Historically, aortic valve surgery typically involved the placement of a mechanical valve. In the past, there were only a few generally accepted indications to use a bioprosthesis for primary, isolated aortic valve replacement: (1) the presence of well-established contraindications to continuous anticoagulation, (2) the inability to monitor prothrombin levels adequately, and (3) patients whose survival was limited and more dependent on non-valve–related issues.18,26 In recent years, however, the use of biologic valves in the aortic position has become more common.24,38
As mentioned, reoperations are technically demanding, and many patients present in a poor functional state that further increases their mortality, in some series up to 19%.32,39,40 Generally, optimal planning for reoperation prior to deterioration to NYHA class III to IV levels and before unfavorable comorbid conditions have arisen is imperative to ensure good outcomes.9 Following these guidelines in the modern era, elective re-replacement of malfunctioning aortic bioprostheses can be performed with results similar to those of the primary operation.18,23,41 The Mayo Clinic, for example, recently reviewed its experience with 162 reoperative aortic valve replacements (AVRs). Early mortality for reoperative AVR was not statistically different from that for primary AVR.42 In light of recent lower operative mortality in reoperative valve surgery, a more conservative approach toward issues such as "prophylactic" AVR in patients with asymptomatic mild to moderate aortic stenosis at the time of coronary artery bypass grafting (CABG) also may be more appropriate.43
In evaluating the reoperative patient, the presence of concomitant coronary artery disease and pulmonary hypertension has been shown consistently to be independent risk factors.18 Patients with these risk factors therefore need careful surveillance once the probability of bioprosthetic dysfunction begins increasing (ie, 6 to 10 years after implantation).16 Regarding valve surveillance and timing of reoperation, the following variables are relevant to the clinical management of patients with an aortic bioprosthesis: a history of endocarditis before the first operation, perioperative infectious complications, coronary artery disease acquired after the first operation, an increase in pulmonary artery pressure, and a decrease in left ventricular function during the interoperative interval.18 Proper timing of the reoperation therefore is paramount because duration of clinical signs with a dysfunctional aortic bioprosthesis may be misleading. This is further supported by the fact that the need for emergency reoperation is the most ominous risk factor and consistently yields a high early mortality rate of 25 to 44%.44
Approaches and Techniques
The evolution of cardiac surgery through the last few decades has led to the popularization of various surgical approaches. Thoracotomy, for example, once was used extensively to gain access to mediastinal structures. Then median sternotomy became the standard approach. In reoperative cases, however, repeating the sternotomy carries definite surgical risks. Before proceeding with a resternotomy, the relationship between certain anterior mediastinal structures (eg, the right ventricle and the aorta) and the posterior aspect of the sternum must be assessed carefully.45 This generally can be visualized on chest radiograph or more accurately with a chest computed tomographic (CT) scan. Recently, it has been shown that multidetector computed tomographic (MDCT) scanning, in combination with retrospective electrocardiographic gating, can be used as a noninvasive way to assess not only the heart's location in relation to the sternum, but also graft location and patency.46–48
Exposure of the femoral vessels and preparation for emergency femoral-femoral cardiopulmonary bypass should be considered before resternotomy. In cases of heightened concern for right ventricle–graft injury or in cases in which a left internal mammary artery (LIMA) graft is patent, the surgeon should consider the use of cardiopulmonary bypass before chest reentry. Sternal wires from the previous operation should be undone carefully but left in place as a posterior safeguard during initial sternal division. An oscillating (not reciprocating) bone saw can be used to divide the anterior sternal table. An Army-Navy retractor, placed inferiorly in-line with the sternotomy can be used to stent open the wound during opening of the posterior table. Most authors recommend dividing the posterior table using a combination of scissors and anterolateral rake retraction.45,48,49 Following this, bilateral pleural spaces should be entered inferiorly, followed by careful dissection of other mediastinal structures. The pericardial dissection plane can be developed by starting at the cardiophrenic angle and advancing slowly cephalad and laterally on the surface of the right side of the heart. Cephalad dissection should start with freeing the innominate vein before spreading the retractor to avoid its injury. Further dissection then is carried down to the superior vena cava, being careful to note the location of the right phrenic nerve. An area of consistently dense adhesions is the right atrial appendage, and caution should be used here. In addition, great care should be taken to avoid "deadventializing" the aorta. The area where the aorta apposes the pulmonary artery is another site of potential injury.
