Journal of the American College of Cardiology
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- Marzia Leacche, MD,
- David X. Zhao, MD and
- John G. Byrne, MD⁎ (john.byrne{at}vanderbilt.edu)
- ↵⁎Department of Cardiac Surgery, Vanderbilt University Medical Center, 1215 21st Avenue South, Nashville, Tennessee 37232
We appreciate the comments of Drs. Colli and Ruyra regarding our paper (1) and the indications for routine completion angiography after coronary artery bypass grafting (CABG) surgery. We agree with Dr. Colli and colleagues that the transit time flow meter (TTFM) is a valuable tool to assess intraoperative graft patency. Moreover, it is relatively inexpensive and readily available in those centers that do not have an operating room with angiography capability. The TTFM, however, has several limitations. It is reasonably accurate in defining graft integrity only at the extremes, which is either patent or occluded, while it cannot define location of the defect either within the conduit or at the anastomosis. Moreover, it cannot discriminate between the influences of the conduit versus the native coronary arteriolar bed. Also, the normal range values have very large variability because TTFM measures the mean graft flow, which is influenced by the systemic arterial pressure, cardiac output, type of conduit used (vein conduit vs. arterial conduit), residual antegrade coronary flow, resistance of the distal coronary bed flow, competitive native flow, and, finally, blood hematocrit (2). Thus, for those grafts with values between the abnormal and normal range, there is a lack of sensitivity for objective clear cutoff values.
For the reasons mentioned in the preceding text, coronary angiography can identify a higher rate of defective grafts compared with TTFM (3). The rate of graft revision based on TTFM is between 1% to 8% (2). These rates are well below the average 20% to 30% 1-year saphenous vein graft (SVG) failure rate reported in the literature (2,4). The PREVENT IV (PRoject of Ex-vivo Vein graft ENgineering via Transfection IV) trial, a multicenter randomized study of 3,041 patients, has confirmed the clinical impact of vein graft failure. In this study, the common end point of death and new myocardial infarction was 0.9% in patients with patent SVG, while for patients with at least 1 occluded SVG this adverse outcome was 14% (p < 0.001) (4).
In order to improve the long-term outcomes of CABG surgery, graft patency is a key factor. Grafts fail early primarily because of technical errors that could be corrected at the time of the surgery. While the TTFM and other techniques such as intraoperative fluorescence imaging are steps toward improving graft patency, they can identify only a limited number of graft defects, mostly occlusive abnormalities, and cannot reliably identify significant (>50%) nonocclusive graft flow abnormalities. These significant graft abnormalities have important clinical impact on the long-term benefits provided by CABG surgery. For the reasons mentioned in the preceding text, routine angiography after CABG has low periprocedural morbidity. It seems that it should perhaps eventually be routine if available in a hybrid suite.
- American College of Cardiology Foundation
