Christian D. Etz

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.

Paraplegia after extensive thoracic and thoracoabdominal aortic aneurysm repair: Does critical spinal cord ischemia occur postoperatively?

OBJECTIVE Spinal cord injury can occur not only during extensive thoracoabdominal aneurysm repair but also postoperatively, causing delayed-onset paraplegia. METHODS A series of 858 thoracoabdominal aneurysm repairs (June 1990-June 2006) with an overall paraplegia rate of 2.7% was analyzed retrospectively. Serial segmental artery sacrifice was monitored by using somatosensory evoked potentials; segmental arteries were not reimplanted. Of a total of 20 cases of paraplegia, 3 occurred intraoperatively and 7 occurred late postoperatively: these will not be analyzed further. In 10 cases (the paraplegia group) spinal cord injury occurred within 48 hours after thoracoabdominal aneurysm repair, despite intact somatosensory evoked potentials at the end of the procedure. These patients with early postoperative delayed paraplegia were compared with 10 matched control subjects who recovered without spinal cord injury. RESULTS In the paraplegia group a median of 9 segmental arteries (range, 5-12 segmental arteries) were sacrificed. There were 9 male subjects: median age was 63 years (range, 40-79 years), and 4 of 10 had cerebrospinal fluid drainage. A median of 9 segmental arteries (range, 2-12 segmental arteries) were also sacrificed in the matched recovery group. There were 4 male subjects; median age was 66 years (range, 40-78 years), and 8 of 10 had cerebrospinal fluid drainage. During the first 48 hours postoperatively, there were no significant differences in arterial and mixed venous oxygen saturation, partial arterial O2 and CO2 pressures, body temperature, glucose, hematocrit, or pH. The mean central venous pressures, however, were significantly higher in the paraplegic patients from 1 to 5 hours postoperatively (P = .03). In addition, although absolute mean aortic pressures did not differ between matched pairs postoperatively, when pressures were considered as a percentage of individual antecedent preoperative mean aortic pressure, paraplegic patients had significantly lower values during the first 5 hours postoperatively (P = .03). CONCLUSIONS This study suggests that paraplegia can result from inadequate postoperative spinal cord perfusion caused by relatively minor differences from control subjects in perfusion parameters. Delayed paraplegia can perhaps be prevented with better hemodynamic and fluid management.

Staged repair of thoracic and thoracoabdominal aortic aneurysms using the elephant trunk technique: a consecutive series of 215 first stage and 120 complete repairs

OBJECTIVES Repair of thoracic aneurysms (TA) involving the ascending, arch, and descending aorta results in substantial morbidity and mortality. This study evaluates outcomes with a two-stage elephant trunk (ET) technique. METHODS Two hundred and fifteen consecutive patients (pts) underwent total arch replacement using an ET (02/90-09/06). One hundred and thirty-nine pts (65%), group PC (planned completion; median age 68; 28-86 years), had extensive descending TA (Ø>/=5 cm) or dissections requiring complete repair. Seventy-six pts (35%), group CS (close surveillance; median age: 68; 20-87 years), had less severe distal dilatation (Ø</=5 cm), and had close follow-up after ET rather than planned distal repair. RESULTS Hospital mortality in group PC pts (descending Ø: 6.2+/-1.2 cm) was 6.5% (9/139) following ET. In group CS pts (descending Ø: 4.1+/-0.7 cm), hospital mortality after ET was 5.3% (4/76); 4.7% (10/215) had strokes but survived. Eighty-six percent (112/130) of group PC pts who survived proximal repair returned for planned surgical (101) or endovascular (11) completion after a median of 56 (0-2189) days. Hospital mortality for distal repair was 7.5% (9/120); two ET stage two pts (2%) developed paraplegia. Eighty-nine percent (16/18; descending Ø: 6.9+/-1.0 cm) of group PC pts who did not undergo planned completion died a median of 5.4 (1.2-91.1) months after ET stage one. Overall cumulative survival in group PC, which includes pts dying before or without stage two, was 69% after 1, and 55% after 5 years. Survival in group CS pts was 88% at 1, and 57% at 5 years. Eight pts in group CS subsequently underwent distal repair, but 22/76 (29%) group CS pts who survived ET stage one died during follow-up despite surveillance. CONCLUSIONS The low mortality after stage one justifies liberal use of the ET technique to facilitate future open or endovascular TA repair of the distal aorta. The 5-year cumulative mortality curves, however, suggest that staged repair of extensive TA is superior to one-step repair only if stage two can be done before rupture occurs. If one-step repair is possible, it may be preferable.

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.

