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Ann Thorac Surg 1999;68:2243-2247
© 1999 The Society of Thoracic Surgeons
a Division of Cardiac Surgery, Brigham and Women’s Hospital, Boston, Massachusetts, USA
Address reprint requests to Dr Byrne, Division of Cardiac Surgery, Brigham and Women’s Hospital, 75 Francis St, Boston, MA 02115
e-mail: jgbyrne{at}bics.bwh.harvard.edu
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Abstract |
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Methods. Between February 1987 and October 1998, we performed 59 consecutive mitral valve operations after previous coronary artery bypass grafting surgery (CABG). A total of 24 patients (41%) had functioning internal mammary artery (IMA) grafts and represent the population for this study. No patients were excluded for any reason. Of the 24 patients, 20 (83%) were men. Mean age was 66 ± 13 years (range 41 to 83 years) and the mean duration from CABG was 5.3 ± 3.6 years (range 0.1 to 12 years). Four (17%) had functioning bilateral internal mammary artery grafts. All had 3 to 4+ mitral regurgitation (MR) at the time of mitral valve surgery and the mean preoperative ejection fraction (EF) was 40% ± 14% (range 20% to 74 %).
Results. Twenty-one (88%) patients underwent mitral valve surgery through an anterolateral right thoracotomy and 3 (12%) through a redo sternotomy. Twenty-two (92%) patients, including the 3 patients in whom a redo sternotomy was used, had cannulation of the femoral artery and vein. Two patients required axillary artery cannulation. All 21 patients in whom the mitral valve was approached through a right thoracotomy underwent deep hypothermia (19.6° ± 2.1°C, range 14° to 25°C) without aortic clamping, with a mean duration of CPB of 138 ± 46 minutes (range 65 to 249 minutes). In 18 (75%), the MR was ischemic in origin and in 6 (25%) there was myxomatous degeneration. Nine (34%) required valve replacement and 15 (66%) underwent repair. There were no operative or hospital deaths and all patients were discharged to home or to a rehabilitation facility. There were 4 (17%) major complications. Two patients suffered respiratory failure requiring tracheotomy, 1 patient developed a perioperative MI requiring an intraaortic balloon pump and 1 developed heart block requiring a permanent pacemaker. There were no neurologic, peripheral vascular, bleeding, or wound complications.
Conclusions. Reoperative mitral valve surgery in the setting of functioning IMA grafts, even in the face of depressed LV function, can be done safely and with minimal morbidity.
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Material and methods |
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Operative approach
Reoperation mitral valve surgery can be approached through either a redo sternotomy, an anterolateral right thoracotomy, or left thoracotomy. The redo sternotomy approach is well established but is not preferred unless coronary revascularization or aortic valve replacement is also necessary and the left thoracotomy approach is rarely used today. Our right thoracotomy approach [3–4], on the other hand, involves several subtle but important details which deserve elaboration in this setting.
Setup
The patient is positioned for a right anterolateral thoracotomy of approximately 10 cm through the fourth intercostal space. The fourth rib is disarticulated anteriorally. An external defibrillator (R2 Stat Padz, Zoll, Inc, Burlington, MA) is placed on the patient prior to draping for subsequent defibrillation, as necessary. A double lumen endotracheal tube is used to decompress the right lung.
Cannulation
Right femorofemoral cardiopulmonary bypass is used when feasible. If the right femoral artery is not suitable for any reason, then the left femoral artery or either axillary artery [10] and a femoral vein or intrathoracic venous cannulation is used. The femoral artery may not be suitable because of (1) iliofemoral peripheral vascular disease, (2) descending thoracic aortic disease, as documented by transesophageal echocardiography (TEE), which precludes safe retrograde femoral perfusion because of the risk of retrograde cerebral atheroembolism, or (3) because of an indwelling IAPB or an arterial line. However, the axillary artery is almost always free of disease [10]. Another option is direct ascending aortic cannulation. We have some early experience with the Heartport (Heartport, Redwood City, CA) endodirect ascending aortic cannulae for this purpose.
