Graft Patency Rate and Clinical Outcome After Coronary Artery Bypass Surgery
To the Editor:
We read with interest the article by Berger and associates1 concerning internal thoracic artery (ITA) graft patency in repeat angiography in conventional coronary artery bypass surgery. We have extensive experience2 with minimally invasive direct coronary artery bypass grafting (MIDCAB) and would like to comment on their analysis.
In their study, the authors describe 2 groups of patients who had ITA bypass to the left anterior descending artery and additional vein grafts. Patients in the first group underwent control angiography (CA) postoperatively. In this group (n=617), the incidence of myocardial infarction (2.5%) and operative mortality (0.2%) was low. In the second group (n=116), which did not have CA postoperatively, 9.5% of patients died, and the incidence of myocardial infarction (8.0%) was significantly higher.
In our study population, 277 of 451 patients (61.4%) underwent CA after MIDCAB. Graft patency was 97.8% (ITA graft stenosis >50%, 7.2%). None of these patients died or experienced myocardial infarction in the early postoperative period. In the group of patients not undergoing CA (174 of 451), the incidence of myocardial infarction (4 of 174; 2.3%; P=0.01) and hospital mortality (3 of 174; 1.7%; P=0.02) was significantly higher.
We hypothesize that the overall patency rate in ITA anastomosis is lower than reported in both Berger et al’s1 and our patients. The clinical outcome in patients not undergoing CA, who had an increased rate of myocardial infarction and mortality, suggests problems with graft patency. In many instances, patients with perioperative complications such as death, emergency redo-revascularization immediately after the first operation, transmural myocardial infarction with circulatory problems, or lengthened mechanical ventilation would not undergo CA.
The authors state that “no important differences in clinical or procedural characteristics were identified between patients who did and did not undergo angiography.” However, a mortality rate of 0.2% versus 9.5% and a rate of myocardial infarction of 2.5% versus 8% in patients with versus without CA clearly reflect important differences in clinical outcome, in our opinion. Thus, patency data from autopsy reports should have been included in the authors’ analysis to clarify the true patency rate in ITA anastomosis after coronary artery bypass grafting. Furthermore, a patient selection comparable to that of the MIDCAB population (a median of 3.0 graft insertions does not seem to represent single-vessel disease) would be appropriate before calling the study a benchmark for the procedure.
- Copyright © 2001 by American Heart Association
Berger PB, Aldermann EL, Nadel A, et al. Frequency of early occlusion and stenosis in a left anterior descending artery bypass graft after surgery through a median sternotomy on conventional bypass. Circulation. 1999;100:2353–2358.
Cremer J, Mügge A, Wittwer T, et al. Early angiographic results after revascularization by minimally invasive direct coronary artery bypass (MIDCAB). Eur J Cardiothorac Surg. 1999;15:383–388.
We appreciate Dr Lichtenberg and colleagues’ interest in our article and the opportunity to respond to the important questions they raise. We agree that the overall patency rate of the left internal mammary artery (LIMA) in the patients in our study who died and were therefore unable to undergo follow-up angiography (1.8%) may well have been lower than the patency rate among patients who underwent follow-up angiography (98.8%), as we acknowledged in our article. Our statement that no important differences in clinical or procedural characteristics were identified between patients who did and did not undergo angiography is, nonetheless, accurate and is not in conflict with this possibility.
Lichtenberg et al’s observation that our patients underwent a median of 3.0 graft insertions, whereas the majority of patients undergoing minimally invasive direct coronary bypass (MIDCAB) have single-vessel disease and receive only a LIMA to the left anterior descending coronary artery (LAD) is worth emphasizing, which we tried to do in the discussion section of our article. One might expect that patients with more extensive disease (3-vessel disease versus 1-vessel disease) would also have more diffuse and severe involvement of the LAD. Therefore, the patency rate of the LIMA in our patients would be expected to be lower than that of patients with single-vessel disease undergoing anastomosis of just the LIMA to the LAD via the less invasive MIDCAB approach. Therefore, when we suggested that our results might be used as a benchmark for the MIDCAB technique, we meant that patients with less severe coronary disease undergoing surgery with the MIDCAB procedure should have a LIMA patency rate at least as high as, if not higher than, that observed in our study.
Regarding the data that Lichtenberg et al cite from their medical center, we would have been delighted to reference the impressive results in their study, but they were published long after our study was submitted for publication. We note, however, that the follow-up angiography of 61.4% in their study, although higher than that of most MIDCAB studies, was significantly less than the frequency of follow-up angiography in our population (91%). The less complete the follow-up angiography in these studies, the less certain we can be about the true frequency of LIMA patency after MIDCAB.