Heart Valve Surgery: Current Review
Sary Aranki, MD
Introduction
Heart valve prostheses were introduced more than 40 years ago. The operation and technical details of valve replacement have been refined and perfected over the years such that it has become a standard procedure that can be reproduced and taught to residents in training.
The type of prostheses used as valve replacement devices remain far from optimal and in no way match the function of a normal native valve. The broad division of these devices into bioprosthetic and mechanical valves has long-term implications that need to be explained in detail to the patients before surgery. In brief, the durability and the potential complications as a result of the presence of prosthesis constitute what may be termed as "prosthetic valve disease."
This review will provide a brief description of available valve prostheses, as well as their advantages and disadvantages. In addition, a brief summary of selected recent presentations on this subject at the American Association of Thoracic Surgery (AATS) meeting held in Philadelphia, Pennsylvania, will be discussed.
Prosthetic Valves
The main difference between mechanical and bioprostheses can be summed up by a simple comparison: the need for life-long anticoagulation with warfarin (Coumadin) vs the need for a repeat operation. In other words, mechanical valves last forever but are associated with an inherent risk for thrombus formation and embolization (thromboembolic complications), and therefore necessitate life-long anticoagulation therapy, which is accompanied by its inherent risk of bleeding (hemorrhagic complications). This poses a great dilemma for young patients who do not want to take warfarin because an active lifestyle will likely increase the risk of injury and hemorrhage. In addition, warfarin use must be carefully monitored as measured by the INR, and noncompliant patients as well as those who live in remote areas may have only limited access to such monitoring. Under these circumstances, the risk of a repeat operation outweighs the risk of taking warfarin.
Another important factor to consider, especially with mechanical valves, is their track record as far as design malfunction is concerned. Therefore, the number of years a certain valve design has been in use without any mechanical malfunctions is of paramount importance in deciding which valve to use. The implications for such failures are huge. Not only can they put a patient's life at risk, but also the financial and litigation burdens could be enormous.
It is not surprising that the pace of progress in the introduction of new prosthetic devices into clinical practice is very slow. It takes, on average, between 8 and 10 years for a new device to be approved by the United States Food and Drug Administration (FDA), and the process is similarly long for regulatory agencies in other countries. It is not unusual for new valve devices to be subjected to clinical studies when the previous models are just approved and introduced into clinical practice.
Mechanical Valves
Forty-five years ago, the ball-and-cage valve was the first commercial mechanical valve introduced to clinical practice. It was a high-profile valve and required intense anticoagulation. The valve subsequently underwent modification with changes made in the ball structure (silastic, stainless steel). Concerns about increased thrombogenicity and the less than perfect hemodynamics led to the next generation of valves -- tilting disc valves (Bjork-Shiley, Medtronic Hall, and Omniscience valve designs). One modification to the Bjork-Shiley valve, in which it was reshaped to form a convexo-concave valve, faced a serious problem with strut fractures and led to a significant decline in the use of these valves.
Constituting the third generation of mechanical valves, the bileaflet valve was first introduced into clinical practice in 1977 by St. Jude Medical (Minneapolis, Minnesota) and is in widespread use today. The device is a low-profile valve that has excellent hemodynamics, requires less intense anticoagulation, and has had no reported structural failures. Other bileaflet valves approved by the FDA are manufactured by CarboMedics, Inc. (Austin, Texas), ATS Medical, Inc. (Minneapolis, Minnesota), Baxter Edwards CVS (Irvine, California), Sorin Biomedica (Saluggia, Italy), Medtronic (Minneapolis, Minnesota), and Medical Carbon Research Institute (Austin, Texas).
Candidates for mechanical valves are usually young patients who have no contraindications to warfarin therapy. Women of childbearing age who want to have children should not take warfarin because of its association with congenital defects. Patients with any bleeding tendencies or those likely to be exposed to repeated injuries should also avoid taking the drug. The rationale for using a mechanical valve in younger patients is related primarily to the long-term durability of the mechanical prosthesis with no concerns about structural valve degeneration or the need for repeat surgery. The only exception to this rule is the development of prosthetic valve infective endocarditis, especially with the virulent staphylococcal infections. Under these circumstances, annular abscess formation can lead to perivalvular leak and the need for premature repeat valve replacement.
