1. Introduction

In the last decade, due to the enormous significance of cardiovascular pathology which occupies a leading position in the list of the socially significant diseases, the interest of scientists all over the world to the study of the heart and vessel calcification, as well as the definition of the atherosclerotic plaque (ASP) has increased significantly [1]. The problem of the coronary arteries (CA) and the heart diseases has attracted the attention of scientists since the days of Virchow [2], but even today there are still many “white spots” and unclear issues in this problem that are pending. These include the causes and pathogenesis of coronary heart disease (CHD), association with atherosclerosis (AS) of CA, determining the type and stability of ASP, indications for screening of coronary Ca. Early, preclinical identification of patients with coronary atherosclerosis and a high risk of coronary complications development is the most important task of a cardiologist and requires studying the possibilities of non-invasive techniques, such as MDCT- coronary angiography (CA). The progress of MDCT has led to a sharp surge of radiologists’ interest around the world to examine patients with CHD [4,10].

A proved high diagnostic efficacy of MDCT CA puts this technique in the first place among screening tests for the presence of coronary atherosclerosis. This technique allows non-invasively, quickly and accurately detect the presence of ASP in the CA, determine the type of ASP, assess the degree of stenotic lesion and clarify the indications for choosing a method of preventing or treating CHD [1,3]. At the same time, MDCT CA is subjected to valid criticism due to radiation exposure, the impossibility of examining patients with arrhythmia, the need to use beta blockers before the study and because of the relatively low specificity of the technique compared with coronary angiography (CAG) [9].

2. Aim

To study the possibilities of volumetric MDCT- coronary angiography in the differentiation of patients with unstable and stable forms of coronary heart disease at the non-invasive examination stage depending on the type of ASP.

3. Materials and Methods

308 patients with coronary heart disease aged from 37 to 77 years, whose average age was 59.6 ± 0.61 years were examined. 209 (68%) of them were men and 99 (32%) - women. All patients were conducted volumetric MDCT CA on a 640-slice CT scanner (detector width 16 cm) with a tube rotation speed of 0.275 sec., with intravenous introduction of a contrast agent in the amount of 0.75 ml / kg, the voltage on the tube was 100 kV, the current strength was 600-900 mA, radiation dose (RD) in prospective mode 1.4-3.5 mSv [5].

All patients, depending on the clinical variants of CHD were divided into 2 groups:

The first group consisted of 196 patients with unstable (progressive) angina of FC II by E. Braunwald et all. (1989) whose average age was 60.7 ± 0.92 years. There were 129 (65.8%) males and 67 (34.2%) females.

The second group included 112 patients with stable angina of FC II-III, whose average age was 59.8 ± 0.82 years. There were 80 (71.4%) males and 32 (28.6%) females (Table 1).

Table 1. Clinical characteristics of patients with stable and unstable angina

4. Results and Discussions

The examination results of patients with CHD were analyzed depending on the form of the angina: stable angina (SA) and unstable angina (UA). The possibilities of MDCT CA in the differentiation of patients with SA and UA forms of CHD were studied depending on the type of the ASP in the non-invasive examination stage. According to the data obtained from the biochemical blood analysis, no statistically significant differences were found between the groups. When analyzing the anatomical characteristics of coronary lesions, such as the frequencies of one-, two-, and multi-vascular lesions, it was found that in the group with UA, the absence of CA angiographic lesion was statistically significantly more frequent (14.8 vs. 8%, p = 0.04). It testifies that the pain behind the sternum, which made suspect UA in these patients, actually had a non-coronary nature. Similar differences were found when analyzing the distribution of CA in patients with SA and UA forms of CHD in the presence by calcification of CA (Fig 1).

Figure 1. The distribution of patients depending on the indicator of coronary calcium index (CCI) (Note: SA- stable angina, UA – unstable angina)

In the group with UA, CA calcification was noted less frequently: 5 vs. 9.78%, p = 0.04. It can indirectly indicate a lower stability of ASP in patients with UA. A comparative analysis of patients with UA and SA at CCI> 400 revealed a significantly more than 2 times the number of patients in the group with SA, which amounted 33.8% relatively to 15% of patients with UA. According to the literature, this is due to the fact that calcification more often occurs in “mature” ASPs, which are less prone to rupture [6,7]. All this testifies in favor of the fact that ASPs in CA were less stable in patients with UA and their damage, apparently, led to the development of an appropriate clinical picture.

Our data coincide with studies of a number of authors in which it was demonstrated that in patients with high CI, the relative risk of cardiovascular diseases complications development is increased: OR 2.1 for CI 11-100 U; OR 5.0 for CI 101-400 U and OR 9.3 for CI more than 400 U [7].

Figure 2. Degree of coronary bed lesion in patients with stable and unstable forms of angina

The analysis of coronary bed lesion degree in patients with stable and unstable angina revealed that single-vessel lesions were detected with the same frequency in both groups, two-vessel lesions more often than 3 times was noted in patients with SA and multi-vessel lesions were more common in the group of patients with UA.

Figure 3. Distribution of patients by atherosclerotic plaque type (Note: SA- stable angina, UA – unstable angina)

When comparing the MDCT CA pattern of CA lesion in patients with UA and SA important differences were found: in the group with UA, calcified ASPs were less common (5% vs. 8.78%, p = 0.04), more often soft-tissue atherosclerotic plaques (STASPs) were detected (80% vs. 16.1%, p = 0.005). All this testifies in favor of the fact that in patients with UA ASPs in CA were less stable and more susceptible to damage which led to the development of specific clinical picture of UA.

Figure 4. MDCT CA and coronaroangiography images of the right coronary artery (RCA). Calcified ASP in the middle third of the RCA

It should be noted that the lack of calcification in the projection of CA does not always indicate the absence of atherosclerotic lesions of this basin. At the same time, the presence of calcification may indicate the importance of stenotic lesion of the vascular bed. Thus, the prevalence and involvement of several CA in the process of atherocalcinosis indirectly reflects the severity of the lesion and determines the prognosis for the development of fatal coronary events [8].

Figure 5. MDCT CA and coronary angiography images of the left circumflex artery (LCX) with presence of STASP in the proximal third

The analysis results by the degree of all CA segments lesion according to MDCT CA in patients with CHD revealed significant differences. In patients with unstable angina compared with stable angina, the occurrence frequency of coronary artery stenosis from 50% to 75% was significantly higher by 2.6 times (χ2 = 22.8 p <0.0001), coronary artery stenosis higher than 75% - by 2.2 times (χ2 = 8.77 p = 0.003), occlusions – by 4.8 times (χ2 = 25.99 p<0.0001).

Table 2. Distribution of identified stenosis of the all CA segments according to the MDCT CA in the patients with SA and UA

Consequently, destabilization of the clinical condition in the patients with UA is caused by the presence of significant stenosis of CA and unstable soft-tissue ASPs.

5. Conclusions

MDCT CA is a highly informative method for estimation the condition of the CA in the patients with CHD, which allows to detect the presence, degree and prevalence of coronary lesion, as well as to determine the type of ASP. When comparing the MDCT CA pattern of CA lesion in patients with different clinical course of CHD (SA and UA) it was found that calcification of the CA was significantly less often (5.1% vs. 9.8%, p = 0.04), low CCI values were significantly often revealed (30.2% versus 21.0%, p = 0.034) and STASPs were detected (80.3% versus 16.1%, p = 0.005).