CT angiography offers noninvasive option for ruling out CAD

Computed tomography performance was superior to MRI in detecting and ruling out clinically relevant coronary artery disease, findings from a recent meta-analysis indicated, suggesting that CT is the better alternative to conventional coronary angiography.

Researchers from Charité Medical School in Berlin analyzed data from 109 sources (CT, 89 studies, n=7,516; MRI, 20 studies, n=989) to determine the potential of both imaging modalities for ruling out CAD in adults with suspected or known CAD. Using bivariate analysis, they determined that CT had higher mean sensitivity and mean specificity compared with MRI (sensitivity 97.2% vs. 87.1%; specificity 87.4% vs. 70.3%; 95% CI).

Additional covariate analysis indicated that CT scanners with more than 16 rows yielded higher sensitivity than older-generation scanners (98.1% vs. 95.6%; P<.050), and that CT performed on patients who had heart rates >60 beats per minute had better sensitivity than patients who had higher heart rates (P<.001).

The researchers said multi-slice CT is often easier to perform than MRI and offers patients the convenience of shorter examination times (15 to 20 minutes vs. one hour) and involves less restraint.

After calculating the pretest probability of CAD to determine the implications of these findings for clinical decision-making, the researchers determined that CT would identify 669 true-negative and 244 true-positive cases in a cohort of 1,000 patients who had suspected CAD. Despite this, six false-negative and 81 false-positive cases would also be possible.

“Because ongoing technical developments may gradually make CT and MRI more potent alternatives to [coronary angiography] and increase the options for clinical decision-making, regular updates on their performance are vital,” the researchers wrote.

They noted that overrepresentation of studies involving CT, possible biases within the individual studies, lack of verification that all studies were prospective and the inclusion of studies published in English and German only may limit their findings.

“Randomized studies are clearly needed to address the potential of coronary CTA for use in triage as a means of positively altering management and outcomes in patients with suspected CAD,” the researchers wrote. – by Nicole Blazek

Schuetz GM. Ann Intern Med. 2010;152:167-177.

This is well recognized from the literature and the basic physics of imaging: MRI has better temporal resolution, but poorer spatial resolution that CT angiography. In addition, arterial calcification gives a positive signal on CT, which helps characterize extraluminal coronary atherosclerosis. The higher number of detector rows (more than 16) improves the logistics and reduces artifacts in cardiac CT, resulting in less missed lesions. Cardiac MRI may play an increasing role in coronary lesion characterization as the technology develops.

– Kim Allan Williams, MD
Cardiology Today Editorial Board