The collateral network concept: a reassessment of the anatomy of spinal cord perfusion.

OBJECTIVE: Prevention of paraplegia after repair of thoracoabdominal aortic aneurysm requires understanding the anatomy and physiology of the spinal cord blood supply. Recent laboratory studies and clinical observations suggest that a robust collateral network must exist to explain preservation of spinal cord perfusion when segmental vessels are interrupted. An anatomic study was undertaken. METHODS: Twelve juvenile Yorkshire pigs underwent aortic cannulation and infusion of a low-viscosity acrylic resin at physiologic pressures. After curing of the resin and digestion of all organic tissue, the anatomy of the blood supply to the spinal cord was studied grossly and with light and electron microscopy. RESULTS: All vascular structures at least 8 µm in diameter were preserved. Thoracic and lumbar segmental arteries give rise not only to the anterior spinal artery but to an extensive paraspinous network feeding the erector spinae, iliopsoas, and associated muscles. The anterior spinal artery, mean diameter 134 ± 20 µm, is connected at multiple points to repetitive circular epidural arteries with mean diameters of 150 ± 26 µm. The capacity of the paraspinous muscular network is 25-fold the capacity of the circular epidural arterial network and anterior spinal artery combined. Extensive arterial collateralization is apparent between the intraspinal and paraspinous networks, and within each network. Only 75% of all segmental arteries provide direct anterior spinal artery-supplying branches. CONCLUSIONS: The anterior spinal artery is only one component of an extensive paraspinous and intraspinal collateral vascular network. This network provides an anatomic explanation of the physiological resiliency of spinal cord perfusion when segmental arteries are sacrificed during thoracoabdominal aortic aneurysm repair.

Axillary cannulation significantly improves survival and neurologic outcome after atherosclerotic aneurysm repair of the aortic root and ascending aorta.

BACKGROUND: The impact of axillary artery cannulation (AXC) on survival and neurologic outcome after operation for ascending aortic disease was retrospectively evaluated. METHODS: We reviewed 869 patients with ascending aorta/root repairs (1995 to 2005), principally for atherosclerotic and degenerative aneurysms and chronic and acute type A dissections. Arterial cannulation was through the ascending aorta (AAC) in 157 patients, the femoral artery (FAC) in 261, and the right axillary artery (AXC) in 451. Patients cannulated at different sites were compared for preoperative comorbidities and outcomes (mortality and stroke) for each cause. RESULTS: Of the 122 patients with atherosclerotic aneurysms, 66 with right AXC had significantly better outcomes (p = 0.02): 64 of 66 survived vs 24 of 26 with FAC and 27 with 30 of AAC; no strokes occurred (vs 2 of 26 with FAC and 4 of 30 with AAC). No significant advantage for AXC was found with ascending aortic operation in 495 degenerative aneurysms, 106 chronic, or 65 acute type A dissections, 41 patients with endocarditis, or in 18 with aneurysms of other causes; AXC was associated with a significantly better outcome (p = 0.05) in the 869 patients taken together. CONCLUSIONS: AXC resulted in superior survival and neurologic outcome in patients with atherosclerotic aneurysms and a marginally better outcome than with cannulation at other sites during proximal aortic procedures for all causes. This study supports AXC in patients with atherosclerotic disease who require complex cardiothoracic operations and in patients requiring proximal aortic intervention regardless of cause.

Long-term survival after the Bentall procedure in 206 patients with bicuspid aortic valve.

BACKGROUND: The recognition that patients with a bicuspid aortic valve (BAV) are at risk for aorta-related death (rupture or dissection) has favored composite aortic root replacement in BAV patients who undergo aortic valve replacement for valve dysfunction as well as in asymptomatic BAV patients with significant aortic root dilatation. We report the results of Bentall operations in 206 BAV patients during an 18-year interval. METHODS: Two hundred six BAV patients (mean, 53 +/- 14 years, 84% male) underwent composite aortic root replacement between September 1987 and May 2005. One hundred nine patients (53%) presented with aortic regurgitation, 24 patients (12%) presented with aortic stenosis, and 55 patients (26%) presented with combined aortic stenosis and aortic regurgitation. Median preoperative aortic diameter was 5.5 cm (range, 3 to 9 cm). Twenty-two patients (11%) underwent urgent or emergent procedures; 11 had acute type A dissection (5%). Sixty-one percent had a mechanical valve Bentall prosthesis; in 39%, a biologic valve was implanted. Thirty-two percent had concomitant procedures. RESULTS: Overall hospital mortality was 2.9% (n = 6), and stroke rate was 1.9% (n = 4). Risk factors for adverse outcome (death or stroke), which occurred in 4.8% (n = 10), were presence of clot or atheroma (p = 0.02) and age older than 65 years (p = 0.05). During a mean follow-up of 5.9 years (1,200 patient-years; range, 5 to 18 patient-years), no patient required ascending aortic reoperation. Long-term survival was 93% after 5 years and 89% after 10 years. Discharged patients enjoyed survival equivalent to a normal age- and sex-matched population and superior to survival reported for a series of patients with aortic valve replacement alone. CONCLUSIONS: In patients with BAV, the Bentall procedure has an operative mortality no worse than that for aortic valve replacement, with superior long-term survival and a lower rate of aortic reoperation.

