Conference Coverage

Cardiac PET/CT can guide CAD therapy



– A PET/CT-derived myocardial ischemic burden in excess of 10% defines a subset of patients with symptomatic CAD who derive significantly greater benefit from an invasive management strategy than a noninvasive one, Kent G. Meredith, MD, reported at the annual meeting of the American College of Cardiology.

Dr. Kent G. Meredith, a cardiologist in Murray, Utah Bruce Jancin/MDedge News

Dr. Kent G. Meredith

Conversely, patients with an ischemia burden of 10% or less have a lower major adverse event rate if they undergo noninvasive treatment.

“We see that cardiac PET/CT-derived ischemic burden provides a convenient and useful tool for predicting clinical outcomes of invasive and noninvasive treatment strategies,”said Dr. Meredith, a cardiologist at Intermountain Medical Center in Murray, Utah.

He presented a retrospective single-center study of 5,528 consecutive patients with symptomatic CAD referred for PET/CT at Intermountain. As a condition for study inclusion, they needed to survive for at least 90 days after imaging, have no elevation of troponin, and have no prior history of CAD.

This was a study of real-world clinical practice featuring standardized institutional protocols. Dr. Meredith explained that the 10% ischemic burden threshold used by cardiologists at Intermountain to help determine an individual’s optimal treatment strategy is based upon “a very important study” in which investigators at Cedars-Sinai Medical Center in Los Angeles showed 16 years ago, in nearly 11,000 consecutive patients, that revascularization had a survival benefit over medical therapy alone at an ischemic burden in excess of 10% as measured by stress myocardial perfusion single photon emission CT (Circulation. 2003 Jun 17;107[23]:2900-7).

Dr. Meredith and his coinvestigators carried out their study to make sure this ischemic burden cutoff is still valid today in view of the considerable changes in imaging technology and optimal medical therapy in the intervening years.

Among the study population, 203 patients had a PET/CT-derived ischemic burden greater than 10% using a well-established scoring system (J Nucl Cardiol. 2006 Nov;13[6]:e157-71), while 5,325 had a lesser ischemic burden. Fifty-six percent of patients with an ischemic burden above the 10% threshold underwent coronary revascularization, 26% had coronary angiography without revascularization, and 18% were managed by optimal medical therapy alone.

The group with an ischemic burden of 10% or less was managed very differently: One percent had revascularization, 3% had angiography without revascularization, and 96% were managed medically.

The higher a patient’s baseline ischemic burden, the higher the major adverse cardiovascular event (MACE) rate during 1-4 years of follow-up. The composite MACE rate, comprising death, hospitalization for acute MI, or late revascularization after 90 days, was 3.9% in patients with an ischemic burden of 10% of less, compared with 8.9% in those above the 10% threshold.

In a multivariate analysis adjusted for demographics, hyperlipidemia, heart failure, and diabetes, patients with an ischemic burden greater than 10% had a 4.6-fold greater risk of MACE if managed medically than if they underwent revascularization. And among those with an ischemic burden of 10% or less, the adjusted risk of MACE was increased 2.8-fold if they received revascularization instead of medical management.

Dr. Meredith reported having no financial conflicts regarding his study, conducted free of commercial sponsorship.

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