Cardiac Imagers: Pay Attention to Clinical Trials

Twitter icon
Facebook icon
LinkedIn icon
e-mail icon
Google icon

The cardiac-imaging community, indeed any imaging community, should pay close attention to clinical trials. Why? The results of the trial will determine the rationale for imaging. The rationale will determine reimbursement, reimbursement will influence demand, and demand will affect supply. This is the new economics of imaging.

Two trials, one completed and one ongoing, could radically alter the landscape of noninvasive cardiac imaging by making us question (a question more likely to be asked post ACA) why we are imaging in the first place.

Cardiac imagers will be familiar with the battle lines in the imaging of patients with suspected stable coronary-artery disease (CAD): Which is the most effective gatekeeper? SPECT, stress MRI, cardiac CT, or stress echo? Is anatomical imaging superior to functional imaging? Is the gold standard for obstructive CAD catheterization angiography (CA), fractional flow reserve, or does it really matter?

These questions are so pervasive that it is impossible to escape a cardiac-imaging meeting without witnessing two imagers on the parapet extolling the virtues of their respective modality; the smaller the difference (and they do tend to be quite small), the more the fervor in their advocacy. It is difficult to denigrate a modality with a sensitivity of 88% and specificity of 82% just because another one has a sensitivity of 90% and a specificity of 84%. One does not throw away the old iPad just because Apple’s annual upgrade produces another with incremental benefits. What is true for iPads is also true for advanced cardiac-imaging modalities, and certainly true for interpreters of these modalities.

Why do we image patients with suspected CAD? So that patients most likely to have obstructive CAD are subjected to CA, an invasive test with measurable morbidity.

Why CA? To select patients for revascularization, a costly procedure that has its own morbidity and mortality.

Why revascularization? Because it makes people live longer than polypharmacy. Well, that’s what we thought until a trial¹ randomized symptomatic patients with proven CAD to percutaneous coronary intervention (PCI) and optimal medical therapy and found little difference in hard endpoints. Pills did just as well as stents (well, almost).

If stents are no better than pills, then why perform the CA? Why not start the patients on optimal medical therapy? Moving upstream, if there is no need for CA, there is nothing to gatekeep—ie, no need for either SPECT or stress MRI.

The Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation trial,² aptly abbreviated to COURAGE, left hope for stents and gatekeeper tests. A subgroup analysis showed that patients who benefited most from PCI had the most amount of objective ischemia on nuclear imaging. Searching for ischemia could still have value.

The International Study of Comparative Effectiveness with Medical and Invasive Approaches (ISCHEMIA) trial 3 will determine whether the subgroup analysis ought to bail out the stent industry. Patients with stable angina with ischemia documented on physiological imaging will be randomized to revascularization (PCI or bypass) or polypharmacy. Then, a primal question will be asked: Any difference?

What if the ISCHEMIA trial says no benefit of revascularization over optimal medical therapy? The ramifications will extend beyond the industry for stents, for which it will only be a partial death knell; stents will still be used for unstable angina. The findings would be portentous for gatekeeper tests. Imaging for objective ischemia would become an academic exercise. In the era of constrained resources, paying for knowledge for the sake of knowledge may not be CMS’ highest priority.

Imagers could find themselves having the following dialogue with the referring clinician:

Imager: “What will you do if the test shows objective ischemia?”

Clinician: “Optimal medical therapy.”

Imager: “What will you do if the test shows no objective ischemia?”

Clinician: “Optimal medical therapy.”

Do you see the problem here? If it is a straight road to your destination, of what use is a GPS? Imaging is the diagnostic cart that is pulled by the therapeutic horse. If the horse is suspect, it is unlikely anyone will pay deference to the cart. Cardiac imagers passionately debating the relative merits of stress MRI and SPECT must appreciate they might be flogging a weak horse or, even worse, a dead horse.

References

1. Boden WE, O’Rourke RA, Teo KK,