The introduc- tion of the elephant trunk technique by Borst et al

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Contents

11.1 The Conventional Elephant Trunk Technique . . . 125

11.2 The Frozen Elephant Trunk Technique . . . . 126

11.3 Own Experience Employing the Frozen Elephant Trunk Technique Using a Hybrid Prosthesis with a Stented and a Nonstented End . . . . 126

11.3.1 Patients and Surgery . . . . 126

11.3.2 Results and Follow-Up . . . . 128

11.4 Comment . . . . 128

11.1 The Conventional Elephant Trunk Technique

Anatomy determines that the proximal segment of the descending aorta is less accessible via median sternotomy than the aortic arch. Therefore most surgeons prefer a multiple-stage approach to treat combined lesion of the aortic arch and the descending aorta. The introduc- tion of the elephant trunk technique by Borst et al. [4]

in 1983 has greatly facilitated surgery on this kind of pathology. The basic principle of the Borst operation for the replacement of the aortic arch resides in the protrusion of a length of tubing into the downstream aorta distal to the actual graft to aortic anastomosis at the level of the left subclavian artery. In the subsequent operation performed through lateral thoracotomy, the graft segment in the descending aorta may be used for further replacing the diseased vessel. More importantly, the difficult and often dangerous dissection of the original distal graft to aortic anastomosis is avoided.

After earlier publications fromour own group and Crawford's landmark paper published in 1990, this method became more and more popular for treating patients with complex aortic diseases [1, 3, 5, 8±10, 26, 27, 31]. Today, the elephant trunk operation is employed in the two classic conditions: aneurysms and chronic dissection of (1) the aortic arch and (2) the descending thoracic aorta involving the respective downstreamportions of the vessel. It may also be cho-

sen for selected patients with acute proximal and distal dissection [9, 23, 24].

Meanwhile, several modifications of the original technique have been reported. Coselli et al. [8] introduced the reversed elephant trunk technique, while Car- rel et al. [5, 6] described a bidrectional variant for the replacement of the descending aorta, thereby facilitating second- and third-stage procedures for the replacement of the aortic arch and the thoracoabdominal aorta.

The idea of using an elephant trunk prosthesis as a stent graft, introduced into the descending aorta, was born and popularized by Buffolo's group [23, 24], who employed this approach in a large series of patients with acute type B dissection. Along with the advent of transfemoral stent grafts for the treatment of descending aortic aneurysms it became even possible to se- curely anchor a stent graft in an elephant trunk prosthesis previously placed during arch surgery [11].

Even though complications following the insertion of elephant trunk grafts have been rare and appear largely avoidable, concerns were reported with regard to increased tension on the suture line distal to the left subclavian artery, thereby increasing the risk of rupture at or near that site during the waiting period for the second-stage operation [18, 32]. This fear has prompted further modifications of the original technique by pre- paring this anastomosis at an upstream and less dilated aortic level. Thus, Svensson et al. [32] have suggested placing the anastomosis in the aortic arch between the left carotid artery and the left subclavian artery. An- other, even more radical approach in this regard was published by Kuki et al. [18], who reported a series of 17 patients in whomthe elephant trunk anastomosis was made at the base of the innominate artery. Using this technique, they reconnected the supraaortic branches to the ascending aortic vascular graft by three small-caliber interposition grafts. The authors suggest that this modification yields a secure and rapid anastomosis, and reduces the risk of aortic tearing even in the case when the suture line that is tailored down to the smaller size of the graft [18]. While the length of the elephant trunk depends on the extent of the down- streamaortic enlargement and should be at least

The New Wave of Elephant Trunk Technique

Matthias Karck, Nawid Khaladj

11

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7±8 cmaccording to Borst's original suggestion, the technical modification described by Kuki et al. requires a length of about 15 cm. Here may reside a potential problemof this variant, because a long elephant trunk is more likely to cause complications due to kinking and graft occlusion. This suspicion is supported by Crawford's finding that there are increased risks of pe- ripheral embolisation caused by flapping action of the elephant trunk and paraplegia as a result of clot formation around the graft, if the trunk is too long [10].

