Primary aortic coarctation in neonates, infants, children,

Selective Use of Left Heart Bypass for Aortic Coarctation Andrew C. Fiore, MD, Mark Ruzmetov, MD, PhD, Robert G. Johnson, MD, Mark D. Rodefeld, MD, Karen Rieger, MD, Mark W. Turrentine, MD, and John W. Brown, MD Section of Cardiothoracic Surgery, St. Louis University School of Medicine, St. Louis, Missouri, and Division of Cardiothoracic Surgery, Indiana University School of Medicine, Indianapolis, Indiana Background. We evaluated left heart bypass (LHB) for spinal cord protection during aortic coarctation repair in patients with mild (primary, postsurgical, or intervention) and complex coarctation. Methods. Between 1990 and 2008, 19 patients (mean age, 21 years; weight, 70 16 kg) using LHB were compared with 27 patients (mean age, 16 years; weight, 65 8 kg) undergoing coarctation repair without LHB (non-lhb). Follow-up was similar (LHB, 5 4 vs non- LHB 4 3 years; p 0.81). Results. Cohorts were similar in age and body surface area. No non-lhb patient lost somatosensory evoked potential or had a femoral artery pressure below 45 mm Hg with test clamping. LHB more often allowed graft interposition (18 of 19 [95%] vs non-lhb, 7 of 27 [26%]; p < 0.003) and a longer clamp time (LHB 44 16 vs non-lhb 31 12 minutes p < 0.003) without spinal cord ischemia. Two non-lhb patients had temporary spinal cord paresis. No early or late deaths occurred. Reintervention (LHB, 2 of 19 [11%] vs non-lhb, 2 of 27 [7%]; p 0.82) and antihypertensive requirements were similar (LHB, 9 of 19 [40%] vs non-lhb, 8 of 27 [30%]; p 0.35). The late peak transcoarctation gradient was 8 6mmHg in the LBH cohort vs 18 11 mm Hg in non-lbh patients (p 0.001). Conclusions. Although the adequacy of spinal cord collateral assessment in coarctation repair is imperfect, no spinal cord ischemia occurred with coarctation repair and LHB. We recommend LHB in patients with mild or complex coarctation. (Ann Thorac Surg 2010;89:851 7) 2010 by The Society of Thoracic Surgeons Primary aortic coarctation in neonates, infants, children, and young adults can be repaired currently with an overall early mortality and morbidity of less than 1% or 2%. Paraplegia complicating coarctation repair remains the most feared postoperative complication. In a landmark meta-analysis of 12,532 patients undergoing repair of aortic coarctation, Brewer and associates [1] reported spinal cord complications in 1 of 250 patients (0.415%). Keen [2] reviewed 5492 patients with aortic coarctation repair and reported an incidence of 0.3%. However, in older children, adults, and those patients undergoing operations for recurrent or mild coarctation, the paraplegia risk is higher, ranging from 2.5% to 3% [3]. Ischemia to the cord may occur because of prolonged proximal aortic occlusion, interruption of vital collateral arteries, or absence of an adequate collateral circulation. The development of collateral arterial perfusion to the spinal cord in patients with coarctation is variable. The development (or lack thereof) of a collateral arterial supply to the spinal cord may be affected by four clinical Accepted for publication Nov 23, 2009. Presented at the Forty-fifth Annual Meeting of The Society of Thoracic Surgeons, San Francisco, CA, Jan 26 28, 2009. Address correspondence to Dr Fiore, Section of Cardiothoracic Surgery, St. Louis University Health Sciences Center, Cardinal Glennon Children s Hospital, 1465 S Grand Blvd, St. Louis, MO 63104; e-mail: fiorem2@slu.edu. circumstances: mild primary coarctation, postsurgical repair recurrent coarctation (with or without aneurysm), origin of a subclavian artery distal to the coarctation, and recently, recurrent coarctation after inadequate balloon dilatation or stent placement by interventionalists. In consideration of these conditions that might decrease the stimulus for collateral development, we have selectively used left heart bypass (LHB), consisting of left inferior pulmonary vein (or left atrial appendage) to descending thoracic aortic perfusion, since 1990. This article reports a study evaluating our selective use of LHB in patients undergoing coarctation repair by comparing their morbidity with that of patients not selected for active augmentation of their distal descending thoracic aortic perfusion. Patients and Methods This study was approved by the Institutional Review Boards at Indiana University and St. Louis University Schools of Medicine. The need for individual consent in this retrospective study was waived. LHB Group From January 1990 to November 2008, 801 patients underwent aortic coarctation repair at Indiana and St. Louis University Schools of Medicine, of whom 46 were aged 7 2010 by The Society of Thoracic Surgeons 0003-4975/10/$36.00 Published by Elsevier Inc doi:10.1016/j.athoracsur.2009.11.060

