ASNC: CT Angiography Warrants Paradigm Shift in Nuclear Cardiology

MONTREAL, Sept. 12 -- While many clinicians remain on the fence about computed tomography angiography (CTA), one expert has firmly chosen his side.

Harvey S. Hecht, M.D., of the Lenox Hill Heart & Vascular Institute in New York declared that it should replace nuclear stress testing as the first imaging study in many patients with suspected cardiovascular disease.

Dr. Hecht considers the advent of CTA such a harbinger of change that he has shifted his personal dating system to BCTA (before CTA) and ACTA (after CTA).

"The first test in the future of the evaluation of the patient, be it symptomatic or asymptomatic, will be a CTA rather than a stress test because it's more accurate, provides more information, and avoids patients having unnecessary cardiac catheterizations which follows in a substantial number of patients who undergo stress testing because of the high false positive rate," he said.

He discussed his rationale at a Philips industry-sponsored symposium here held in conjunction with the annual meeting of the American Society of Nuclear Cardiology (ASNC).

CTA offers information previously obtainable only with invasive angiography and intravascular ultrasound, Dr. Hecht said. While some features of angiography are superior to CTA, a crucial advantage of CTA is the ability to visualize vessels in three dimensions and at any angle, said Dr. Hecht.

This enables the reader to fully appreciate the universality and eccentricity of stenosis. In addition, there is no risk of overlap, since each vessel is tracked individually. It also eliminates the risk of underestimating disease associated with insufficient sampling during catheterization. "What are the chances that you have accurately identified the most stenotic view of any particular artery by sampling just five units of the left coronary and three of the right?" he asked. "Very, very low."

Most clinicians using angiography "eyeball" stenotic lesions, which typically results in overestimation, said Dr. Hecht. In contrast, CTA quantitates lesions by calculating the exact area of a vessel, which, since no vessel is perfectly round, is far more relevant data than minimal luminal diameter.

A primary function of nuclear stress testing is to determine which patients require catheterization. Based on American College of Cardiology National Cardiac Data Registry data on 376,000 diagnostic catheterizations that occurred in stable patients for the evaluation of chest pain or dyspnea, fully 37% of patients were found to have < 50% stenosis. That means one-third of patients are undergoing an invasive, expensive procedure and significant radiation exposure unnecessarily, Dr. Hecht said. In many of these cases, said Dr. Hecht, patients are sent for catheterization following an abnormal nuclear stress test. Clearly, a better way of selecting appropriate patients for catheterization is warranted.

Based on Dr. Hecht's analysis of several trials exploring use of CTA, the agent has a weighted average sensitivity of 90%, specificity of 95% and negative predictive value of 98%, with only about 3% of patients being unevaluable. These values are as good or better than those obtainable using nuclear stress testing. In addition, a CTA scan typically exposes patients to less radiation than nuclear stress testing.

Another primary function of nuclear stress testing is to assess degree of functional stenosis. But Dr. Hecht pointed out that patients can very reliably be categorized as having >75% stenosis or < 50% stenosis with CTA. If a patient with >75% stenosis were to have a negative nuclear stress test, the result would not be believed. Similarly, if a patient with < 50% stenosis were to have a positive nuclear stress test, this result would also not be beloved. "So, why do the nuclear stress test?" he asked.

Where nuclear stress testing does have a role, according to Dr. Hecht, is in patients whose CTA reveals a 50 to 75% stenosis rate. In these patients, nuclear stress testing can be used to determine degree of functional stenosis and help determine which patients require catheterization.

Given that serial testing should be avoided, both for the benefit of patients and the cash-strapped healthcare system as a whole, Dr. Hecht sees the future of imaging for detecting of coronary artery disease as clear-cut.

CTA, the direct route to anatomy and plaque, should be used for low and high risk patients, with nuclear stress testing being reserved for intermediate risk patients. A normal CTA reliably indicates that there is no significant disease, while an abnormal CTA, depending on the specific results, suggests that patients require nuclear stress testing to determine the presence of functional ischemia or direct catheterization.