Coronary CT angiography (CCTA) identified plaques in acute MI (AMI) patients whose coronary angiograms did not produce evidence of significant coronary stenosis. The majority of the plaques CCTA identified were in the infarct-related arteries (IRA). These results were published online Nov. 20 in Circulation.
Coronary angiography of patients who experience AMI typically, but not always, reveals arterial stenosis. According to author Annachiara Aldrovandi, MD, of Azienda Ospedaliero-Universitaria di Parma in Italy, and colleagues, “The absence of angiographic evidence of significant coronary stenosis may challenge a diagnosis of AMI, but coronary artherosclerosis may be present even in angiographically normal coronary arteries.” Because patients who survive an MI have a significant risk of experiencing further ischemic events, it is important to pinpoint the etiology of the event. Their study attempted to determine whether CCTA could identify the presence and characteristics of coronary artherosclerosis in patients with AMI whose coronary angiography did not reveal significant stenosis.
The researchers studied 50 patients who were admitted to their institution between Jan. 1, 2009, and Dec. 31, 2010, for AMI but who did not show any coronary lesion with 50 percent or greater lumen diameter stenosis on angiography. Patients were diagnosed with MI if they had chest pain lasting more than 20 minutes, persistent electrocardiographic changes and increased cardiac enzymes. MI in the study participants was confirmed by late gadolinium-enhanced cardiac MR (LGE-CMR).
The patients underwent coronary angiography using standard techniques. Experienced angiographers visually estimated the severity of stenosis, presence of calcifications and changes in lumen contour.
Each patient also underwent a prospective electrocardiogram-triggered unenhanced scan in order to determine the coronary artery calcium score, followed by the CCTA. Two experienced, independent readers who were unaware of the patients’ coronary angiography and cardiac MR findings analyzed the CCTA data. The readers used original axial images, multiplanar reconstruction and cross-sectional reconstruction to determine whether plaques were present. Readers assessed plaque localization, type, maximum plaque area, remodeling index, vessel stenosis, minimal noncalcified plaque attenuation and the presence of spotty calcifications, if any.
Coronary angiography found all the patients in the study were without significant stenosis; the coronary angiography findings indicated that 25 patients had normal coronary arteries and the other 25 patients had a total of 41 nonsignificant lesions. According to the results of the angiography, 18 patients had one-vessel disease, five had two-vessel disease, and two had nonobstructive three-vessel disease.
CCTA found eight patients had no coronary plaques; it showed 101 plaques in 151 vessels in the remaining 42 patients. CCTA showed that 24 patients had one-vessel artherosclerosis, 12 had two-vessel artherosclerosis and six had three-vessel artheroscerosis. The CCTA found 61 plaques in IRAs and 40 in non-IRAs. The plaques in the IRAs were characterized as noncalcified (22), mixed (17) and calcified (22). In the non-IRAs, five of the plaques were noncalcified, eight were mixed and 27 were calcified.
CCTA “revealed the presence of a significant number of artherosclerotic coronary plaques, which were underestimated by conventional coronary angiography,” the authors wrote. They discussed the challenges of diagnosing AMI in patients whose coronary angiography does not reveal significant stenosis, noting that “other clinical entities, such as myocarditis, may mimic the presentation of acute coronary syndrome.” By limiting the study only to those patients whose MIs were confirmed by LGE-CMR, the researchers were able to compare the effectiveness of coronary angiography and CCTA as diagnostic tools.
They pointed out that CCTA found a higher percentage of artherosclerotic plaques in the IRA sites than in the non-IRA sites, and a difference in the plaques, depending on location. “The plaques located on culprit coronary arteries were mainly noncalcified or mixed (39/61), whereas those in nonculprit coronary arteries were more frequently calcified (27/40),” they wrote. This result is consistent with other studies showing that “noncalcified lesions contribute more to total plaque burden in patients with acute coronary syndrome than in those with chronic stable coronary disease,” they explained.
Aldrovandi et al suggested that their findings “support the pathophysiology of MI due to artherosclerosis, with the disruption of mild coronary plaques, although it is not possible to exclude a different mechanism such as coronary embolism or prolonged vasospasm.” As for those patients whose CCTA revealed no plaques, the authors postulated that they may have experienced embolic MI, and encouraged closer follow-up to detect asymptomatic arrhythmias.