Tissue Valves (Bioprostheses)
The first bioprosthetic valves used were antibiotic-treated aortic and pulmonary homografts removed from cadavers. The valve is used mainly in the aortic position, but can also be implanted in a subcoronary position or as a full root with reimplantation of the right and left coronary arteries. Surgically implanting homografts requires more skill, as well as more operative time. In addition, the valves are of limited availability and are not widely used. Homografts are indicated in the presence of acute infective endocarditis of the native or prosthetic aortic valve. The use of a homograft does reduce the chance of recurrence of endocarditis because of the absence of any prosthetic materials in the operating field.
The most commonly used bioprostheses are the stented porcine or pericardial valves, which are glutaraldehyde-treated tissues that are mounted on a prosthetic frame. They are usually trileaflet because they are harvested from a porcine aortic valve or constructed to be trileaflet from bovine pericardium. These valves are simple to implant. Examples of stented porcine valves include the Carpentier-Edwards valves (Edwards LifeSciences), the Medtronic Hancock and Mosaic valves, and the St. Jude Medical Biocor valve. Some of the porcine valves are stentless (Medtronic Freestyle, Edwards Prima Plus, and the St. Jude Medical stentless valve). These valves are supposed to have better hemodynamics than the stented counterparts but are more difficult and time-consuming to implant.
Since Prof. Alain Carpentier (Hopital Europeen Georges Pompidou, Paris, France) introduced the porcine Carpentier-Edwards valve some 30 years ago, its use has been on the increase. The design of the porcine valve prosthesis has changed over the years, including changes in the frame design (plastic, steel, titanium) and in the pharmacologic treatment of the leaflets to reduce calcium buildup that is usually responsible for structural valve degeneration. The first pericardial valve (Ionescu-Shiley valve) had major design flaws that led to early structural valve degeneration and the need for early reoperation. Modifications of the pericardial valve designs have led to a much more durable prosthesis with excellent results. The Carpentier-Edwards pericardial valve series are widely used and have excellent track records.
Whereas bioprostheses do not require anticoagulation, they are not as durable as mechanical valves. On average, structural valve degeneration occurs between 10 and 15 years after implantation (depending on patient age at the time of implantation). These valves are usually used for elderly patients whose life expectancies are less than the life span of a bioprosthesis. Another indication for its use includes younger patients in whom the use of anticoagulation is contraindicated. It should be noted that with the increasing popularity of minimally invasive valve surgery, and the improved results in valve reoperations, many younger patients choose to have a bioprosthesis. Many of these patients believe that the risk of a second heart operation outweighs the risk of long-term anticoagulation and its associated lifestyle limitations.
Presentations From the American Association of Thoracic Surgeons Meeting
The Adult Cardiac Surgery Scientific Session held at the AATS meeting comprised a total of 49 presentations, 13 of which addressed heart valves. Some of these presentations are summarized below.
Management of Patients With an Aortic Root Sepsis
In one presentation, Arvind K. Agnihotri, MD (Massachusetts General Hospital, Boston),[1] discussed the management of aortic root sepsis in patients with acute infective endocarditis. The major emphasis of the discussion was on the surgical technique of aortic root replacement with a homograft. The basic principle of operating in an infected area is to remove all the infected tissues, repair any structural defects arising from this extensive debridement, and then replace the aortic root with a homograft with reimplantation of the right and left coronary arteries. This emphasizes what is already known about aortic root sepsis and the fact that in most acute infections, homografts are the treatment of choice. Not only is reconstruction of a badly infected aortic root in some cases only possible with a homograft, but long-term data suggest that recurrence of endocarditis also is markedly reduced with the use of a homograft.
Radiation-Induced Heart Disease
In this excellent presentation, Bruce W. Lytle, MD (Cleveland Clinic, Cleveland, Ohio),[2] described a constellation of changes that occur in the heart many years (usually about 20 years) after exposure to radiation therapy. Not only is the heart affected, but other radiation-related noncardiac comorbidities also exist in these patients, such as sternal necrosis, recurrent pleural effusions (occluded lymphatics), radiation tracheo-bronchitis/pneumonitis, pulmonary entrapment, and gastroesophageal reflux disease.
Actual heart changes that can occur include valvular calcification causing aortic stenosis/incompetence, mitral incompetence, and tricuspid incompetence. Coronary artery disease is also an important manifestation that may be associated with restrictive cardiomyopathy (diastolic dysfunction), pericardial constriction, and aortic calcification.
