Acute Type A Aortic Dissection R. Morton Bolman, III, MD Acute type A aortic dissection (Type I, proximal, ascending) is a true surgical emergency. It is estimated that patients suffering this calamity experience approximately a 1% per hour mortality in the first 48 hours and 90% of these patients will be dead by the end of 3 months without surgery. The majority of type A dissections propagate through the aortic arch and the descending and thoracoabdominal aorta. The dissection flap can be associated with malperfusion of virtually any major artery emanating from the aorta by virtue of either static or dynamic obstructive physiology. That said, however, the most common modes of death in type A dissection are the following two: (1) rupture into the pericardial space with acute tamponade or (2) compromise of the coronary circulation with resultant myocardial ischemia. Forty to 50% of cases are accompanied by significant degrees of aortic insufficiency. This is not due necessarily to any inherent abnormality in the aortic valve, but rather to dissection involving the aortic root with diastolic prolapse of one or more commissures causing the insufficiency. The symptoms and syndromes that can accompany type A aortic dissection are numerous and variable. It is of the utmost importance in this setting that the surgeon remains focused on the immediately life-threatening consequences of proximal dissection in planning the approach to the patient. Once the proximal aorta is stabilized, the risk of rupture into the pericardium and of acute compromise of one or both coronary arteries is removed. This allows a more deliberate and systematic approach to any distal malperfusion that may be present. Perioperative Procedure The patient is positioned supine and prepped and draped from the chin to the feet. It is important to include the lower extremities in the operative field in case conduit for bypassing the coronary arteries becomes necessary. Routine transesophageal echocardiography is employed for perioperative management, confirmation of the diagnosis, quantitative evaluation of aortic valve competence, and left ventricular Division of Cardiac Surgery, Brigham and Women s Hospital, Boston, Massachusetts. Address reprint requests to R. Morton Bolman, III, MD, Division of Cardiac Surgery, Brigham and Women s Hospital, 75 Francis Street, Boston, MA 02115. E-mail: rbolman@partners.org function, as well as screening for any other cardiac abnormalities. Incision The approach is via midline sternotomy with the option of extending the incision along the left sternocleidomastoid muscle on the left if necessary (Fig. 1). Cannulation for Bypass The patient can be cannulated for bypass either via the right axillary artery through an incision in the deltopectoral groove on the right (Fig. 2A) or via the femoral artery with the best pulse (Fig. 2B). We prefer to attach a 6-mm woven Dacron graft to either the axillary or the femoral artery, into which is inserted the arterial cannula or connector. Bicaval venous cannulation is preferred, and the superior vena cava is encircled with a tourniquet. A left ventricular vent is inserted through the right superior pulmonary vein and a retrograde cardioplegia catheter is positioned in the coronary sinus. Handheld cannulae should be available for direct administration of cardioplegic solution directly into the coronary ostia in the event that significant aortic insufficiency is present. In this article, we focus our attention on a typical situation in which the aortic tear occurs in the ascending aorta, the situation in 70 to 85% of cases. Conduct of the Operative Procedure With the patient on cardiopulmonary bypass and the left ventricle vented, cooling can be initiated to a depth of 16 to 20 C. Once ventricular fibrillation occurs, it is acceptable to clamp the ascending aorta proximal to the intended level of distal repair to allow assessment and reconstruction of the proximal aorta to begin during the period of systemic cooling. In the presence of the dissected ascending aorta, it is safest to open the aorta, once the clamp is placed, during a period of retrograde administration of cardioplegia. Once the coronary ostia are identified, antegrade induction doses of blood cardioplegia should be administered individually into each coronary ostium. Once the heart is cold and arrested, protection should consist of retrograde cold blood cardioplegia supplemented by intermittent antegrade doses into the coronary ostia. Myocardial protection is challenging and of the utmost importance in these cases (Fig. 3). 124 1522-2942/09/$-see front matter 2009 Elsevier Inc. All rights reserved. doi:10.1053/j.optechstcvs.2009.05.001
Acute type A aortic dissection 125 Figure 1 The patient is positioned supine and prepped and draped from the chin to the feet. The incision is a midline sternotomy, with the option of extending the incision along the left sternocleidomastoid muscle on the left, if necessary. m muscle. Proximal Aortic Reconstruction The aorta is transected at the level of the sinotubular junction. Careful assessment of the aortic root is now performed. The transesophageal echocardiogram offers the best assessment of aortic root dimension. It is important that this measurement be obtained before arresting the heart and opening the aorta, as evaluation of aortic size is very difficult in the arrested heart. In the situation where the aortic root size is determined to be normal, careful assessment of the valve anatomy and integrity is performed. If the transesophageal echocardiogram demonstrates no aortic insufficiency, and the valve appears anatomical relatively normal, proximal reconstruction is relatively straightforward. Strips of Teflon felt, approximately 1 cm in width and approximating the circumference of the aorta in length, are positioned, one inside and one outside the dissected aorta. These strips of Teflon felt are employed to sandwich the dissected walls of the aorta together. A horizontal mattress suture of 3-0 monofilament suture is used to approximate these strips, taking care to capture all layers of the aorta (Fig. 4). If one or more of the aortic commissures is dissected, leading to prolapse and aortic insufficiency, the commissure(s) can be restored to its appropriate level with a felt-reinforced monofilament suture passed through all walls of the remaining aorta (Fig. 5). The reconstruction as previously described then ensues, creating a proximal aorta to which a woven Dacron graft can be attached. Dissection can extend to the level of the coronary ostia. If the coronary artery remains intact, even in the presence
126 R.M. Bolman, III Figure 2 This figure demonstrates the cannulation for bypass. Either the axillary artery (A) or the femoral artery with the strongest pulse (B) can be cannulated. We favor attaching a 6 mm Dacron graft to the artery, and cannulating the graft for bypass, as shown. Bicaval venous cannulation is favored for venous return. A left ventricular vent is positioned via the right superior pulmonary vein (RSPV) and a retrograde cardioplegia cannula is positioned in the coronary sinus. a. artery; IVC inferior vena cava; SVC superior vena cava.
