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J Thorac Cardiovasc Surg 2001;121:S29-S31
© 2001 The American Association for Thoracic Surgery
Developing the Academic Surgeon: A Symposium |
From the Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation, Cleveland, Ohio.
Address for reprints: Delos M. Cosgrove, MD, The Cleveland Clinic Foundation (F24), 9500 Euclid Ave, Cleveland, OH 44195.
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Abstract |
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Introduction |
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Mark Twain said, "the name of the greatest of all inventors is accident." A classic example of this truth is one of the best accidents that ever happened in cardiothoracic surgery. In 1957, Mason Sones, a pediatric cardiologist, mistakenly injected the right coronary artery with dye during an angiographic examination of a young man with aortic stenosis. Sones immediately recognized the problem and pulled the catheter out of the artery while the injection of dye continued. The heart stopped but started again spontaneously.
Sones happened by one afternoon while I was reviewing this historic angiogram and said, "That day I realized that I had discovered something very important." Clearly, discovery favored the prepared mind. Soon thereafter, Sones deliberately repeated this exercise and continued to refine the technique and to define coronary anatomy and the pathoanatomy of coronary atherosclerosis, the most important cause of death in the western world.
In 1672, Wycherly stated in one of his plays, "necessity is the mother of invention." It is a line that has been frequently quoted because it is so true. Several years ago, in preparation to perform aortic valve replacement, I found the ascending aorta entirely calcified and both femoral arteries occluded. Recognizing the danger of cannulating either one of these vessels, I raised the patient's arm to expose the axillary artery, which I used as the cannulation site. The aortic valve replacement was successfully performed with circulatory arrest. Bruce Lytle has expanded this idea and refined the process of cannulating the subclavian artery for this problem. The idea has been taken further with cannulation of the innominate artery for arterial return in these difficult situations.
William Shakespeare's quote "What's past is prologue" is engraved on the United States Archives in Washington, DC. In the early 1980s, my co-workers and I described use of a balloon cannula to occlude the ascending aorta for patients with a calcified ascending aorta. This led to an attempt to develop an arterial return cannula with an occlusion balloon and a port for cardioplegia and venting. Although this effort was unsuccessful because balloon technology had not been adequately developed, it did provide impetus for development of the Heartport technology and is the first paper cited in the patent application for the Heartport aortic occlusion cannula. Understanding previous efforts in dealing with the problem can lead to important new developments.
Robert Frost observed that all thought is a feat of association: "Having what is in front of you brings up something in your mind that you almost didn't know you knew. Putting this-and-that together. Then, click." In the early days of mitral valve surgery, we fully embraced the approaches and the retractor developed by Alain Carpentier. We were, however, unable to achieve precise positioning of the retractor arm in all cases. At that time, we had a huge experience dissecting internal thoracic arteries with a Favaloro retractor. This retractor had universal joints that allowed positioning of the retractor blades for any angle or location. We combined these universal joints with the retractor Denton Cooley had developed for exposure of the mitral valve. The combination proved to be a self-retaining retractor that was infinitely variable and has been in continuous use since the mid 1980s.
Another example of the importance of association in developing new technology is attempts to develop a flexible handle clamp. We were trying to develop a clamp with a flexible handle so that we could activate the occlusion mechanism from a distance and keep the handle from protruding into the surgeon's line of sight. The principle of the activation of bicycle hand brakes connected to the brake portion by cable came to mind. From this hypothesis and over a year and a half of trial and error, we developed a clamp that allowed us to clamp the aorta and position the clamp out of the way. With this innovation, the aorta could be clamped with little compromise of the working space of a very small incision.
