Patient Selection
Introduction
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| Figure 1 |
The aortic arch has long been considered an “off-limits” area for the majority of cardiothoracic surgeons, mainly due to the adverse neurologic sequelae following such a complex surgical reconstruction. The source of this excessive morbidity is twofold : First, with the traditional two anastomosis reconstruction (
Figure 1), the circulatory arrest time required to construct the two main anastomoses (head vessel “island” anastomosis and distal arch/proximal descending thoracic aortic anastomosis) often exceeds 45 minutes, which can lead to devastating neurologic complications.
Second, the roof of the arch containing the head vessel “island” is one of the most atherogenic areas in the aorta, and its intra-operative manipulation and post-reconstruction pressurization often leads to catastrophic neuroembolic events. If the patient displays bovine arch anatomy (with the right brachiocephalic, right carotid and left carotid arteries all originating from the same origin), the traditional island re-implantation technique may lead to incomplete aneurysm excision, since it leaves behind a significant amount of dilated tissue on the common vessel. Furthermore, if the origin of the main head vessel is calcified, which is often the case, re-implantation may be technically impossible.
We have been using several variants of an individual head vessel re-implantation technique (“Taniguchi Procedure”) utilizing a pre-fabricated trifurcated Hemashield vascular graft (Boston Scientific, Wayne, NJ), in order to achieve complete aneurysm excision, avoid manipulation of pressurized atheromatous areas of the aorta and decrease the circulatory arrest times by shifting some of the reconstructive work away from the circulatory arrest period and toward a selective cerebral perfusion/lower body ischemia phase of the operation.
Anatomic Considerations
It is very rare to encounter a patient with an isolated aortic arch aneurysm. Usually, the dilated arch is accompanied by an ascending (Figure 2) or descending (Figure 3) aortic aneurysm, or a combination of all three areas (Figure 4). Since no size criteria exist for surgical intervention on the aneurysmal arch, the decision to operate on a patient usually arises from having met criteria in either the ascending or descending aorta. If the ascending aorta is critically dilated and the dilatation involves a portion of the arch, we proceed with ascending aortic and arch replacement. If the patient has a dilated distal arch which continues into a dilated descending aorta, we perform the same operation (ascending and arch replacement), leaving an “elephant trunk” (as first described by Hans Borst in 1983) inside the descending aorta to facilitate the second stage of the reconstruction, either through a thoracotomy or, more recently, through stent grafting. With this technique, replacement of the ascending aorta is part of the aortic arch replacement. The reasons for this will be explained later in this presentation.
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| Figure 2 |
Figure 3 |
Figure 4 |
Overall pre-operative condition
There are no stringent exclusion criteria (including age or myocardial/pulmonary condition for aortic arch replacement. Valvular or coronary artery disease can be addressed at the same operation. A good rule of thumb is that if the patient is a candidate for ascending aortic replacement with circulatory arrest, they will also be a candidate for aortic arch replacement with three vessel re-implantation. Obviously, pulmonary function tests, left ventricular ejection fraction, previous sternotomy, pre-operative creatinine levels, age and previous cerebrovascular events should be taken into account when stratifying the risk profile of the patient. The decision to operate should stem from the relationship between the operative risk and the one year risk of catastrophic event (rupture or dissection) based on the natural history literature, if the aneurysm is simply observed.
Pre-operative Studies
A contrast enhanced CT scan of the chest is of utmost importance to identify the “culprit” section (the section of the aorta that mandates surgical intervention) and also to provide the surgeon with a pre-operative assessment of the arch anatomy and aid with pre-operative planning of the surgical approach. As will become evident in the next section, the only anatomic consideration that can change the course of the operation is the takeoff of the left subclavian artery. If it is obvious from the CT scan that the subclavian artery originates from a nearly intrapleural position (Figure 5), the arch replacement should be preceded by a left carotid-to-subclavian bypass, which will greatly facilitate the final reconstruction. On the other hand, if the left subclavian originates from a more central position in the arch (Figures 6, 7), then the three vessel re-implantation through the sternotomy should pose no technical problems. We have found that a left carotid-to-subclavian bypass is necessary in about 10% of arch reconstructions. If it is discovered intra-operatively that the left subclavian artery cannot be safely transected and re-anastomosed to the graft due to its anatomic location, there are several bail-out maneuvers which can be safely employed, and will be discussed in the next section.
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| Figure 5 |
Figure 6 |
Figure 7 |
Coronary angiography and trans-thoracic or trans-esophageal echocardiography are necessary pre-operative studies, in order to delineate any coronary or valvular abnormalities that will have to be addressed at the time of surgery. Coronary angiography should be performed even in young individuals, in case the root needs to be reconstructed through a Bentall or a valve sparing technique requiring coronary button re-implantation.