In summary, previous radiation is an extremely difficult problem, and first-time operation should be carefully planned. A mechanical prosthesis should be strongly considered to avoid repeat surgery, because that could be an extremely difficult procedure in the presence of pericardial constriction along with challenging cardiac and noncardiac changes.
Mitral Valve Repair
At the meeting, David H. Adams, MD (Mount Sinai Hospital, New York, NY),[3] discussed the surgical management of ischemic mitral regurgitation (MR), stressing the fact that the pathology of regurgitation is more of a left ventricular problem rather than a leaflet or annular problem. The ventricular remodeling that can occur in the presence of ischemic coronary artery disease can cause annular dilation and tethering of the posterior leaflet near the postero-medial commissure, resulting in asymmetric coaptation of the mitral leaflets. Etiology-specific mitral ring prosthesis is strongly advised to effectively deal with the problem. It is believed that mitral valve repair with such rings during coronary artery bypass graft surgery will allow reverse modeling of the left ventricle, reduce the risk of congestive heart failure, and improve survival.
In a long-term comparison of clinical results of mitral valvuloplasty using flexible (Medtronic Duran) and rigid (Carpentier-Edwards) rings; Byung-Chul Chang, MD (Yonsei University, Seoul, Korea),[4] presented the results of a prospective randomized study that enrolled a total of 411 patients from 1995-2005 (mean follow-up was 43.6 months). Left ventricular end-systolic diameter and left atrial size significantly decreased in both groups. There was no significant difference in survival or in the recurrence of significant MR. Predicators for recurrence of MR were large preoperative left atrial size, and residual MR at discharge.
A study from the Mayo Clinic (Rochester, Minnesota) presented by Rakesh M. Suri, MD,[5] addressed the question of whether the mitral valve should be re-repaired following a failed mitral repair. A total of 148 patients had reoperation for recurrent MR from 1970-2005. Median duration from initial repair was 1.8 years (range, 0-25 years). New valve pathology was found in 51% and failure of the mitral repair was noted in 39% of patients. The mitral valve was re-repaired in 45% and replaced in 55% of the patients. Operative mortality was the same, but long-term survival was significantly better at 5 years in the re-repair group (81% vs 96%; P = .009). Six patients in the re-repair group required a third mitral operation compared with 1 patient from the replacement group. Anterior leaflet repair was the only predictor of a third mitral operation.
Aortic Valve-Sparing Operations
The aortic valve-sparing operation is one of the hot cardiac surgery topics in recent years. This procedure is aimed at preserving normal aortic valves in the presence of aortic root aneurysms such as in patients with Marfan's syndrome or patients with normal but congenital bicuspid aortic valves, and in some cases of acute type A aortic dissections. The alternative to a valve-sparing procedure is a total root replacement with a prosthetic valve/tube graft with reimplantation of the right and left coronary arteries. In a valve-sparing operation, 2 basic techniques are used. In the remodeling technique (Yacoub's), a tube graft is fashioned to the remnant of the aortic root. In the reimplantation technique, the remnant of the aortic root is reimplanted inside a tube graft, which provides an added subannular support to prevent further dilatation of the aortic annulus. In theory, the latter procedure may prevent future annular dilatation that may cause recurrence of aortic incompetence. However, this procedure requires extensive mobilization of the aortic root. In both techniques, the right and left coronary arteries are reimplanted on the tube graft.
Alan D. Hilgenberg, MD (Massachusetts General Hospital),[6] gave an extensive presentation covering indications, the 2 different surgical techniques, and late results of aortic valve-sparing surgeries. He concluded that both techniques are extensive and complex and are associated with a low risk of surgery when performed by experienced hands. Medium-term results are favorable, with no anticoagulation and low risk of valve related mortality and morbidity. However, the main concern remains the durability of the aortic valve and the risk of reoperation. Although it appears that the reimplantation technique may be more advantageous in that respect, no randomized controlled studies to date support this conclusion.
Tirone David, MD (Toronto, Ontario, Canada), presented his group's experience with valve-sparing procedures.[7] The study group included 220 consecutive patients operated on from 1988 to 2005. Forty percent of the patients had Marfan's syndrome, 18% had type A aortic dissection, and 7% had bicuspid aortic valve. Twenty-eight percent had no aortic insufficiency (AI), 17% had mild AI, and 42% had moderate to severe AI. In 53 patients (24%), the remodeling technique was used, and in 167 (76%), the reimplantation technique was used. Follow-up was 100% complete with a mean follow-up of 5.2 ± 3.7 years (range, 0-16 years). The operative mortality rate was 1.4%. The rate of late deaths was 5.9%. Of the 217 survivors, only 13 patients had moderate to severe AI. At 10 years, freedom from moderate to severe AI was 94.5% with the reimplantation technique and 76% with the remodeling technique (P = .04); however, by multivariate analysis, the difference was no longer significant. Only 4 patients required reoperation for AI and freedom from reoperation at 10 years was 95%. Dr. David concluded that aortic valve-sparing operations provided excellent survival with low rates of valve-related complications. The reimplantation technique may result in a more stable valve function.