852 FIORE ET AL Ann Thorac Surg BYPASS FOR AORTIC COARCTATION 2010;89:851 7 years or older and 19 selectively had LHB. Recurrent postsurgical coarctation was present in 12, primary coarctation of a mild degree in 4, and 3 were presenting after a catheter-based intervention. Of the 12 patients with previous coarctation repair, the original operation included patch aortoplasty with Dacron (DuPont, Wilmington, DE) in 6 or Gore-Tex (W. L. Gore and Assoc, Flagstaff, AZ) in 1, Dacron interposition graft in 3, subclavian flap aortoplasty in 1, and resection with end-toend anastomosis in 1. The interventional procedures included stent placement with fracture in 2 patients and balloon dilation in 1. Five patients had a coarctation aneurysm after previous patch angioplasty at a mean interval of 18 7.5 years (range, 9 to 28 years), and 3 patients had saccular aneurysms in association with unrepaired coarctation. The mean coarctation gradient in these 8 aneurysmal patients was 13.2 mm Hg (range, 0 to 35 mm Hg). During the period of this review, patients considered to be at risk for poor collateral development underwent a variety of tests in an attempt to access their collaterals. Collateral blood flow to the spinal cord was judged insufficient by one or more of the following preoperative and intraoperative criteria. Preoperative criteria were: absence of adequate spinal cord collaterals on magnetic resonance imaging or a coarctation gradient of 20 mm Hg or less at diagnostic catheterization, or both. Intraoperative criteria were determined during a period of aortic test clamping and included the loss of spinal somatosensory evoked potential (SSEP) or a decrease in mean femoral artery pressure (FAP) to less than 45 mm Hg. The indications for selecting LHB included mild coarctation (primary, postsurgical, or intervention), aneurysm, complex coarctation anticipated to require prolonged cross-clamp time, or coarctation with demonstrated collateral circulation insufficiency. Non-LHB Group From the remaining 782 patients, 27 patients aged 7 years or older underwent coarctation repair without extracorporeal circulation. The mean age of the LHB cohort was older than the overall mean age because most children Table 1. Patient Demographics and Preoperative Variables Variable a LHB Non-LHB p Value Patients, No. 19 27 Age, y 21.2 10.3 16.5 8.1 0.06 Male sex 10 (53) 16 (59) 0.40 BSA, m 2 1.8.1 1.7.1 0.50 Prior operations 12 (63) 4 (15) 0.001 Trans-CoA gradient, 25 19 46 11 0.001 mm Hg b Test clamp FAP, mm Hg 33 5 50 13 0.01 a Continuous variables are presented as mean standard deviation; categoric variables as number (%). b Obtained at cardiac catheterization. BSA body surface area; CoA coarctation of the aorta; FAP femoral artery pressure; LHB left heart bypass. are repaired before age 6. Therefore, we selected as a comparison group patients aged 7 years or older who did not have LHB. This operations in this group included primary coarctation in 22, recurrent coarctation in 4, and postballoon coarctation repair in 1. Table 1 compares patient demographics and characteristics of the two groups. Surgical Technique Our use of LHB follows the elegant description by Backer and colleagues [4]. After placement of an endotracheal tube for selective right lung ventilation, right radial and femoral arterial catheters, and a selective epidural catheter for postoperative pain management and SSEPs, patients were placed on a beanbag for a left thoracotomy. We selectively used upper and lower extremity nearinfrared spectroscopy. Hypercapnia (arterial pressure of CO 2 at 45 to 55 mm Hg) was used to enhance cerebral blood flow. A posterior fourth interspace left thoracotomy incision was followed by dissection of the left common carotid artery, the left subclavian artery, the coarctation site, and the descending thoracic aorta beyond the inferior pulmonary vein. The aortic arch proximal to the left subclavian artery was test clamped for 7 to 10 minutes, keeping the right upper extremity blood pressure of 150 to 200 mm Hg with volume expansion and inotropic drugs, if necessary. Vasodilatory drugs (eg, nitroprusside) were assiduously avoided. If the mean FAP fell below 45 mm Hg or loss of the SSEP signal was recorded, then the test clamp was removed and extracorporeal circulation was instituted. Heparin was administered (75 to 100 U/kg) to maintain the activated clotting time from 200 to 250 seconds. Pursestring