The collateral network concept: Remodeling of the arterial collateral network after experimental segmental artery sacrifice

OBJECTIVE A comprehensive strategy to prevent paraplegia after open surgical or endovascular repair of thoracoabdominal aortic aneurysms requires a thorough understanding of the response of the collateral network to extensive segmental artery sacrifice. METHODS Ten Yorkshire pigs underwent perfusion with a low-viscosity acrylic resin. With the use of cardiopulmonary bypass, 2 animals each were perfused in the native state and immediately, 6 hours, 24 hours, and 5 days after sacrifice of all segmental arteries (T4-L5). After digestion of surrounding tissue, the vascular cast of the collateral network underwent analysis of arterial and arteriolar diameters and the density and spatial orientation of the vasculature using light and scanning electron microscopy. RESULTS Within 24 hours, the diameter of the anterior spinal artery had increased significantly, and within 5 days the anterior spinal artery and the epidural arterial network had enlarged in diameter by 80% to 100% (P < .0001). By 5 days, the density of the intramuscular paraspinous vessels had increased (P < .0001), a shift of size distribution from small to larger arterioles was seen (P = .0002), and a significant realignment of arterioles parallel to the spinal cord had occurred (P = .0005). CONCLUSIONS Within 5 days after segmental artery occlusion, profound anatomic alterations in the intraspinal and paraspinous arteries and arterioles occurred, providing the anatomic substrate for preservation of spinal cord blood flow via collateral pathways.

Current status and recommendations for use of the frozen elephant trunk technique: a position paper by the Vascular Domain of EACTS

The implementation of new surgical techniques offers chances but carries risks. Usually, several years pass before a critical appraisal and a balanced opinion of a new treatment method are available and rely on the evidence from the literature and experts opinion. The frozen elephant trunk (FET) technique has been increasingly used to treat complex pathologies of the aortic arch and the descending aorta, but there still is an ongoing discussion within the surgical community about the optimal indications. This paper represents a common effort of the Vascular Domain of EACTS together with several surgeons with particular expertise in aortic surgery, and summarizes the current knowledge and the state of the art about the FET technique. The majority of the information about the FET technique has been extracted from 97 focused publications already available in the PubMed database (cohort studies, case reports, reviews, small series, meta-analyses and best evidence topics) published in English.

How does the ascending aorta geometry change when it dissects

OBJECTIVES The purpose of this study is to delineate changes in aortic geometry and diameter due to dissection. BACKGROUND Aortic diameter is the major criterion for elective ascending aortic replacement for dilated ascending aortas to prevent aortic dissection. However, recommendations are made on the basis of clinical experience and observation of diameters of previously dissected aortas. METHODS Six tertiary centers on 2 continents reviewed their acute aortic dissection type A databases, which contained 1,821 patients. Included were all non-Marfan patients with nonbicuspid aortic valves who had undergone computed tomography angiography <2 years before and within 12 h after aortic dissection onset. Aortic geometry before and after dissection onset were compared. RESULTS Altogether, 63 patients were included (27 spontaneous and 36 retrograde dissections, median age 68 [57; 77] years; 54% were men). In all but 1 patient, maximum ascending aortic diameter was <55 mm before aortic dissection onset. The largest increase in diameter and volume induced by the dissection were observed in the ascending aorta (40.1 [36.6; 45.3] mm vs. 52.9 [46.1; 58.6] mm, +12.8 mm; p < 0.001; 124.0 [90.8; 162.5] cm(3) vs. 171.0 [147.0; 197.0] cm(3), +47 cm(3); p < 0.001). Mean aortic arch diameter increased from 39.8 (30.5; 42.6) mm to 46.4 (42.0; 51.6) mm (+6.6 mm; p < 0.001) and descending thoracic aorta diameter from 31.2 (27.0; 33.3) mm to 34.9 (30.9; 39.5) mm (+3.7 mm; p < 0.001). Changes in thoracic aorta geometry were similar for spontaneous and retrograde etiology. CONCLUSIONS Geometry of the thoracic aorta is affected by aortic dissection, leading to an increase in diameter that is most pronounced in the ascending aorta. Both spontaneous and retrograde dissection result in similar aortic geometry changes.

Flow-sensitive four-dimensional magnetic resonance imaging: flow patterns in ascending aortic aneurysms.

OBJECTIVE Pathological aortic flow patterns differ significantly from haemodynamics within the healthy aorta. Development and impact of pathological flow is largely unknown and might affect pathogenesis and the progression of thoracic aortic diseases. This study presents pathological blood-flow patterns within a series of six patients suffering from ascending aortic aneurysms investigated with high-detail flow-sensitive, four-dimensional (4D)-MRI and three-dimensional (3D) computer-aided flow-visualisation strategies. METHODS Data were acquired on a 3T magnetic resonance system (TRIO, Siemens, Erlangen, Germany) using a flow-sensitive 4D (time-resolved 3D) sequence protocol. Measurements were taken in synchrony with the cardiac cycle and under respiration control. After data pre-processing, blood-flow was visualised by means of systolic 3D streamlines and time-resolved 3D particle traces using the software EnSight (CEI, Apex, NC, USA) and homemade visualisation tools. We investigated six adult patients with ascending aortic aneurysms and one healthy individual and findings were compared to 3D-haemodynamics of the dilated ascending aorta described in current literature. RESULTS Normal blood-flow in the healthy volunteer resulted in highest velocities of up to 1 ms in the ascending and descending aorta, a right-handed helical flow pattern featuring 0.5-1.5 revolutions within the ascending aorta was present. Two atherosclerotic aneurysms presented either increased right-handed helical flow with flow acceleration along the great curvature, or multiple vortical flows in the sinuses and middle of the ascending aorta. One Marfan-associated aneurysm exhibited increased vortical flow in the dilated sinuses. One pseudo-aneurysm at the proximal anastomosis of an earlier supracoronary aortic replacement showed extensive vortex formation inside the aneurysms lumen. An aneurysm in a patient with a bicuspid aortic valve revealed one major vortex formation directly above the aortic valve. One aneurysm following congenital valvular stenosis and commissurotomy in childhood was characterised by helical diastolic backflow in the central ascending aorta and a vortex at the small curvature. CONCLUSION Patients with ascending aortic aneurysms reveal considerable differences in local flow patterns among themselves and compared to healthy individuals. Further investigations are necessary to identify flow patterns predisposing to aortic aneurysm development or adverse events in the course of aortic disease.