Valve Replacement With Prosthetic Valves
Only 2 presentations addressed heart valve replacement with a prosthesis. The first study, presented by Alan J. Bryan, MD (Bristol Royal Infirmary, Bristol, United Kingdom),[8] was a prospective randomized comparison of 2 bileaflet mechanical heart valves (St. Jude Medical vs CarboMedics valves). Between 1992 and 1996, of 485 patients were enrolled in the study and randomized to receive the St. Jude valve (n = 251) or the CarboMedics valve (n = 234). Aortic valve replacement, mitral valve replacement, and double valve replacement were performed in 288, 160, and 37 patients respectively, with equal distribution between the 2 valve groups. Median follow-up was 10 years and was 98% complete with a total of 3879 patient-years of follow-up. Dr. Bryan reported no difference in clinical outcomes between the 2 valve groups. However, he noted that there was strong evidence to suggest a difference in freedom from death/valve-related complications depending upon valve position, which favored aortic valve replacement over both mitral valve and double valve replacement. The authors believe that the strength of this study is the fact that it was prospective, randomized, well-matched, and had a complete and consistent approach to follow-up. The weakness, however, lies in the fact that the study lacks the power to detect any meaningful differences in thromboembolic rates.
The second study, presented by Buu-Khanh Lam, MD (University of Ottawa Heart Institute, Ottawa, Ontario, Canada),[9] looked at the impact of potential patient-prosthesis mismatch (PPM) on late outcomes after mitral valve replacement. PPM was defined as an indexed effective orifice area (IEOA) < 1.2 cm2/m2. The study included a total of 884 patients who received a mitral valve prosthesis between 1985 and 2005. The incidence of PPM was 13.8% and was a predictor of poor late survival and recurrenceof congestive heart failure. Residual pulmonary hypertension was associated with a small mitral valve prosthesis. The use of a bioprosthesis was associated with recurrence of congestive heart failure. The authors stress the importance of implanting a sufficiently large prosthesis in adult patients undergoing mitral valve replacement in order to optimize clinical results.
Comment
It is not surprising that new data regarding heart valve replacement prosthesis is sparse, as reflected by the fact that only 2 studies were presented at the AATS meeting on the subject. This is likely due to the fact that the introduction of new devices to clinical practice takes anywhere from 8-10 years, and it takes another 10 years to gather any meaningful data. In addition, the optimal valve remains an illusive dream. It is therefore not a coincidence that, at such a prestigious meeting, more studies would address the importance of mitral valve repairs and aortic valve-sparing procedures, namely because native valves are far superior and are associated with far better long-term outcomes.
Future directions in human valve design have to meet the criteria of increased durability without the need for anticoagulation, with comparable hemodynamics to that of native valves.
References
Agnihotri AK. Management of the patient with an aortic root sepsis. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Lytle BW. Radiation-induced heart disease. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Adams DH. Surgical management of ischemic mitral regurgitation. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Chang B-C, Youn Y-N, Ha J-W, Lim S-H, Hong Y, Chung N. Long term clinical results of mitral valvuloplasty using flexible and rigid ring: prospective and randomized study. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Suri RM, Schaff HV, Zehr KJ, et al. Recurrent mitral regurgitation following repair: should the mitral valve be re-repaired? Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Hilgenberg AD. Valve sparing aortic root replacement. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
David TE, Feindel CM, Colman J, Armstrong S, Maganti MD. Long term results of aortic valve sparing operations for aortic root aneurysm. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Bryan AJ, Rogers CA, Bayliss K, Wild J, Angelini GD. Prospective randomised comparison of Carbomedics and St Jude Medical bileaflet mechanical heart valve prostheses: 10 year follow-up. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Chan V, Lam B-K, Ruel M, et al. The impact of patient-prosthesis mismatch on late outcomes after mitral valve replacement. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Sary Aranki, MD
Introduction
Heart valve prostheses were introduced more than 40 years ago. The operation and technical details of valve replacement have been refined and perfected over the years such that it has become a standard procedure that can be reproduced and taught to residents in training.