sutures were placed at the lowest convenient location in the descending aorta and in the inferior pulmonary vein or, in 3 patients, the left atrial appendage. LHB entailed use of a centrifugal or roller pump without an oxygenator, keeping the pump flow at 50% to 60% of maximal flow (2.5 L/min/m 2 ) for each patient. Flow was thereafter adjusted to maintain targeted right radial mean pressures of 110 to 130 mm Hg and a FAP greater than 45 to 50 mm Hg. Rectal or nasal pharyngeal temperature was maintained at 33 to 35 C. The proximal clamp was applied before the left common carotid artery origin or between the left common carotid and left subclavian arteries. After distal clamp application just above the aortic cannula, the coarctation was repaired with a Hemashield (Boston Scientific, Natick, MA) woven-double velour impregnated interposition graft or Gore-Tex (polypropylene) patch angioplasty using continuous 4-0 Prolene (Ethicon, Somerville, NJ) for interposition grafts and 5-0 Gore-Tex suture for Gore-Tex patches. To insert the largest possible interposition graft, the clamps were applied to permit enlargement of the proximal aorta along the lesser curvature and the distal aorta along the greater curvature. Air was removed from the graft by removal of the distal clamp, followed by slow removal of the proximal clamp. After bypass was termi-

Ann Thorac Surg FIORE ET AL 2010;89:851 7 BYPASS FOR AORTIC COARCTATION 853 nated, the left subclavian artery was reimplanted into a Dacron side arm (7 to 9 mm) previously attached to the aortic graft in 8 patients and left in situ in the others. Decannulation was performed after heparin reversal with protamine. If LHB was not required, the test clamp was removed for 5 to 7 minutes to permit lower body reperfusion. The subsequent operation was identical except clamp application proximal to the left common carotid artery was avoided whenever possible and FAP was continuously monitored with SSEPs. Ambient room temperature, irrigation fluid, and surface cooling were adjusted to facilitate the maintenance of core temperature from 34 to 36 C. Steroids were used selectively, and no patient received cerebrospinal fluid drainage. Definitions We defined coarctation if any of the following was present: aortic diameter reduced 50% or more compared with the diaphragmatic aorta, hypertension in the upper extremity at or beyond the 95th percentile for age and gender, symptoms of associated distal ischemia, or an arm/leg gradient at rest of 20 mm Hg or more. Mild coarctation was defined as an aortic diameter reduced less than 50%, upper extremity limb hypertension less than the 95th percentile, or a resting arm/leg gradient of 0to20mmHg. Spinal SSEP recordings were obtained before test clamping and repeated every 5 minutes during the period of aortic occlusion and during reperfusion until full recovery was observed. A positive response was defined as more than a 50% loss at the first negative to the first positive interpeak amplitude of the evoked potential. Follow-Up Data were obtained for each patient from outpatient, surgical, and cardiology records and by direct communication with patients, family members, and primary care physicians. Statistical Analysis Data analysis was performed using SPSS 10 software (SPSS Inc, Chicago, IL). Values are expressed as means, medians, and ranges, as indicated. Data were analyzed using the 2 test for categoric variables and continuous variables were examined with the t test. Event-free rates are presented with 1 standard error of the estimate. Early death is defined as death in the hospital or within 30 days of discharge, and all other deaths are considered late. Results Patient Demographics The two groups were similar with respect to age, weight, and body surface area. Consistent with our LHB selection criterion of operation complexity, a significantly greater number of patients in the non-lhb cohort underwent a primary coarctation operation compared with the LHB Table 2. Operative Characteristics Variable a LHB Non LHB p Value Patients, No. 19 27... CPB, min 82 20 (48 120) N/A... Cross clamp, min 44 16 (26 90) 31 12 0.003 Graft diameter, mm 18 4 16 2 0.46 Interposition graft 18 (95) 7 (26) 0.0001 Patch aortoplasty 1 (5) 20 (74) 0.0001 End-to-end anastomosis 0 1 0.24 Reimplantation of LSCA 8 (42) 0 0.0003 a Continuous variables are presented as mean standard deviation (range); categoric variables as number (%). CPB cardiopulmonary bypass; LHB left heart bypass; LSCA left subclavian artery; N/A not applicable. cohort. Patients selected for LHB had a mean preoperative arm/leg gradient