Another concern with regard to staged repair of extensive thoracic aortic aneurysms using the conventional elephant trunk operation resides in the fact that the risks of two major surgical procedures and the risk during the time interval between the two interventions add up cumulatively. This was highlighted in a more recent report by Estrera et al. [12]. They calculated early mortality rates of 9% after the stage one operation and 7% mortality after the stage two procedure. Among the 124 patients who survived the stage one operation, there were 56 patients discharged fromhospital who failed to return for the second-stage repair. In this group of patients follow-up surveys at 5 years revealed as many as 18 out of 56 (32.1%) deaths. In addition, a mortality rate within the small time window between 4 and 6 weeks following the stage one operation of 8%

with the majority of fatalities due to aortic rupture clearly indicates the limitations of staged approaches. A similar observation was made by Schepens et al. [29], who reported survival rates between 80 and 90% in patients who completed the stage two procedure within 4 years, compared with as low as 50% survival in patients, who did not.

11.2 The Frozen Elephant Trunk Technique

The complications that may be attributed to the elephant trunk itself and the cumulative risks of the staged approach are drivers for change towards new procedures and implants, which allow for risk reduction in the surgical treatment of large aortic aneurysms. Exten- sive one-stage repair techniques performed through a clamshell incision or through the left chest bear re- markable technical challenges and risks, too [17, 19, 28, 35]. They may therefore be limited to selected patients.

A new wave of the elephant trunk technique that may accomplish this goal approached with reports using a new type of homemade vascular prosthesis carrying a stent at its distal end. Suto et al. [30] described a patient with an aneurysmof the distal aortic arch and the descending aorta which was replaced via median sternotomy during circulatory arrest by antegrade implantation of a Gianturco stent connected to a conventional vascular prosthesis. Based on Buffolo's earlier experience and Kato's description of endovascular covered

stent grafting through median sternotomy, Usui et al.

[33] reported a series of 12 patients who underwent implantation of a covered stent graft for distal aortic arch aneurysmvia median sternotomy under pigtail catheter guidance. Two patients in this cohort underwent additional procedures such as aortic arch replacement and aortocoronary bypass grafting, respectively. Shortly thereafter, Orihashi et al. [22] published a report on a cohort of 15 patients, mainly with descending aortic aneurysms not treatable with transfemoral stent grafts.

Again, homemade grafts were prepared from a Giantur- co stent introduced in a conventional vascular prosthesis prior to antegrade implantation during circulatory arrest. Almost half of the patients underwent additional procedures, including ascending and/or aortic arch replacement using separate vascular grafts, which were connected to the stented graft in the descending aorta.

While these reports describe the use of the frozen elephant trunk technique in patients with aneurysms or chronic dissections, more recent publications focus on its use in patients with acute A aortic dissection, too [15, 16, 21]. Both, early and midterm results using this approach appear favourable, particularly with regard to the promotion of thrombus formation in the false channel. In the vast majority of patients in the study of Ishi- hara et al. [15] the false channel had even disappeared as distal as at the diaphragmatic aortic level at a maxi- mum follow-up at 38 months postoperatively. In accor- dance with this finding, Kato et al. [16] observed a marked reduction of the diameter of the false lumen in the descending aorta excluded by the stent graft in their cohort comprising 19 patients. Whether these promis- ing results justify the use of a frozen elephant trunk in patients with arch tears only or possibly in all patients with acute type A dissection is debatable. Given the fact, that up to 25% of patients who undergo ascending aortic replacement with an open distal anastomosis of the proximal aortic arch will develop critical down- streamdilatation of native dissected aortic segments, this option should be taken into consideration [14].

11.3 Own Experience Employing

the Frozen Elephant Trunk Technique Using a Hybrid Prosthesis with a Stented and a Nonstented End

11.3.1 Patients and Surgery

Between September 2001 and April 2004, 22 patients with combined pathologies of the aortic arch and the descending aorta were operated on using a ªhybrid prosthesisº (Chavan±Haverich endograft, Curative, Dresden, Germany) made of a woven vascular prosthesis with stainless steel stents affixed to the inner aspects

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at its distal end (Fig. 11.1). The mean patient age was 62 years (range, 47±77 years). There were seven patients who were older than 70 years. Nine patients were wom- en. The majority of patients (n=11) presented with type A aortic dissection, ten in its chronic formand one with its acute variant. The second most frequent pathology (n=7) was an aneurysmproximal and distal of the left subclavian artery. A smaller cohort (n=4) presented with chronic aortic dissection type B. Addi- tional cardiac pathology comprised severe coronary artery disease in nine patients and aortic valve disease in three patients.

