Monday, October 31, 2011

Many so called NSTEMIs are really STEMI equivalents

That is, they represent acute epicardial coronary occlusion nonetheless. These tricky situations have deprived many patients of a timely trip to the cath lab, even though the infarcts can be just as serious as STEMIs meeting the generally accepted criteria. Many of these infarcts are termed electrocardiographically silent although in most cases, under the careful scrutiny of an experienced reader subtle abnormalities come to light.

Dr. Smith at his ECG blog presents such a case here. This was a Cx/OM occlusion with subtle ECG changes but ultimately a very large infarction. Aside from the fact that the circumflex territory is relatively electrocardiographically silent this was probably a posterior infarction, which characteristically lacks classic STEMI changes.

I have seen countless examples of this sort of thing between my own practice and numerous postings on ECG blogs. These represent patients with STEMI equivalents whose door to balloon times are prolonged due to the subtlety of their ECG manifestations. These long door to balloon times are not tracked as a quality measure because the cases are not captured by the simplistic criteria (ST segment elevation of at least 1 mm in two contiguous leads) for the performance metric.

Despite progressive improvement in door to balloon time as a performance measure overall mortality from acute MI has not declined over the last several years. This may reflect the fact that the performance measurement represents only a fraction of the patients who present with acute coronary occlusion.

Cases like this also help us understand the recent findings in this paper, that STEMIs and NSTEMIs are indistinguishable in terms of prognosis, clinical course and pathology, leading the author, Brendan Phibbs, to conclude that STEMI vs NSTEMI is a baseless distinction. ST segment elevation will identify many patients who need an immediate trip to the cath lab, but simple reliance on this finding will result in some patients with acute coronary occlusion being deprived of timely reperfusion.

There is no obvious solution to this problem. Lack of typical ECG changes in a patient with acute coronary occlusion puts both patient and clinician at a disadvantage. Dr. Smith's advice is that if chest pain is unremitting, then as soon as one has evidence that the pain is ischemic an urgent trip to the cath lab is warranted, ST elevation or not.

No comments: