504.
  2. Myers GB, Klein HA, Hiratzka T. Correlation of electrocardiographic and pathologic findings in posterolateral infarction. Am Heart J. 1949 Dec;38(6):837-62.
  3. BayƩs de Luna A, Wagner G, Birnbaum Y, Nikus K, Fiol M, Gorgels A, Cinca J, Clemmensen PM, Pahlm O, Sclarovsky S, Stern S, Wellens H, Zareba W; International Society for Holter and Noninvasive Electrocardiography. A new terminology for left ventricular walls and location of myocardial infarcts that present Q wave based on the standard of cardiac magnetic resonance imaging: a statement for healthcare professionals from a committee appointed by the International Society for Holter and Noninvasive Electrocardiography. Circulation. 2006 Oct 17;114(16):1755-60.