Fabian A. Kari

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.

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.

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.

Spinal cord blood flow and ischemic injury after experimental sacrifice of thoracic and abdominal segmental arteries

OBJECTIVE Spinal cord blood flow (SCBF) after sacrifice of thoracoabdominal aortic segmental arteries (TAASA) during thoracoabdominal aortic aneurysm (TAAA) repair remains poorly understood. This study explored SCBF for 72 h after sacrifice of all TAASA. METHODS Fourteen juvenile Yorkshire pigs underwent complete serial TAASA sacrifice (T4-L5). Six control pigs underwent anesthesia and cooling to 32 degrees C with no TAASA sacrifice. In the experimental animals, spinal cord function was continuously monitored using motor evoked potentials (MEPs) until 1h after clamping the last TAASA. Fluorescent microspheres enabled segmental measurement of SCBF along the entire spinal cord before, and 5 min, 1 h, 5 h, 24 h and 72 h after complete TAASA sacrifice. A modified Tarlov score was obtained for 3 days after surgery. RESULTS All the pigs with complete TAASA sacrifice retained normal cord function (MEP) until 1h after TAASA ligation. Seven pigs (50%) with complete TAASA sacrifice recovered after 72 h; seven pigs suffered paraparesis or paraplegia. Intraoperatively, and until 1h postoperatively, SCBF was similar among the three groups along the entire cord. Postoperatively, SCBF did not decrease in any group, but significant hyperemia occurred at 5h in controls and recovery animals, but did not occur in pigs that developed paraparesis or paraplegia in the T8-L2 segments (p=0.0002) and L3-S segments (p=0.0007). At 24h, SCBF remained marginally lower from T8 caudally; at 72h, SCBF was similar among all groups along the entire cord. SCBF in the segments T8-L2 at 5h predicted functional recovery (p=0.003). CONCLUSIONS This study suggests that critical spinal cord ischemia after complete TAASA sacrifice does not occur immediately (intraoperatively), but is delayed 1-5h or longer after clamping, and represents failure to mount a hyperemic response to rewarming and awakening. The short duration of low SCBF associated with spinal cord injury suggests that hemodynamic and metabolic manipulation lasting only 24-72 h may allow routine preservation of normal cord function despite sacrifice of all TAASA secondary to surgical or endovascular repair of large TAAA.

Redo Lateral Thoracotomy for Reoperative Descending and Thoracoabdominal Aortic Repair: A Consecutive Series of 60 Patients

BACKGROUND Reoperative descending thoracic aorta (DTA) or thoracoabdominal aortic aneurysm (TAAA) surgery is a challenge because of increased risk of lung injury and diffuse bleeding. METHODS Sixty patients (34 male, mean age 54.4 years) underwent redo thoracotomy for DTA (22 patients) or extended thoracoabdominal incision for reoperative TAAA (38 patients) from March 1988 to June 2007, after 1.7 +/- 0.9 previous cardioaortic procedures. Forty-one patients were hypertensive (68%), 18 were smokers (30%), 9 had Marfan syndrome (15%), 9 had coronary artery disease (15%), 5 had chronic obstructive pulmonary disease (8%), and 3 had diabetes mellitus (5%). In all, 45% (27 patients) had previous dissection, 30% (18) had atherosclerotic aneurysms, 15% had coarctation surgery (9), and 6 patients had other etiologies. Mean follow-up, 100% complete, was 6.5 years. RESULTS Hospital mortality for reoperative DTA/TAAA was 13.3% (8 patients). Although 6.3 +/- 2.9 (0 to 14) segmental artery pairs were sacrificed at reoperation-and 6.2 +/- 2.3 (1 to 12) initially-for a total of 10.6 +/- 3.9 (2 to 15) segmental artery pairs sacrificed, only 1 patient had paraplegia (1.6%). Four patients had a 2-day procedure, with 12 to 24 hours of intensive care unit recovery after lysis of extensive adhesions: all survived. Respiratory complications occurred in 13 patients (21.6%), and permanent dialysis was required in 2 (3.3%), but there were no strokes. Adverse outcome-1-year mortality, stroke, permanent dialysis, or paraplegia-occurred in 13 patients (21.6%). Adverse outcome was marginally associated (p < 0.2) with increased age, atherosclerotic aneurysms (33% versus 17% other), TAA incision (30% versus 9%), and greater aneurysm extent, and was significantly associated with perfusion technique (p = 0.02). Adverse outcome occurred in 3 of 4 patients who had clamp-and-sew technique, 6 of 21 using partial cardiopulmonary bypass (28.6%), and 3 of 17 with partial left heart bypass (17.7%), but only 1 of 18 with hypothermic circulatory arrest (5.6%). CONCLUSIONS Reoperative DTA/TAAA repair was significantly safer with hypothermic circulatory arrest rather than partial cardiopulmonary bypass, partial left heart bypass, or clamp-and-sew strategy. A 2-day procedure may be advisable for patients with extensive adhesions.