Vascular graft replacement of the ascending and descending aorta: do Dacron grafts grow?

BACKGROUND: The tendency of Dacron vascular grafts to expand after placement in the ascending and descending thoracic aorta has been noted, but never described in detail. METHODS: From 1986 to 2005, two or more computed tomography studies were obtained as part of routine postoperative surveillance in patients with Dacron grafts implanted to replace diseased aortic segments. Scans were digitized to evaluate the entire thoracic aorta. The median diameters of 547 grafts (18 to 34 mm) in the ascending (349) and descending (198) aorta were calculated from more than 2,000 postoperative computed tomography scans. RESULTS: In scans obtained 7 or fewer days after implantation, the median graft diameters increased from the manufacturer's measurement by 17% in the ascending aorta (n = 169; interquartile range, 11% to 21%; p < 0.0001) and 21% in the descending aorta (n = 63; interquartile range, 12% to 25%; p < 0.0001). From an initial scan within 30 days to at least one other within 18 months after implantation, ascending aorta grafts dilated further, at a median rate of 2.8% per year (n = 143; interquartile range, -2.2% to +6.9%; p = 0.0001). Descending grafts dilated less markedly: 1.1% per year (n = 80; interquartile range, -4.0% to +6.1%; p = 0.14). After 18 months, median graft expansion gradually diminished to less than 1% per year. CONCLUSIONS: Significant initial expansion and early growth of woven vascular Dacron grafts occurs; it is slightly different in the ascending and descending aorta. Graft expansion should be anticipated when selecting grafts for aortic valve-sparing procedures to prevent development of regurgitation, and, for endoluminal repair of thoracoabdominal aneurysms, to prevent development of type III endoleaks in the projected landing zone.

Aortic arch replacement with a trifurcated graft.

BACKGROUND: The purpose of this study was to review the results of aortic arch replacement using a trifurcated arch graft in conjunction with hypothermic circulatory arrest (HCA) and selective antegrade cerebral perfusion (SCP). METHODS: One hundred fifty consecutive patients (91 male; mean age, 63 +/- 14 years; range, 20 to 87) had aortic arch replacement using a trifurcated arch graft and HCA/SCP from September 1999 to December 2005. The axillary artery was used for cannulation; a trifurcated graft was sewn to the arch vessels during a short interval of HCA; SCP was utilized through the trifurcation graft during the proximal and distal arch repair, and then the trifurcation graft was sewn to the arch graft. Fifty-five patients had chronic dissection; 48 had atherosclerotic and 29 had degenerative aneurysms; 74 had undergone previous cardiac surgery. Isolated arch reconstruction was undertaken in 38 patients: concomitant procedures included ascending aortic replacement in 74; ascending aorta and root replacement in 21; descending replacement in 4, and coronary artery bypass grafting in 36. An elephant trunk was used in 144, but distal to the left subclavian artery in only 87; in 34, it was distal to the left carotid, in 9, it was between the brachiocephalic and left carotid, and in 18, it was proximal to all arch branches. Mean HCA duration was 31.1 +/- 6.5 minutes; SCP lasted 66.6 +/- 21.0 minutes, at a mean temperature of 15.8 +/- 2.1 degrees C. RESULTS: Adverse outcome occurred in 13 of 150 patients (8.7%): there were 7 hospital deaths and 6 permanent strokes. Temporary neurologic dysfunction was seen in only 7 patients, and renal failure was transient in 9 patients requiring dialysis. CONCLUSIONS: The use of a trifurcated arch graft with HCA and SCP is a safe and versatile technique for repair of arch aneurysms.