Study Shows Preoperative Fractional Flow Reserve Associated with 6-Month Anastomotic Graft Functionality in Patients Undergoing Coronary Artery Bypass Graft IMPAG trial

Amandeep Singh, M.D.
By Amandeep Singh, M.D. on

A team led by Dr David Glineur working in Canada and Europe on the IMpact of Preoperative fractional flow reserve on Arterial bypass Graft anastomotic function(IMPAG) trial published in European Heart Journal  that  fractional flow reserve(FFR) measured  before surgical revascularization and anastomotic function are significantly related to each other at 6 months with a cut-off value of 0.78. They also found that measuring FFR before Coronary Artery Bypass Grafting(CABG)surgery had improved function of the anastomotic graft.

FFR is a unique way of assessing the severity and effect of coronary stenosis by measuring its ischemic potential and also used even when ischemia is not there. It hasn’t been used during the workup of the patient in abundance in the past. IMPAG study was conducted to asses the relation between FFR before the CABG surgery and anastomotic function after 6 months. IMPAG study is a prospective double-blinded observational study conducted in Canada and Belgium. The patients included were those being selected for new CABG using multiple arterial bypass grafts and those who had previous CABG/ cardiac surgery or those who are not candidates for them were excluded.

 “We found a significant association between the preoperative FFR measurement and anastomotic function in arterial bypass grafts 6 months after surgery. The best FFR cut-off value was 0.78 and those <0.78 were found to be non-functional at the follow-up angiogram. However, FFR evaluation is not part of the standard assessment of patients referred for CABG, and limited information on the role of FFR in cardiac surgery is available. Further studies are necessary to evaluate if the increase in anastomotic function translates to improved clinical outcomes.” -Dr David Glineur M.D., Ph. D. 

The patients required were calculated to be 120 with 456 anastomoses but 68 patients were enrolled and 199 lesions were checked for FFR and all the grafts used were arterial grafts. The statistical measure used to show the association between FFR and degree of stenosis were measured by linear regression and r square. ROC curves were used to identify the cutoffs for FFR and degree of stenosis. The patient characteristics and functionality of anastomoses were assessed by t-test and chi-square test.

Dr. Glineur and his team found that out of 68 patients, 64 went 6-month angiogram and in those 199 anastomoses; the median percentage of degree of stenosis was 70 for Left intrathoracic artery(LITA), 80 for Right intrathoracic artery(RITA) and 82.5 for radial arteries(RA) and FFR was 0.71 for LITA,0.77 for RITA and 0.72 for RA anastomoses and in 49 anastomoses that were non-functional, the preoperative FFR was lower. Out of these 49, 27 were frankly occluded. The r-square was 3 % for preoperative FFR and degree of stenosis which is weaker but significant. FFR was significantly higher (0.83) in functional while >0.78 for non-functionality was the cutoff.<0.78 was found to have a 98% relative risk reduction of the non-functional anastomosis through multivariate and univariate analysis.

“Arterial grafts have better short-term patency when applied to vessels with low FFR. Does this translate into improved clinical outcomes? According to the largest study,there is a late reduction in death or myocardial infarction (MI) for FFR-guided CABG conduits whether artery or vein. We ask again, ‘Will a CABG procedure needing fewer graft anastomoses, associated with higher graft patency and reduced late death and MI move the revascularization “needle” (as in a gauge) to complete “functional” rather than angiographically dependent revascularization?’ While we await the results of adequately powered randomized trials, given the present data it would seem that simpler will be better especially as applied to CABG with total arterial revascularization.”-Dr Morton J Kern M.D. (Editorial comment)

The IMPAG study has some strengths in that it was a prospective study which used only arterial graft conduits for its assessment but there were some major limitations. The study was underpowered and a type 1 error can be seen being underpowered. It also had a short follow up period. As the study was done at only two centers and won’t be able to generalize the results into other centers. Dr. Kern mentioned in his editorial comment that some latest trials like FARGO showed that it might be possible for FFR to have no significant role in predicting graft patency. So, until we have more studies coming in, we have to wait.

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