Image source: Siemens Healthcare

With the advent of 64-slice CT, coronary CT angiography (CCTA) exams of low-risk patients presenting to the emergency department with chest pain are feasible given the nearly 100 percent negative predictive value of the test, according to a scientific statement from the American Heart Association (AHA) published in the Aug. 17 issue of Circulation.

"Obstructive CAD [coronary artery disease] can be excluded reliably in many patients, and available data support the safety and feasibility of ED discharge after a normal or nonobstructive CCTA," according to the statement issued by the AHA Exercise, Cardiac Rehabilitation and Prevention Committee, led by Chair Ezra A. Amsterdam, MD, from the University of California at Davis.

Much of the positive data for CCTA come from small and single-center studies. Therefore, the committee recommended that larger multicenter studies are required before this technology can be considered widely applicable.

The review of the available data showed that CCTA has several limitations, including an inability to image patients who are obese, intolerant to beta-blockers, and have contrast allergies, arrhythmia, renal insufficiency or a history of CAD.

Other limitations include suboptimal coronary artery visualization because of extensive calcium, and radiation exposure, particularly regarding younger patients, especially women.

The AHA committee noted that newer protocols and technology can reduce radiation dose per scan by more than 50 percent, but those studies are just emerging and need to be validated further.

CCTA's strength is in its negative predictive value and therefore when used appropriately can help rapidly distinguish between those who require admission for urgent management and those with a benign cause of chest pain who can be discharged directly from the ED.

The statement noted the ample research validating the use of SPECT myocardial perfusion imaging (MPI) and echocardiography to triage patients with chest pain. While both can be performed with exercise or pharmacological stress, MPI can also be used at rest to detect ischemia.

"The latter capability represents an important advance, because reduced regional myocardial perfusion at rest is the pathophysiological basis of ACS [acute coronary syndrome]," according to the statement.

"By contrast, stress-induced ischemia reflects an inadequate increase in coronary blood flow in response to augmented myocardial oxygen demand, which may characterize both stable CAD and ACS."

MPI and echocardiography can more accurately detect CAD compared with an exercise stress test, and these methods give information on left ventricular function, as well as the location and extent of ischemia. However, MPI carries the risk of radiation exposure, which must be taken into consideration.

Patients negative for ACS often have ongoing concerns. The researchers noted many of these patients need further evidence that their chest pain is of a noncardiac nature. They suggested that CCTA "may be considered in some patients" to alleviate concern.