The same thought process extended to our use of venous drainage through small incisions. In the late 1970s and early 1980s, we developed a system for placing vacuum on a cardiotomy reservoir and then autotransfusing the shed mediastinal blood. A venous reservoir was developed that had an extra port so that we could use this in a similar way. After struggling for adequate visualization around large venous cannulas through a small incision, it occurred to me that perhaps we could use a smaller venous cannula in the heart by applying negative pressure to the venous reservoir on the vacuum port that was in place for another purpose. We connected wall suction to the cardiotomy and were able to use smaller venous cannulas and reap other unexpected advantages. We no longer had to prime the venous lines so that we could siphon the blood and we no longer had to have the oxygenator as close to the floor as possible to increase the siphon affect. This allowed us to move the heart-lung machine closer to the field and substantially reduce the prime of the cardiopulmonary bypass to less than 1 L of crystalloid solution. This resulted in higher hematocrits on pump and less postoperative bleeding. In a randomized study, the percentage of patients undergoing transfusion decreased from 40% with conventional cardiopulmonary bypass to 15% for vacuum-assist venous drainage. In addition, air leaks around venous cannulas no longer caused air lock in the venous lines, which would interrupt the venous drainage.
Isaac Newton allegedly was asked how he discovered the laws of gravity. Newton is reputed to have responded that it was by thinking about it all the time. Early in my experience with mitral valve repair, I was consumed with a particular problem and thought about it constantly. As knowledge accumulated, I learned more about the physiologic mechanism of the mitral valve. Echocardiographers at Massachusetts General Hospital described the saddle-shaped contour of the mitral annulus. Alain Carpentier found that dilation of the mitral annulus occurred along the posterior annulus and not uniformly throughout the annulus. Several groups of investigators recognized the potential for the development of systolic anterior motion among patients undergoing mitral valve repair. This information coalesced as we began to think about the optimal annuloplasty ring that would produce measured plication of the posterior annulus and would be universally flexible. A search for a mechanism to accomplish this triggered thoughts about an embroidery hoop. This wooden circle holds a piece of cloth taut during embroidery. The stitches are pulled tight, but when the ring is removed, there is a flexible piece of cloth. Using this as a basis, we placed the embroidery hoop on the concave portion of the annuloplasty cloth and were able to achieve measured plication of the posterior annulus that was universally flexible during the cardiac cycle.
Another valuable lesson was learned from this exercise. This device languished for 5 years before it was developed into a product because the manufacturer could not be convinced of the usefulness of this approach. This demonstrates F. M. Cornford's observation that "nothing is ever done until everyone is convinced that it ought to be done."
Newton stated, "Pygmies placed on the shoulders of giants see more than the giants themselves." We are fortunate that we, the members of our profession, stand on the shoulders of many giants who have preceded us. As I began to become interested in repair of aortic valves, I became interested in repairing incompetent bicuspid valves. I began to notice that bicuspid valves were incompetent because of prolapse of conjoined leaflets that were longer along the free edge than was the opposite member. Earlier I had seen Alain Carpentier resect a portion of one leaflet of a tricuspid aortic valve and resuture it to correct prolapse of these leaflets. I was also aware of the work of Duran and Ankeney with plication of the annulus of the aortic valve to increase leaflet coaptation. My coworkers and I combined the procedures developed by both these giants in thoracic surgery and were able to successfully repair more than 150 incompetent bicuspid valves.
Victor Hugo said, "nothing is so powerful as an idea whose time has come." In the late 1970s and early 1980s, we were struggling with the problem of ruptured intraventricular septum. The thought occurred to us that we could temporarily occlude the ventricular septal defect with a balloon catheter that would go through the defect and be inflated. From this idea—the device was never successfully implanted—we expanded and built on the experience of Noel Mills with collapsing umbrellas. We developed a catheter for delivery of two umbrellas that could be locked together and a centering device that would keep them in the center of the defect. We had hoped to use these catheters to close atrial septal defects and patent ductus arteriosus. This effort took place considerably before the development of percutaneous transluminal coronary angioplasty and the regular use of catheters for intervention. The company with which I was pursuing this idea decided that delivery of material into a patient's heart on the end of the catheter was not practical. The effort collapsed. This was an idea whose time had not yet come.