of 33 18 mm Hg that trended lower than the gradient of 40 13 mm Hg in non-lhb patients (p 0.32). LHB was indicated for spinal cord collateral insufficiency by the following (nonmutually exclusive) variables: collateral arteries were not visualized by magnetic resonance angiogram in 8 of 15 patients (53%) and the coarctation gradient was less than 20 mm Hg in 8 of 14 (57%). After aortic test clamping, the SSEP signal was lost in 8 of 15 patients (53%) and the FAP was less than 45 mm Hg in 14 of 17 (82%). According to our selection criteria, all non-lhb patients had a transcoarctation gradient exceeding 20 mm Hg and a FAP exceeding 45 mm Hg after test clamping. None of the non-lhb patients lost the SSEP signal after test clamping. Follow-up was complete in all patients with a mean of 4.5 3.6 years (range, 0.2 months to 11 years). The mean follow-up was 5 4 years for LBH vs 4 3 years for non-lhb, which was not significantly different (p 0.81). Surgical Outcomes Surgical outcomes are summarized in Table 2. Patients required cardiopulmonary bypass from 48 to 120 minutes, during which time the mean FAP was maintained at 46 5.2 mm Hg and the core temperature at 33 2 C. In the LHB cohort, 18 patients, (95%) received an interposition graft that ranged in size from 12 to 26 mm. Most of the non-lhb patients received patch angioplasty, and none required reimplantation of the left subclavian artery. The mean duration of hospital stay was 2 days longer when patients were supported with extracorporeal circulation (LHB, 10 7 days vs non-lhb, 8 7 days; p 0.24). Hospitalization was prolonged in 3 patients, all in the LHB cohort. One patient required two operations because of endocarditis involving a stent graft, and nonspecific abdominal pain developed in the 2 remaining outliers that resolved without any surgical intervention.

854 FIORE ET AL Ann Thorac Surg BYPASS FOR AORTIC COARCTATION 2010;89:851 7 Mortality and Morbidity At the last follow-up, there were no early or late deaths in either cohort. No patients required reoperation for chylothorax or for bleeding, and no permanent left recurrent laryngeal nerve injury was documented. Transient spinal cord paresis developed in 2 patients in the non-lhb cohort with clamp application proximal to the left common carotid artery. One was a 14-year-old with a transcoarctation gradient of 25 mm Hg who inadvertently had vasodilator infusion with a FAP of 55 mm Hg during a 37-minute cross-clamp for interposition graft insertion. Weakness developed with loss of pain and temperature sensation. In a 16-year-old with a 35 mm Hg coarctation gradient and FAP of 55 mm Hg during cross-clamping, similar paresis with urinary incontinence developed after a 48-minute cross-clamp time for patch angioplasty. In each case, the SSEP amplitude remained constant. Both patients were neurologically normal by 48 hours postoperatively. Late Outcome Reoperation was required at 3 weeks for patch enlargement of proximal aortic stenosis in 1 patient and at 5 and 8 years for insertion of a large interposition graft in 2 patients. During the follow-up period, the frequency of any intervention was 11% (2 of 19) in the LHB cohort vs 7% (2 of 27) non-lhb, which was similar (p 0.82). At the latest follow-up, the peak echocardiographic transcoarctation gradient was lower in LHB patients (8 6vs18 11 mm Hg; p 0.001). The need for antihypertensive medication trended higher in the LHB group at 47% (9 of 19) vs 30% in the non-lhb (8 of 27, p.35), perhaps consistent with the fact that this cohort was older and had been hypertensive longer than non-lhb patients. Comment This brief clinical review with relatively short follow-up demonstrates that our selective use of LHB as an adjunctive procedure for lower body and spinal cord perfusion is a safe technique that allows longer cross-clamp times with similar morbidity and mortality as that achieved in those not selected for LHB. Given the retrospective nature of the study, it is impossible to know that patients selected for LHB were indeed at greater risk for spinal cord injury, but the selection criteria are known risk factors. That no spinal cord morbidity occurred in the LHB group despite these risk factors and longer crossclamp times may be evidence of the benefit for distal aortic perfusion in redo coarctation patients, older patients, and a subset of primary repairs. Several of our LHB selection criteria were variables measured preoperatively and intraoperatively. Which of these might be appropriate for the routine evaluation of these patients remains to be further elucidated, but intraoperative test clamping