The diameters of the stents within the hybrid prosthesis ranged between 30 and 46 mm and the stents had a length of 22 mm each. The proximal portion of the hybrid prosthesis was not stented and consisted of a Dacron sleeve ready for conventional surgical handling.

The delivery systemcomprised a flexible 39-French (F) outer sheath, a 34-F inner sheath, as well as a central pusher. Withdrawal of the outer sheath while holding the inner sheath and the pusher steady released the stented portion of the hybrid prosthesis. The proximal Dacron tube was then released by pulling back both sheaths simultaneously while holding the pusher steady.

Spiral computed tomographic angiography of the thoracic aorta was performed preoperatively to assess the extent of the aneurysmand/or dissection as well as to determine the appropriate stent graft size.

All patients were operated on using cardiopulmonary bypass. Central cannulation of the ascending aorta and the right atriumwas preferred. In three patients who underwent resternotomy the groin vessels were cannu- lated before, because an ascending aortic aneurysmen- croached upon the sternum. Then, core cooling was accomplished to 258C rectal temperature. After induction of cardioplegic cardiac arrest, cardiopulmonary bypass was discontinued. The aortic arch was then opened longitudinally. Selective antegrade cerebral perfusion

with cold blood at 158C and a volume of 250±450 ml/

min was initiated after ostial cannulation of the left common carotid artery and the brachiocephalic trunk.

Then, the stented end of the hybrid prosthesis was deployed in the descending aorta. In the first five patients it was implanted over an antegradely placed superstiff guide wire. Prompted by perforation of the aortic wall with the introducer systemin a patient with a tortuous descending aorta, a through-and-through transfemoral guide-wire technique was employed in all subsequent patients.

The distal landing site of the graft was at or above the tenth thoracic vertebra in all patients. After deployment, the stented portion of the prosthesis was modu- lated onto the aortic wall with the help of an appropriately sized balloon catheter (Medtronic, USA). Then, the nonstented Dacron graft segment was sutured circumferentially to the aorta distal to the origin of the left subclavian artery before the supraaortic branches were reimplanted enbloc into an appropriately sized Fig. 11.1.The ªhybrid prosthesisº (Chavan-Haverich endograft,

Curative, Dresden, Germany) was made of a woven vascular prosthesis with stainless steel stents affixed to the inner aspects at its distal end

Fig. 11.2. aThe stented end of the hybrid prosthesis is deployed in the descending aorta distal of the dilated segment. Selective antegrade cerebral perfusion is accomplished during hypothermic circulatory arrest. bAfter suturing the hybrid prosthesis circumferentially into the descending aorta directly distal of the origin of the left subclavian artery, the supraaortic branches are reimplanted into the graft as a single tissue patch.

c The reconstruction may then be completed at any desired level of the ascending aorta while cardiopulmonary bypass is reestablished

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window of the graft. A proximal graft-to-aortic anastomosis at any desired level of the ascending aorta completed the repair (Fig. 11.2). In six patients with previously implanted valved conduits a graft-to-graft anastomosis was sutured accordingly.

In 20 patients the entire aortic arch and the proximal segment of the descending aorta were replaced using this procedure. In ten of themthe ascending aorta had to be replaced additionally.

In two other patients with aneurysms limited to the proximal descending aorta, implantation of the hybrid prosthesis into the descending aorta was enabled by a limited, 3±4-cm-long longitudinal T-shaped incision of the aortic arch. The nonstented endograft segment was sutured circumferentially distal to the level of the left subclavian artery before the aortotomy was closed. One of the two patients required additional complete myocardial revascularization and the other aortic valve replacement for aortic valve stenosis using a biological aortic valve prosthesis. Except for these two patients there were ten other patients who required additional procedures (myocardial revascularization, eight patients;

aortic valve replacement, two patients).

11.3.2 Results and Follow-Up

There were no intraoperative deaths. The implantation of the prosthesis was successful in all but one patient.

