Ten years experience of thoracic and thoracoabdominal aortic aneurysm surgical repair: lessons learned

Assessment of genetic risk factors for thoracic aortic aneurysm in hypertensive patients

BACKGROUND

Conventional risk factors for thoracic aortic aneurysm including dissection (TAA) are thought to include age, arteriosclerosis, and hypertension. In addition, evidence suggests that genetic factors play a role in the development of this condition. The purpose of the present study was to identify genetic variants that confer susceptibility to TAA in hypertensive subjects.

METHODS

Study subjects comprised 1,351 hypertensive individuals: 88 patients with TAA and 1,263 subjects without this condition. The genotypes for 142 polymorphisms of 119 candidate genes were determined by a method that combines the PCR and sequence-specific oligonucleotide probes with suspension array technology.

RESULTS

Evaluation of genotype distributions by the chi2-test and subsequent multivariable logistic regression analysis with adjustment for covariates revealed that the 3949T-->G (3' untranslated region) polymorphism of the thrombospondin-2 gene (THBS2; odds ratio, 4.6), the -110A-->C polymorphism of the heat shock 70-kDa protein 8 gene (HSPA8; odds ratio, 0.4), the C-->T (Pro198Leu) polymorphism of the glutathione peroxidase 1 gene (GPX1; odds ratio, 0.3), the -6G-->A polymorphism of the angiotensinogen gene (AGT; odds ratio, 0.3), and the -850C-->T polymorphism of the tumor necrosis factor gene (TNF; odds ratio, 0.5) were significantly (P < 0.05) associated with TAA.

CONCLUSIONS

The variant allele of THBS2 is a risk factor for TAA in hypertensive patients, whereas the variant alleles of HSPA8, GPX1, AGT, and TNF are protective against this condition. Determination of genotypes for these polymorphisms may prove informative for assessment of the genetic risk for TAA.

A biologic basis for asymmetric growth in descending thoracic aortic aneurysms: a role for matrix metalloproteinase 9 and 2

OBJECTIVE

This study was undertaken to define matrix metalloproteinase (MMP) expression in the anterior and posterior wall of descending thoracic aortic aneurysms (TAAs) and correlate it with specific computed tomography (CT) image sites within the descending thoracic aorta.

METHODS

Serial CT images of patients with TAAs were compared with age- and gender-matched normal descending thoracic aortas at levels T4-T12. The mean circumference of the TAAs was 153 mm (n = 12) and 148 mm (n = 11) at T8 and T10, respectively, compared with 75 mm (n = 12) and 75 mm (n = 10) in controls (P < .001). Aortic tissue was collected from a separate set of eight patients undergoing descending TAA resection (processed < or =12 hours of excision) and six cadavers (processed < or =24 hours of death). Tissue collected between the intercostals arteries was defined as posterior wall, and directly opposite was the anterior wall. MMP-9 and MMP-2 messenger RNA (mRNA) extracted from aortic tissue was analyzed by quantitative real time polymerase chain reaction (PCR) and normalized to beta-actin. Immunohistochemistry was performed for MMP-9 and MMP-2. CT aortic measurements and MMP expression were compared by t tests and analysis of variance, respectively.

RESULTS

The ratio of arc distance between the intercostals on the posterior wall to total aortic circumference was 0.14 in healthy controls compared with 0.08 in TAAs at vertebral level T8 (P = .001). At T10, the ratio was 0.15 in healthy controls compared with 0.11 in TAAs (P = .001). MMP-9 expression in TAAs was 4.3-fold higher in the anterior wall compared with the posterior wall (P = .03). Conversely, MMP-2 expression in TAAs was 3.2-fold higher in the posterior wall compared with the anterior wall (P = .008). MMP expression was not detected in control cadaver aortas.

CONCLUSION

Anterior walls of expanding TAAs grow at a greater rate than the posterior wall, as determined from the lower ratio of intercostal arc distance to total circumference in TAAs. Differential MMP expression appears to be a biologic marker for asymmetric growth in the TAA wall.

