CAD is a leading cause of morbidity and death. Coronary computed tomography angiography (CCTA) is an anatomic, non-invasive imaging technique that can diagnose and risk stratify CAD, without the risks associated with invasive coronary angiography, the gold standard. This research first carried out a review of the literature to appraise current clinical applications of CCTA, its prognostic power and future directions in terms of advances. The segment involvement score (SIS), also termed the total plaque score (TPS), is a semi-quantitative score that gives an indication of coronary disease burden, and is consistent with the move from qualitative to quantitative CCTA reporting. Although SIS is often reported in scientific studies, it is not reported routinely in clinical CCTA studies.
This research in sequential phases sought to first define the prognostic value of SIS by systemic review and meta-analysis of published literature. In addition to atherosclerosis burden, atherosclerotic progression has been advocated as a superior predictor of outcomes. Hence the novel measure ‘age adjusted SIS’ (aSIS) was devised. It was hypothesised that aSIS is a surrogate marker of ‘vascular age’, as it gives greater weighting to segments involved in those who are younger, and so may account for premature atherosclerotic disease.
Evaluation of aSIS first in a hypothesis-generating study, and then with external validation in a large multinational registry, demonstrated that it has independent, incremental prognostic value to traditional risk factors and CCTA measures of CAD. In a subanalysis to compare directly to the well-established coronary artery calcium (CAC) score, aSIS also showed incremental prognostic value, but has the benefit of not needing additional concomitant scanning as CAC score requires. In the final phase of this research, aSIS was applied with other CCTA measures to evaluate CAD in French Canadians, a suggested vulnerable population with increased risk for premature coronary artery disease and clinical events. Taken together, this research supports the inclusion of SIS in routine clinical CCTA reports. The simplicity of SIS and aSIS makes them easily calculable on a routine basis for clinical reports of CCTA, and they have potential to be calculated by automated software algorithms.