Case No. 4 A: Atypical Symptoms with a Critical Lesion
A 64 yr old white female presented to EMS with n/v/d times three days and a recent episode of orthostatic syncope. She had no complaints of chest discomfort or shortness of breath. She was pale in apearance and found to be hypotensive on exam.
Although AV dissociation can be appreciated in the first three tracings, the fourth appears consistent with undifferentiated 2nd degree conduction block and prolonged (>200 ms) PR interval with bigeminal junctional escape. Close examination of II and V4-6 reveal a subtle morphological variation in the complexes, supporting the argument for multiple depolarization foci. A narrow-complex junctional escape rhythm is typical of a culprit RCA lesion resulting in often transient ischemia to the superior portion of the nodal tissue. Wide-complex 3rd degree block more frequently reflects a significant LCA infarction which has resulted in distal, more inferior conduction system damage that is less likely to recover. Note that the ST elevation in III is greater than that in II— a finding that has been correlated with RV involvement, although I know of no EBM trials to support this. It is regrettable that right-sided and posterior leads were not recorded.
AV conduction abnormalities can be appreciated in as much as 30% of inferior wall MIs owing to the ~70% prevalence of the RCA as the dominant vessel supplying the AV nodal branch. Left dominant coronary systems present a variation to the predictability of progressive conduction pathway ischemia but constitute only 10% of the populace. This leaves 20% with co-dominant systems. In the absence of confounding factors, it would be interesting if there has been a study demonstrating a decreased incidence of AV conduction blocks in pts with redundant AV nodal circulation who present with acute coronary syndrome.
Despite what appear to be convalescent ECG changes over the course of these three 12-leads, the pt. deteriorated rapidly in the ED and required pressor support and intubation before she could be transported to the cath lab. The outcome is unknown.