CLINICAL RELEVANCE

The pathogenesis of thoracic aortic aneurysms (TAAs) is poorly understood. Multiple lines of evidence suggest that matrix metalloproteinases (MMPs), a family of enzymes, are important in aneurysm development. Earlier experiments documented a regional variation of MMP-9 in stimulated rodent aortas, with production greater in the abdominal aorta compared with the thoracic aorta. The present study extends that observation and documents asymmetric aneurysm development in the TAA wall, with increased anterior wall growth in correlation to increased MMP-9 production. An improved understanding of the mechanisms by which MMP production is regulated is critical.

Preservation of Spinal Cord Function After Extensive Segmental Artery Sacrifice: Regional Variations in Perfusion

BACKGROUND

Sacrifice of intercostal and lumbar arteries simplifies thoracoabdominal aneurysm surgery and enables endovascular stenting. Little is known about alterations in cord perfusion after extensive segmental artery sacrifice. We explored this question using hypothermia to reduce metabolism.

METHODS

Twelve juvenile Yorkshire pigs (mean weight, 22.3 kg) were randomized to segmental artery sacrifice at 32 degrees C or 37 degrees C. Cord integrity was assessed with myogenic-evoked potential (MEP) monitoring. Stepwise craniocaudal sacrifice of segmental arteries was continued until MEP diminution occurred; the last segmental artery was then reopened. Fluorescent microspheres were used to measure spinal cord blood flow (SCBF) at baseline, 5 minutes, 1 hour, and 3 hours after segmental artery sacrifice. Hind limb function was monitored for 5 days.

RESULTS

All animals recovered normal hind limb function. At 32 degrees C, more segmental arteries, 16.5 versus 15 (p = 0.03), could be sacrificed without MEP loss. Baseline SCBF at 32 degrees C was 50% that at 37 degrees C (p = 0.003) and remained fairly stable throughout. At 37 degrees C, SCBF to the craniocaudal extremes of the cord (C1 to T3 and L2 to L6) increased markedly (p = 0.01) at 1 hour and returned toward normal at 3 hours. Concomitantly, SCBF fell in the middle portion of the cord (T9 to T13) at 1 hour before returning to normal at 3 hours.

CONCLUSIONS

Almost all segmental arteries can be sacrificed with preservation of spinal cord function. No major change occurs in the central cord in normothermic animals, but there is significant transient hyperemia in segments adjacent to extrasegmental vessels. Hypothermia reduces SCBF and abolishes this possible steal phenomenon. Metabolic and hemodynamic manipulation should enable routine sacrifice of all segmental arteries without spinal cord injury.

Spinal cord ischemia may be reduced via a novel technique of intercostal artery revascularization during open thoracoabdominal aneurysm repair

OBJECTIVE

To describe a novel technique for maximal reimplantation of intercostal arteries during thoracoabdominal aortic aneurysm repair.

METHODS

Eight patients underwent thoracoabdominal aortic aneurysm (TAAA) repair with this new technique from 2005 to 2006. Follow-up ranged from 6 to 14 months. All patients had a previous type B dissection with subsequent aneurysmal degeneration into an extent I TAAA. Aneurysm repair was performed through a thoracoabdominal incision and circulatory arrest in seven and left atrial-left femoral (LA-FA) bypass in one. The grafts extended from the distal arch at the subclavian artery to the visceral and renal arteries. An 8 mm graft was then extended from the proximal to the distal graft with a spatulation of the graft allowing a side-to-side anastomosis of the graft to the posterior aortic wall incorporating multiple pairs of intercostal arteries. Intraoperative electroencephalogram (EEG) and somatosensory evoked potentials (SSEP) were monitored during each operation.

