False positive Activation: early repolarization with changing degree of ST elevation
Posted Jul 30 2010 8:50am
This 45 year old male with known CAD and inferior STEMI 4 months ago called 911 because of intermittent anginal symptoms all day. The paramedics recorded a prehospital ECG that is identical to the following. They activated the cath lab from the field.
There is 2-3 mm of ST elevation in leads V2-V4, and also ST elevation in V5, V6, I, II, and aVL. However, the ST elevation in anterior leads looks very much like early repolarization. I have derived and validated a 3 part rule to differentiate early repol from acute LAD occlusion (paper submitted). If 2 of the following 3 questions are answered "yes", then it is MI with an accuracy of about 85%: 1) is the QTc > 392 ms? (here, yes) 2) Is the ST elevation at 60 ms after the J-point in lead V4 > 2mm (here, yes) 3) Is the R-wave in V4 < 13 mm (here, no). So by this rule, the ECG leans toward acute LAD occlusion.
Then it was compared with the following previous ECG
This ECG shows the inferior Q-waves from his inferior MI, with persistent ST elevation and persistent reciprocal ST depression in aVL. Thus, today's ST elevation in II is not new, but it is new in I and aVL, and V2-V6.
Thus, one must activate the cath lab, or give thrombolytics, right?
However, there are other considerations: First, review of the previous angiogram showed a chronic LAD occlusion, with left (circumflex) to LAD collateral circulation supplying the anterior wall. (In fact, the patient did indeed have severe CAD and was supposed to get CABG but was unwilling). With this anatomy, any anterior STEMI would have to be due to circumflex or left main occlusion, either of which would result in an unstable patient and a far more abnormal ECG. Second, the patient's chest pain resolved in the ED, and 3 subsequent ECGs remained exactly the same, with all the same ST elevation. Third, we did a bedside ultrasound which showed excellent contraction and thickening of both anterior and lateral walls.
Thus, we were convinced that this was not an acute STEMI. The cath lab was de-activated. The patient ruled out for MI with serial negative troponins. .