Letter by Nežić et al Regarding Article, “The Impact of Diabetic Status on Coronary Artery Bypass Graft Patency: Insights From the Radial Artery Patency Study”
To the Editor:
We read with great interest the article by Singh and associates1 that was recently published in Circulation. We respect all subsequent analysis arising from an excellent, prospective, randomized basic study presented by Desai and colleagues2 a few years ago that compared the angiographic patency of radial artery (RA) grafts with that of saphenous vein (SV) grafts 1 year after surgery. Although that study demonstrated significantly better angiographic patency of RA conduits compared with SV grafts (occlusion rate of 8.2% for RA conduits versus 13.6% for SV conduits), the existence of a string sign was assigned to 7% of RA grafts and to only 0.9% of SV grafts. Subsequent analysis of those data3 showed that 48.4% (15 out of 31) of the RA conduits with a string sign presented with thrombolysis in myocardial infarction (TIMI) 1 flow. A significantly higher rate of postoperative angina has been registered in patients whose RA conduits were found to have a string sign and TIMI 1 flow.3
The primary end point of the study by Singh et al1 was to determine overall study graft failure, and the secondary objective was to compare graft failure of the study RA conduits versus the study SV conduits within nondiabetic and diabetic patients. All RA conduits with a string sign were considered to be patent. In our opinion, if we are discussing the failure and occlusion of study grafts, RA grafts with an angiographic string sign should be included in the category of failed conduits (at least those with TIMI 1 flow because TIMI 1 flow has been defined as some penetration of contrast material beyond the point of obstruction but without perfusion of the distal coronary bed4). Although only the perioperative use of α-adrenergic agonists and target vessels stenosis <90% were pointed out as significant factors for a string sign3 appearance of RA conduits, we assume that RA conduits with a string sign and TIMI 1 flow were similarly distributed among diabetic and nondiabetic patients. Some of the authors’ conclusions are based on the border level of statistical significance (ie, RA protectiveness against graft failure compared with SV grafting in both diabetic and nondiabetic cohorts). It is possible that, with the inclusion of all RA conduits that have definitely failed (36 occluded, 15 with a string sign and TIMI 1 flow), the findings of the study would no longer be statistically significant.
Singh S, Desai N, Petroff S, Deb S, Cohen E, Radhakrishnan S, Schwartz L, Dubbin J, Fremes S, for the Radial Artery Patency Study Investigators. The impact of diabetic status on coronary artery bypass graft patency: insights from the radial artery patency study. Circulation. 2008; 118: S-222–S-225.