This patient presented with marked kinking of the descending aorta distal of the aneurysmatic segment to be excluded. Implantation was attempted over an antegradely placed guide wire. The tip of the introducer systemcould not be advanced beyond the kinked segment; thus, perforation of the aortic wall occurred at this point, and required surgical repair and additional transfemoral stent-graft implantation to bridge the per- forated and aneurysmatic segment. In all subsequent patients the transfemoral through-and-through guide- wire technique for the implantation of the stented segment of the hybrid prosthesis in the descending aorta (s.a.) was used.

In one patient with chronic aortic dissection type A the aortic wall of the false lumen directly distal to the origin of the left subclavian artery was accidentally in- jured during surgical preparation. Even though this la- ceration was sutured and the further course of the operation was uneventful, the patient died fromfatal bleeding into the left hemithorax 2 days postoperatively.

Autopsy revealed that exsanguination was caused by a reopening of the repaired segment.

The mean duration (Ô standard deviation) of total cardiopulmonary bypass time, aortic cross-clamp time, hypothermic circulatory arrest time, antegrade selective cerebral perfusion time and the time required for the deployment of the stented end of the hybrid prosthesis

were 239Ô76, 136Ô43, 74Ô19, 62Ô14 and 12Ô 5 min respectively. Reexploration for bleeding was necessary in two patients.

Four patients awoke with central neurological dysfunction. In two of them, it was transient and resolved completely before discharge. Two of the four patients had a history of cerebrovascular events with anatomical correlates in the preoperative computed tomography scan of the brain. Documented (by direct laryngoscopy) left recurrent nerve paralysis occurred in two patients.

There was no late mortality after a mean follow-up of 14 months. Postoperative computed tomography scans revealed completed thrombus formation in the perigraft space around the stented segment of the hybrid prosthesis in the descending aorta in all seven patients with atherosclerotic aneurysms. The same holds true for the arch aneurysms in two patients with asso- ciated type B aortic dissections.

In the remaining 12 patients with aortic dissections in follow-up, initiation of thrombus formation in the false lumen in the descending aorta up to the level of the stents was noted in all but one patient, who exhibited a small endoleak into the false lumen at the origin of the left subclavian artery; otherwise, the false lumen was thrombosed. As the patient refused a reintervention, the exact aetiology of the endoleak remains unclear.

In one patient with chronic aortic dissection type A, the stented segment of the graft could not be anchored successfully in a previously implanted thoracoabdominal aortic vascular graft. The stents slipped proximally during and after release, giving rise to a distal endoleak. This was treated 2 weeks later by placing a com- mercially available endograft (Talent endograft, Medtro- nic) transfemorally, thus extending the hybrid endograft distally into the thoracoabdominal graft. At discharge, he still presented with a type III endoleak, which was found to be reduced to a tiny contrast extravasation at 6-months follow-up. As the actual aneurysm has thrombosed and its size remains constant, the patient is being treated conservatively at present.

11.4 Comment

In Sect. 11.3 we described our approach that allows for definite treatment of lesions of the aortic arch and beyond during a single-stage procedure by using a hybrid prosthesis, which combines the features of a stent graft and a conventional vascular prosthesis. The stented distal segment of the hybrid prosthesis is implanted into the descending aorta through the opened aortic arch under fluoroscopic control, while the proximal nonstented segment is used for conventional replacement of the upstreamaorta. The procedure is performed through median sternotomy, thereby facilitating additional surgery on the heart and/or the ascending aorta.

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In this series of 22 patients, implantation of the hybrid prosthesis was successful in all but one patient with pronounced tortuosity of the descending aorta.

With the through-and-through transfemoral guide-wire technique (s.a.) we have used ever since, no malposi- tioning of the stented segment of the hybrid prosthesis occurred anymore.

The conventional elephant trunk operation necessi- tates a reoperation through lateral thoracotomy, because the perigraft space around the elephant trunk remains perfused, thereby promoting further aneurysmatic dila- tation of that aortic segment [12, 17, 20]. As opposed to this, the ªfrozenº elephant trunk technique as described here allows for progressive thrombus formation in the perigraft space in the descending aorta up to the level of the stents. Widening of the descending aorta has not been observed in our patients, regardless of whether thrombus formation was complete or still incomplete.

This observation suggests that the stents within the distal segment of the hybrid prosthesis are effective in pre- venting retrograde flow into the aneurysm.

