Volume 11, Issue 3 , Pages 200-206, Autumn 2006
Technique of Mechanical Pulmonary Valve Replacement
Article Outline
The vast majority of patients, especially children, who require pulmonary valve replacement (PVR), obtain a tissue valve because of the relative good durability and the lack of a need for anticoagulation. Since the need for repeat operation is inevitable, and the population of adults with congenital heart disease continues to grow, there are increasing situations in which a mechanical pulmonary prosthesis may be appropriate. Most patients being considered for mechanical PVR have a congenital cardiac diagnosis and have undergone one or more previous operations. In many situations, the patient may have had numerous prior cardiac operations. The ideal patient for mechanical PVR is one who requires anticoagulation for another reason, eg, left-sided mechanical valve, or a patient who has had numerous prior operations. Although the technique described in this review is for mechanical valve replacement, the principles and steps outlined are identical for bioprosthetic valve replacement.
At the time of PVR, associated defects, which are commonly present, are also repaired. This most commonly includes tricuspid valve repair, patch angioplasty of proximal pulmonary artery stenoses, and closure of any intracardiac shunts. Preoperative transthoracic echocardiography is performed routinely. Computed tomography (CT) angiography or magnetic resonance imaging is performed selectively; it is helpful in determining the relationship of the aorta, pulmonary artery, or extracardiac conduit to the sternum, and in assessing pulmonary artery anatomy. Coronary angiography or CT angiography is often performed to identify coronary distribution since extensive scar tissue can obscure coronary artery visualization during operation. In addition, it is important to identify any obstructive coronary lesions preoperatively so that they may also be addressed at the time of operation. Intraoperative transesophageal echocardiography is performed routinely, and direct pressure measurements of the cardiac chambers, aorta, and pulmonary artery are obtained before cardiopulmonary bypass.
Sternal reentry can be challenging, especially in the presence of right-sided pathologic changes (eg, pulmonary hypertension or enlarged right heart structures). Repeat sternotomy is performed with special care because an enlarged ascending aorta, the conduit and valve ring, or calcified homograft often can be adherent to the sternum or can be eroded into it. Central cannulation is preferred whenever possible, but femoral artery and vein cannulation may be required to establish cardiopulmonary bypass before or during resternotomy. After resternotomy has been safely completed, sufficient dissection is performed to allow central cannulation. The conduit is identified, but usually not dissected free. When feasible, direct pressure measurements in the cardiac chambers, conduit, and distal pulmonary arteries are obtained. We prefer aortic and right atrial cannulation with normothermia or mild hypothermia without aortic occlusion in the absence of atrial or ventricular septal defects. Bicaval cannulation is performed when additional intracardiac repair is required. Aortic occlusion is used for additional procedures that would require cardioplegic arrest (eg, repair of atrial septal defect, ventricular septal defect, aortic valve replacement, etc). Intracardiac procedures are performed first and PVR is performed at the end. We often use a short period of aortic clamping with cardioplegia for the removal of heavily scarred or calcified pulmonary (usually right) ventricular outflow tract (RVOT) patches or excision of prior pulmonary prostheses/conduits to minimize injury to the closely adjacent left main and anterior descending coronary arteries.
The decision to proceed with peripheral cannulation is dependent on the experience of the operating surgeon and by the assessment of the individual patient’s risk. Groin cannulation is most commonly used because of the ability to establish complete cardiopulmonary bypass. If arterial cannulation is desired, axillary artery cannulation is also an option. If it is necessary to initiate cardiopulmonary bypass before, or during sternal reentry, it is important to maintain a positive central venous pressure (>5 mm Hg) to avoid airlocks in the venous return line, but more importantly to avoid the disastrous complication of air embolism, which can occur if there is inadvertent entry into the right heart in the presence of an intracardiac shunt.
Operative Technique
Isolated PVR
Figure 1.
The native pulmonary artery, which is often dilated, is opened longitudinally through the previous patch (middle dotted line) and stay sutures are placed on each side (not shown). The incision is extended proximally into the high RVOT. The incision is confined to the previously placed patch and rarely is it necessary to extend it into the right ventricular muscle. In cases of significant main pulmonary artery dilation, the proximal extent of the incision is confined to the proximal main pulmonary artery and an incision in the RVOT is avoided. Removal of the prior patch is outlined by the lateral dotted lines. LAD = left anterior descending coronary artery; LV = left ventricle; RCA = right coronary artery; RV = right ventricle; RVOT = right ventricular outflow tract.
Figure 2.
