CT Angiography Helpful in Suspected Stable Angina, but Not Needed for All

As a second test after the exercise ECG, CT angiography may improve risk stratification for people with suspected stable angina, according to a post hoc analysis of the SCOT-HEART trial.

For people who had abnormal or inconclusive results on stress testing, the addition of coronary CT angiography led to numerically fewer clinical events (3% vs 6% for ECG alone), according to researchers led by Trisha Singh, BM, British Heart Foundation Centre for Cardiovascular Science at University of Edinburgh, Scotland. Their report was published online in JAMA Cardiology.

Randomization to exercise stress testing with or without CT angiography was telling of future events either way, but “coronary CT angiography more accurately detects coronary artery disease [CAD] and is more strongly associated with future risk compared with exercise ECG,” the authors wrote.

Abnormal results of exercise ECG were associated with coronary revascularization at 1 year (HR 14.47, 95% CI 10.00-20.41) and coronary heart disease death or nonfatal MI at 5 years (HR 2.57, 95% CI 1.38-4.63) compared to normal or inconclusive results.

With coronary CT angiography, coronary revascularization at 1 year was predicted both by obstructive CAD (HR 1.70, 95% CI 1.47-1.97) and nonobstructive CAD (HR 1.17, 95% CI 1.04-1.33) versus no CAD. The same was true for 5-year coronary heart disease death or nonfatal MI for both obstructive CAD (HR 10.63, 95% CI 2.32-48.70) and nonobstructive CAD (HR 5.32, 95% CI 1.16-24.40).

“Overall, an exercise ECG generally serves the clinician well for risk stratification and the selection of patients for coronary revascularization when results are abnormal, but for most patients without abnormal results of exercise ECG, coronary CT angiography provides additional information regarding the presence of CAD, the need for preventive treatments, and the potential for improved long-term clinical outcomes,” they concluded.

People who underwent coronary CT angiography were more likely to experience changes in preventive therapies and be referred for invasive coronary angiography.

Perhaps the real value of CT angiography for patients with stable chest pain is just guiding better preventive therapy by better identifying coronary plaque, said Pamela Douglas, MD, of Duke University School of Medicine in Durham, North Carolina, in an accompanying editorial.

“In the interest of moving beyond functional vs anatomical binary thinking, what if the best initial ‘test’ in these stable outpatients is simply ensuring optimal use of statins and aspirin (the ostensible pathway of benefit of CTA [CT angiography] in SCOT-HEART)?” she suggested.

Nevertheless, the study’s positive results of exercise ECG are important in validating to current guidelines that include exercise ECG as a first-line strategy in evaluating stable chest pain, she wrote.

“Although falling short of recommending the addition of CTA for every patient with normal or inconclusive results of exercise ECG, a strategy that was not tested here, the implication of this study is that exercise ECG alone, for most individuals, is not sufficient to optimize outcomes,” according to her.

The ISCHEMIA trial had shown that stress tests aren’t enough to send patients with stable angina to be revascularized, as early stenting or surgery was no better than medication for moderate-to-severe cases.

SCOT-HEART investigators had previously reported that CT angiography resulted in fewer clinical events but no uptick in invasive coronary angiography or revascularization compared with standard care alone.

But not every patient with stable chest pain needs coronary CT angiography, stressed Raymond Gibbons, MD, MSc, of the Mayo Clinic in Rochester, Minnesota, who argued against broadly generalizing the results of SCOT-HEART.

Even though secondary prevention was recommended to the roughly 64% of patients in the CT angiography group with obstructive or nonobstructive disease, secondary prevention was never recommended to the standard care group regardless of the patient’s stress test results (except for the 9% with known coronary heart disease), Gibbons pointed out in a separate viewpoint article.

Considerable differences in medical therapy likely contributed to the differences in reported outcomes, according to Gibbons.

The open-label trial had been conducted at 12 outpatient cardiology clinics across Scotland in 2010-2014. Patients were randomized to standard care with or without coronary CT angiography.

The present analysis was limited to the 3,283 patients who underwent an exercise ECG (57.5% men, median age 57.0 years). Of this group, 1,417 got additional coronary CT angiography.

Exercise ECGs were normal in two-thirds of cases.

Invasive coronary angiography in 768 people helped investigators confirm that exercise ECG has limited power to rule out CAD: abnormal results had a sensitivity of 39%, a specificity of 91%, a positive predictive value of 58%, and a negative predictive value of 82% for detecting any obstructive CAD.

The post hoc analysis was limited by the potential for misclassification of exercise ECGs, Singh’s group acknowledged.

Additionally, the authors did not exclude the 15% of patients randomized to receive usual care plus CTA who ultimately did undergo CTA, Douglas noted. “This results in an as-tested analysis that excludes more [than] one-third of the randomized population, greatly weakening the power of randomization and introducing selection bias, making this essentially an observational study.”