Repairing small ventricular or atrial lacerations should not be attempted before releasing the tension of the surrounding adhesions. Repair of great vessel injuries or severe right ventricle injuries is best done under cardiopulmonary bypass.45 Severe active hemorrhage during a second sternotomy usually is caused by adherence of the heart or great vessels to the posterior sternum. Prevention of this ominous complication by interposition of pericardium or other mediastinal tissue at the time of the first operation has been suggested but has debatable relevance.48 The incidence of resternotomy hemorrhage is between 2 and 6% per patient reoperation.50–52 In a report of 552 patients who had undergone reoperative prosthetic valve surgery, 23 patients (4%) had complications related directly to sternal opening.17 Of these, five patients had entry into the right atrium, seven patients had lacerated right ventricles, nine patients had injuries to the aorta, and two patients had a previously placed coronary artery graft divided. Nineteen of the 23 complications occurred during a first reoperation. Overall, there were two operative deaths related to resternotomy. The first death involved division of a previously placed coronary artery graft during reentry. The second death was caused by laceration of the aorta with subsequent exsanguination.17 Of note, prior use of a right internal mammary artery (RIMA) graft can be particularly challenging because it frequently crosses the midline, and extreme caution must be used in first dissecting out this vessel.
Macanus and colleagues reviewed their experience with 100 patients undergoing repeat median sternotomy.51 Eighty-one patients had one repeat sternotomy, whereas the others had undergone multiple sternotomies. All had had a previous valve procedure and were reoperated on for progressive rheumatic valvular disease or for complications related to the prosthesis. Complications included operative hemorrhage in eight patients, postoperative hemorrhage in two, seroma in four, and dehiscence, wound infection, and hematoma in one patient each. There was one operative death directly related to resternotomy hemorrhage.51 When major hemorrhage does occur on sternal reentry, attempts at resternotomy should be abandoned, and the chest should be reapproximated by pushing toward the midline. The patient should be heparinized immediately while obtaining femoral arterial and venous cannulation. Blood loss from the resternotomy should be aspirated with cardiotomy suction and returned to the pump. Once bypass has been established, core cooling should be commenced with anticipation of the need for circulatory arrest. Once cool, flow rates can be reduced, and the remaining sternal division can be completed, followed by direct repair of the underlying injury.48 Anticipating the possibility of this scenario, we frequently expose peripheral cannulation sites prior to beginning a resternotomy. In cases of heightened concern for right ventricle or graft injury, or in patients with a patent LIMA to left anterior descending (LAD) artery graft, cardiopulmonary bypass and cardiac decompression may be initiated before sternal reentry. After safe sternal entry, the patient may be weaned from bypass for further dissection of adhesions to avoid prolonged pump times.
Minimally Invasive Reoperative AVR
Reoperative procedures are challenging owing to diffuse mediastinal and pericardial adhesions. A large incision that increases the operative exposure also has been associated with a higher risk of injury to cardiac structures and coronary artery bypass grafts and results in greater bleeding with its associated transfusion requirements.53–56 A smaller incision with a limited sternotomy, on the other hand, reduces the area of pericardiolysis, thus mitigating these effects. The intact lower sternum that remains also preserves the integrity of the caudal chest wall, thereby enhancing sternal stability and promoting earlier extubation.57,58Minimallyinvasive valve procedures gradually have become more accepted as new technologies and instrumentation have been developed.57 Reoperative procedures in which there is risk for graft injury are an area where minimally invasive strategies may be of direct benefit.59,60 Our surgical approach in reoperative AVR is shown in Fig. 49-1.57 In our series of patients, peripheral cannulation sites were exposed or cannulated before beginning the partial upper resternotomy. An external defibrillator was placed on the patient before draping for anticipated defibrillation as necessary. Transesophageal echocardiography (TEE) was used in every patient. A partial upper resternotomy was carried out to the third or fourth intercostal space depending on the estimated position of the aortic valve as documented by chest x-ray (CXR)/TEE and then was "T'd to the right."61 The oscillating saw was used to divide the anterior sternal table, whereas the straight Mayo scissors, under direct visualization, was used to divide the posterior sternal table. In the setting of a patent LIMA-LAD graft or