After patch removal, the attenuated, dysplastic pulmonary valve cusps (arrow) are visualized, examined, and excised. Any additional dysplastic or calcified tissue, or foreign body material, is carefully debrided. At this juncture, the branch pulmonary arteries are probed with dilators to insure that any proximal stenoses are identified. If a proximal stenosis is present, then the distal pulmonary artery incision is extended into the stenotic pulmonary artery.
Figure 3.
A bileaflet mechanical prosthesis is selected and the size is determined based on the size of the aortic annulus. When significant right ventricular dysfunction is present, the valve is increased one size to minimize the gradient across the prosthesis (average size for an adult is 23 or 25 mm). If a bioprosthetic (porcine or pericardial) valve were being used, we would upsize even more to minimize any residual gradient across the RVOT (average size is 27 or 29 mm). The level of implantation is usually just proximal to the native pulmonary annulus to avoid any compression of the left main coronary artery. We arrange the discs in a vertical orientation as shown. Mattress sutures backed with felt pledgets are utilized posteriorly. Suture placement medially, adjacent to the aorta, must be performed with extra care since this area can be quite thin, making needle penetration of the aorta more likely. It is critical to ensure that any extraneous tissue, calcification, pledgets, etc, are carefully removed in the area adjacent to the sewing ring of the valve (proximally and distally) to ensure there is no compromise of disc motion. MPA = main pulmonary artery; RVOT = right ventricular outflow tract.
Figure 4.
The closure of the pulmonary artery is routinely performed with glutaraldehyde-preserved bovine pericardium. The exposed anterior sewing ring of the prosthesis is approximated to the pericardial patch with continuous monofilament suture. At this time, the discs are inspected one final time to insure completely normal disc motion. When the incision extends into the right ventricle, care is taken with the lateral suture line since it may be close to the poorly visualized left anterior descending coronary artery.
Bypass is discontinued and air is aspirated from the right ventricle and pulmonary artery. Post bypass transesophageal echo is performed, and measurement of right ventricle and pulmonary artery pressures are obtained.
Operative Technique
PVR for Conduit Failure
Figure 5.
After previous placement of a porcine-valved Dacron conduit from the pulmonary ventricle to the pulmonary artery, it is important to note that the left main coronary artery is immediately posterior to the midportion of the conduit, and the left anterior descending coronary artery is close to the lateral aspect of the conduit. The conduit is usually leftward of the midline sternotomy with the diagnosis of tetralogy of Fallot or pulmonary atresia. The conduit is often directly posterior to the sternum with the diagnosis of truncus arteriosus or transposition of the great arteries (TGA).
Figure 6.
After cardiopulmonary bypass is established, an initial longitudinal incision is made over the anterior aspect of the obstructed conduit (not shown in this picture). The conduit is then detached distally over the RVOT (shown), and the conduit is dissected free from the external fibrous peel and excised. The sides and floor of the conduit bed are preserved. Calcified homografts are managed by an endarterectomy technique that leaves the adventitia of the homograft and adjacent fibrous tissue as the floor of the new reconstruction. It is important to know the location of any coronary arteries that course posterior to the conduit to avoid injury during removal of the obstructed conduit. The left main coronary artery is often at risk. The LAD can also be in close proximity to the left lateral aspect of the conduit bed. If any resistance to conduit removal is encountered in an area close to the left main coronary artery or LAD, a small piece of conduit material is left behind to avoid injury to the coronary artery. In addition to potential injury to a major coronary artery during conduit removal, the artery can be compressed by an inappropriately placed valve or can be distorted or obstructed by sutures used for valve placement or roof reconstruction. The right and left pulmonary arteries are then measured with probes and distal suture line stenoses are relieved. The RVOT is examined and any fibrous muscular outlet obstruction is resected and any calcific, dysplastic tissue is carefully debrided. LAD = left anterior descending coronary artery; RVOT = right ventricular outflow tract.
Figure 7.
Glutaraldehyde-preserved bovine pericardium is utilized for construction of the roof of the new conduit. The distal suture line and the shape of the patch are altered as necessary to provide relief of any proximal right or left pulmonary artery stenoses. The suture line is restricted to the fibrous peel at the edge of the conduit bed to avoid injury to the adjacent, obscured coronary arteries. Insertion of a bioprosthetic valve is routine and mechanical valves are used selectively. The valve is generally positioned to minimize compression by the sternum. In patients with TGA, truncus arteriosus, and congenitally corrected TGA, this is usually close to the distal anastomosis (inset). In patients with pulmonary atresia and tetralogy of Fallot, the prothesis is usually placed just proximal to the level of the pulmonary annulus in the pulmonary ventricular outflow tract. The valve is usually secured with mattress sutures that are buttressed with pledgets posteriorly and laterally in the conduit bed. The sewing ring is attached anteriorly to the pericardial roof with continuous monofilament suture. It is important to emphasize that removal of all extraneous tissue in the area of the valve position be thoroughly accomplished so that disc motion is not compromised in any way. The reconstruction is completed by sewing a proximal pericardial patch to the RVOT.
