Tuesday, August 23, 2011

Tutorials in the Tetons 2011---noninvasive cardiovascular imaging

Dr. George Beller, Professor of Cardiology at the University of Virginia, spoke on noninvasive imaging with a focus on CT calcium scoring. He was one of the authors of the 2010 ACCF/AHA guidelines on screening of asymptomatic persons, which cover calcium scoring and other noninvasive techniques.

What did I take away from the talk? Despite the fact that the test characteristics, radiation safety and cost have improved dramatically since the early days of screening via electron beam CT the test remains widely over promoted.

Who should have CT calcium scoring? Let's start with this: there is weakness in the supporting evidence and no slam dunk (level I) recommendation that anyone should have CT calcium scoring.

The highest level of recommendation in the guideline is IIa. For the general population the IIa recommendation is for any patient with an intermediate Framingham risk score (because it misses a substantial number of patients who are at high risk). For diabetics the IIa recommendation applies to all (because, despite the popular notion that all asymptomatic patients with DM-2 have CAD whether it has been officially diagnosed or not there is a significant subset with zero calcium scores whose cardiac prognosis is as good as that of the general population). There are nuances of clinical judgment, of course, as to age cutoffs beyond which screening is not appropriate even in these populations.

A zero calcium score offers reassurance. Would a positive score lead to a stress imaging test or cardiac catheterization? That's a difficult question to answer in the present era, post COURAGE and BARI 2b. A high score would lead to more intensive medical management of risk factors than would otherwise be indicated.

What is the pathophysiologic rationale for calcium scoring? Early in the preclinical stage of the atherosclerotic process intramural plaques form. When they rupture it is an asymptomatic event because they do not compromise the lumen. Calcium soon deposits in these asymptomatic ruptured plaques, thus providing an early marker of the atherosclerotic process.

Carotid IMT measurement for screening of asymptomatic individuals is backed by similar evidence and recommendations in the guidelines. It has the disadvantage of being more operator dependent.

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