Treatment of acute aortic dissections with expandable metallic stents: experimental study

Custom-made Stent-Grafts for Aortic Aneurysm Repair Using Gianturco Z Stents and Woven Polyester: Healing in an Animal Model

The purpose of this study was to evaluate the healing at 6 months of aortic stent-grafts custom-made by using Z stents and woven polyester in an animal model. Stent-grafts were built by a published method using autoexpandable stainless steel stents continuously compiled with polyester sutures and covered with a woven polyester membrane. Fourteen stent-grafts of 3 different designs were deployed under fluoroscopic control into the thoracic and the abdominal aorta of 7 adult sheep. At 6 months, all the implants of the sheep that survived the implantation were angiographed and harvested for macroscopy and microscopy. All stentgrafts were implanted successfully and remained patent from then to the explantation procedure. All stent-grafts implanted among the 6 of 7 (86%) animals that survived after the implantation remained patent, stayed free from local complications, and did not migrate during more than 6 months. In all these cases during this period, the implant functioned as a satisfactory aortic substitute while the aortic segment containing the graft kept a normal structure. There was no adverse effects of the presence of the implant upon the aorta or the animal. Stent-grafts home-made according to the described methods gave results at 6 months in this animal model compatible with a safe clinical application among humans.

An experimental model of Stanford type B aortic dissection

PURPOSE

To create an experimental model of aortic dissection with a long-lasting patent false lumen as a proper animal model for development of less-invasive treatment for aortic dissection.

MATERIALS AND METHODS

Fifteen adult beagle dogs (weight, 10-12 kg) were used. The descending aorta was exposed by a left thoracotomy at the sixth intercostal space. The entry for the aortic dissection was created surgically just distal to the origin of the left innominate artery and the reentry was 5 cm distal to the entry point. Normal saline solution was injected into the aortic wall (ie, media) between these two points to create the dissection. The dogs were followed up at 1 day, 3 months, 1 year, and 2 years.

RESULTS

All 12 surviving dogs had completely patent true and false lumina without any thrombi. Microscopic examination showed that the dissection was created in the tunica media layer, making it identical to aortic dissection in humans. Color Doppler imaging confirmed the patency of the true and false lumina and the relatively narrowed true lumen.

CONCLUSION

In this canine model of aortic dissection, the false lumen has excellent long-term patency and the dissection plane is histologically similar to that in human aortic dissection. This model may contribute to the development of new treatments for Stanford type B aortic dissection.

Aortic Dissections: New Perspectives and Treatment Paradigms

Aortic dissection is a complex manifestation of disease of the arterial wall. The severity and consequences of a dissection are related to the physical characteristics and anatomic location of the tear as well as the underlying patient physiology. Despite in vitro and in vivo modeling advances, our understanding of the pathophysiology has been limited to evaluations of the success and failure of various treatment modalities. The indications for intervention have historically included rupture, intractable pain or hypertension, distal ischemia and degeneration of the aortic wall causing aneurysm formation. The management decisions for patients with dissections are dependent upon the abnormal anatomy, the acuity of the patient presentation, and physiology. Despite the availability of open surgery as a therapeutic option, acute dissections with evidence of ischemia are now handled using an endovascular approach that is specifically directed at the cause of the ischemia. Endovascular treatments include the placement of a stentgraft into the proximal aorta, branch vessel stenting, uncovered stent placement in the abdominal aorta, and aortic fenestrations. Chronic dissections, in contrast, are still most frequently managed with open surgical techniques. However, a subset of patients that are not candidates for traditional surgical repair of the thoracoabdominal aorta may be managed with a combined open mesenteric revascularization with subsequent endovascular grafting of the thoracoabdominal aorta.

Contemporary management of acute aortic dissection

The development of endovascular techniques has introduced a new dimension to the management of acute aortic dissection. Conventional therapy has traditionally been relegated to patients who experience severe clinical sequelae; unfortunately, clinicians have not been able to accurately predict the clinical consequences of a dissection. However, recent attention to true and false lumen characteristics, the distal extent of the dissection, and branch vessel involvement has demonstrated that these independent predictors of outcome can serve as surrogate indications for endovascular or surgical treatment. We review the pathophysiological mechanisms associated with the sequelae of aortic dissection and summarize the treatment paradigms we have developed.

Thoracic aortic stent-grafting

The surgical management of thoracic disease has improved steadily over the past 20 years due to advances in diagnostic and surgical techniques. Despite this progress, a less invasive approach to treatment is desirable. Patients with coexisting cardiovascular or pulmonary diseases may not tolerate aortic replacement under general anesthesia, particularly combined with extracorporeal bypass. Endovascularly placed stent-grafts offer an alternative therapy, which is less invasive and associated with a shorter hospital recuperation time than with traditional operative therapy. The authors discuss the development of stent-grafts for use in the thoracic aorta, along with the various techniques utilized during these complex procedures.

Treatment of chronic aortic dissection by transluminal endovascular stent-graft placement: preliminary results

PURPOSE

To investigate efficacy of stent-graft repair for the treatment of patients with chronic aortic dissection.

