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Thoracoabdominal aortic aneurysm (TAAA) repair is one of the most extensive operations undertaken by a surgeon. The size of the incision, as well as the number of organ systems that are at considerable risk during the procedure, places TAAA repair among one of the most major procedures the human body can tolerate. Fortunately, methods of organ protection (particularly for the spinal cord) have been developed to reduce these risks. We have built upon these techniques, resulting in an operative strategy that has improved outlook for our patients. We will give a brief history of the treatment of these aneurysms before discussing the rationale for our techniques. We will then discuss our operative results and some of the emerging endovascular techniques becoming available for treatment of select patients. The results reported in this monograph represent our standard for repair of thoracic and thoracoabdominal aortic aneurysms (TAAs), using the open technique. Durability of descending thoracic aortic repair has been established in our series.¹ Because of the questionable durability of endovascular repair in the thoracic aorta, most thoracic aneurysms are still best treated by the open technique.

In the late 19th century, the routine treatment for an aortic aneurysm was to simply ligate the aorta. Rupture was prevented, but disastrous consequences often resulted. The patient frequently suffered gangrene and a painful death. In 1955, Dr. Samuel Etheredge completed the first repair of a TAAA using a homograft,² and the following year, Dr. Debakey introduced the Dacron tube graft for repair of TAAA.³ Later, Dr. E. Stanley Crawford developed the clamp-and-sew method, which stressed three principles of aortic surgery: inclusion, use of Dacron tube graft, and reimplantation of visceral and renal arteries.⁴ This treatment vastly improved the efficacy of TAAA repair, but it required expediency on the part of the surgeon in order to avoid complications from extended cross-clamping of the aorta. Much work has gone into alleviating this necessity.

During the clamp-and-sew era, aortic cross-clamp time was the most important predictor of immediate postoperative neurologic deficit during repairs of the thoracic and thoracoabdominal aorta. Analysis of Crawford’s population of 1509 patients demonstrated that a cross-clamp time greater than 60 minutes was associated with an overall incidence of paraplegia of 27%; incidence when clamp time less than thirty minutes was still significant at 8%.⁵ We reported similar findings in our own population when the clamp-and-go technique was used.⁵ Results from the clamp-and-sew era were superior to those of earlier series, yet still troubling.

One report on the use of cerebrospinal fluid drainage⁷ and another on the use of distal aortic perfusion for thoracic aortic aneurysm (TAA) repairs,⁸ led us to hypothesize that increased distal aortic perfusion pressure using left heart bypass in combination with decreased cerebrospinal fluid pressure with drainage, we could lead to improved spinal cord perfusion and ultimately, neurologic outcome, during thoracoabdominal aortic repair. As such, in the last 15 years, we have settled on the adjunct, consisting of three elements: distal aortic perfusion, in which oxygenated blood is taken from the left atrium directly to the femoral artery via the left lower pulmonary vein, using the centrifugal pump; cerebrospinal fluid drainage; and moderate, passive hypothermia in which core temperature is allowed to drift to 33–34 degrees Centigrade. Since 1992, we have employed this method to protect the spinal cord and the descending thoracic aorta as well as the thoracoabdominal aorta. We chose this avenue based on a study that showed the signficant impact of protecting the spinal cord by using these three modalities. We refer to the combination of distal aortic perfusion as described above, cerebrospinal drainage and moderate hypothermia as a single adjunct because the emergent protective effect of these three elements when used together is greater than their individual efficacies.

Between 1991 and 2004, we repaired 1,106 TAAAs and descending TAAs. Women comprised 36% of those studied, and the median age was 67 years (range 8 to 92 years). Cerebrospinal fluid (CSF) pressure is maintained below 10 mmHg throughout the surgery and for 3 days postoperatively, using a lumbar drain placed percutaneously in the 3rd or 4th lumbar space immediately prior to surgery. To achieve distal aortic perfusion, we cannulate the left atrium through the left inferior pulmonary vein or atrial appendage. We employ sequential cross-clamping technique to minimize ischemic time. Other adjunctive measures include perfusion of the visceral and renal vessels with blood or a crystalloid solution.

The neurologic deficit (ND) per quartile was obtained (Table 1). The overall incidence of ND was 3.3%, with an incidence of neurologic deficit of 1.1% during the last quartile (Figure 1).
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Risk factors associated with neurologic deficit were age, TAAA extent II, history of cerebrovascular disease, and history of renal dysfunction (OR = 2.55, p = 0.007). The use of the adjunct and female gender were protective against ND. Aortic cross-clamp time was not associated with ND. Independent risk factors for neurologic deficit were extent II TAAA and renal dysfunction (Table 2). The changing relationships of the aortic cross-clamp time with the incidence of neurologic deficit without and with adjunct use, respectively, can be seen (Figures 2 and 3).⁹

We found that aortic cross-clamp times have increased significantly (34 seconds/year) since 1991. However, neurologic deficit rates have declined for the period of surgery in the same period (Figure 1). The use of the adjunct has increased the aortic cross-clamp time by a mean of 12 minutes, but is associated with a significant protective effect against neurologic deficit. Although other risk factors remain, cross-clamp time is no longer a significant predictor of neurologic deficit in our series (Figure 3).⁹

As presented above, the use of adjuncts decreased the overall incidence of ND to 1.1%. This has dramatically affected the overall quality of life and recovery of these patients. What has not been affected, however, has been the overall mortality. Although improvements in critical care, surgical technique and anesthetic care have been observed over the past several years, mortality still remains the same. The reason for this may be related to the preoperative renal dysfunction.

