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| Guest Commentary |
| by V.A. Subramanian, MD and James D. Fonger, MD |
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Minimally Invasive Conduit Harvesting for Coronary Bypass Grafting
The initial work on less invasive conduit harvesting involved removal of the saphenous vein from the leg through one or two small access incisions. The improvements in leg wound healing were obvious and particularly compelling in the obese diabetic patient who required a number of coronary vein bypass grafts. Initial patient experience demonstrated that this could be done safely and subsequent prospective randomized clinical trials showed a definite patient benefit over the conventional open approach. Histology and vascular reactivity of the harvested conduits was also evaluated and did not show additional trauma to the conduit as a result of this new harvesting technique. Several vendors have now developed their variations of less invasive saphenous vein harvesting systems.
More recently, beginning at Lenox Hill Hospital, the same principles of less invasive conduit harvesting have been successfully applied to radial artery harvesting. Through a small access incision at the wrist the radial artery is harvested proximally to just below the bifurcation with the ulnar artery at the elbow. This has been greatly facilitated by the use of the harmonic scalpel which allows for simultaneous division of fascia, muscle, and arterial branches that invest and tether the radial artery along its course in the forearm. There are now two commercially available systems for less invasive radial artery harvesting and the number of centers adopting this approach continues to increase.
Despite all the development work to date on these new harvesting techniques, a number of important questions remain. These include how we assess patients before surgery to determine if their conduits will be suitable for grafting, how we evaluate the true clinical performance of the harvested conduits once they are placed on the heart, and who should be doing the conduit harvesting in the changing model of surgical cardiovascular care. As the adoption of these harvesting techniques expands, it will become increasingly important to know the answers to these critical questions.
How do we know the quality of the conduit before actual harvesting at the time of surgery? In the case of saphenous vein, the issues are the course and size of the vein, particularly in the obese patient, and whether the vein has unexpected varicosities that might render it unusable for grafting. Venous mapping before surgery can help define the course of the vein but does not give a good indication of the quality of the conduit. Vein dissection can be made less traumatic with new strategies borrowed from plastic surgery by first infusing saline around the vein and then driving the saline throughout the surrounding fat using surface ultrasound. Subsequent dissection with the scope is facilitated as the moist fat falls away from the vein and exposes the branches. Division of the venous branches and investing tissue is now done with bipolar cautery devices that dissect, grasp, and cauterize the branches with a single instrument. More innovation is still required to further minimize the number of instrument exchanges required by the operator.
The radial artery presents a different set of unique challenges. The course of the radial artery is linear and much more predictable than the vein. Exposure of the radial artery is more likely to be impaired by a muscular forearm than by subcutaneous fat. We now have several effective techniques to confirm that the ulnar circulation and the palmar arch are adequate to support the circulation to the hand. However what is still required is a better way to visualize the body of the radial artery to be able to tell if there is calcification that will prohibit the use of the radial artery for grafting. Surface scanning of the radial artery with an ultrasound probe on the skin or intra-arterial catheter evaluation for calcium are two possibilities. These new modalities will have to be correlated with post-operative graft patency to validate their clinical utility.
After surgery, the performance of vein grafts and radial artery conduits harvested less invasively is still not fully understood. Patency at 6 months and a year for both conduits needs to be more fully evaluated and correlated with non-invasive evaluations done prior to surgery. This will help develop better predictive models for conduit suitability and subsequent performance once they are placed on the heart. The new generations of fast CT and MR scanners offer the promise of having patients agree to be evaluated for graft patency after surgery as part of their routine post-operative office visit. Patency data from these studies will help us confirm that the conduits harvested less invasively indeed perform equally or better than conventionally harvested veins and arteries.
Finally, operative training remains a hurdle to wider adoption and acceptance of these less invasive harvesting techniques. Training physician assistants (PA’s) can be time consuming and frustrating for the operative staff. The natural tendency is for the already experienced PA’s to do the minimally invasive harvesting, but that doesn’t leave the team with depth in staffing for vacations and illness. In addition, there is often significant turnover within the PA staff as well as some PA’s who are simply not suited to learn the techniques. In the new economics of cardiac surgery, this begets the question of whether it may now be time for assistant surgeons to take a greater role in harvesting of the conduits used for bypass grafting. This would reduce the overall cost of the operative team, assure the harvesting person is surgically competent, and presumably not be a model subject to as many staffing turnovers. With feedback from postoperative scans of graft patency, surgeons might make new observations about these harvesting techniques and adopt improved approaches by applying this additional information. Minimally invasive conduit harvesting has been a tremendous advance in our ability to perform cardiac surgery with less surgical trauma and postoperative complications. However the ultimate measure of enhanced quality will be documented postoperative graft patency. Although these less invasive techniques are already in relatively widespread use, there are still important questions to ask and improvements to be made. Hopefully this Commentary will serve to stimulate the CTSNet readership to do the studies and report the results that will get us closer to some of these answers.
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