Different means to the same end, or just different?

The study by Schuijf and Bax

, which compares multislice computed tomography (CT) versus myocardial perfusion imaging, is very timely, as this new cardiac imaging modality has gained rapid acceptance by cardiologists for managing patients. The title of the article, however, also hints at the question frequently asked when 64-slice CT first became available. Will this technology reduce diagnostic cardiac catheterization or replace myocardial perfusion imaging? (I emphasize 64-slice images, because 16-slice CT does not provide the same information.)

In my mind, 64-slice CT is an additional, not a substitute, test, as it frequently provides information that cannot be revealed by any other diagnostic. The article from these Dutch authors demonstrates this, as most of the patients with coronary artery disease (CAD) on CT had a normal myocardial perfusion study (55%). From my own experience, frequently patients who have a "normal" cardiac catheterization demonstrate significant plaque and disease on CT scan.

In the

Schuijf and Bax study

a lot

, CAD was detected in 49 of the 114 patients and confirmed on catheterization in all cases, whereas only 29 of these 49 patients with CAD had an abnormal perfusion scan. In addition, 114 patients with chest pain had both of these studies within 1 month of each other (which is of radiation exposure). The patients were divided into low-, intermediate-, and high-pretest likelihood of CAD. Most patients were in the intermediate group (85%). In 58 of the 114 patients, cardiac catheterization was performed as well (leading to even more radiation exposure).

What the authors correctly imply is that a normal perfusion study may give the physician and patient a false sense of security as to the presence of CAD, which can lead to less aggressive risk-factor reduction when in fact the opposite is required. There is nothing more convincing about the need for treatment than a scan full of plaque or calcium. In this study, 48% of patients with considerable plaque had a normal perfusion scan. Perfusion enthusiasts will argue that years of predictive data guide the treating physician between choosing more-or less-invasive routes. However, a study from researchers at Cedars-Sinai Medical Center first presented at the American Heart Association meeting in November 2006 and subsequently published showed the excellent predicative value of CT angiography, maybe even better than perfusion scans for low- and intermediate-risk patients.¹

I believe that the future algorithm for evaluating a low- or intermediate-risk cardiac patient will be to do a CT scan as an initial test, and a perfusion scan only if the lesion looks obstructive. I think that this study from the Netherlands confirms this approach.