• cardiac computer tomographic (CT) imaging
• advanced cardiac imaging
• chronic coronary disease

The incidence of chronic total occlusion (CTO) is reported to be as high as 25%, at least in individuals referred to invasive coronary angiography (ICA).1 In this scenario, CTO is also associated with a high mortality and Major Adverse Cardiac Events (MACE) incidence.1 Interestingly, this incidence of events is reported to be high even after the clinical profile and extent of coronary artery disease (CAD) in other vessels is accounted for.2 This relatively high prevalence and disproportionate rate of events has driven the attention of the interventional cardiologists in a quest to improve prognosis in the CTO setting. However, individuals referred for ICA represent a selected population of the individuals with suspected or known CAD, and the actual prevalence and event rates associated with CTO might be significantly lower if a less selected population is studied.

Coronary CT angiography (CTA) has been increasingly used in the investigation of suspected CAD. Over the last two decades, it has proven to provide adequate diagnostic and prognostic information for the presence, extent and severity of CAD.3 4 Recent evidence also suggests it can also have a meaningful impact on the management of CAD.5 6 More specifically, recent reports even suggest that coronary CTA might be useful for interventional procedural guidance in CTO.7 However, more comprehensive data on CTO detected by coronary CTA are still lacking.

In a previous study published in Heart in 2015, Opolski et al 8 have started to shed light on this topic by demonstrating that CTO prevalence in individuals referred to coronary CTA was exceedingly low, at 1.4%. This reported CTO prevalence is in sharp contrast with previous ICA studies of up to 25%.1 This apparent discrepancy derives from the fact that the present coronary CTA studies and prior ICA-based reports investigated completely different patient populations in markedly different clinical scenarios. The former included a lower risk population in which patients with prior known CAD were excluded; 41% were asymptomatic and 80% had low or intermediate pretest probability of significant CAD. The latter included a much higher risk population in which as many as 60% of the patients had a medical history of myocardial infarction and/or coronary revascularisation.

In the current volume of Heart, the same group provides novel additional information on the prognostic value of this somewhat uncommon finding in coronary CTAs in a large registry of patients being evaluated for suspected CAD.9 They observed that the presence of CTO was associated with higher all-cause mortality when compared with patients without CAD or with non-obstructive CAD (<50% obstruction). Interestingly, CTO was not associated with higher all-cause mortality when compared with patients with moderate-to-severe CAD (50%–99% obstruction). However, when a composite endpoint including mortality, myocardial infarction and late revascularisation was used, the presence of CTO was associated with higher rate of events even when compared with the subgroup with moderate-to-severe CAD, though this higher event rate was primarily driven by late revascularisations.

In a similar fashion to the reported differences in prevalence between ICA and coronary CTA, CTO prognosis is also different between the populations evaluated by each imaging modality. While observational studies of patients with CTO evaluated by ICA report a 1-year cardiac mortality of 1.4% for individuals who underwent percutaneous coronary intervention, 4.7% for those who were managed medically and 6.3% for those who underwent coronary artery bypass graft surgery,10 the study by Opolski reports a 2.3% all-cause mortality for the entire population.9 Assuming that approximately half of the deaths are of cardiovascular causes, as previously reported in other coronary CTA studies, there is a lower rate of cardiovascular death in the overall coronary CTA population, regardless of treatment strategy, when compared with ICA reports. These findings emphasise the important role of the clinical presentation of individuals found to have CTO, given that most individuals referred to coronary CTA are of a lower risk than individuals referred to ICA, even after accounting for anatomical findings.

These differences in risk and prognosis may have important implications for management, particularly since coronary CTA is becoming more popular in the investigation of stable CAD. Considerable data support the use of revascularisation strategies for symptomatic relief and improvement in the quality of life of individuals with CTO,11 though the event rates seem to be comparable between medical management and revascularisation groups. While the revascularisation procedures are associated with non-negligible periprocedural complications,12 these are probably matched by the high event rate reported for the medically managed CTO population in the ICA studies. However, if such management is replicated in the lower absolute risk CTO population usually evaluated by coronary CTA, the revascularisation strategy might prove to be more harmful than the baseline reported risk. Thus, instead of an automatic incorporation of the current practice approach to the treatment of patients with CTO, the population coming from coronary CTA evaluation might benefit from a more selective use of revascularisation procedures.

Interestingly, the solution for this problem might come from coronary CTA itself. Several studies have demonstrated the value of coronary CTA in predicting the recanalisation success rate and also in optimising the pre-procedural planning of percutaneous coronary revascularisation of CTO. Indeed, the CT-RECTOR score, which combines several CTA-derived parameters to predict CTO recanalisation success, was found to have a better discriminatory performance than the invasive angiography-based J-CTO score.7 Taken together, these findings highlight the potential of coronary CTA in providing a comprehensive assessment of patients with CTO that may guide patient management and possibly even improve patient outcomes. Future studies aiming to compare medical management and revascularisation of CTO should include routine coronary CTA in both arms. This may allow the development of comprehensive non-invasive risk–benefit scores based on both clinical and imaging-derived parameters to more carefully select the best candidates for the intervention. Until then, the current prognostic data for CTO from coronary CTA is insufficient to support revascularisation strategies except if solely for symptomatic relief.