RESULTS

All patients were ambulatory at the time of admission. One patient had suffered a previous spinal cord infarction from the original dissection and had residual unilateral leg weakness prior to the TAAA repair. There was an average of seven pairs of patent intercostal arteries upon opening the aorta. We reimplanted an average of five pairs of vessels. There were no perioperative complications. No patients sustained transient or permanent paraplegia in the postoperative or follow-up period. The one patient with preoperative leg weakness had reported subjective increased strength in the affected leg after the operation. In four cases, normalization of SSEP waveforms did not occur until after reimplantation of the intercostal arteries despite full return of EEG waveforms, restoration of lower extremity perfusion, and rewarming of the patient. Follow-up CT scan angiogram demonstrated that all reconstructions were patent through the follow-up period.

CONCLUSIONS

Paraplegia is an extremely morbid complication associated with TAAA repair. We describe a technique that allows reimplantation of almost all intercostal arteries as one patch circumventing the need for selective reimplantation. Furthermore, our technique ensures continued patency of this patch graft as the outflow resistance is decreased by creating a continuous flow loop. Although this is a small case series, we had no incidence of acute or delayed paraplegia in this high risk group. Our technique of intercostal reimplantation is applicable to all open TAAA repair at high-risk for paraplegia and may be an important adjunct in preventing spinal cord ischemia.

Delayed Spinal Cord Deficits After Thoracoabdominal Aortic Aneurysm Repair

BACKGROUND

Limited information is available about the treatment and outcomes of delayed paraplegia after thoracoabdominal aortic aneurysm (TAAA) repair. The objective of this study was to assess factors that precipitate and favorably affect delayed-onset neurologic deficits.

METHODS

Over a 19-year period, 2,368 TAAA repairs were performed. Of the 93 patients (3.9%) who had postoperative paraplegia or paraparesis, 34 (37%) initially had intact neurologic function, but a delayed spinal cord deficit developed. We retrospectively examined clinical factors and events associated with development of the deficits, treatments used, and outcomes. Factors related to functional status were evaluated by comparing survivors who were ambulatory at discharge or transfer with those who were not.

RESULTS

The delayed deficits occurred between 13 hours and 91 days postoperatively and were associated with a period of hypotension in 9 patients (26%). Two patients (6%) died in hospital. Of the 32 patients discharged or transferred, 13 (41%) were ambulatory. Poor functional outcomes were associated with female sex, intraoperative cerebrospinal fluid drainage, fewer intercostal arteries reattached, and administration of corticosteroids or osmotic diuretics. The actuarial survival rate at 2 years was 80% +/- 13% for the ambulatory patients and 32% +/- 12% for the nonambulatory patients (p = 0.002).

CONCLUSIONS

Although precipitating episodes of hypoperfusion were common, most cases of delayed paraplegia occurred without such events, suggesting that other factors may play an important role in the development of this complication. Ambulatory status at discharge significantly predicts midterm survival.

The Hybrid Aneurysm Repair: Extending the Landing Zone in the Thoracoabdominal Aorta

We present two cases of concomitant management of a type I thoracoabdominal aneurysm and an infrarenal aneurysm via laparotomy, open infrarenal aortic replacement, visceral bypasses from the infrarenal graft, and finally endovascular exclusion of the thoracoabdominal aneurysm. While there are other reports of hybrid procedures for patients with preexisting aortic grafts in place or with retrograde visceral perfusion from a native iliac artery for type II thoracoabdominal aneurysm, these are the first reported cases of concurrent management of a type I thoracoabdominal aneurysm and an infrarenal aneurysm using the infrarenal graft as a distal landing zone for the thoracoabdominal endograft.