Mediastinal dissection
The interatrial groove or right superior pulmonary vein is dissected for venting of the left ventricle (LV) prior to systemic cooling on cardiopulmonary bypass (CPB). Dissection of the right atrium (RA) should be limited to that which is required to safely perform the valve surgery and placement of the SVC cannulae. Care should be exercised to avoid dissection in the region of the right phrenic nerve and right-sided CABGs. We prefer to not dissect either cavae unless a transseptal approach is needed.
Conduct of cardiopulmonary bypass
On CPB, the patient is cooled to 20°C and placed into the Trendelenburg position. No attempts to limit IMA flow are performed. Once the heart undergoes fibrillation, the left atrium (LA) is opened and vented and complete systemic cooling achieved. Routine use of deep hypothermia (about 20°C) and LV venting ensures adequate myocardial protection in the setting of functioning IMA grafts. Low CPB flows (about 1 L/min) may be necessary to ensure adequate exposure of the mitral valve and these are well tolerated at 20°C. Avoidance of aortic clamping and cardioplegia minimizes aortic manipulation and the potential for injury to CABG grafts.
Choice of mitral valve operation
While cooling and after opening the LA, the mitral valve is analyzed and replacement or reparative procedures are planned. The simplest and most efficacious method to achieve mitral valve competence is the procedure of choice. Prolonged attempts to repair an extensively diseased valve should be avoided in this high-risk group of patients.
Air removal and avoidance of cerebral air embolism
We have found that air removal and avoidance of cerebral air embolism through the right thoracotomy approach may be more tedious but can be performed safely by using the following techniques. Before the LA is opened, the patient is placed in Trendelenburg and maintained in that position throughout the valve surgery and until all the air is evacuated as documented by TEE. During rewarming, on full CPB flows, and closure of the LA, air removal is performed on the heart by first placing a small vent across the mitral valve or prosthesis and then temporarily decreasing the flows on CPB and ventilating the lungs. This also helps avoid LV distention and subsequent subendocardial ischemia. Tilting the patient left side down may help expel air from the LV apex. The aortic valve may also be made incompetent by temporarily distorting the aortic annulus, allowing blood to flood the LV. Then, after the LA is closed and the heart regains a rhythm, a vent is made in the ascending aorta. If the heart does not defibrillate spontaneously, then the previously placed external defibrillator (R2 Stat Padz, Zoll, Inc) is used to obtain a rhythm. The flows on CPB are again temporarily reduced and the lungs are ventilated to expel air out the aortic vent. The patient can then be turned from side to side to help expel air. The ascending aortic vent is maintained open until the patient is separated from CPB and complete air removal is documented by TEE.
Pacing wire and external defibrillator
The temporary epicardial pacing wire should be positioned while the patient is on full CPB with the heart decompressed, because once the patient is separated from CPB and the heart is full, it is difficult to place the wires, especially with patent CABGs in the vicinity of the RV. If a temporary epicardial pacing wire cannot be placed, then a pacing Swan-Ganz catheter may be used in these circumstances. On rare occasions, if a backup temporary epicardial or pacing Swan-Ganz catheter cannot be placed, then external defibrillator/pacing pads (R2 Stat Padz, Zoll, Inc) can be placed on the patients prior to draping to provide backup external pacing.
After a rhythm is obtained and complete air removal is documented by TEE, the vent in the aorta is closed and the remainder of the closure is routine.
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Comment |
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Redo sternotomy usually requires dissection of at least the anterior and right lateral aspect of the heart and aorta for cannulation and exposure for entry into the LA, respectively. The left side of the heart may also require dissection so that it can drop down, giving better exposure of the mitral valve upon opening the LA. This requisite dissection risks injury to the right ventricular (RV) free wall, patent saphenous vein grafts (SVGs) as well as the functioning IMA grafts. Three patients in the present report were successfully approached by the redo sternotomy, but these were early in the series. Based on our recent experience, we now advocate routine use of a right thoracotomy, femorofemoral CPB, and deep hypothermia (about 20°C) with low flows (about 1 L/min). This avoids dissection in the vicinity of the functioning IMA grafts, provides adequate myocardial protection, and provides satisfactory access to the mitral valve for a wide range of reparative or replacement procedures.