As has been previously established, aneurysm rupture and pre-existing renal disease were strong predictors for early mortality. This was both in the era of the clamp-and-sew and with the use of the adjuncts. Previously, our definition of preoperative renal dysfunction was a baseline serum creatinine of 2.0 mg/dl or the need for renal dialysis. Previous risk factor analysis for repairs of the descending and thoracoabdominal aorta used this definition. In our most recent study, however, we discovered that glomerular filtration rate (GFR) as determined by the formula of Cockcroft-Gault equation, was a better predictor for renal dysfunction, as well as the most significant predictor for mortality following these repairs.¹⁰ GFR was a much stronger predictor of mortality than serum creatinine in patients without clinically apparent renal disease. Mortality in these patients, mortality ranged from 5% in the best GFR quartile to 27% in the worst.10 Mortality also correlated strongly with worsening renal disease, in relation to the severity stages defined by the National Kidney Foundation (Table 3). Serum creatinine did not discriminate in patients without clinical disease (p = 0.73), where GFR remained a strong predictor (p = 0.0001). Only rupture and GFR were significant predictors of early mortality (Table 4). Figure 4 shows a plotting of serum creatinine versus GFR demonstrating that GFR correctly identifies abnormal serum creatinine in all but two cases. However, 71% of the time, serum creatinine does not identify abnormal GFR. Mortality was evaluated based on these thresholds, it was 94/804 (11.7%) among patients with normal creatinine, compared to 13/234 (5.6%) among those with normal GFR.¹⁰

Patients with descending TAAs had the highest preoperative GFR, compared to all other TAAA extents (Table 5). These patients were able to maintain postoperative GFR closer to preoperative levels whereas those with other extents exhibited significant decreases (Table 6). Patients with extent IV (Table 7), and the postoperative changes in serum creatinine did not correlate with the TAAA extent (Table 8).¹⁰

The importance of GFR has also been validated when endovascular therapies were used. In another report, we showed that GFR also predicted outcomes during endovascular repairs of the abdominal aorta.¹¹ Although these were abdominal aortic repairs, similar correlations will likely be made with endovascular repairs of the thoracic aorta.

Most reports on endovascular repair of thoracic aorta remain limited both in number and period of observation. There is a definite role for endovascular therapies of the thoracic aorta, but many questions still remain with regards to its durability.^12–14 Relative contraindications for thoracic aortic endografting still exist in patients with chronic dissection, as well as patients with connective tissue disorders. Until larger observational studies and registries on the late follow-up of thoracic endovascular repair are reported, or more desirable multicenter (preferably) randomized controlled trials comparing open repair to endovascular repair are performed, thoracic aortic endografting will be of limited utility for select patients. Thus, open repair still remains the standard approach for repairs of the thoracic aorta.


Commentary

I congratulate the authors on a report that reflects, undoubtedly, one of the most significant and impressive clinical experiences with surgical treatment of thoracic aortic aneurysms (TAA). The results they have managed to achieve in this most difficult field rank in the same unique category as the landmark contributions of DeBakey, Crawford, Coselli and only a few other master aortic surgeons. If their accomplishments could be reproduced or duplicated by most surgeons doing this type of work, there would be very little stimulus for the development of less invasive endovascular approaches! But that’s certainly not the case....

As impressive as these results are, their views and derived conclusions do not seem to be in line with current thinking and developments. This whole field is moving away from surgery, not towards it! And a majority of their colleagues have already embraced the endovascular approaches wholeheartedly.

Having said that, I must confess to be in agreement with them that the proponents and enthusiasts (myself included!) of stent-graft repair for most thoracic aortic lesions still have much more work to do and much more evidence to generate. While early results are very encouraging, little or no data exist on long-term device and repair integrity, and on the overall clinical results and protection from aneurysm growth and rupture. I would completely agree with the notion that thoracic endograft technologies are in a relatively early stage of development, and that we continue to encounter numerous unresolved issues and unmet needs. However, I feel confident that progress and technological refinements will continue. And in the end, endograft techniques — with and without hybrid combinations — will emerge as the preferred treatment modalities for many if not most patients. Surgical reconstruction will likely retain a significant, albeit diminished, role in the foreseeable future.

Frank J. Criado, MD
frank.criado@medstar.net