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.