Acute type A aortic dissection 127 Figure 3 With the patient on bypass and the left ventricle vented, cooling can begin. When the heart fibrillates, the ascending aorta can be clamped at a level proximal to the intended site of distal reconstruction. This is accomplished during the delivery of retrograde cardioplegia through the coronary sinus. Once the aorta is opened, the cardioplegia is delivered directly into the coronary ostia as demonstrated. a. artery. of dissection extending down to the level of coronary artery, the method of reconstruction described above will usually suffice. If, however, the intima at the coronary ostium is disrupted, it is difficult to preserve such a coronary artery, and other methods of reconstruction will have to be employed. Distal Aortic Reconstruction by the Open Technique When the patient reaches the desired systemic temperature, attention should be directed to the distal aortic reconstruction. There will be an obligate period of at least 1
128 R.M. Bolman, III Figure 4 The delaminated proximal aortic layers are reapproximated between strips of Teflon felt using a continuous 3-0 monofilament horizontal mattress suture. a. artery.
Acute type A aortic dissection 129 Figure 5 This figure depicts the reconstructed proximal aorta. The dissected layers of the aorta have been reapproximated between layers of Teflon felt. The aortic commissures are resuspended to their normal location in the aortic root with felt-reinforced sutures. hour of rewarming. Efficient conduct of the operation requires that the distal reconstruction be completed, so that rewarming can be initiated during the completion of the proximal reconstruction. The patient is placed in steep Trendelenburg position, and the tourniquet around the superior vena cava cannula is tightened. The surgeon should have selected a woven Dacron graft for reconstruction of the ascending aorta on sizing the proximal aorta at the level of the sinotubular junction. Valve sizers can be helpful in this estimation. Care should be taken to minimize the period of deep hypothermia with circulatory arrest. This can be accomplished by becoming organized for this distal reconstruction before discontinuing cardiopulmonary bypass. When ready, the pump is turned off; the inferior vena cava cannula is clamped, and the tourniquet about the superior vena cava is tightened. Then retrograde cerebral perfusion via the superior vena cava is initiated at the level of the heart lung machine. Central venous pressure should be monitored and should not exceed 25 mm Hg. This usually allows flows of 500 to 800 ml/min. The aortic cross-clamp is removed. The aorta is inspected from within. The aorta is transected at the base of the innominate artery. If, as is usually the case, the dissection extends into the aortic arch and beyond, distal aortic reconstruction will be necessary before attaching the ascending conduit. One-centimeter Teflon felt strips cut in length to approximate the circumference of the distal aorta are placed, one inside and one outside the aorta. These are approximated with a horizontal mattress suture of 3-0 monofilament suture, taking care to capture all aortic layers (Fig. 6). This creates an excellent landing zone for the Dacron graft. The graft is then brought to the field and anastomosed to this reconstructed distal aorta using 2-0 or 3-0 running monofilament suture, again taking care to capture all layers of the reconstructed distal aorta (Fig. 7A). If the patient is cannulated via the right axillary artery, and if flows have been adequate, the retrograde cerebral perfusion can be turned off once the anastomosis has been completed. Antegrade flow is then started at a low rate of 500 ml/min to fill the ascending aorta and cerebral vessels and to remove any air. This is accomplished as a clamp is placed on the graft just proximal to the anasto-
130 R.M. Bolman, III Figure 6 When the patient reaches the desired temperature, the period of circulatory arrest is initiated with the patient in steep Trendelenburg position. The aorta is transected at the base of the innominate artery. The delaminated layers of the distal ascending aorta are reapproximated between layers of Teflon felt with a continuous 3-0 monofilament horizontal mattress suture, in a manner analogous to that employed on the proximal ascending aorta. Note that the tourniquet surrounding the superior vena cava is tightened, and the patient is receiving continuous retrograde cerebral perfusion via the superior vena cava cannula during this portion of the procedure.
