Lateral Myocardial Infarction


Duration and amplitude of Diagnostic Q Waves: at least 40 milliseconds in duration, at least 25% the amplitude of the following R wave and they must occur in two adjacent or contiguous leads. If not all criteria are met, the Q waves are non-diagnostic. Lateral extension can accompany an inferior or anterior MI and Q waves only in I and AVL are called a high lateral MI. Marked ST elevation in the same area is consistent with a recent MI. If it persists and is present in an older infarction, it is associated with a wall motion abnormality or an aneurysm.

Lateral infarcts are associated with diagnostic Q waves in at least 2 of the lateral leads, I,AVL, V4,5,6. This is the least common MI pattern and is associated with lesions and/or thrombus that occurred in the left circumflex coronary artery.


If this is a new pattern and the patient is presenting with typical ischemic chest pain and ST elevation, then ASA and thrombolysis should be given as soon as possible unless there is a contraindication. While less complicated and at lower risk than anterior MI's, these patients usually should be placed on a beta-blocker for at least 2 years after their MI occurred. ACE inhibitors are indicated in those with documented LV dysfunction. If the Q waves are borderline or mainly reach the amplitude criteria and not the duration criteria, consider the presence of asymmetrical septal hypertrophy (or IHSS). Cardiomegaly and a systolic murmur that increases with the Valsalva maneuver is characteristic of this congenital abnormality. An echocardiogram can confirm the diagnosis and if confirmed, the patient should be referred to a cardiologist.