Wednesday, November 18, 2009

From AHA 09 scientific sessions: CT-STAT

It's always fun, after national meetings, to observe how the popular press botches the reporting of important findings that were presented. CT-STAT compared two diagnostic strategies for ER evaluation of chest pain in low and intermediate risk patients: initial cardiac markers and electrocardiograms followed by either traditional stress imaging or CT coronary angiography. Here's an Associated Press report on the findings. Nowhere in the report is there a link to the primary source (other than a link to the AHA website) and nowhere is the name of the study mentioned. Moreover, the article failes to inform readers of which of the several types of CT scans was used (it was CT coronary angiography). The article gets it wrong right out of the gate:

A CT scan — a kind of super X-ray — provides a faster, cheaper way to diagnose a heart attack when someone goes to the emergency room with chest pains, a new study suggests.

On the whole CT scanning was indeed cheaper and resulted in faster determination of disposition. And, it was just as good as traditional work up in terms of freedom from events, short term and at 6 months. What's wrong with the statement is the notion that CT diagnosed heart attacks. Wrong, wrong, wrong. Patients enrolled in CT-STAT had already ruled out for MI via cardiac biomarkers and electrocardiograms. CTA is a rule out, not a rule in, test. Over two thirds of patients undergoing CTA had normal or near normal coronary arteries. Of the remaining patients it was not always possible to determine whether visualized disease was significant or “culprit” in nature, and this led to further evaluation.

An important caveat is that the CT strategy is not applicable to higher risk patients, in whom the negative predictive power is not as good. For those patients who rule in subsequent evaluation may be complicated. First, a cardiac catheterization would expose the patient to a second dye load and increased risk of renal failure. This might necessitate waiting an extra day with hydration before proceeding to cath. Second, after visualization of disease on CTA functional testing may then be necessary to establish the physiologic significance of the lesion(s). In other words, some patients, after CTA, may end up getting a stress nuc anyway. For patients who don't rule out with CTA the subsequent diagnostic strategies may in fact be slower and more expensive. We really don't know because the study was not designed to answer that question. Based on these study results, though, the CT strategy is cheaper and faster over all when used in low risk patients because the cost and time savings in the patients who rule out outweigh any increase in cost for the other patients, who are in the minority.

Additional resources about this study, direct from AHA, can be found here, here and here.

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