has become routine in our practices. The use of LHB during coarctation operations is an intuitively appropriate practice because proximal aortic cross-clamping acutely interrupts the distal aortic flow and, in the absence of adequate collaterals, may result in ischemia to the spinal cord and lower body organs. The ability to quantitatively determine adequate collateral flow to the spinal cord preoperatively in patients with coarctation is highly desirable, but problematic. In this study, among 27 patients in whom we believed had appropriate spinal cord collateral flow and therefore did not use LHB during proximal aortic clamping, 2 patients (7.4%) manifested cord injury albeit transient paresis. Patients presenting with recurrent coarctation after repair or catheter intervention (with or without aneurysmal change), mild primary coarctation, or a left subclavian artery distal to the coarctation site represent the highest risk for insufficient collateral spinal cord perfusion during operation. We, and others, have observed lower transcoarctation gradients at the time of catheterization in such patients [5]. Magnetic resonance angiography (MRA) is an important current screening modality to visualize the presence or absence of collateral vessels in patients with aortic coarctation. Holmqvist and coworkers [6] recently quantified collateral flow with magnetic resonance velocity mapping in patients with varying degrees of coarctation [6]. Patients with no or mild collaterals had a 12% 20% increase in proximal-to-distal aortic flow, whereas aortic velocity increased to 69% 55% in patients with pronounced collaterals. Christenson and associates [7] observed that poor collateral flow observed using MRA was strongly correlated with lower FAP after aortic clamping. MRA can also be used to define blood flow in the circle of Willis and spinal cord perfusion through the left subclavian artery. This additional information is useful in suggesting a benefit of LHB during repair. We now recommend this preoperative imaging modality in all of our patients. Evidence during the last 30 years has suggested that patients in whom the FAP remains at 45 to 50 mm Hg after proximal aortic clamping have a low incidence of spinal cord infarction [8]. Watterson and coworkers [9] made the important observation that hypotensive drugs must be avoided during proximal aortic clamping to achieve the desired higher FAP. In our series and in those of other investigators, patients with mild coarctation had significantly lower FAP with test clamping, indicating poor collateral circulation of the spinal cord and would benefit with LHB [10, 11]. However, this positive response to test clamping was present in 8 of 15 patients in the LHB cohort. The 3 patients measured with an FAP greater than 45 mm Hg and 2 additional patients not measured had coarctation aneurysms, necessitating their selection for LHB. Spinal SSEPs to monitor electrophysiologic function during thoracic aortic operations is another modality to assist in the assessment of spinal cord perfusion. Degradation of SSEPs in signal amplitude or latency indicates posterior and lateral spinal column dysfunction, implying cord ischemia. Laschinger and colleagues [12] demonstrated that during proximal aortic clamping, a FAP below 45 to 50 mm Hg is associated with loss of baseline

Ann Thorac Surg FIORE ET AL 2010;89:851 7 BYPASS FOR AORTIC COARCTATION 855 negative and positive SSEP signals. The main disadvantages of SSEPs are that they cannot detect motor deficits, and false-positive tracings can occur from cortical dysfunction secondary to the effects of ischemia, anesthetic agents, and peripheral nerve injury. Although none of the patients in the non-lhb cohort experienced loss of evoked potentials with crossclamping, transient cord paresis did develop in 2 patients. This observation illustrates the important conclusion that compromised spinal cord blood flow in a patient with coarctation can be caused by multiple factors and a single means of assessment may be insufficient and certainly inconclusive. Our intraoperative assessment of cord perfusion during aortic test clamping is imperfect, leading us to our current routine practice of also using noninvasive diagnostic technology preoperatively and spinal SSEPs with FAP monitoring intraoperatively as guidelines for the use of LHB. In 1994 Von Oppell and coworkers [13] published an important meta-analysis on spinal cord protection in patients with acute traumatic aortic transection, a milieu where enhanced collateral circulation to the spinal cord is absent. They demonstrated two important