After rewarming and discontinuation of cardiopulmonary bypass, pressures are routinely measured in the pulmonary ventricle and the distal pulmonary artery. Assessment is performed by intraoperative transesophageal echocardiography. Occasionally, resection of overlying sternal bone and costal cartilage is required to prevent compression of the reconstruction at the time of sternal closure.
Technique of PVR for Conduit Failure
Our operation of choice for malfunctioning pulmonary ventricle to pulmonary artery conduits has evolved into an autologous tissue reconstruction in which a pericardial roof is placed over the fibrous bed of the explanted conduit.1, 2
Conclusions
At the Mayo Clinic, we have performed 2265 pulmonary valve replacements since 1965. These have included a bioprosthesis in 1540 patients, a homograft in 697, and a mechanical valve in 28 (1.2%). Historical concern regarding the placement of a mechanical valve in the pulmonary position is based on old literature, which documented a high rate of valve thrombosis. This was observed, however, in patients who received inadequate anticoagulation, or none at all.3, 4, 5, 6, 7 More recently, low rates of mechanical pulmonary valve thrombosis have been reported with adequate warfarin anticoagulation.8, 9, 10 In our practice, we recommend lifelong anticoagulation with warfarin (target INR 3.0), and low-dose aspirin (81 mg). With follow-up extending up to 25 years (median 8.5 years), we have observed no perivalvular leaks, endocarditis, or pannus formation. Importantly, there have been no known valve thromboses noted to date.
With the advent of patient self-testing for INR and a new generation of direct thrombin inhibitors, the risks of long-term anticoagulation as well as the risk of thromboembolism are expected to decrease significantly.11
The need for a mechanical pulmonary valve replacement is infrequent. We consider the use of a mechanical pulmonary prosthesis in carefully selected adult patients. The appropriate patient is one who requires anticoagulation for another reason (eg, left-sided mechanical prosthesis), one who has undergone multiple prior operations, or a patient that has demonstrated accelerated degeneration of prior tissue prostheses.
References
- Late results of the peel operation for replacement of failing extracardiac conduits. Ann Thorac Surg. 2004;77(3):881–887
- Late follow-up of 1095 patients undergoing operation for complex congenital heart disease utilizing pulmonary ventricle to pulmonary artery conduits. Ann Thorac Surg. 2003;75(2):399–410
- Experience with St. Jude Medical valve prosthesis in children: a word of caution regarding right-sided placement. J Thorac Cardiovasc Surg. 1987;93:73–79
- In vitro closing behavior of the St. Jude Medical heart valve in the pulmonary position: valve incompetence originating from the prosthesis itself. J Thorac Cardiovasc Surg. 1992;104:779–785
- Successful thrombolysis after prosthetic pulmonary valve obstruction under aspirin monotherapy. Ann Thorac Surg. 1997;64:255–258
- . St. Jude Medical valve in pulmonary position: anticoagulation and thrombosis. Asian Cardiovasc Thorac Ann. 2002;10:181–183
- Cardiac valve prostheses in children without anticoagulation. J Thorac Cardiovasc Surg. 1984;87:832–835
- Mechanical valves in the pulmonary position: a reappraisal. J Thorac Cardiovasc Surg. 1998;115(5):1074–1079
- Comparative study between St. Jude Medical and bioprosthetic valves in the right side of the heart. Jpn Circ J. 1991;55:553–562
- Is there a role for mechanical valved conduits in the pulmonary position?. Ann Thorac Surg. 2005;79(5):1662–1667
- . ESCAT early self controlled anticoagulation trial. Ann Thorac Surg. 2001;72:44–48
Presented as part of the Controversies in Cardiothoracic Surgery Session of the 86th Annual Meeting of the American Association for Thoracic Surgery, Philadelphia, Pennsylvania, April 29–May 3, 2006.
PII: S1522-2942(06)00082-1
doi:10.1053/j.optechstcvs.2006.05.003
© 2006 Elsevier Inc. All rights reserved.
Volume 11, Issue 3 , Pages 200-206, Autumn 2006