The type of prostheses used as valve replacement devices remain far from optimal and in no way match the function of a normal native valve. The broad division of these devices into bioprosthetic and mechanical valves has long-term implications that need to be explained in detail to the patients before surgery. In brief, the durability and the potential complications as a result of the presence of prosthesis constitute what may be termed as "prosthetic valve disease."
This review will provide a brief description of available valve prostheses, as well as their advantages and disadvantages. In addition, a brief summary of selected recent presentations on this subject at the American Association of Thoracic Surgery (AATS) meeting held in Philadelphia, Pennsylvania, will be discussed.
Prosthetic Valves
The main difference between mechanical and bioprostheses can be summed up by a simple comparison: the need for life-long anticoagulation with warfarin (Coumadin) vs the need for a repeat operation. In other words, mechanical valves last forever but are associated with an inherent risk for thrombus formation and embolization (thromboembolic complications), and therefore necessitate life-long anticoagulation therapy, which is accompanied by its inherent risk of bleeding (hemorrhagic complications). This poses a great dilemma for young patients who do not want to take warfarin because an active lifestyle will likely increase the risk of injury and hemorrhage. In addition, warfarin use must be carefully monitored as measured by the INR, and noncompliant patients as well as those who live in remote areas may have only limited access to such monitoring. Under these circumstances, the risk of a repeat operation outweighs the risk of taking warfarin.
Another important factor to consider, especially with mechanical valves, is their track record as far as design malfunction is concerned. Therefore, the number of years a certain valve design has been in use without any mechanical malfunctions is of paramount importance in deciding which valve to use. The implications for such failures are huge. Not only can they put a patient's life at risk, but also the financial and litigation burdens could be enormous.
It is not surprising that the pace of progress in the introduction of new prosthetic devices into clinical practice is very slow. It takes, on average, between 8 and 10 years for a new device to be approved by the United States Food and Drug Administration (FDA), and the process is similarly long for regulatory agencies in other countries. It is not unusual for new valve devices to be subjected to clinical studies when the previous models are just approved and introduced into clinical practice.
Mechanical Valves
Forty-five years ago, the ball-and-cage valve was the first commercial mechanical valve introduced to clinical practice. It was a high-profile valve and required intense anticoagulation. The valve subsequently underwent modification with changes made in the ball structure (silastic, stainless steel). Concerns about increased thrombogenicity and the less than perfect hemodynamics led to the next generation of valves -- tilting disc valves (Bjork-Shiley, Medtronic Hall, and Omniscience valve designs). One modification to the Bjork-Shiley valve, in which it was reshaped to form a convexo-concave valve, faced a serious problem with strut fractures and led to a significant decline in the use of these valves.
Constituting the third generation of mechanical valves, the bileaflet valve was first introduced into clinical practice in 1977 by St. Jude Medical (Minneapolis, Minnesota) and is in widespread use today. The device is a low-profile valve that has excellent hemodynamics, requires less intense anticoagulation, and has had no reported structural failures. Other bileaflet valves approved by the FDA are manufactured by CarboMedics, Inc. (Austin, Texas), ATS Medical, Inc. (Minneapolis, Minnesota), Baxter Edwards CVS (Irvine, California), Sorin Biomedica (Saluggia, Italy), Medtronic (Minneapolis, Minnesota), and Medical Carbon Research Institute (Austin, Texas).
Candidates for mechanical valves are usually young patients who have no contraindications to warfarin therapy. Women of childbearing age who want to have children should not take warfarin because of its association with congenital defects. Patients with any bleeding tendencies or those likely to be exposed to repeated injuries should also avoid taking the drug. The rationale for using a mechanical valve in younger patients is related primarily to the long-term durability of the mechanical prosthesis with no concerns about structural valve degeneration or the need for repeat surgery. The only exception to this rule is the development of prosthetic valve infective endocarditis, especially with the virulent staphylococcal infections. Under these circumstances, annular abscess formation can lead to perivalvular leak and the need for premature repeat valve replacement.