findings: (1) simple aortic cross-clamping without augmented lower body perfusion was associated with the highest risk of paraplegia, and the risk exponentially increased beyond 25 to 30 minutes of cross-clamp time; and (2) active perfusion with LHB provides the most optimal spinal cord protection compared with cross-clamping alone or the use of passive perfusion techniques. They did not observe paraplegia in the setting of lower body perfusion with the extracorporeal circuit unless the cross-clamp time exceeded 70 minutes. Mindful of these observations, the surgeon should err on the side of using LHB if a prolonged cross-clamp period is anticipated. In our series, selecting the use of LHB for more complex repairs was associated with longer cross-clamp times, but without any postoperative spinal cord injury. Patients with complex coarctation undergoing LHB received a more extensive repair of their thoracic aorta with excision of the aortic pathology, graft interposition, reimplantation of the left subclavian artery, and had a lower peak transcoarctation gradient at follow-up. Patch angioplasty, a technique associated with false aneurysm development, was more frequently used in non-lhb patients and was associated with a higher late trancoarctation gradient. From the literature and our experience in this series, we believe the safest technique to provide adjunctive spinal cord perfusion in patients with coarctation is LHB, which can deliver 50% to 60% of the cardiac output to the lower body by the extracorporeal circuit. This modality can be used safely and expeditiously in children of any age, if necessary. Clinical and experimental observations have shown LHB is superior to passive shunts in properly unloading the proximal aorta, normalizing to baseline the rise in cerebrospinal fluid pressure seen with proximal aorta clamping, and controlling precisely the proximal and distal flow throughout the procedure [14]. LHB also permits accurate regulation of core temperature (33 to 35 C) to ensure a uniform degree of hypothermia, an important variable to enhance protection of the lower body organs and spinal cord [15]. From this experience, we believe indications to use LHB include: 1. a FAP of less than 45 mm Hg or a loss of more than 50% of the interpeak SSEP amplitude with test clamping, indicating the potential for spinal cord infarction; 2. complex coarctation anatomy such as true or false aneurysm, infection in a previously placed graft, left subclavian artery arising distal to the coarctation, mild coarctation after operation or intervention, or the need for proximal clamp application before the left common carotid artery; and 3. patients in whom the surgeon believes the crossclamp time needed to repair the coarctation might exceed 20 to 25 minutes. Limitations This retrospective observational study was limited by small numbers and the lack of randomization. The intergroup comparisons were compromised by the active selection of nonequivalent patients into the two groups, perceived to have different operative risk factors. The non-lhb group underwent more primary coarctation operations and did not include children aged 1 to 6 years. Conclusions This review compares a selective strategy to use LHB in patients at increased risk of spinal cord ischemia. Using our selection criteria, we find that LHB is a safe and highly effective technique to augment spinal cord perfusion during complex coarctation operations. Recognizing the limitations in the assessment of lower body collateral flow in this setting, we recommend either routine use of LHB or selective use based on multiple modalities of evaluation in an effort to avoid postoperative spinal cord injury. We gratefully acknowledge Terri Wriley for her expert technical assistance with manuscript preparation and Jerry Pratt, Che Patrick-King, Shelly Wolfe, and Sherry Utterback for their assistance with monitoring SSEPs. References 1. Brewer LA 3rd, Fosburg RG, Mulder GA, Verska JJ. Spinal cord complications following surgery for coarctation of the aorta. A study of 66 cases. J Thorac Cardiovasc Surg 1972;64: 368 81. 2. Keen G. Spinal cord damage and operations for coarctation of the aorta: aetiology, practice, and prospects. Thorax 1987; 42:11 8. 3. Westaby S. Parnell B. Pridie RB. Coarctation of the aorta in adults. Clinical presentation and results of surgery. J. Cardiovasc Surg (Torino) 1987:28:124 7. 4. Backer CL, Stewart RD, Kelle AM, Mavroudis C. Use of partial cardiopulmonary bypass for coarctation repair through a left thoracotomy in children without collaterals. Ann Thorac Surg 2006;82:964 72.

