This study had four main findings. First, DSCTA could depict coronary plaques and their morphology as well as assess grading of stenosis. Patients did not require excessive preparations to obtain high-quality images. Second, the diabetic patients had a high plaque burden that was mainly distributed in the LAD artery and proximal segment of each coronary vessel. Third, an analysis of plaque composition revealed a relatively high proportion of calcified plaques. Fourth, obstructive stenosis was as prevalent as non-obstructive stenosis. These findings indicated that non-invasive DSCTA was a valuable modality for depicting and evaluating possible coronary atherosclerosis in symptomatic diabetic patients. In addition, results also showed that DM reduced the sex differential in CT findings of CAD.
Three-fourths of the diabetic patients had multi-vessel disease and the plaques involved multiple coronary segments, which indicated that CAD in symptomatic diabetic patients was extensive. This finding was in agreement with those of previous studies [12, 13]. The heavy plaque burden in diabetic patients is probably because they have more cardiovascular risk factors resulting from metabolic syndromes [14–16]. In addition, current treatments for DM have limited impact on cardiovascular risk . Multiple coronary plaques in diabetic patients may be related to the increased risk of major adverse cardiac events. It has been established that diabetic patients had a similar risk for cardiac mortality as non-diabetic patients with a history of myocardial infarctions .
Our results showed that plaques were more prevalent in the LAD artery and the proximal segment of each vessel in diabetic patients. This finding is similar to those observed in the general population [18–20]. Different susceptibilities of different coronary vessels and segments to atherosclerosis may be explained by their different hemodynamics . However, the precise pathogenetic mechanism still needs further study. Although the plaques in the proximal segments of the vessels may not result in significant stenosis in a short time due to their larger calibre, myocardial ischemia or infarction would be extensive and serious once the lumens were occluded.
Regarding plaque composition, the most frequently detected type in this series was the calcified type followed by the mixed type. This was similar to results of previous studies [13, 22, 23]. However, one study has shown that non-calcified plaques were the main type of plaques in asymptomatic diabetic patients . In addition, the current study indicated that the proportion of calcified plaques and calcium score increased and that of non-calcified plaques decreased as patients aged. Therefore, the calcium score may underestimate the risk of CAD in diabetic patients, especially in relatively young or asymptomatic individuals.
The future adverse event rate was significantly higher in patients with any coronary plaque than in those with a normal MDCT scan . This may be due to the possibility of each type of plaque causing acute or chronic obstructive stenosis. Non-calcified plaques, which are unstable plaques, were vulnerable and frequently detected in patients with acute coronary artery syndrome [26, 27]. Patients with a higher likelihood of stenotic CAD were more likely to have a higher underlying burden of calcified and mixed plaques . Diabetic patients are at a higher risk of CAD: hence, it is important to timely evaluate the potential CAD and treat the remediable plaques.
In this study, the mild narrowing was the most common degree of stenosis, but nearly a half the plaques caused obstructive stenosis in symptomatic patients. This result was consistent with that of a previous study . Obstructive stenosis was seen as a significant indicator of poor prognosis . However, plaques in asymptomatic diabetic patients were usually non-obstructive . The lesion may have been very severe in diabetic patients when symptoms of CAD developed because of the following two reasons. First, the patients may have had DM for many years before it was diagnosed because of lack of typical clinical symptoms [29, 30]. Second, painless myocardial ischemia may have developed in a higher percentage of patients and which masked the progress of CAD [31, 32]. Therefore, people with risk factors for DM and diabetic patients with cardiovascular risk factors should pay more attention to their blood glucose levels and potential cardiovascular complications.
This study also showed that manifestations of CAD displayed on CT were very similar between men and women. It may be because DM is a major independent cardiovascular risk factor with almost the same risk level in men and women. This result could partly explain the reduced sex differential in CAD mortality and acute CAD risk revealed in previous studies [33, 34]. Other studies also showed that the impact of DM on the risk of fatal CAD was significantly greater in women than in men [35, 36]. It is believed that DM eliminated the advantage that women had for being at a much lower risk for CAD mortality than men. Therefore, increased attention should be paid to CAD in female diabetic patients.
In light of the severity of CAD in diabetic patients, it is necessary to take measures to prevent or delay its occurrence and development. Diabetic patients should always control their cardiovascular risk factors and recognize the symptoms and signs of potentially fatal CAD as early as possible. Individualized risk estimates and lifestyle advice on physical activity are expected to reduce cardiovascular diseases in high-risk group patients . In contrast, impaired glucose tolerance and type 2 DM should also be suspected in patients with CAD having no previous diagnosis of DM. However, an oral glucose tolerance test was not recommended performing very early after ST-elevation myocardial infarction due to its high false positive rate . As a non-invasive modality, MDCTA has been well established for identification of CAD [5–8]. It is worth mentioning that DSCT not only ensured high-quality images but also promised an impressive reduction in radiation dose . The mean radiation dose for patients who underwent DSCT examination in this study (4.9 mSv) was significantly lower than that in patients who underwent 16-slice (9.8 mSv) or 64-slice (8.6 mSv) MDCT examinations .
This study was a cross-sectional study and only diabetic patients with plaques were enrolled. Thus, there was a selection bias. In addition, the patients in this study also had some co-existent cardiovascular risk factors besides type 2 DM, which may affect the results. However, several previous studies had confirmed that the difference in CAD between diabetic and non-diabetic patients was independent of cardiovascular risk factors other than DM [13, 22, 23]. Thus, the present results demonstrated the current condition of CAD in diabetic patients, which may be more consistent with the practice because diabetic patients often had other concomitant cardiovascular risk factors.