Tissue Valves (Bioprostheses)
The first bioprosthetic valves used were antibiotic-treated aortic and pulmonary homografts removed from cadavers. The valve is used mainly in the aortic position, but can also be implanted in a subcoronary position or as a full root with reimplantation of the right and left coronary arteries. Surgically implanting homografts requires more skill, as well as more operative time. In addition, the valves are of limited availability and are not widely used. Homografts are indicated in the presence of acute infective endocarditis of the native or prosthetic aortic valve. The use of a homograft does reduce the chance of recurrence of endocarditis because of the absence of any prosthetic materials in the operating field.
The most commonly used bioprostheses are the stented porcine or pericardial valves, which are glutaraldehyde-treated tissues that are mounted on a prosthetic frame. They are usually trileaflet because they are harvested from a porcine aortic valve or constructed to be trileaflet from bovine pericardium. These valves are simple to implant. Examples of stented porcine valves include the Carpentier-Edwards valves (Edwards LifeSciences), the Medtronic Hancock and Mosaic valves, and the St. Jude Medical Biocor valve. Some of the porcine valves are stentless (Medtronic Freestyle, Edwards Prima Plus, and the St. Jude Medical stentless valve). These valves are supposed to have better hemodynamics than the stented counterparts but are more difficult and time-consuming to implant.
Since Prof. Alain Carpentier (Hopital Europeen Georges Pompidou, Paris, France) introduced the porcine Carpentier-Edwards valve some 30 years ago, its use has been on the increase. The design of the porcine valve prosthesis has changed over the years, including changes in the frame design (plastic, steel, titanium) and in the pharmacologic treatment of the leaflets to reduce calcium buildup that is usually responsible for structural valve degeneration. The first pericardial valve (Ionescu-Shiley valve) had major design flaws that led to early structural valve degeneration and the need for early reoperation. Modifications of the pericardial valve designs have led to a much more durable prosthesis with excellent results. The Carpentier-Edwards pericardial valve series are widely used and have excellent track records.
Whereas bioprostheses do not require anticoagulation, they are not as durable as mechanical valves. On average, structural valve degeneration occurs between 10 and 15 years after implantation (depending on patient age at the time of implantation). These valves are usually used for elderly patients whose life expectancies are less than the life span of a bioprosthesis. Another indication for its use includes younger patients in whom the use of anticoagulation is contraindicated. It should be noted that with the increasing popularity of minimally invasive valve surgery, and the improved results in valve reoperations, many younger patients choose to have a bioprosthesis. Many of these patients believe that the risk of a second heart operation outweighs the risk of long-term anticoagulation and its associated lifestyle limitations.
Presentations From the American Association of Thoracic Surgeons Meeting
The Adult Cardiac Surgery Scientific Session held at the AATS meeting comprised a total of 49 presentations, 13 of which addressed heart valves. Some of these presentations are summarized below.
Management of Patients With an Aortic Root Sepsis
In one presentation, Arvind K. Agnihotri, MD (Massachusetts General Hospital, Boston),[1] discussed the management of aortic root sepsis in patients with acute infective endocarditis. The major emphasis of the discussion was on the surgical technique of aortic root replacement with a homograft. The basic principle of operating in an infected area is to remove all the infected tissues, repair any structural defects arising from this extensive debridement, and then replace the aortic root with a homograft with reimplantation of the right and left coronary arteries. This emphasizes what is already known about aortic root sepsis and the fact that in most acute infections, homografts are the treatment of choice. Not only is reconstruction of a badly infected aortic root in some cases only possible with a homograft, but long-term data suggest that recurrence of endocarditis also is markedly reduced with the use of a homograft.
Radiation-Induced Heart Disease
In this excellent presentation, Bruce W. Lytle, MD (Cleveland Clinic, Cleveland, Ohio),[2] described a constellation of changes that occur in the heart many years (usually about 20 years) after exposure to radiation therapy. Not only is the heart affected, but other radiation-related noncardiac comorbidities also exist in these patients, such as sternal necrosis, recurrent pleural effusions (occluded lymphatics), radiation tracheo-bronchitis/pneumonitis, pulmonary entrapment, and gastroesophageal reflux disease.
Actual heart changes that can occur include valvular calcification causing aortic stenosis/incompetence, mitral incompetence, and tricuspid incompetence. Coronary artery disease is also an important manifestation that may be associated with restrictive cardiomyopathy (diastolic dysfunction), pericardial constriction, and aortic calcification.
In summary, previous radiation is an extremely difficult problem, and first-time operation should be carefully planned. A mechanical prosthesis should be strongly considered to avoid repeat surgery, because that could be an extremely difficult procedure in the presence of pericardial constriction along with challenging cardiac and noncardiac changes.
