Positive findings of obstructive coronary artery disease (CAD) via elective coronary angiography varies widely across centers, 23 percent to 100 percent, according to a study published Aug. 9 in the Journal of the American College of Cardiology. This variation may pave the way for quality improvement and appropriate use criteria (AUC) for diagnostic coronary angiography.

“Diagnostic invasive coronary angiography is an important tool for identifying those patients with obstructive coronary disease who may benefit from coronary revascularization,” wrote Pamela S. Douglas, MD, of the Duke Clinical Research Institute and Duke University School of Medicine in Durham, N.C., and colleagues. “However, this procedure has associated costs, exposes patients to radiation and has a small but well-described risk for procedural complications.”

AUC has not yet been put in place for coronary angiography diagnostic imaging exams. “A balanced consideration of all the relevant steps inherent in a decision to proceed to elective invasive coronary angiography, as well as the finding of CAD at catheterization, is needed to optimize coronary angiography utilization,” Douglas and colleagues wrote.

For this reason, the decision to perform coronary angiography is selective and may be limited to patients with moderate to high pre-test probability for obstructive CAD. To date, the variability of CAD diagnosis between centers via coronary angiography has not been studied.

To bolster these data, Douglas and colleagues performed a restrospective analysis of 565,504 patients within the National Cardiovascular Data Registry CathPCI Registry between 2005 and 2008 who did not experience a previous MI or revascularization to evaluate the rate of finding obstructive CAD found during coronary angiography. The study took place at 691 hospitals throughout the U.S.

These types of analyses are valuable as several groups have proposed using hospitals’ obstructive CAD findings at coronary angiography as quality metrics.

During the study, Douglas and colleagues found that the rate of CAD found during elective coronary angiography varied from 23 percent to 100 percent among hospitals. These rates were consistent from year to year and when alternative definitions of coronary stenosis were applied.

“These results showed that we have regional geographic and programmatic variability in what tests individuals want done. In order to make the decision to perform a catheterization, some of that may be related to the patients seen or the setting they are seen in or some are related to the tests themselves,” study author Steven R. Bailey, MD, the past-president of the Society of Coronary Angiography Interventions (SCAI) and chief of the division of cardiology at the University of Texas Health Sciences Centers at San Antonio, said in an interview.

While Bailey said they now have an idea of the types of variation that are occurring, the next question becomes, “What is the right frequency for performing these types of tests?

“If we have a 100 percent presence of significant coronary disease in the patients we cath, are we missing patients?” he asked. “The answer is that we probably are."

The results of the study also showed that sites with lower rates of obstructive CAD rates were more likely to perform these exams in younger patients, patients with lower Framingham Risk Scores, blacks, women and outpatients. Patients at low-rate centers were also less likely to have stable angina symptoms (27 percent vs. 42 percent) or positive stress tests prior to coronary angiography (66 percent vs. 71 percent).

Hospitals with smaller volume cath labs also had lower rates of CAD; however, this was not found to be associated with hospital ownership or teaching program status, the authors noted.

Bailey said that the next question that should be asked is: Is evaluating a patient’s clinical history alone sufficient? It must then be taken a step further to decipher whether a patient should undergo an exercise test, a nuclear imaging test or a stress test. “We must determine what the best modality is, or what a better modality is to evaluate patients prior to them coming into the cath lab.”

Bailey said that there must be an understanding as to why patients are referred for a test, not just the result of these tests.

“Although our data cannot indicate what the ideal or 'optimal' CAD rate is for elective coronary angiography, these associations suggest that improved patient selection could increase the rate of finding CAD in these institutions,” the authors wrote.

Bailey said that currently a document is being developed to assess various imaging modalities. Physicians from multiple specialties—surgeons, electrophysiologists, general cardiologists, among others—have been gathered to look at the current clinical practice and attempt to develop a rating scale for how these imaging exams should be performed, on which patients and how often. Additionally, the group will look at outcomes and determine what modality is best, which Bailey said will be very difficult to answer.

Because there are currently no standards for the optimal percentage of positive diagnostic coronary angiography tests, the current study provides background data to potentially develop quality measures, AUC and strategies to decrease the wide variation gap between hospitals.

"Most importantly," according to Bailey, "the absence of CAD was not a negative finding of the study."

He said that this variation may reflect how patients are referred for these types of tests and “subsequently we will need to look at how we can do a better job of performing diagnostic angiography before they get a catheterization and that will be the next important step.”