Operative Steps
Preparation for surgery
The patient is placed supine on the operating table and intubated with a single lumen endotracheal tube, ideally larger than 7.5, so that flexible bronchoscopy can be easily performed in the post-operative period if necessary. Invasive hemodynamic monitoring is established by means of a left radial arterial line, a right or left femoral arterial line and a PA line placed through a right internal jugular approach. The right subclavian approach for the PA line should be avoided since the right axillary artery will be used for arterial cannulation; the left jugular or subclavian venous approach should be avoided, in case the innominate vein needs to be divided to faciliate arch exposure. Finally, the right radial line can be used instead of the left, if right axillary cannulation will be performed through a graft instead of directly.
Intravenous antibiotics (Ancef 2g IV) and intravenous steroids (Solumedrol 2g IV) are administered for antibiotic prophylaxis and neuroprophylaxis (from circulatory arrest) respectively.
Preparation for cardiopulmonary bypass
All patients are approached through a standard median sternotomy, with the skin incision occasionally extended along the superior border of the left clavicle, to facilitate exposure of the left subclavian artery and distal arch. The inominate vein can usually be preserved without hindering the exposure if it is retracted cephalad after it is extensively dissected, from its confluence with the superior vena cava all the way to its left infra-clavicular location. If it still hinders the exposure, it can be permanently divided without long term sequelae.
The head vessels should be dissected out anteriorly and laterally, but they should not be manipulated posteriorly, encircled in vessel silastics etc. We feel that one advantage of this technique is avoiding manipulation or clamping of the arch vessels and potential distal embolization.
After the above dissection is completed, heparin can be administered.
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| Figure 8 |
The right axillary artery should be used for arterial return. We prefer to use a size 22 or 24 Fr. angled cannula (Edwards Lifesciences LLC, Irvine, CA) directly inserted into the vessel (
Figure 8). If the surgeon is not comfortable with this technique, a side graft (8mm Hemashield) can be anastomosed to the side of the axillary artery and a standard aortic cannula can be used for perfusion.
A single, two stage cannula is used for venous return. A retrograde cardioplegia cannula is inserted through the right atrium. An antegrade cardioplegia needle is placed on the aortic root.
Cardiopulmonary Bypass/Cooling
The patient is placed on cardiopulmonary bypass slowly, reaching full flow in 30-60 seconds. The aortic arch is monitored constantly while the flow is increasing through TEE. Using the direct axillary cannulation technique and slow induction of cardiopulmonary bypass, we have not had a single dissection or malperfusion complication. Once full flow is reached, ventilation is ceased and cooling is initiated.
The heart is arrested in diastole after a cross clamp is placed just inferior to the origin of the right brachiocephalic artery. During this cooling phase, all proximal work is done (ascending aortic replacement, Bentall reconstruction, mitral repair/replacement, distal coronary anastomoses etc). Even if the aneurysm involves only the arch and/or the proximal descending aorta, we always proceed with supracoronary ascending aortic replacement, in order to avoid the need for further surgery due to future dilatation of the ascending aorta. Reoperation for disease in the ascending aorta after an anterior approach to replace the arch is very challenging, given the attachment of the trifurcated graft to the ascending aorta (see below). Furthermore, the construction of a supra-coronary aortic anastomosis only adds 15 additional minutes to the operation, usually completed while waiting adequate cooling. We allow cooling to proceed down to a bladder or rectal temperature of 16 degrees Celsius and have found that this takes approximately 60 minutes, leaving us with ample time to perform all proximal work prior to arch reconstruction. If jugular venous blood oxygen saturations are followed, they should reach 95% prior to proceeding with deep hypothermic circulatory arrest.
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| Figure 9 |
Circulatory Arrest
With the patient at 16 degrees (or with the jugular venous O2 saturation at 95%) we stop the pump, the head is packed in ice, the patient is drained and the aortic cross clamp is removed. The three head vessels are transected 1cm from their origin and three anastomoses are constructed utilizing a prefabricated trifurcated Hemashield graft (Boston Scientific, Wayne, NJ) (Figure 9) and 4-0 polypropelene suture. The graft comes in two sizes : A main graft at 14mm with two side grafts at 10mm, or a main graft at 12mm with two side grafts at 8mm. We have found these two grafts to be adequate for any combination of arch vessel diameter. Obviously, the surgeon can construct their own trifurcated graft if the prefabricated one is not available. The take-off of the two side braches should be at 45 degrees from the main graft, in order to ensure proper orientation at the time of implantation. The time to construct the three head vessel anastomoses rarely exceeds 30 minutes. We do not use retrograde cerebral perfusion or EEG monitoring as part of our hypothermic circulatory arrest procedure.
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| Figure 10a |
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| Figure 10b |
Selective Cerebral Perfusion/Lower Body Ischemia
Once the anastomoses are completed, the base of the trifurcated graft is clamped and axillary perfusion is commenced with a cold perfusate at 10cc/kg/min, thus re-establishing flow to the brain and left upper extremity, using the trifurcated graft. This marks the end of circulatory arrest and the continuation of lower body ischemia. Note that the atherogenic “roof” of the arch is now completely excluded from flow to the brain.