856 FIORE ET AL Ann Thorac Surg BYPASS FOR AORTIC COARCTATION 2010;89:851 7 5. Wong CH, Watson B, Smith JR, Hamilton AH, Hasan A. The use of left heart bypass in adult and recurrent coarctation repair. Eur J Cardiothorac Surg 2001;20:1199 201. 6. Holmqvist C, Stahlberg F, Hanseus K, et al. Collateral flow in coarctation of the aorta with magnetic resonance velocity mapping: correlation to morphological imaging of collateral vessels. J Magn Reson Imaging 2002;15:39 46. 7. Christenson JT, Sierra J, Didier D, Beghetti M, Kalangos A. Repair of aortic coarctation using temporary ascending to descending aortic bypass in children with poor collateral circulation. Cardiol Young 2004;14:39 45. 8. Robertazzi RR, Acinapura AJ. The efficacy of left atrial to femoral artery bypass in the prevention of spinal cord ischemia during aortic surgery. Semin Thorac Cardiovasc Surg 1998;10:67 71. 9. Watterson KG, Dhasmana JP, O Higgins JW, Wisheart JD. Distal aortic pressure during coarctation operation. Ann Thorac Surg 1990;49:987 90. 10. Hughes RK, Reemtsma K. Correction of coarctation of the aorta. Manometric determination of safety during test occlusion. J Thorac Cardiovasc Surg 1971;62:31 3. 11. Lousto R, Kyllonen KE, Merikallio E. Surgical treatment of coarctation of the aorta with minimal collateral circulation. Scand J Thorac Cardiovasc Surg 1980;14:217:220. 12. Laschinger JC, Cunningham JN Jr, Copper MM, Baumann FG, Spencer FC. Monitoring of somatosensory evoked potentials during surgical procedures on the thoracoabdominal aorta. I. Relationship of aortic cross-clamp duration, changes in somatosensory evoked potentials, and incidence of neurologic dysfunction. J Thorac Cardiovasc Surg 1987;94:260 5. 13. Von Oppell UO, Dunne TT, de Groot KM, Zilla P. Spinal cord protection in the absence of collateral circulation: meta-analysis of mortality and paraplegia. J Card Surg 1994;9:685 91. 14. Cartier R, Orszulak TA, Pairolero PC, Scharff HV. Circulatory support during cross clamping of the descending thoracic aorta. Evidence of improved organ perfusion. J Thorac Cardiovasc Surg 1990;99:1038 47. 15. Crawford FA, Sade RM. Spinal cord injury associated with hyperthermia during aortic coarctation repair. J Thorac Cardiovasc Surg 1984;87:616 8. DISCUSSION DR CARL BACKER (Chicago, IL): Andy, that was a very nice presentation. We presented our results with left heart bypass for coarctation at the Society of Thoracic Surgeons meeting 3 years ago using a very similar technique. We have now used this in 20 patients with results identical to yours: no major morbidity, no mortality. In our group of patients, there was no difference in length of stay between the patients that had left heart bypass or not. I have two questions for you. One relates to the use of SSEP [somatosensory evoked potential]. I note that none of those patients in the nonleft heart bypass group had a drop in their SSEPs with their test clamp, and you took that as an indication that it was safe to proceed without the use of cardiopulmonary bypass. Then two of those patients had temporary postoperative paralysis. It seems to me that it was not helpful here. We have not used SSEP for our patients. Are you still using SSEP? DR FIORE: Thank you, Carl. As you know, the use of somatosensory evoked potentials to predict spinal cord ischemia is very controversial. Based on the information we learned from this study, my co-authors and I usually do not employ somatosensory evoked potential measurements in those patients in whom we know left heart bypass will be employed to repair complex coarctation. DR BACKER: The second question I had relates to the bypass circuit. We use a very short length of tubing, a pump with no oxygenator, and a small heater/cooler. It is a minor point, but we have been trying to do this without administering blood products. When we first started this, we used our regular circuit with an oxygenator and built-in heater/cooler and it took a lot of blood to prime the circuit. Now, the priming volume is very small. If there are any of the known potential risk factors for