Discussion
The use of CAG relies on visual estimation to determine if the coronary arteries are in need of surgical revascularisation. This typically involves gauging the extent of the stenosis and the appearance of the lesion, which is often subject to the preference and possibly bias of the physician20. Using the irregularities observed in diseased coronary arteries, the degree of stenosis of the coronary vessels is quantified as a percentage and used as a basis of classification of the lesion into three categories: mild, intermediate or severe21,22. Intermediate coronary stenoses fall into a “grey zone”, where the decision of what intervention is used and if an intervention is needed at all can become difficult20. The FFR is thus a useful tool in quantifying the degree of vessel narrowing to better assess coronary arteries with intermediate-stenosis23,24. Previously, research compared the outcomes of FFR-guided PCI versus conventional CAG-guided PCI25, showing that FFR was useful in guiding the use of percutaneous interventions and particularly so when the target vessel stenosis was in the order of ≤0.8026. However, the role and scope of the use of FFR in guiding CABG has yet to be determined14,27.
To the best of our knowledge, this is the first systematic review and meta-analysis comparing the clinical outcomes of FFR and CAG for the use of CABG. In this meta-analysis the use of FFR was associated with significantly less overall death than CAG-guided CABG surgeries. These results were also observed in our pooled analysis of overall death rates, which demonstrated an average of 6.1% for the FFR cohort, as compared to 7.1% for the CAG cohort. In the subgroup analyses of overall death rates, however, we noted that a significant difference was present solely in the two retrospective double-arm studies14,15. Hence, there is a need for further randomised controlled trials to investigate whether the use of FFR to guide CABG can lead to lower overall death rates.
Apart from lower rates of overall death, the results from the pooled analysis also showed a lower rate of spontaneous MI in the FFR cohort (2.5%) as compared to the CAG cohort (5.0%). Fournier et. al.14 has previously described the presence of a linear relation between the number of vein grafts used and the incidence of spontaneous MI and overall death and suggested that the significantly higher number of vein grafts used in CAG-guided CABG group was responsible for the observed higher incidence of MI and death14 (Table 3). On the other hand, in the study of Toth et. al.15 the FFR and CAG groups were linked with similar rates of spontaneous MI and death despite the use of a significantly higher number of vein grafts (and significantly lower number of arterial grafts) in the CAG group (Table 3).
In any case, the positive effect of the FFR on the occurrence of spontaneous MI seen in our pooled analysis was not present in our meta-analysis, where there were no significant difference in the rates of spontaneous MIs between the two groups. Once again, whether there truly is an association between the use of FFR and the probability of occurrence of spontaneous MI needs to be determined in future studies.
Graft occlusion was seen to be lower in FFR guided group in the retrospective study by Toth et al15, however on meta-analysis, there was no statistically significant difference between the two study groups (Figure 4E). Likewise, our meta-analysis did not reveal any statistically significant difference in the remaining primary and/or secondary end points of MACCE and target vessel revascularisation between the FFR and CAG guided CABG groups.