Thomas Edison said, "Genius is one percent inspiration, ninety-nine percent perspiration. Yes sir, it's mostly hard work." He should have added that it may not be successful. In 1970, John Kirklin, at the University of Alabama, attempted to develop a closed-loop system for controlling hypertension among patients who had undergone surgical procedures. Although he succeeded in doing this, the idea never became commercially viable. In the early 1980s, my coworkers and I picked up on his idea. An associate, John Petre, developed a system to monitor arterial blood pressure and put the information through a microprocessor that would signal an infusion pump to deliver sodium nitroprusside at the rate needed to achieve a desired blood pressure. The work consumed more than 5 years. It started with a Radio Shack computer and became progressively more sophisticated. It resulted in clinical trials at our institution, licensing and commercial development by IVAC, and randomized trials in three institutions. These trials showed much better control of blood pressure with the closed-loop system than could be achieved by nurses regulating the nitroprusside infusion rate. This system was approved by the US Food and Drug Administration and was launched commercially. Another important lesson was learned from this enterprise. The company that developed the technology had little experience dealing with intensive care specialists or cardiac surgeons. It consequently had difficulty selling the product. After dealing with five chief executive officers in the same number of years, the company decided to stop manufacture of this product, although the device was highly effective in controlling postoperative hypertension.
Whenever we embark on a project, we must remember the words of Toa Tzu (604 BC) who said, "A journey of a thousand miles begins with a single step." We were concerned about the increasing incidence of stroke among patients undergoing cardiac operations. At morbidity and mortality conferences, our cardiac pathologist, Norman Ratliff began to show slides of cholesterol crystals in various organs. At the same time, transesophageal echocardiography began to show atherosclerosis of the ascending and descending aortas. Gary Roach and his coworkers, in a study reported in the New England Journal of Medicine,
1 found that age was directly related to neurologic injury whether the injury was frank stroke or neurologic dysfunction. To try to understand the course of the neurologic injury, we undertook a study of autopsy records to find the incidence of atheroemboli in various organ systems. We found that the incidence increased rapidly beginning at 60 years of age and had reached 30% by the time the patients were 70 years of age. The incidence of atherosclerosis of the ascending aorta closely paralleled the incidence of atheroemboli as age increased. There was little or no incidence of atheroemboli without atherosclerosis of the ascending aorta. Recognizing that manipulation of the ascending aorta was probably the provocateur for atheroemboli, we eliminated the partially occluding clamp during proximal anastomosis. We also were concerned that the jet lesion of blood coming from the arterial return cannula in the ascending aorta could dislodge atherosclerotic plaques in the ascending aorta and arch by means of a sandblasting affect. Aware that the underwater portion of freighters and submarines had bulbous bows to deflect the bow wave, we used that association to close the tip of the cannula and place a deflecting tip to diffuse the jets through multiple side ports. This decreased the velocity of the jet, making it less traumatic on the aorta, decreased the resistance of the arterial cannula by increasing the total orifice area, and was associated with a lower incidence of stroke. Although our attempts to avoid stroke during cardiac operations have improved and our understanding of the cause of stroke has increased, the problem has yet to be eliminated. Achieving this will take substantial work and will only be solved by substantially more work. Louis Pasteur wrote, "Let me tell you the secret that has led me to my goal. My strength lies solely through my tenacity." It will be through sheer tenacity that this devastating problem in cardiac surgery will eventually be eliminated.
Finally, let me share with all you would-be inventors and innovators, a quote from Machiavelli's The Prince: "There's nothing more difficult to plan, nor more dubious of success, nor more dangerous to manage than creation of a new order of things. Whenever his enemies have the ability to attack the innovator, they will do so with a passion of partisans while others defend him sluggishly so that the innovator and his party are likely to be vulnerable."
I can attest that new enterprise receives little support and much criticism. Nonetheless, it is a wonderful pursuit. It is intellectually stimulating and, more importantly, is the only way to improve the quality of our patients' care. I encourage you to pursue it.
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