The right thoracotomy approach to the mitral valve in reoperations is not new [3–9]. Berreklouw and associates [9] were among the first to report on the revival of using right thoracotomy to approach the mitral valve in reoperation. They reported on the use of a right thoracotomy to approach the mitral valve in 8 patients who had previously undergone a cardiac operation through a sternotomy. Indications for a right thoracotomy included an extremely enlarged right heart, a dilated ascending aorta, or to the presence of anteriorly placed CABG grafts.
Cohn and associates [3] reported on right thoracotomy, femorofemoral bypass, deep hypothermia, and low-flow perfusion without aortic cross-clamping or cardioplegia for re-replacement of the mitral valve in an initial series of 10 patients. The indications for this approach were previous mediastinitis, severe RV hypertension with multiple previous sternotomies, intact CABGs, or previous aortic valve replacement (AVR). There was 1 operative death, which was due to end-stage pulmonary hypertension and intractable right heart failure. Blood loss was minimal, and there was no major postoperative morbidity in the 9 surviving patients. In a brief follow-up report, including 115 patients, Cohn [4] reported that the most common indication for reoperative mitral valve surgery via right thoracotomy was previous CABG with functioning grafts, especially IMA grafts.
Tribble and associates [7], in a comparative study, reported on right thoracotomy as an alternative to redo sternotomy for replacement of the mitral valve. They compared 33 patients undergoing redo sternotomy to 10 patients undergoing right thoracotomy. Significant differences between the two groups, favoring right anterolateral thoracotomy, were apparent when comparisons were made for length of CPB, incidence of reexploration for bleeding, and blood transfusions. They concluded that the right thoracotomy is an effective alternative to redo sternotomy for replacement of the mitral valve in patients who have had a previous median sternotomy. In a follow-up report, Tribble and associates [8] suggested that the right thoracotomy may be less useful than in previous years because of the increased familiarity with redo sternotomy. However, they did note that the right thoracotomy may be particularly useful in patients in whom a functioning IMA graft is present.
Braxton and associates [5], in another comparative paper, reported that reoperative mitral valve surgery by right thoracotomy decreased blood loss and improved hemodynamics compared to redo sternotomy. Fifteen patients having reoperative mitral valve surgery by right thoracotomy approach were compared to 33 patients who underwent redo sternotomy. All thoracotomy patients underwent mitral valve surgery with ventricular fibrillation, without aortic cross-clamping. Significant findings included that the thoracotomy approach was associated with a reduction in blood loss and the amount of blood transfused. Despite decreased access to the heart for air removal maneuvers, no cerebrovascular events were noted with the thoracotomy approach. There was one death in the thoracotomy group. The investigators observed that with the increased use of IMA grafts for CABG, the avoidance of IMA grafts may emerge as a principle indication for the right thoracotomy approach to reoperative mitral valve surgery.
In review of our four major complications, the 2 patients who suffered respiratory failure had compromised lung function due to chronic obstructive pulmonary disease (COPD) and required tracheostomy to be successfully weaned from the ventilator. Preoperative pulmonary function tests may have helped in screening for this potential complication [5]. However, we believe that respiratory failure, even requiring tracheostomy but with eventual recovery, is preferable to redo sternotomy in most patients. The perioperative MI may have been due to LV distention on fibrillation and subsequent subendocardial ischemia. That patient had aortic insufficiency and, despite venting through the valve on closure of the LA, still sustained a subendocardial MI. Despite decreased access to the heart for air removal procedures, and the need for meticulous and sometime tedious air removal procedures, no cerebrovascular events occurred in our series. Another option for air removal is the use of CO2 air removal techniques [5]. By judicious use of peripheral cannulation techniques, with no hesitation to use the axillary artery when indicated, we were able to avoid peripheral vascular complications in this series. There were also no reoperations for bleeding, a result likely related to the limited mediastinal dissection used in right thoracotomy approach. Wound complications, generally associated with redo sternotomy, were avoided in this series.