Mitral Valve Repair
At the meeting, David H. Adams, MD (Mount Sinai Hospital, New York, NY),[3] discussed the surgical management of ischemic mitral regurgitation (MR), stressing the fact that the pathology of regurgitation is more of a left ventricular problem rather than a leaflet or annular problem. The ventricular remodeling that can occur in the presence of ischemic coronary artery disease can cause annular dilation and tethering of the posterior leaflet near the postero-medial commissure, resulting in asymmetric coaptation of the mitral leaflets. Etiology-specific mitral ring prosthesis is strongly advised to effectively deal with the problem. It is believed that mitral valve repair with such rings during coronary artery bypass graft surgery will allow reverse modeling of the left ventricle, reduce the risk of congestive heart failure, and improve survival.
In a long-term comparison of clinical results of mitral valvuloplasty using flexible (Medtronic Duran) and rigid (Carpentier-Edwards) rings; Byung-Chul Chang, MD (Yonsei University, Seoul, Korea),[4] presented the results of a prospective randomized study that enrolled a total of 411 patients from 1995-2005 (mean follow-up was 43.6 months). Left ventricular end-systolic diameter and left atrial size significantly decreased in both groups. There was no significant difference in survival or in the recurrence of significant MR. Predicators for recurrence of MR were large preoperative left atrial size, and residual MR at discharge.
A study from the Mayo Clinic (Rochester, Minnesota) presented by Rakesh M. Suri, MD,[5] addressed the question of whether the mitral valve should be re-repaired following a failed mitral repair. A total of 148 patients had reoperation for recurrent MR from 1970-2005. Median duration from initial repair was 1.8 years (range, 0-25 years). New valve pathology was found in 51% and failure of the mitral repair was noted in 39% of patients. The mitral valve was re-repaired in 45% and replaced in 55% of the patients. Operative mortality was the same, but long-term survival was significantly better at 5 years in the re-repair group (81% vs 96%; P = .009). Six patients in the re-repair group required a third mitral operation compared with 1 patient from the replacement group. Anterior leaflet repair was the only predictor of a third mitral operation.
Aortic Valve-Sparing Operations
The aortic valve-sparing operation is one of the hot cardiac surgery topics in recent years. This procedure is aimed at preserving normal aortic valves in the presence of aortic root aneurysms such as in patients with Marfan's syndrome or patients with normal but congenital bicuspid aortic valves, and in some cases of acute type A aortic dissections. The alternative to a valve-sparing procedure is a total root replacement with a prosthetic valve/tube graft with reimplantation of the right and left coronary arteries. In a valve-sparing operation, 2 basic techniques are used. In the remodeling technique (Yacoub's), a tube graft is fashioned to the remnant of the aortic root. In the reimplantation technique, the remnant of the aortic root is reimplanted inside a tube graft, which provides an added subannular support to prevent further dilatation of the aortic annulus. In theory, the latter procedure may prevent future annular dilatation that may cause recurrence of aortic incompetence. However, this procedure requires extensive mobilization of the aortic root. In both techniques, the right and left coronary arteries are reimplanted on the tube graft.
Alan D. Hilgenberg, MD (Massachusetts General Hospital),[6] gave an extensive presentation covering indications, the 2 different surgical techniques, and late results of aortic valve-sparing surgeries. He concluded that both techniques are extensive and complex and are associated with a low risk of surgery when performed by experienced hands. Medium-term results are favorable, with no anticoagulation and low risk of valve related mortality and morbidity. However, the main concern remains the durability of the aortic valve and the risk of reoperation. Although it appears that the reimplantation technique may be more advantageous in that respect, no randomized controlled studies to date support this conclusion.
Tirone David, MD (Toronto, Ontario, Canada), presented his group's experience with valve-sparing procedures.[7] The study group included 220 consecutive patients operated on from 1988 to 2005. Forty percent of the patients had Marfan's syndrome, 18% had type A aortic dissection, and 7% had bicuspid aortic valve. Twenty-eight percent had no aortic insufficiency (AI), 17% had mild AI, and 42% had moderate to severe AI. In 53 patients (24%), the remodeling technique was used, and in 167 (76%), the reimplantation technique was used. Follow-up was 100% complete with a mean follow-up of 5.2 ± 3.7 years (range, 0-16 years). The operative mortality rate was 1.4%. The rate of late deaths was 5.9%. Of the 217 survivors, only 13 patients had moderate to severe AI. At 10 years, freedom from moderate to severe AI was 94.5% with the reimplantation technique and 76% with the remodeling technique (P = .04); however, by multivariate analysis, the difference was no longer significant. Only 4 patients required reoperation for AI and freedom from reoperation at 10 years was 95%. Dr. David concluded that aortic valve-sparing operations provided excellent survival with low rates of valve-related complications. The reimplantation technique may result in a more stable valve function.