MATERIALS AND METHODS

Fifteen patients with chronic aortic dissection were treated with endovascular stent-grafts. Entry tears were located in the descending thoracic aorta in all patients. The mean maximum diameter of the descending thoracic aorta was 47 mm +/- 8. The mean diameter of the true lumen at the same level was 20 mm +/- 5. The mean interval between diagnosis and stent-graft procedure was 32 months +/- 91. Stent-grafts were fabricated from expanded polytetrafluoroethylene and Z-stents.

RESULTS

Stent-grafts were placed successfully in all patients. Two stent-grafts were required in one patient. Entry closure and thrombosis of the false lumen of the descending thoracic aorta were also achieved in all patients. No procedure-related complications were observed except for postimplantation syndrome, including fever and leukocytosis. The diameter of the true lumen was significantly increased (mean, 31 mm +/- 6) at the level of the descending thoracic aorta (P <.01) and the diameter of the aorta was significantly decreased (mean, 44 mm +/- 8) at the same level (P <.01). There were no deaths and no instances of aortic rupture during the subsequent average follow-up period of 24 months. Secondary stent-graft procedures were required to treat the abdominal component of dissection during follow-up in one patient.

CONCLUSIONS

Stent-graft repair of chronic aortic dissection is a safe and effective method and may be an alternative to surgical graft replacement in selected patients. However, further evaluation is mandatory before this method is widely employed.

Aortic stent grafting and side-branch embolization in an expanding chronic type B dissection

OBJECTIVE

This is a report of endovascular treatment of a case of type B thoracoabdominal aortic dissection in a patient with progressive dyspnea, dorsolumbar pain, and expanding aortic diameter over a 1-year period.

METHODS

Pretreatment imaging evaluation showed that the false lumen supplied only the celiac trunk. Endovascular treatment combined (1) embolization of the first segment of the celiac trunk to avoid distal back-flow into the false lumen and (2) stent grafting to occlude the initial entry tear.

RESULTS

The treatment resulted in technical and clinical success. The patient remains asymptomatic 12 months after treatment.

CONCLUSION

Stent grafting offers an interesting therapeutic alternative to exclude the initial entry tear in aortic dissection and may be combined with other endovascular procedures.

Endovascular stent-graft placement for the treatment of acute aortic dissection

BACKGROUND

The standard treatment for acute aortic dissection is either surgical or medical therapy, depending on the morphologic features of the lesion and any associated complications. Irrespective of the form of treatment, the associated mortality and morbidity are considerable.

METHODS

We studied the placement of endovascular stent-grafts across the primary entry tear for the management of acute aortic dissection originating in the descending thoracic aorta. We evaluated the feasibility, safety, and effectiveness of transluminal stent-graft placement over the entry tear in 4 patients with acute type A aortic dissections (which involve the ascending aorta) and 15 patients with acute type B aortic dissections (which are confined to the descending aorta). Dissections involved aortic branches in 14 of the 19 patients (74 percent), and symptomatic compromise of multiple branch vessels was observed in 7 patients (37 percent). The stent-grafts were made of self-expanding stainless-steel covered with woven polyester or polytetrafluoroethylene material.

RESULTS

Placement of endovascular stent-grafts across the primary entry tears was technically successful in all 19 patients. Complete thrombosis of the thoracic aortic false lumen was achieved in 15 patients (79 percent), and partial thrombosis was achieved in 4 (21 percent). Revascularization of ischemic branch vessels, with subsequent relief of corresponding symptoms, occurred in 76 percent of the obstructed branches. Three of the 19 patients died within 30 days, for an early mortality rate of 16 percent (95 percent confidence interval, 0 to 32 percent). There were no deaths and no instances of aneurysm or aortic rupture during the subsequent average follow-up period of 13 months.

CONCLUSIONS

These initial results suggest that stent-graft coverage of the primary entry tear may be a promising new treatment for selected patients with acute aortic dissection. This technique requires further evaluation, however, to assess its therapeutic potential fully.

Percutaneous creation of acute type-B aortic dissection: an experimental model for endoluminal therapy

PURPOSE

To evaluate the feasibility of a percutaneously created type-B aortic dissection as an experimental model for percutaneous therapy. This model was used to evaluate the hemodynamic effects of single-balloon fenestration of the intimal flap.

MATERIALS AND METHODS

Acute type-B dissections were created in descending aortae of 15 swine via a femoral (n = 6) or carotid (n = 9) approach. The initial subintimal tear was made with use of a Colapinto needle. The dissections were extended to a predefined position in the aorta. The proximal and distal tears were balloon dilated. The mural flap was balloon fenestrated in six animals, just above the celiac artery. Aortograms were obtained to establish the presence and extent of the dissection. Manometry was performed in both lumina to evaluate the hemodynamics of the dissected aorta and the effects of balloon fenestration in this model. Pathologic specimens were also examined.

RESULTS

Creation of dissection was successful in 11 of 15 animals, with six developing true lumen narrowing (group A). The other five animals (group B) had flow in both lumina without evidence of true lumen narrowing. After the creation of a single-balloon fenestration in the group A swine, the arteriograms revealed no evidence of blood admixture between the true and false lumina, and there was no change in the intravascular pressures. Examination of the explanted aortae showed a more extensive circumferential dissection in group A animals as compared with group B.