Other indications for approaching the mitral valve through the right chest are (1) a previous aortic valve replacement, (2) multiple previous sternotomies, (3) previous mediastinitis, (4) recent sternotomy in which adhesions are likely dense, and (5) ascending aortic aneurysm [3–9]. There are several relative contraindications to the right thoracotomy approach to reoperative mitral valve surgery (Table 1). Severe left ventricular (LV) hypertrophy makes LV protection, by use of the hypothermic fibrillation technique, more problematic. In these situations high perfusion pressures on CPB maintained with IV phenylephrine hydrochloride, phenylephrine bitartrate or vasopressin injection, may enhance myocardial viability. The inability to safely perform TEE, for example, in patients in whom an esophageal stricture is present, is also a relative contraindication. The inability to perform TEE precludes routine use of femoral cannulation. This is because detection of descending thoracic aortic diseases is necessary prior to retrograde perfusion and subsequent risk of retrograde cerebral emboli. In these circumstances, axillary artery or ascending aortic cannulation should be considered. The inability to safely perform TEE also requires "blind" evaluation of air, which may be safe if done in a meticulous fashion. However, epicardial echocardiography may also be used to help document evacuation of intracardiac air. Moderate to severe AI is another relative contraindication to the right thoracotomy approach. All patients considered for reoperative mitral valve surgery by right thoracotomy must have preoperative screening by echocardiography, specifically looking for aortic insufficiency. If moderate AI is found, then either redo sternotomy and double-valve surgery, or the use of the Heartport (Heartport Inc, Redwood City, CA) system, should be considered. We believe that mild to moderate AI is not necessarily an absolute contraindication to mitral valve surgery by the right thoracotomy approach, as has been suggested by others [5]. If concomitant aortic valve replacement is deemed unnecessary, then care must be exercised to avoid LV distention and subsequent subendocardial ischemia on LV fibrillation. Therefore, the interatrial groove or the right superior pulmonary vein must be dissected and available for venting prior to systemic cooling on CPB. Once the heart undergoes fibrillation, the PA pressures, as documented by a Swan-Ganz catheter, are observed and, if elevated above 10 mm Hg, the LV is vented and rapid cooling achieved so that flows on CPB can be safely decreased. Upon closure of the LA, we routinely place a small vent across the valve or prosthesis to decompress the LV to avoid LV distention. Another option in the presence of moderate to severe AI, to avoid redo sternotomy, is the use of the right thoracotomy and the transfemoral or transthoracic Heartport (Heartport Inc) system for endoaortic balloon occlusion of the ascending aorta, cardioplegia delivery, and pulmonary artery venting [11]. We had inserted the Heartport (Heartport Inc) system in 1 patient in the present series but its use proved unnecessary, because the AI did not result in significant LV distention on fibrillation and the operation could proceed on fibrillatory arrest. Severe peripheral vascular disease (PVD), making femoral cannulation difficult, is another relative contraindication to the right thoracotomy approach. Axillary cannulation is almost always feasible and safe [10], and direct ascending aortic cannulation is also feasible. The inability to place PA catheter for the detection of LV distention is another relative contraindication. However, if the TEE is available, then LV distention can be detected and treated. Severe pulmonary dysfunction, as determined by the PO2/FiO2 ratio [5], is also a relative contraindication to the right thoracotomy approach. In the present series, 2 patients had severe COPD; weaning them from the ventilator required tracheostomy, but they recovered fully. Careful patient selection is needed in these circumstances. Perhaps the only absolute contraindication to the right thoracotomy approach is the "hostile" right hemithorax, a condition which can manifest in patients who have undergone right thoracic pleurodesis, multiple previous right thoracotomies, or previous right pneumonectomy. Another absolute contraindication would be a large right chest wall arterio-venous (A-V) malformation. In these situations, redo sternotomy or left thoracotomy may be the only options.
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