other anterior coronary artery bypass grafts, patients were placed on cardiopulmonary bypass before partial resternotomy. Mediastinal dissection was limited to only the ascending aorta as was necessary for clamping and aortotomy. The right atrium was dissected only if it was cannulated. Although intrathoracic cannulation was preferred, we frequently used peripheral cannulation to avoid clutter in the chest. Retrograde cardioplegia, if necessary, was delivered via a transjugular coronary sinus catheter or with right atrial placement under TEE guidance. Vacuum assistance of venous drainage was used in the majority of patients. Once on cardiopulmonary bypass, all patients were systemically cooled to 20 to 25°C. Patients with patent LIMA-LAD grafts were cooled routinely to 20°C for additional myocardial protection and in so doing avoided the need and potential hazard of dissecting out the LIMA for clamping in an attempt to avoid cardioplegia washout. If flow from the patent LIMA-LAD graft led to significant blood flow out of the coronary ostium and obscured the operative field, pump flows were turned down temporarily to allow visualization. Venting was accomplished by placing a pediatric vent through the aortic annulus. The aortic valve surgery then was performed based on patient indications. While closing the aortotomy, intracardiac air was removed by insufflating the lungs and decreasing flows on cardiopulmonary bypass. Carbon dioxide was used and flooded the operative field. Patients also were tilted from side to side to help with deairing, and the ascending aortic vent was left open until separation from cardiopulmonary bypass. Temporary epicardial pacing wires were placed on the anterior surface of the right ventricle while the heart was decompressed and before the aortic cross-clamp was removed. Two 32 French right-angled submammary chest tubes then were placed through the right pleural space, one angled medially into the mediastinum and one angled posterior into the pleural space. Decannulation and closure then were performed in the standard manner.
Partial upper resternotomy for reoperative AVR. The previous sternotomy incision is exposed to the third or fourth intercostal space depending on the position of the aortic valve, as documented by TEE. After dissection of the ascending aorta, paying particular attention to the position of coronary artery bypass grafts and their proximal anastomoses, cannulation is carried out. In this figure, the ascending aorta and innominate vein are cannulated. Frequently, however, other cannulation sites are required owing to space limitations in the chest. The ascending aorta is cross-clamped, and the aortic valve re-replacement is conducted in a standard fashion. (Used with permission from Byrne JG, Karavas AN, Adams DH, et al: Partial upper re-sternotomy for aortic valve replacement or re-replacement after previous cardiac surgery. Eur J Cardiothorac Surg 2000; 18:282.)
With our increasing experience in minimally invasive reoperative AVR, we have refined our technique as an alternative to conventional full resternotomy.57 In so doing, we have ascertained the technical details of the partial upper resternotomy approach (Table 49-2). By following these guidelines, we have yet to convert any patient to a full resternotomy. Lateral CXR and/or TEE is helpful in locating the level of the aortic valve and determining the proximity of the aorta to the posterior aspect of the sternum.61 If necessary, additional information can be obtained with CT scanning or magnetic resonance imaging (MRI) preoperatively. Also, extension of the sternal incision laterally on both sides through the intercostal spaces helps to later reapproximate the sternum. We have tried to limit mediastinal and pericardial dissection primarily to the aorta, believing that this is the principal reason for decreased bleeding and transfusion requirements postoperatively.57,60,62,63 The right ventricle, which often is attached to the sternum, does not need to be dissected. Also, injuries to patent but atherosclerotic vein grafts can be reduced with this "no touch" technique.64
Table 49-2 Thirteen Technical Details for Successful Aortic Valve Replacement after Previous Cardiac Surgery by Use of Partial Upper Resternotomy |Favorite Table|Download (.pdf)
Table 49-2 Thirteen Technical Details for Successful Aortic Valve Replacement after Previous Cardiac Surgery by Use of Partial Upper Resternotomy
|1. Routine exposure of peripheral cannulation sites prior to partial upper resternotomy|
|2. Placement of Zoll (Zoll, Inc., Burlington, MA) defibrillator pads before prepping|
|3. Use of intraoperative transesophageal echocardiography for air removal and inspection of valve|
|4. In patients with patent left internal mammary artery to left anterior descending coronary artery (LIMA-LAD) graft, peripheral cannulation, and cardiopulmonary bypass (CPB) established before partial upper resternotomy|
|5. Mediastinal dissection limited to ascending aorta for clamping and aortotomy and atrium (RA), only if RA is cannulated|