The distal aortic anastomosis is then constructed, usually employing the elephant trunk technique. Even if there is no proximal descending aortic aneurysm, we prefer to leave a short elephant trunk since sewing a circular open anastomosis with a folded graft is much easier than sewing an end-to-end graft to tissue anastomosis. A strip of Teflon felt is used to reinforce the anastomosis.
We then unfold the inner portion of the elephant trunk graft back into the operative field, and connect it end-to-end to our ascending graft. Finally, we connect the main (bottom) limb of the trifurcated graft to the proximal graft and complete the reconstruction. The main limb of the trifurcated graft is then unclamped and re-warming is initiated with the entire body now perfused. After separation from cardiopulmonary bypass and decannulation, the final product is achieved (Figures 10A, 10B) (Video 1)
Variations on a Theme…
In some cases, the aorta at the level of the distal anastomosis (distal to the left subclavian) is very calcified (Figure 11) or very dilated (Figure 12), which makes construction of an elephant trunk or end-to-end anastomosis impossible. In these cases, the elephant trunk can be initiated proximal to the takeoff of the brachiocephalic artery (Figure 13). The arch is left in place, but the orifices of the head vessels are oversewn with 4-0 polypropelene. The remainder of the case is carried out as described above. Note that in these patients, the aneurysmal arch and head vessel stumps will remain pressurized until the stage II (descending thoracic) reconstruction is completed. (Video 2)
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| Figure 11 |
Figure 12 |
Figure 13 |
If the patient has undergone left carotid-to-subclavian bypass prior to arch replacement, only two anastomoses need to be performed under circulatory arrest (right brachiocephalic and left subclavian). The left subclavian artery is snared throughout the selective cerebral perfusion phase and eventually it is tied off after the reconstruction is completed.
If the patient has not undergone left carotid-to-subclavian bypass prior to arch replacement and the surgeon realizes intra-operatively that the subclavian artery is too far distal to be safely anastomosed to the trifurcated graft, it can be permanently tied off. The carotid-to-subclavian bypass can be performed at a later time, if the patient develops left arm or subclavian steal symptoms. In the acute setting, ligation of the left subclavian artery is well tolerated.
In both of the above scenarios, the third limb of the trifurcated graft is not used in the reconstruction. It can be used for placement of the arterial cannula for the remainder of the case (selective cerebral perfusion and full perfusion/rewarming).
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| Figure 14 |
If a bifurcated reconstruction is planned from the beginning because of tapering of the aneurysm between the left carotid and the left subclavian, the ascending aorta can be used for arterial return during the cooling, and the third limb of the trifurcated graft can be used for selective cerebral perfusion and re-warming, thus eliminating the need for axillary cannulation. The distal anastomosis is constructed proximal to the left subclavian artery (
Figure 14).
Re-warming/Separation from Cardiopulmonary Bypass
Separation from cardiopulmonary bypass and decannulation are performed following standard procedures. The pericardium is used to cover the aortic reconstruction field, but not the right ventricle. This may play a protective role in cases of wound infection or sternal dehiscence.
Postoperative Care
The patients are usually conscious within the first 24 hours and extubated within the first 36 hours. Chest tubes are left in place for at least 72 hours, even if minimal drainage is recorded. We have found this practice to reduce the incidence of postoperative pericardial effusion in patients with aortic reconstructions. If the patients need to be on Coumadin, we start low dose administration as soon as the chest tube drainage has decreased to 20cc/hr or less. Heparin bolus or drip infusion is avoided.
Need for re-operation
If a patient who has had a trifurcated graft ascending and arch replacement needs to have a re-operation employing cardiopulmonary bypass, the left subclavian artery or any of the femoral vessels can be used for inflow. If the heart needs to be isolated and arrested, there need to be two sources of inflow, with independent blood pressure monitoring of the upper and lower body. The left subclavian artery can be used for upper body perfusion (to avoid re-dissection of the previously used right subclavian) with monitoring from the right radial artery. Any femoral artery can be used for lower body perfusion, with monitoring of the contralateral femoral artery pressure. Two clamps need to be applied, one at the base of the trifurcated graft, and one at any point along the course of the main aortic graft. Cardioplegia can be delivered through the proximal aortic graft or through the coronary sinus.
The source of inflow for saphenous venous or radial arterial grafts should be the subclavian artery limb of the trifurcated graft. This can be safely clamped (temporarily) either on or off pump, without compromising the cerebral circulation. It is also the most anterior of the three limbs and can be easily isolated. In an off pump setting, the proximal anastomoses to the subclavian artery limb should be constructed prior to the LIMA to LAD anastomosis, in order to avoid temporary LAD territory ischemia during construction of these anastomoses.
Right thoracotomy approaches to the mitral and tricuspid valves can be safely performed without further technical considerations.
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