Long-Term Survival After Open Repair of Chronic Distal Aortic Dissection

BACKGROUND The optimal treatment of chronic distal aortic dissection remains controversial, with endovascular stent-graft techniques challenging traditional surgery. METHODS From January 1994 to April 2007, 104 patients (82 male, median age 60.5 years) with chronic distal aortic dissection underwent surgical repair, 0 to 21 years after initial diagnosis of acute type A or B dissection (median 2.1 years). Twenty-three (22%) patients underwent urgent-emergent surgery. Mean aortic diameter was 6.9 +/- 1.4 cm. Indications for surgery, other than aortic expansion, were pain in 6 (6%) patients, malperfusion in 6 (6%), and rupture in 11 (11%). Forty-nine (47%) had previous cardioaortic surgery (29% dissection-related), 21 (20%) had coronary artery disease, 12 (12%) had Marfan syndrome, and 4 (4%) were on chronic dialysis. Twenty-six (25%) had a thrombosed false lumen. Thirty (29%) patients required reimplantation of visceral arteries; 8.3 +/- 2.7 segmental artery pairs were sacrificed. RESULTS Hospital mortality was 9.6% (10 patients). Paraplegia occurred in 5 (4.8%). Twenty-seven patients (26%) experienced adverse outcome (death within one year, paraplegia, stroke, or dialysis). Adverse outcome was associated with atheroma (p = 0.04, odds ratio = 4.3). Survival was 78% at 1, 68% at 5, and 59% at 10 years (average follow-up, 7.7 +/- 4.1 years). Freedom from distal aortic reoperation was 99% at 1, 93% at 5, and 83% at 10 years. After one year, patients enjoyed longevity equivalent to a normal age-sex matched population (standardized mortality ratio = 1.38, p = 0.23). By multivariate analysis, atheroma (p = 0.0005, relative risk = 9.32) and age (p = 0.0003, relative risk = 1.15/year) were risk factors for long-term survival. CONCLUSIONS The efficacy of open repair for distal chronic dissection is highlighted by normal survival after the first year, and a low reoperation-reintervention rate.

Selective cerebral perfusion at 28 °C - is the spinal cord safe?

OBJECTIVE To shorten cooling/rewarming associated with hypothermic neuroprotection strategies during complex aortic arch surgery, selective cerebral perfusion (SCP) at 28 degrees C has recently been advocated, although its safe limits - especially with regard to the ischaemic tolerance of the spinal cord - have not been systematically examined. METHODS Twenty juvenile Yorkshire pigs (30.3+/-2.8kg) were randomly allocated to undergo circulatory arrest and SCP at 28 degrees C for 90 min (group A; N=12) or 120 min (group B; N=8) at 50 mmHg using alpha-stat pH management. Spinal cord blood flow (SCBF) was assessed using fluorescent microspheres at baseline (prior to SCP); at 5 and 80 min during SCP, and at 1, 5 and 48 h after cardiopulmonary bypass (CPB). A modified Tarlov score was used to evaluate neurobehavioural recovery in all survivors blindly from videotapes for 5 days postoperatively. Histological ischaemic spinal cord injury was scored after sacrifice. RESULTS All pigs could be weaned from CPB and ventilation, but seven pigs (58%) in group A and five (63%) in group B developed multi-organ failure and died within 24h. SCBF diminished immediately after initiation of SCP and was absent throughout SCP in all segments below T8/9, recovering to baseline 1h after SCP at all cord levels. All survivors suffered moderate-to-severe histological lumbar spinal cord damage, more severe in group B (p< or =0.049). Three of five group A pigs recovered normal function, but two suffered paraparesis. Group B survivors had a worse neurologic outcome (p<0.0001): all suffered paraplegia (one immediate, and two on day 2, after initial recovery). CONCLUSION SCP provides insufficient SCBF below T8/9 to sustain cord viability. At 28 degrees C, the ischaemic tolerance of the cord may be exceeded enough by 90 min to impair function; by 120 min, SCP at 28 degrees C invariably results in paraplegia.