|6. Use of peripheral cannulation to avoid clutter in the chest|
|7. Use of vacuum assistance on CPB|
|8. Use of retrograde cardioplegia (CP) delivered by transjugular retrograde CP catheter in addition to antegrade CP|
|9. Use of aprotinin unless absolute contraindication|
|10. Cooling to at least 25°C in all patients primarily for myocardial protection; if a patent LIMA-LAD graft is present, cooling to 20°C without isolation and clamping LIMA graft|
|11. If visualization is poor because of LIMA-LAD collaterals flowing from coronary ostia, temporary low flows on CPB to improve visualization|
|12. Venting with a pediatric vent placed through the aortic annulus|
|13. Placement of temporary pacing wires on the right ventricular free wall before aortic clamp removal|
Arterial and venous cannulation sites can vary considerably, reflecting the individual choice of the operating surgeon and the sufficiency of intrathoracic space. Possible cannulation sites, other than standard ones, include the axillary artery, innominate vein, and percutaneous femoral vein.13,65 Innominate vein or percutaneous femoral vein cannulation, as well as the use of TEE to place the retrograde cardioplegia catheter, has been extremely helpful in minimizing dissection of the right atrium. At present, we consider this approach to be useful for isolated, elective reoperative aortic valve surgery.57
Reoperative AVR after Homograft/Root/Allograft
AVR with homografts and autografts was performed increasingly because of excellent freedom from thromboembolism, resistance to infection, and reasonable hemodynamic performance.27 Although improved durability of current tissue valves has slowed this trend, autografts and, to a lesser degree, homografts remain popular in younger patients owing to durability and, in the case of autografts, the potential for growth.30,66 Consequently, many patients will require aortic valve re-replacement for structural degeneration of their homograft or autograft valve.67 It is expected that about one third of patients younger than 40 years of age will require aortic valve re-replacement within 12 years of homograft placement. This is owing primarily to calcification and structural valve degeneration. As such, the issue of homograft or autograft durability is particularly pertinent in this subgroup of younger patients who are expected to live beyond 15 years from time of operation.66
The incidence of patients with homografts or autografts in need of a second valve operation is expected to increase owing to the aforementioned recent popularity and availability of these conduits. Also, there is varied opinion as to the optimal surgical method of primary homograft AVR, with increased rates of aortic insufficiency in patients with the subcoronary implantation technique. Importantly, the selected technique of primary homograft operation may have relevance at reoperation because calcification or aneurysmal dilatation of the homograft may pose surgical challenges at reoperation. Despite these challenges, Sundt and others29,68,69 have documented the feasibility of aortic valve re-replacement after full-root replacement with a homograft. In our own series of 18 patients, full-root, mini-root, and subcoronary techniques all were amenable to valve re-replacement.27
How to best approach the reoperative root scenario and which valve to reimplant, however, have been debated. At one extreme, Hasnet and colleagues documented the results of 144 patients who underwent a second aortic homograft replacement with a hospital mortality rate of only 3.5%.67 Although Kumar and colleagues, in a multivariate analysis of reoperative aortic valve surgery, did not show that a previous homograft added significant risk,70 the technical aspects of reoperative AVR in this patient population consistently have been found to be challenging owing to the heavy calcific degeneration that invariably occurs. With this in mind, and owing to the typical absence of the need for a second root operation, we and others71 believe that a more simplified approach to reoperative aortic valve surgery in patients with previously placed homografts may be optimal. Our approach has been to perform aortic valve re-replacement using a mechanical valve or, less commonly, a stented xenograft while reserving a second homograft and root operation for specific indications such as endocarditis, associated root pathology, or a very young patient with contraindications to a mechanical valve.
Homograft re-replacement nonetheless is performed but it is much less common, and hospital mortality varies widely across many centers, ranging between 2.5 and 50%.29,68,69 David and colleagues, for example, recently reviewed their experience with root operations in 165 patients who previously had undergone cardiac surgery. Of these, 28 had a previous root operation. Overall, 12 operative (7%) and 20 late deaths (12%) occurred.72 Variations in sample size, valve selection, surgical techniques, and patient factors, as well as the experience of the surgeons, may account for these wide differences.