Proteinase systems and thoracic aortic aneurysm progression

Thoracic aortic aneurysms (TAAs) are a rare but potentially devastating condition. Current surgical treatment of TAAs usually involves a major operation, which conveys many risks to the patient. Better knowledge of the cellular events that lead to aneurysm formation may elucidate less morbid treatment options for this condition. A number of recent studies have identified that the relative abundance and activity of extracellular matrix (ECM) proteolytic systems are increased with TAAs. Specifically, the matrix metalloproteinases (MMPs) have been linked through numerous studies to TAA formation. MMPs comprise a family of ECM-degrading proteinases. Endogenous tissue inhibitors (TIMPs) normally regulate MMP activity, and the activation of MMPs is complex and tightly controlled. Aneurysm formation may be related to relative changes in the balance between MMP/TIMP abundance favoring proteolysis. Through ECM degradation, the medial layer will undergo structural remodeling and a loss of structural integrity, leading to TAA formation. The goals of this review are to examine the structure of the normal and aneurysmal thoracic aorta and to place the new findings regarding ECM proteolysis in perspective with regard to TAA formation and progression. Through an integration of basic and clinical studies regarding the underlying molecular basis for proteolysis of the thoracic aorta, improved diagnostic, prognostic, and therapeutic strategies for this disease process are likely to be realized.

Spatiotemporal expression and localization of matrix metalloproteinas-9 in a murine model of thoracic aortic aneurysm

OBJECTIVE

Matrix metalloproteinase-9 (MMP-9) has been widely described to play a critical role in aneurysm development. The goal of this study was to determine the spatiotemporal changes in MMP-9 expression and abundance in the early stages of aortic dilatation during the course of thoracic aortic aneurysm (TAA) formation in a mouse model.

METHODS

In this study, TAAs were surgically induced in a transgenic reporter mouse strain expressing the beta-galactosidase (beta-gal) gene under control of the MMP-9 promoter. Terminal studies were performed during the early stages of TAA development at 1 week (n = 6), 2 weeks (n = 6), and 4 weeks (n = 6) post-TAA induction surgery. Changes in aortic outer diameter were determined in vivo by video micrometry. MMP-9 transcriptional activity (beta-gal staining) and protein content (immunohistochemistry) were quantified at each time point and expressed as a percentage of unoperated reference control mice (n = 6).

RESULTS

Aortic dilatation was evident at 1 week and reached maximal size at 2 weeks (21% +/- 6% increase from baseline, P < .05). MMP-9 transcriptional activity was detected at 1 week post-TAA induction (722% +/- 323%, P = .19), reached a maximum within the adventitia at 2 weeks (1770% +/- 505%, P < .05), and returned to baseline by 4 weeks (167% +/- 47%, P = .21). MMP-9 transcription at 2 weeks colocalized with fibroblasts and smooth muscle cells. MMP-9 protein content within the aortic adventitia was increased at 2 weeks post-TAA induction (413% +/- 124%, P < .05) and remained elevated at 4 weeks (222% +/- 41%, P < .05). MMP-9 staining was most intense at the adventitial-medial border and could be detected throughout the elastic media.

CONCLUSIONS

These findings demonstrate a unique spatiotemporal pattern of MMP-9 transcriptional activation and protein content in the developing TAA. Colocalization studies suggest that early dilatation may be driven in part by MMP-9 produced by endogenous cells residing within the aortic vascular wall.

Thoracic stent-graft

The stent-graft is a device constructed from a stent and vascular graft and is inserted by means of an interventional procedure under imaging guidance. In 1986, Balko et al. reported the first stent-graft experiment, in which a Z stent covered with polyurethane was inserted into an animal aorta. In the early 1990s, Parodi et al. reported clinical introduction of the stent-graft for abdominal aortic aneurysm. In comparison to the abdominal aortic stent-graft, the thoracic stent-graft has several disadvantages, including difficulties associated with the aortic arch curvature and the relatively large caliber of the stent-graft, and the risk of central nervous system or spinal complication. However, the thoracic stent-graft is advantageous because of minimal procedural invasiveness in comparison to surgical graft replacement. In 1994, Dake et al. reported transluminal placement of an endovascular stent-graft for thoracic aortic aneurysm, and Kato et al. reported use of a stent-graft for aortic dissection and suggested that the stent-graft could be considered an alternative to surgical treatment.