Valve Replacement With Prosthetic Valves
Only 2 presentations addressed heart valve replacement with a prosthesis. The first study, presented by Alan J. Bryan, MD (Bristol Royal Infirmary, Bristol, United Kingdom),[8] was a prospective randomized comparison of 2 bileaflet mechanical heart valves (St. Jude Medical vs CarboMedics valves). Between 1992 and 1996, of 485 patients were enrolled in the study and randomized to receive the St. Jude valve (n = 251) or the CarboMedics valve (n = 234). Aortic valve replacement, mitral valve replacement, and double valve replacement were performed in 288, 160, and 37 patients respectively, with equal distribution between the 2 valve groups. Median follow-up was 10 years and was 98% complete with a total of 3879 patient-years of follow-up. Dr. Bryan reported no difference in clinical outcomes between the 2 valve groups. However, he noted that there was strong evidence to suggest a difference in freedom from death/valve-related complications depending upon valve position, which favored aortic valve replacement over both mitral valve and double valve replacement. The authors believe that the strength of this study is the fact that it was prospective, randomized, well-matched, and had a complete and consistent approach to follow-up. The weakness, however, lies in the fact that the study lacks the power to detect any meaningful differences in thromboembolic rates.
The second study, presented by Buu-Khanh Lam, MD (University of Ottawa Heart Institute, Ottawa, Ontario, Canada),[9] looked at the impact of potential patient-prosthesis mismatch (PPM) on late outcomes after mitral valve replacement. PPM was defined as an indexed effective orifice area (IEOA) < 1.2 cm2/m2. The study included a total of 884 patients who received a mitral valve prosthesis between 1985 and 2005. The incidence of PPM was 13.8% and was a predictor of poor late survival and recurrenceof congestive heart failure. Residual pulmonary hypertension was associated with a small mitral valve prosthesis. The use of a bioprosthesis was associated with recurrence of congestive heart failure. The authors stress the importance of implanting a sufficiently large prosthesis in adult patients undergoing mitral valve replacement in order to optimize clinical results.
Comment
It is not surprising that new data regarding heart valve replacement prosthesis is sparse, as reflected by the fact that only 2 studies were presented at the AATS meeting on the subject. This is likely due to the fact that the introduction of new devices to clinical practice takes anywhere from 8-10 years, and it takes another 10 years to gather any meaningful data. In addition, the optimal valve remains an illusive dream. It is therefore not a coincidence that, at such a prestigious meeting, more studies would address the importance of mitral valve repairs and aortic valve-sparing procedures, namely because native valves are far superior and are associated with far better long-term outcomes.
Future directions in human valve design have to meet the criteria of increased durability without the need for anticoagulation, with comparable hemodynamics to that of native valves.
References
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Lytle BW. Radiation-induced heart disease. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Adams DH. Surgical management of ischemic mitral regurgitation. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Chang B-C, Youn Y-N, Ha J-W, Lim S-H, Hong Y, Chung N. Long term clinical results of mitral valvuloplasty using flexible and rigid ring: prospective and randomized study. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Suri RM, Schaff HV, Zehr KJ, et al. Recurrent mitral regurgitation following repair: should the mitral valve be re-repaired? Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Hilgenberg AD. Valve sparing aortic root replacement. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
David TE, Feindel CM, Colman J, Armstrong S, Maganti MD. Long term results of aortic valve sparing operations for aortic root aneurysm. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Bryan AJ, Rogers CA, Bayliss K, Wild J, Angelini GD. Prospective randomised comparison of Carbomedics and St Jude Medical bileaflet mechanical heart valve prostheses: 10 year follow-up. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
Chan V, Lam B-K, Ruel M, et al. The impact of patient-prosthesis mismatch on late outcomes after mitral valve replacement. Program and abstracts from the 86th Annual Meeting of the American Association for Thoracic Surgery, April 29 - May 3, 2006, Philadelphia, Pennsylvania.
