CT Coronary Angiography Identifies Significant Plaques in 'Normal' Arteries

November 26, 2012

PARMA, Italy — Computed-tomography coronary angiography (CTCA) can be used to identify acute myocardial infarction (AMI) patients who have significant plaque in the infarct-related coronary artery but have angiographically normal or mild coronary plaque as detected by conventional angiography, researchers say [1]. The use of CTCA identified plaque in 60.4% of the infarct-related arteries of patients with AMI but without coronary stenosis observed during coronary angiography.

Dr Annachiara Aldrovandi (University of Parma, Italy) and colleagues state that AMI patients without a significant coronary stenosis during coronary angiography are a diagnostic challenge for physicians, but CTCA (often called coronary CT angiography, or CCTA) is a reliable means to noninvasively detect coronary atherosclerosis and characterize plaque morphology. The paper appeared online November 20, 2012 in Circulation.

"In our population, the CTCA demonstration of coronary plaques located in the infarct-related artery identified by means of LGE-CMR [late-gadolinium-enhanced cardiac magnetic resonance] and their morphological characteristics support the pathophysiology of MI due to atherosclerosis, with the disruption of mild coronary plaques, although it is not possible to exclude a different mechanism such as coronary embolism or prolonged vasospasm," report the investigators.

In an accompanying editorial, Drs Jason Kovacic and Valentin Fuster (Mount Sinai School of Medicine, New York) say that the researchers have identified the "smoking gun" for patients with a missing MI--those being individuals with a clinically typical atherosclerotic MI who lack angiographically confirmed coronary artery lesions [2]. In addition to identifying plaques with CTCA in these patients, the researchers reported that the plaques in the infarct-related artery had less calcification, greater plaque area, and greater extent of positive remodeling--all features that characterize 'vulnerable' atherosclerotic lesions.

"In our opinion, this amounts to reasonably strong (albeit circumstantial) evidence implicating angiographically nonobstructive but unstable plaques as being causative in a subset of patients with unexplained MI," write Kovacic and Fuster. "Furthermore, these data are intuitive and fit comfortably with our current paradigms for plaque biology."

Picking up Undetected Plaques With CTCA

The study included patients with a documented AMI but without evidence of coronary stenosis on the coronary angiogram. These patients then underwent LGE-CMR within 10 days of the angiography, but only patients who had an area of late enhancement on the CMR with a pattern compatible with MI were included in the analysis. Of the 50 patients, 34 presented with non-ST-segment elevation MI and 16 presented with STEMI. The LGE-CMR images identified an interior MI in 29 patients, an inferior MI in 13 patients, and a lateral MI in eight patients.

Coronary angiograms showed that 25 of the 50 patients had normal coronary arteries, while the remaining 25 patients had 41 nonsignificant lesions. Patients then underwent CTCA approximately six days after the AMI. The CTCA scan identified 101 plaques in 151 coronary vessels in 42 patients and the complete absence of coronary plaque in eight patients. Roughly half of the identified patients had single-vessel disease, while 24% had two-vessel atherosclerosis, and 12% had multivessel disease.

In total, CTCA identified 61 plaques in infarct-related arteries and 40 in noninfarct-related arteries. Of the plaques in infarct-related arteries, 22% were noncalcified, 17 had mixed calcification, and 22 were calcified. Mean plaque area was greater in infarct-related arteries, but there was no significant difference in terms of mean percent stenosis.

"In our study, CTCA revealed the presence of a significant number of atherosclerotic coronary plaques, which were underestimated by conventional coronary angiography," write Aldrovandi and colleagues. "Coronary angiography is the gold standard for evaluating coronary stenosis, but it only images the lumen contour of coronary vessels and does not provide any information concerning the vessel wall and plaques."

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