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Dr Timothy Harward (Orange, Calif). The University of Oregon group is to be congratulated for continuing to investigate the various aspects of diagnosing and treating mesenteric arterial occlusive disease. The presentation is said to center around duplex scan-determined flow characteristics in bypass grafts following mesenteric bypass surgery; however, from review of the manuscript, I suspect the investigators’ original intent was to evaluate the short- and long-term graft patency rates in their surgical bypass population.

That said, as I reviewed the manuscript, I frequently had to jump from unrelated clinical data to arterial pulse wave Doppler characteristics as independent of the clinical data. Not surprising, the authors found that resting peak systolic velocities after mesenteric arterial bypass did not vary from patient to patient when the bypass grafts were widely patent. In addition, basic hemodynamic knowledge would have predicted the noted trend toward higher mid-graft blood flow velocities in 6-mm versus 7-mm prosthetic grafts and in the smaller diameter inflow iliac arteries compared to the much larger diameter supraceliac aortas. Even though the only individual who had an 8-mm prosthetic graft was excluded from the analysis, I suspect its peak systolic velocity value was even lower than that seen in the 7-mm grafts.

The manuscript concluded that its data can serve as a standard for postoperative mesenteric bypass graft surveillance. I am a bit confused as to what standard one is talking about, what has been proven or added to our knowledge of postoperative mesenteric bypass grafts. I do not believe that one can accurately predict short- or long-term graft durability or function by looking at only resting velocity values, especially in an organ with such reactive outflow arteries as the small intestines. I would be very interested in graft flow changes with a meal or pharmacologic stimulation as determined in each patient compared with itself over time. With these data, one might in be able to predict impending problems with the graft such as early anastomotic stenosis or development of distal mesenteric artery bed resistance brought on by progression of distal arteriolar disease as is sometimes seen in diabetic patients. If I know Greg Moneta as well as I think I do, this thought has already crossed his mind. Do you have any comments in this area?

Finally, despite my feelings that the clinical data in this manuscript do not add anything to my interpretation of the duplex scan results, I do believe that they do reiterate a concept dear to my heart… that prosthetic bypass grafts to mesenteric arteries, whether done antegrade or retrograde, do quite well long term. At the time I left the University of Florida, Jim Seeger and I had done 48 antegrade mesenteric bypass procedures over a 5-year period, 43 with Dacron bifurcated grafts and five with a single reversed vein to the superior mesenteric artery. At that time, all prosthetic grafts in surviving patients were patent without problems, while 4 of the 5 vein grafts developed significant vein wall fibrosis and narrowing. My feelings were that the veins could not tolerate the high flows seen in the mesenteric circulation, leading to hyperplasia similar to that seen in veins used as outflow for hemodialysis accesses. I would be interested to hear your comments concerning this issue of prosthetic versus vein graft long-term durability.

Tim apologizes for not being here to personally present his comments. Someone had to say home and work; however, he would like to say thank you for the opportunity to comment on this presentation … and he will see everyone in Hawaii next year, the site where he caught the bug to do ironman triathlons while at the Western Vascular meeting 6 years ago!

Dr Timothy Liem (Portland, Ore). From its inception, the objective of this study was the evaluation of duplex scan characteristics for mesenteric artery bypass grafts. Our data regarding the patency of superior mesenteric artery bypass grafts were previously presented at the Western Vascular Society meeting in 2000.

With regard to the 8-mm graft diameter, that one particular graft did have a decreased velocity when compared with the 6- and 7-mm grafts.

With regard to the question of what has been proven with this study, it has lent support to our intuitive ideas that decreased mesenteric graft diameter is associated with elevated peak systolic velocities. As far as standards for comparison, there really are very little published data regarding the average velocities in the mesenteric bypass grafts. Our study demonstrated that there is a fairly consistent range of peak systolic velocities within the mid-graft, proximal, and distal anastomoses. Regardless of the graft orientation, graft material, or single versus bifurcated graft configuration, the mean peak systolic velocity ranged from approximately 140 to 200 cm per second plus or minus 50 or 60 cm per second as a standard deviation. This would give us a relatively normal range for graft velocity on which to base our judgments regarding further evaluation with angiography or CT angio. Perhaps patients who fall significantly out of that range, outside of two standard deviations, should be evaluated if their velocities were perhaps in the 250 to 300 cm per second range or higher.

We have thought about and are planning on performing fasting and postprandial duplex scans. That study for the native circulation has already been performed by one of our colleagues, Dr Gentile, who is here today.

With regard to the durability, we agree that antegrade and retrograde bypasses have a fairly equal durability.

As far as prosthetic graft versus vein, we tend to use prosthetic graft, and we think it has an excellent durability in people who have chronic mesenteric ischemia. In people who have acute ischemia with bowel infarction, we tend to use saphenous vein if it is of good quality.

Dr Bruce Gewertz (Los Angeles, Calif). I enjoyed the paper and thought it was a contribution, particularly contrasting the retrograde and the antegrade bypasses. I guess when you get old, a problem like Tim alluded to in his comment is that everything you hear tends to reinforce your prejudices. My prejudice as well is that these grafts do well if you do not make a technical error in the operating room, particularly with the retrograde bypasses, and get a kink. As well, our exhibitors next door providing us with breakfast should be happy because it is one of those great operations that may do better with a prosthetic graft. Finally, the prejudice of the single patient in whom you had a bad result is parallel to mine. Since these patients are relatively young, they have advanced atherosclerosis, they are frequently female with small vessels, I really prefer to avoid using the iliac as an inflow source, and although it was a rare instance in your series, it is interesting that was the one case.

I guess the one question I would ask to try to make this even more relevant to us, since the issue particularly with a retrograde bypass if you sort of have to do it is, is this lying right and is there any problem in the graft. Whether you think that, maybe the true value of your paper would be to use an intraoperative duplex in some way to determine whether the graft configuration is perfect, particularly after you lie it back down and you are ready to close.

Dr Liem. Thanks, Dr Gewertz, for your comments. For people who have suboptimal infrarenal aortas and iliac arteries, such as women who have very small arteries, especially diseased and calcified arteries, we really do not hesitate to go to the supraceliac aorta if it is of good quality.

Dr Ahmed Abou-Zamzam (Loma Linda, Calif). Tim, I was hoping, given the title of this paper, that you would actually give us some insight as to the need for surveillance of these bypasses. From your data it appears that if the first duplex looks okay, then there is really no benefit to doing surveillance. So, going back to what Dr Gewertz just said, if an intraoperative duplex or an early postoperative duplex looks okay, is there any reason to follow these patients with duplex?

Dr Liem. We think there is a reason to follow these patients with surveillance duplex imaging. One reason is to monitor for progression of atherosclerosis at the inflow or outflow artery. Our study demonstrated that on average, the duplex velocities did not change significantly between the index scan and the latest postoperative scan. However, there are still some instances when a significant velocity change will be detected with follow-up duplex scanning. In these cases, some form of intervention may be required. So we think that surveillance duplex imaging every 6 months, or every 12 months if the patient is further out, would still be appropriate. These are not large numbers of patients, and we do not think it is an over-utilization of resources.

Dr Abou-Zamzam. So you are still staying with every 6 months. You have not changed your policy based on this report?

Dr Liem. No.