Evidence-Based Cardiac Imaging Getting Closer



DENVER – The historically shaky evidence base for cardiac imaging strategies is in the midst of being shored up by a strong new foundation.

Just a couple of years ago, analysts concluded that cardiac imaging guidelines have among the weakest supporting evidence bases of any of the 53 American College of Cardiology/American Heart Association practice guidelines they looked at. The investigators found that only 2.4% of the evidence supporting the imaging guidelines had a level of evidence of A, meaning supported by multiple randomized trials. Thirty-seven percent of the evidence was level B, coming from multiple observational studies. Another 17% was based on expert opinion, and the rest of the imaging guideline recommendations were not supported by any conclusive evidence (JAMA 2009;301:831-41).

Dr. James E. Udelson

All that is clearly in the process of changing, and in a big way, Dr. James E. Udelson observed at the annual meeting of the American Society of Nuclear Cardiology.

An unprecedented raft of multicenter randomized trials is underway in patients with chest pain. The government-supported studies range in size from 4,300 to 10,000 patients. They are variously aimed at determining whether anatomic imaging via coronary CT angiography (CTA) or functional imaging by SPECT myocardial perfusion imaging stress ECG, or stress echocardiography is the best initial strategy for the diagnosis of coronary artery disease, and at using imaging results to identify optimal management strategies, explained Dr. Udelson, chief of cardiology and director of the nuclear cardiology laboratory at Tufts Medical Center, Boston.

Here’s what’s underway:

PROMISE. The PROspective Multicenter Imaging Study for Evaluation of chest pain), funded by the National Heart, Lung, and Blood Institute, involves 10,000 patients with symptoms suggestive of CAD and low to intermediate pretest probability of CAD. They’ll be randomized to CTA or functional imaging by SPECT myocardial perfusion imaging, stress ECG, or stress echo, with the study results immediately available to the care team for use in management decisions.

The primary end point is the 30-month composite of death, MI, major complications due to cardiac catheterization, or hospitalization for unstable angina. The study hypothesis is that noninvasive anatomic imaging via CTA will result in superior long-term outcomes.

Enrollment is progressing quickly, with 2,800 randomized patients, according to Dr. Udelson, who is a PROMISE investigator.

RESCUE. In the Randomized Evaluation of patients with Stable angina Comparing Utilization of diagnostic Examinations, 4,300 symptomatic outpatients are being randomized to SPECT myocardial perfusion imaging or CTA, with their subsequent management being driven by an algorithm based on their test results. The hypothesis here is that CTA will be associated with no increase in adverse events, similar outcomes, lower cost, less radiation exposure, and resultant superior cost-effectiveness. Dr. Udelson is an investigator in RESCUE, which is supported by the Agency for Healthcare Research and Quality and the American College of Radiology Imaging Network.

ISCHEMIA. The most ambitious of the studies is the International Study of Comparative Health Effectiveness with Medical and Invasive Approaches.

The National Institutes of Health has awarded an $84 million grant to conduct ISCHEMIA, a study of an early invasive versus conservative strategy in patients with stable CAD and moderate to severe ischemia.

The trial involves 8,000 patients with a left ventricular ejection fraction of 35% or more and at least 10% cardiac ischemia. They will undergo blinded CTA to rule out high-risk left main disease or normal coronary arteries. Then they will be randomized to catheterization and revascularization plus optimal medical therapy or to optimal medical management alone with revascularization reserved for worsening symptoms. Follow-up will be for 3-6 years.

ISCHEMIA is designed to provide answers to questions left open by the COURAGE and BARI 2D trials. The key design difference is that ISCHEMIA participants will be randomized to the invasive or conservative strategy before cardiac catheterization. The study hypothesis is that the invasive strategy will prove superior in terms of the primary composite end point of cardiovascular death, MI, or adjudicated hospitalization for unstable angina, heart failure, or cardiac arrest. Secondary end points will include cost-effectiveness and quality of life measures.

Dr. Udelson declared having no financial conflicts.

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