Dynamic cine-CT angiography for the evaluation of the thoracic aorta; insight in dynamic changes with implications for thoracic endograft treatment

OBJECTIVE

Thoracic aneurysm preoperative imaging is performed using static techniques without consideration of normal aortic dynamics. Improved understanding of the native aortic environment into which thoracic endografts are placed may aid in device selection. It is unclear what comprises normal thoracic aortic pulsatility. We studied these phenomena dynamically using ECG-gated 64-slice CTA.

METHODS

Maximum diameter and area change per cardiac cycle was measured at surgically relevant anatomic thoracic landmarks in ten patients; 1.0 cm proximal and distal to the subclavian artery, 3.0 cm distal to the subclavian artery, and 3.0 cm proximal to the celiac trunk. Data was acquired using a novel ECG-gated dynamic 64-slice CT scanner during a single breath hold with a standard radiation dose and contrast load. Eight gated data sets, covering the cardiac cycle were reconstructed, perpendicular to the central lumen.

RESULTS

There is impressive change in both maximum diameter and area in the thoracic aorta during the cardiac cycle. Mean maximum diameter changes of greater than 10% are observed in the typical sealing zones of commercially available endografts corresponding to diameter increases of up to 5mm. Aortic area increases by over 5% per cardiac cycle.

CONCLUSIONS

ECG-gated dynamic CTA with standard radiation dose is feasible on a 64-slice scanner and provides insight into (patho) physiology of thoracic aortic conformational changes. Clinicians typically oversize thoracic endografts by 10%. With aortic pulsatility resulting in diameter changes of up to 17.8%, the potential exists for endograft undersizing, graft migration, intermittent type I endoleak, and poor patient outcome. Furthermore, aortic pulsatility is not evenly distributed, and non-circular stentgraft designs should be considered in the future since aortic distension in the aneurysm neck is not evenly distributed.

Stacked Proximal Aortic Cuffs:An “Off-the-Shelf” Solution for Treating Focal Thoracic Aortic Pathology

PURPOSE

To report our early experience with the endovascular placement of stacked Zenith main body extensions (cuffs) in the treatment of focal thoracic aortic pathology in high-risk patients.

METHODS

Between January 2003 and May 2004, 6 patients (3 men; mean age 59 years, range 37-82) with focal aortic pathology underwent endovascular repair using stacked 30 and 32-mm-diameter Zenith main body extensions. The setting was a university tertiary referral center for vascular disease. Indication for treatment included 2 descending thoracic aneurysms and individual cases of traumatic thoracic tear, diverticulum of Kommerell, thoracic pseudoaneurysm, and aortoesophageal fistula.

RESULTS

All procedures were performed successfully, with a mean of 3 cuffs used. The patient with an aortoesophageal fistula expired after successful cuff placement due to sequela of massive pretreatment hemorrhage; fistula coverage was confirmed at autopsy. There were no type I endoleaks. Morbidity included an occluded right subclavian artery from traumatic passage of the device through the artery. No left subclavian arteries were covered. No neurological deficits or paraplegia was observed. The cuffs were patent in all surviving patients at an average follow-up of 7 months (range 3-12). Computed tomography in all survivors confirmed adequate cuff placement, absence of endoleak, and lack of cuff migration. Based on this experience, the following technical recommendations are offered: (1) right subclavian cutdown when needed to reach a lesion beyond the range of the sheath, (2) Dacron chimney placement, (3) stiff guidewire usage, (4) wire placement from the right subclavian artery through the common femoral artery if necessary to ease a sharp bend in the arch, and (5) cuff overlap of 25% to 50%.

CONCLUSIONS

In high-risk patients, focal aortic pathology can be successfully treated with off-the-shelf commercially available cuffs using a stacking technique with acceptable mortality, morbidity, and short-term durability.