Acute type A aortic dissection 131 Figure 7 (A) The previously-chosen Dacron graft is brought to the field and anastomosed endto-end to the reconstructed distal ascending aorta using 2-0 or 3-0 monofilament suture. (B) Once the distal anastomosis is completed, the ascending aorta and its branches are carefully deaired by a combination of retrograde and antegrade flushing maneuvers. The graft is clamped proximal to the anastomosis, and flow is restored to the patient s head and body via the axillary artery inflow. Systemic rewarming can now be initiated.
132 R.M. Bolman, III Figure 8 Distal reperfusion has been initiated through a side arm of the ascending graft. This can also be accomplished by direct cannulation of the ascending graft just proximal to the distal suture line. This method would be employed if the patient had previously placed on bypass with femoral artery cannulation, or if there was some concern regarding the adequacy of perfusion via the right axillary artery. Once the distal suture line has been completed, it is critical that reperfusion be initiated in an antegrade manner.
Acute type A aortic dissection 133 Figure 9 This figure depicts the completion of the anatomic repair. The Dacron graft is shown being anastomosed to the reconstructed proximal aorta using a continuous 2-0 or 3-0 monofilament suture.
134 R.M. Bolman, III Figure 10 The completed procedure is depicted. The dissected ascending aorta has been removed, the valve resuspended, all air evacuated from the left circulation, and the patient has been decannulated. mosis; full flow is initiated to the head and body of the patient and rewarming is initiated (Fig. 7B). If the patient was cannulated via a femoral artery, it is very important at this time to cannulate the ascending graft, so that perfusion can occur in an antegrade fashion (Fig. 8). If one perfuses retrograde through a femoral artery, blood can easily traverse both true and false channels in the distal aorta. This can serve to pressurize and potentially disrupt the reconstructed distal aortic suture line. Completion of Proximal Reconstruction With the distal aorta repaired, attention can be redirected to the proximal reconstruction. The sinotubular junction, sandwiched between two layers of Teflon felt, can be readily anastomosed to the ascending Dacron graft using a running monofilament suture, and taking care to capture all layers of the reconstructed proximal aorta (Fig. 9). Other Situations Should the valve need to be replaced because of intrinsic valve pathologic problems (eg, bicuspid aortic valve with stenosis, unrepairable commissural dissection, etc.), valve replacement can take place in the usual fashion. It is often helpful to anastomose a short segment of the Dacron conduit to the proximal aorta before inserting the valve. This makes for ready graft-to-graft anastomosis as a completion procedure.
Acute type A aortic dissection 135 Aortic Root Intact, Valve Requires Replacement In this instance, there are two options. If the valve (either bicuspid or tricuspid) appears salvageable, a valve-sparing aortic root replacement can be performed. This can be either total root replacement or replacement of only the sinus or sinuses containing the damaged coronary artery ostium. Although the prospect of embarking on a procedure of this magnitude in this setting can be daunting, in actuality, this is one of the more hemostatic methods to reconstruct the aortic root. Dissection Involves Aortic Root, as Well as One or Both Coronary Ostia If the valve is abnormal (calcium deposits, fenestrations, etc), in the interest of preserving time, a composite valve graft can be employed to reconstruct the proximal aorta. With either the valve-sparing root replacement or the composite root replacement, reimplantation of severely dissected coronary arteries is highly unpredictable and fraught with risk. It is often preferable to ligate the proximal coronary artery and to perform a saphenous vein bypass or bypasses in this setting. Completion of Procedure The patient is returned to normal temperature and, following deairing, is separated from cardiopulmonary bypass, and the operation is completed in the usual fashion (Fig. 10). Suggested Reading Danner BC, Natour E, Horst M, et al: Comparison of operative techniques in acute type A aortic dissection performing the distal anastomosis. J Card Surg 22:105-110, 2007 Fann JI, Glower DD, Miller DC, et al: Preservation of aortic valve in type 1 aortic dissection complicated by aortic regurgitation. J Thorac Cardiovasc Surg 102(1):62-73, 1991, discussion 73-75 Immer FF, Aeschimann R, Englberger L, et al: Resuspension of the aortic valve in acute type A dissection: Long-term results. J Heart Valve Dis 17:94-97, 2008, discussion 97 Lai DT, Miller DC, Mitchell RS, et al: Acute type A aortic dissection complicated by aortic regurgitation: Composite valve graft versus separate valve graft versus conservative valve repair. J Thorac Cardiovasc Surg 126(6): 1978-1986, 2003