Inferior Myocardial Infarction


Knowledge

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. 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.

Inferior infarcts are associated with diagnostic Q waves in at least 2 of the inferior leads, II, III, and AVF. They are usually due to lesions and/or thrombus that occurred in the right coronary artery and/or left circumflex. When they occur they are often associated with transitory heart blocks. They are less likely to be complicated but can be associated with posterior infarctions (R wave greater than the S wave in V1/2) and right ventricular MI's.


Recommendations

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. If there is neck vein distension yet the lungs are clear to auscultation record right sided V leads to see if there is ST elevation due to right ventricular infarction. If so, a fluid challenge might be helpful if the patient is hypotensive since the neck vein distension is not due to CHF. While less complicated and at lower risk, these patients usually should be placed on a beta-blocker for at least 2 years after the occurrence of their MI. ACE inhibitors are indicated in those with documented LV dysfunction. ACE inhibitors can cause a cough, hyperkalemia and renal dysfunction requiring a switch to a long acting nitrate and hydralazine.

View an ECG Example