Owing to the necessity of mounting the hybrid prosthesis in an adequately flexible and thin delivery sys- tem, we utilized Dacron (0.36 mm in width) which is thinner than the Dacron used in conventional aortic surgery. In addition to pretreatment with collagen during fabrication of the hybrid prosthesis, extra sealing of the graft with fibrin glue was necessary in some cases to render the graft completely haemostatic.

While the perioperative mortality rate of 4.5% is very acceptable, the incidence of stroke in four out of 22 patients remains a concern, even though in two of the four patients symptoms resolved completely and two had had previous cerebrovascular incidents. The circulatory arrest time of 70 min on average has to be regarded as a risk factor for stroke despite the routine use of selective antegrade cerebral perfusion [2]. De- ployment of the stented segment of the hybrid prosthesis currently takes 15±20 min. Further reduction of this time is therefore desirable, because this will shorten the phase of circulatory arrest, thereby lowering the central neurological risk [13].

No patient in our series developed paraplegia as a result of spinal cord injury. Even though this result is in line with those of endovascular stent grafting of descending aortic aneurysms it is still intriguing in view of the significant paraplegia rates reported with open surgical approaches similar to ours [21, 25, 34, 36]. One aspect that could have reduced the risk of spinal cord injury in our series was the keeping of exclusion crite- ria with regard to the extent of the descending aortic aneurysmto be treated together with a stent-graft fabrication that was adjusted specifically to the patient's in- dividual pathology. Therefore, this treatment was limited to patients with aneuryms involving only the first half of the descending aorta regardless of their size.

The proximal extent of the aneurysm with regard to

arch involvement was not critical, because the quality of the anastomosis distal to the origin of the subclavian artery depends on the condition of the aortic tissue rather than on the actual aortic diameter at that segment.

In the two patients with aneurysms limited to the descending aorta, other options such as retrograde or isolated antegrade stent-graft implantation with or without transposition of the subclavian artery would have been conceivable treatment alternatives to our approach. We believe, however, that the favourable results that can be obtained with circulatory arrest at moderate hypothermia and selective cerebral perfusion in surgery involving the aortic arch well justifies the technique described here [2, 13]. The use of the hybrid prosthesis enables safe anchoring of its proximal vascular graft segment by a circumferential, hand-sewn anastomosis distal to the origin of the left subclavian artery at the expense of a probably somewhat extended circulatory arrest time, when compared with the time required for antegrade implantation of a conventional stent graft with or without its fixation by internal stay sutures. In addition, both patients presented with landing zones distal to the left subclavian artery too short to allow for safe anchoring of a conventional stent graft.

Therefore, we considered both antegrade and retrograde implantation of a conventional stent graft as suboptimal treatment options. On the other hand, transpositioning of the left subclavian artery together with conventional stent grafting is not less complex in comparison with the implantation of a hybrid prosthesis when other car-

Fig. 11.3. Contrast computed tomography scans of a patient with a chronic aortic dissection type A following implantation of a hybrid prosthesis. The perigraft space around the stented segment of the hybrid prosthesis in the descending aorta is thrombosed partially at 1 week postoperatively

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diac pathologies are treated simultaneously using extra- corporeal circulation.

Similar to observations during follow-up after endovascular stent grafting we observed either advanced (Fig. 11.3) or completed thrombus formation around the frozen elephant trunk after the mean follow-up of 14 months that has accumulated so far (Fig. 11.4) [7].

In some cases we found additional shrinkage of the thrombosed aneurysms, which is a common finding after endovascular stent grafting, too [37].

Both phenomena, thrombus formation of the perigraft space and shrinkage of the excluded aneurysm, are indicative for a reduction of aortic wall stress, thereby reducing the risk of rupture of the stented aortic segment. This finding together with a relatively low perioperative mortality and morbidity support the ther- apeutic concept of a single-stage antegrade combined open and endovascular repair of complex thoracic aortic aneurysms using a hybrid prosthesis or other vari- ants summarized under the term frozen elephant trunk technique. Further evaluation of this treatment modality appears therefore warranted.

Acknowledgements.The authors wish to thank Axel Ha- verich and Ajay Chavan for the development and the design of the hybrid prosthesis described here.

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