Letter from the Editor

Coronary CT Angiography: A view from the cath lab

Morton Kern, MD, Clinical Editor, Clinical Professor of Medicine, Associate Chief Cardiology, University of California Irvine, Orange, California
Morton Kern, MD, Clinical Editor, Clinical Professor of Medicine, Associate Chief Cardiology, University of California Irvine, Orange, California
We had a dilemma. An asymptomatic, well-conditioned 52-year-old runner with mild, treated hyperlipidemia was concerned about heart disease because of a strong family history of coronary artery disease (CAD). He underwent coronary CT angiography (CTA) which demonstrated some calcific plaques in the left anterior descending (LAD) and circumflex arteries, with 2 intermediately severe lesions in the LAD and normal left ventricular function. As a result, he underwent an exercise stress echocardiography test. Upon achieving 11 minutes of exercise and his maximal predicted heart rate, left ventricular (LV) wall motion and stress ECG were normal. Now, the problem. Because of the uncertainty as to the significance of the CTA findings, his physician requested coronary angiography. It demonstrated a 60-70% mid-LAD lesion in a calcific vessel segment. What should be done? The patient had no symptoms and a negative ischemia test, with known but treated CAD. Should we intervene based on the angiogram alone under these circumstances? I'm sure opinions on such a situation will vary greatly. Our best alternative was to be sure we could justify the risk of coronary intervention. He underwent a fractional flow reserve (FFR) measurement in the LAD which was 0.69 (clearly abnormal, i.e., not borderline) and a coronary artery drug-eluting stent was implanted with some difficulty in the calcified vessel segment. The patient has done well with a drug-eluting stent in the mid-LAD. He feels the same clinically, but better psychologically. This patient example highlights the dilemma facing clinicians who will use CT angiography as a screening test. Without evidence of myocardial ischemia, should we proceed down the angiographic pathway that often elicits an oculostenotic reflex, leading to a drug-eluting stent or bypass surgery? Many clinicians have a problem with this approach and believe that more study is necessary before subjecting the patient to a high radiation dose screening test with potentially no benefit in long-term outcome. Having said that, there are many examples of early detection of important CAD that have been revealed by CTA, thus justifying a confrontation of the above dilemma. There is no doubt the future of CAD diagnosis will heavily involve the CT angiogram. This rapidly expanding technology, made possible by high-speed scanners, provides detailed information of all structures within the chest, and specially designed programs can analyze the details of the coronary arterial tree. One of the most important and immediate uses of the CTA in clinical practice is the “triple rule-out" in the emergency room of the acute chest pain patient, excluding a dissecting aorta, pulmonary embolus and severe CAD all in one scan. Other current indications for CT angiography include evaluating bypass graft patency in the coronary artery bypass graft (CABG) patient, and evaluating significant CAD in patients with abnormal or equivocal stress test results and in young patients with high coronary calcium scores. Less specific uses have included evaluating patients with an unexplained chest pain or shortness of breath, and cardiomyopathies. At this time, CT angiography, with its inherently high radiation exposure (5x that of a cardiac cath) should not be used as a routine screening test for CAD, since the approach to treatment requires more than just the presence of atherosclerosis. Lesser et al1 discuss the clinical utility of coronary CT angiography for stenosis detection and prognosis in ambulatory patients. CT angiography accurately detected obstructive coronary disease in 86% of patients with possible cardiac symptoms and helped triage them for invasive angiography. CTA was highly accurate for detecting left main and right coronary artery disease. More importantly, negative CTA results were highly accurate (91%) in ruling out obstructive disease. The six-month prognosis of such patients was excellent. Of course, there are limitations to CT angiography for this study, which include: 1) a small percentage of uninterpretable CTA studies due to motion artifact, blurring, or poor selection of the vessel slices; 2) a 16-slice CT scanner may be inadequate for detailed coronary imaging. The 64-slice scanner now available is far superior in reducing problems such as partial volume averaging and image distortion. Heavy vessel calcification will always remain a confounding problem for any type of scanner, reducing the accuracy of stenosis quantitation. Finally, regardless of the imaging technique (including invasive coronary angiography), interpretation of the clinical significance of intermediately severe stenosis still requires a thoughtful approach. For CTA and invasive coronary angiography, the oculostenotic reflex approach to these lesions should be carefully considered, given the small but significant downside of drug-eluting stents. We now have excellent methods to answer questions with regard to lesion severity, especially in the asymptomatic patient undergoing CTA without evidence of myocardial ischemia. The biggest advantage of CTA is that a completely negative scan eliminates the need for invasive angiography in those patients having equivocal or unreliable ischemic testing. For those asymptomatic patients with suspected coronary artery disease, ischemic testing should be performed before subjecting them to CTA or invasive angiography. For symptomatic patents with high likelihood of coronary artery disease on effective medical therapy, with or without ischemia testing, coronary angiography may be the best, quickest and most cost-effective approach. CT angiography before an ischemia evaluation, followed by a trip to the cath lab, will produce the clinical dilemma addressed above and is probably unwarranted at this time. However, if this does occur, the opportunity for the interventionist and cath lab to contribute to the best patient outcome would be made by lesion assessment in the cath lab (with either intravascular ultrasound [IVUS] or FFR) for those lesions not associated with evidence of myocardial ischemia. CTA is an important advance in cardiology. Its use is growing. Let's use it wisely. PS. Cardiovascular Professionals Week is February 11-17th. Let's remember to say thanks for the great job our CV professionals do every day. We are only as good as our team makes us. MK
References
1. Lesser JR, Flygenring B, Knickelbine T, et al. Clinical utility of coronary CT angiography: Coronary stenosis detection and prognosis in ambulatory patients. Catheterization and Cardiovascular Interventions January 2007;69(1):64-72.