Conventional coronary angiography is considered the gold standard in the assessment of coronary arteries. However, the continued advancement in CT technology, as well as the development of a new CAD-RAD system, have increased the dependence on CT coronary angiography as a gatekeeper for the coronary artery disease assessment with limitation of the coronary artery angiography to cases that require revascularization [9].
This study included forty-eight patients, 24 patients (50%) had normal angiograms, 8 patients (16.67%) had a non-significant disease and the other 16 patients (33.33%) had a significant disease, which was similar to the previous study done by Raff et al. [10] that showed 35% of the patients with normal angiograms, 28% with non-significant coronary disease and 37% had a significant disease. The right-sided dominance of coronary circulation was most commonly seen (83.33%) compared to (62.5%) at Madhok and Aggarwal et al. [11].
In the 48 patients, only two patients showed significant lesions on the conventional angiography images and were missed or underestimated on CT coronary angiography (7.2%). These lesions were at the small branch arteries. That can be explained by the fact that despite the improvement in the temporal and spatial resolution of CT reaching 0.4 to 0.5 mm it is still not comparable to conventional coronary angiography which is 0.1 to 0.2 mm [12]. On the other hand, only two patients showed lesions that were overestimated at the CT angiography as significant yet they proved to be insignificant at conventional angiography. The over-estimated lesions at CT angiography are usually attributed to the presence of extensive atheromatous calcification of the vessel wall with subsequent beam hardening artefact that gave the false impression of being significant. The false positive and false negative results in this study were lower than that of Raff et al. [10] study that showed about 17% false negative and 20% false positive, this difference is likely due to the continuous advancement in CT technology and post-processing algorithms aiming at improving the resolution and limiting the effect of beam hardening artefacts.
In the current study, the MDCT coronary angiography had an overall sensitivity of 92.9%, which was higher than the value reported in the previous studies done by Raff et al. [10], Madhok and Aggarwal et al. [11] and Leber et al. [13] that reported sensitivity of 86%, 87% and 82%, respectively. The specificity of the MDCT coronary angiography in this study was 90%, near to the specificity (95%) which was reported in Raff et al. [10], Madhok and Aggarwal et al. [11]. Leber et al. [13] studies. The positive predictive value in this study was 92.9% being relatively higher compared to the values reported by Raff et al. [10], Madhok and Aggarwal et al. [11] and Leber et al. [13] which were 66%, 75% and 72%, respectively. Our negative predictive value was 90% which was similar to the values of Raff et al. [10], Madhok and Aggarwal et al. [11] and Leber et al. [13] who reported negative predictive value of 98%, 98% and 97%, respectively. The higher value of sensitivity and the positive predictive value in this study is partially explained by the ability of the new CT generation which correctly identify the smaller lesions in the distal segments.
On the contrary, the sensitivity, specificity, negative predictive values and positive predictive values in this study were relatively lower than values noted in Basha et al. [14] study that were 100%, 98%, 98% and 100%, respectively; this can be attributed to a large number of significant lesions in Basha et al. [14] study that represented about 45% of the sample size which could represent a form of selection bias.
Regarding the per-segment evaluation of the coronary arteries, the agreement between CT angiography and the conventional angiography was an excellent agreement for the left main trunk at its all segments, similar to that of Waseem et al. [15] and Mannan et al. [16] who revealed excellent agreement (k = 1).
As regards the left anterior descending artery at its proximal, mid- and distal segments as well as the second diagonal branch there was excellent agreement between conventional and CT angiography in the current study with good agreement seen at the first diagonal branch (K = 0.765), similar results were also noted in two different studies done by Waseem et al. [15] and Mannan et al. [16] with K range from 0.788 to 1.
An excellent agreement was noted for the left circumflex artery (LCX) at its proximal, mid- , distal segments and the obtuse marginal branch, Waseem et al. [15] and Mannan et al. [16] also found an excellent agreement for the LCX and OM branch yet with k range from 0.846 to 0.9.
In this study, there was excellent agreement (K = 1) in the proximal and mid-segments of the right coronary artery, as well as the posterior descending artery, with a good agreement in the distal segment of the RCA (K = 0.782), which was similar to the results of Waseem et al. [15] and Mannan et al. [16] who reported excellent agreement for all RCA segment and PDA but the distal segment showed a good agreement with k = 0.765.
The CAD-RADS classification has several limitations, the most important is that it does not account for the total plaque volume which is found to be a strong predictor for acute coronary syndrome and important discriminator from stable coronary artery disease [17, 18], another important limitation is that it is not applicable for vessels less than 1.5 mm which limits its ability is the assessment of diagonal branches distal segments [19]. Another important drawback is that due to potentially complex conditions in coronary anatomy, CAD-RADS might not appropriately classify patients with coronary anomalies. These patients continue to require comprehensive reports and individual management recommendations [20]. Apart from these limitations, the standardized reporting algorithm ensures detailed and reliable reporting, as well as clear communication between clinicians, radiologists and patients [21,22,23,24].
The limitation of our study was that we included a relatively small number of patients. Also as we were focusing upon comparing the results of CT with conventional angiography, we did not include incidental coronary anomalies, calcium scoring and incidental non-coronary and extra cardiac findings in our results.
