CT Technique Could Obviate Angiography in Heart Recipients

CLEVELAND, Aug. 8 -- For heart transplant patients, a multidectector spiral CT image could substitute for the annual coronary angiography they need.

Using multidetector CT with multicycle reconstruction, Mario J. Garcia, M.D., and colleagues at the Cleveland Clinic and Favaloro Foundation in Buenos Aires determined that the noninvasive technique correctly identified 94% of heart transplant recipients with coronary disease, confirmed by quantitative angiography.

In addition, the technique correctly identified 78% of patients determined on angiography to be free of significant stenosis, the investigators reported in the Aug. 15 issue of the Journal of the American College of Cardiology.

The multicycle recontruction technique uses a high-speed helical CT scanner coupled with ECG gating and image reconstruction of multiple cycles within the RR interval to overcome the problem of motion artefact in imaging the coronary vasculature.

The technique allows scans to be performed at higher heart rates than multidetector CT with half-scan reconstruction, which often requires patients to be under beta-blockade to slow heart rates. Heart transplant recipients are often insensitive to beta-blockade, the authors noted.

They tested the technique in 54 consecutive heart transplant recipients (89% male) who were scheduled for surveillance coronary angiography. The CT scans were performed within 6 + 11 days of quantitative coronary angiography.

The scans were performed using ECG-gated contrast-enhanced multidetector CT with 16 x 0.75 mm detectors, 420 millisecond rotation, and 100 mL of a contrast agent and multisegment reconstruction.

Patient heart rate at the time of the scan was 90 + 11 beats/min. Images of coronary arterial segments > 1.5 mm in diameter were acquired and analyzed by independent investigators.

The authors limited their study to arterial segments greater than 1.5 mm in diameter because it gives multidetector CT a value in detecting the lesions that are of the greatest clinical significance. "Smaller vessels are not as well visualized, but as this technique evolves and spatial resolution improves, the accuracy of detecting stenosis in smaller vessels will likely improve," they wrote.

They found that there was good correlation between multidetector CT and percentage of stenosis on quantitative angiography (r = 0.75, P< 0.01, standard error of the estimate = 15%). In all, 754 of 791 (95%) arterial segments identified by angiography were also analyzable by multidetector CT.

In comparison with angiography for detection of segments with significant stenosis (>50%), CT had 86% sensitivity, 99% specificity, 81% positive predictive value, and 99% negative predictive value.

Multidetector CT correctly identified 15 of 16 patients who were found to have stenotic coronary artery disease on angiography, and 29 of 37 (78%) who had been found on angiography to be without significant stenosis.

The only complication occurred in one of three patients who received intravenous Lopressor (metoprolol) 10 to 20 mg before the procedure. This patient developed transient bradycardia and hypotension requiring temporary pacing.

"Our results indicate that multidetector CT seems to be both feasible and safe, and should not be limited to patients with a low heart rate," the investigators concluded. "It detects significant coronary stenoses with excellent diagnostic accuracy. In particular, the high negative predictive value makes multidetector CT ideal for screening."

"If vessel wall analysis with newer-generation multidetector CT proves to be clinically valuable, multidetector CT could also represent an alternative to intravascular ultrasound in patients with suspected transplant vasculopathy," they wrote.