CONCLUSION

The percutaneously created acute type-B aortic dissection is a feasible model for experimentation. The hemodynamics of the aorta did not change after single-balloon fenestration in this model.

Percutaneous fenestration of aortic dissection: salvage of an ischemic solitary left kidney

The false channel of a type III aortic dissection caused acute renal ischemia by compression of the origin of the left renal artery in a patient with status post-right nephrectomy. To relieve the ischemia and restore renal function, percutaneous balloon fenestration was performed successfully.

Clinical application of transluminal endovascular graft placement for aortic aneurysms

BACKGROUND

In recent years, transluminal endovascular graft placement techniques have been developed for the treatment of aortic aneurysms. We report our initial clinical experience with endovascular graft placement using a graft developed in our laboratory.

METHODS

The procedure was performed in 20 patients with a diagnosed aortic aneurysm. The graft is constructed from a Dacron cylinder, and the surface of the graft is supported with multiple rings of extraflexible wire. After the compactly folded graft is delivered through the sheath to the predetermined target point, the graft is deployed and then pressed against the vessel by balloon inflation. Straight graft insertion was attempted in 10 patients, bifurcated graft insertion in 8, and branched graft insertion in 2.

RESULTS

Graft placement was successful in 19 of the patients and unsuccessful in 1. There were no cases of graft migration, aneurysm rupture, or graft destruction during a mean follow-up period of 9 months.

CONCLUSIONS

Initial clinical results demonstrated the efficacy and safety of endovascular graft placement using this graft.

Aortic dissection: percutaneous management of ischemic complications with endovascular stents and balloon fenestration

PURPOSE

The purpose of this study was to evaluate endovascular stenting (EVS) and balloon fenestration (BF) of intimal flaps for the management of lower extremity, renal, and visceral ischemia in acute or chronic aortic dissection.

METHODS

Twenty-two patients (16 male, 6 female) with a median age of 53 years (range 35 to 77 years) underwent percutaneous treatment for peripheral ischemic complications of 12 type A (five acute, seven chronic) and 10 type B (nine acute, one chronic) aortic dissections.

RESULTS

Ten patients had leg ischemia, 13 had renal ischemia, and 6 had visceral ischemia. Sixteen patients were treated with EVS including 11 with renal, 6 with lower extremity, 2 with superior mesenteric artery, and 2 with aortic stents. Three patients had BF of the intimal flap, and three had BF in combination with EVS. Revascularization with clinical success was achieved in all 22 patients. Two patients died 3 days and 13.4 months after the procedure was performed, respectively. Of the remaining 20 patients, 1 is lost to follow-up, and 19 have persistent relief of clinical symptoms. Mean follow-up time is 13.7 months (range 1.1 to 46.5 months). One case was complicated by guidewire-induced perinephric hematoma.

CONCLUSION

EVS and BF provide a safe and effective percutaneous method for managing peripheral ischemic complications of aortic dissection.

Endovascular graft placement in experimental dissection of the thoracic aorta

PURPOSE

To test the effectiveness of endoluminal exclusion of the false lumen in experimental thoracic aortic dissection by occlusion of the entry site with a balloon-expandable endograft.

MATERIALS AND METHODS

Thoracic aortic dissections were induced surgically in six beagles. The endograft consisted of an ultrathin, 12-mm-wide polyester tube sutured over a Strecker stent that was already crimped onto an angioplasty balloon. Fluoroscopic and intravascular ultrasonographic (IVUS) guidance were used. Endografts were introduced by means of femoral arteriotomy, via a 12-F sheath positioned in the aorta, and were then expanded on the angioplasty catheter.

RESULTS

IVUS and aortography showed an extensive thoracic dissection in all animals. Only four of six endografts were successfully placed. At 1 month, all thoracic endografts were patent, but the false lumen was never thrombosed. IVUS scans demonstrated a malpositioned endograft in two cases and persistent reentry in all cases.

CONCLUSION

Endovascular grafting of the aorta was feasible in experimental thoracic aortic dissection, but thrombosis of the false lumen was not achieved.

Treatment of aortic dissections with a percutaneous intravascular endoprosthesis: comparison of covered and bare stents

PURPOSE

The authors developed a percutaneous endoprosthesis for treatment of aortic dissections. The device is a Gianturco stent wrapped with Dacron or nylon mesh. Effectiveness of the covered stent versus a bare stent was compared in the treatment of acute aortic dissection.

MATERIALS AND METHODS

Experimental aortic dissections were created in 10 mongrel dogs. Occlusion of intimal tears was attempted with covered stents in five dogs (group 1) and with bare stents in the remaining five dogs (group 2).

RESULTS

In group 1, entry tears were obliterated within 1 day (n = 3) or 1 week (n = 2) after stent placement and false lumina were thrombosed within 1 week (n = 3) or 1 month (n = 2). In group 2, entry tears and false lumina remained patent. Histologic specimens showed that the covered stents were entirely covered with smooth neointima.

CONCLUSIONS

This endoprosthesis offers an alternative to surgical treatment for dissections of the descending aorta.