paraplegia; low preoperative gradient, major drop in the femoral pressure with test clamp, no collaterals preoperatively, et cetera, we always err on the side of using left heart bypass. It has a very low morbidity, and obviously paraplegia is a devastating complication. So, if you could make a comment about the mechanics of your bypass circuit. DR FIORE: We do not use an oxygenator. We do use a heat exchanger in the blood line. We try to keep the activated clotting time approximately 200 seconds using the HMS system. The pump is a biomedicus pump which contains tubing and an inline flow probe. The tubing is trillium coated to decrease the interaction between blood and the foreign surface. Unfortunately, I do not have any information with respect to blood product usage. It is important to remember that implicit in this technique is placement of a cross clamp on the mid or distal transverse aortic arch. In primary and more frequently in redo operations, this clamp may obscure exposure for performing the proximal suture line. As we all know, poor exposure can lead to an imperfect proximal graft anastomosis which may result in bleeding or the need for reoperation. The surgeon must be prepared to utilize the alternative technique employing femoral arterial and femoral venous cannulation with an oxygenator. The proximal graft anastomosis is performed open without any clamp application under a brief period of deep hypothermia and circulatory arrest. The distal anastomosis is completed with lower body perfusion from the femoral vessels, while the brain, heart and upper body are simultaneously perfused from a separate roller head through a Dacron perfusion side arm on the main graft. At the termination of bypass, the perfusion arm can be used for left subclavian artery reimplantation if needed. We have employed this alternative technique successfully for several patients in the setting of coarctation reoperation. DR JOSEPH AMATO (Chicago, IL): That was a great presentation. I believe that I am correct in making the following statement. There have been several centers that have advocated taking 2 or 3 or even more collaterals in repairing a primary coarctation. I have always been against this because I believe that taking those collaterals could cause ischemia. A second question I would like to ask is whether you used hypothermia and to what degree. DR FIORE: Thank you, Joe. I think in the majority in these cases, we have taken the first two intercostal arteries because it is usually necessary to extend the incision in the descending thoracic aorta along the greater curvature to perform an appropriate spatulated distal anastomosis with the Dacron graft. To answer your second question, we do use mild hypothermia to

Ann Thorac Surg FIORE ET AL 2010;89:851 7 BYPASS FOR AORTIC COARCTATION 857 approximately 33 34 degrees which we feel may enhance spinal cord protection. DR CHRISTOPHER CALDARONE (Toronto, Ontario, Canada): It is quite frightening that the 2 patients who had paraplegia had femoral artery pressures in the 50s after you test occluded them. At what age do you stop bothering to test and just go ahead with the repair anyway? DR FIORE: I think you should probably test all patients. DR CALDARONE: Okay. Even an infant? DR FIORE: No. Well, let me back up. Obviously, we do not test neonates or infants. DR CALDARONE: There is some crossover where we stop worrying about this. What is your crossover? DR FIORE: Well, the crossover age is unknown. The operating surgeon must analyze each case individually and decide for him or herself whether or not a high index of suspicion exists. We believe one can follow the guidelines proposed in our study. If so, then left heart bypass should be employed. In general, we error on the side of using left heart bypass. DR BROWN: I will make one comment. The 2 patients who had the transient neurologic events were transient. Both patients went home walking within a week post-op without any limp or any permanent deficit, but they did have demonstrable neurologic findings in the very early postoperative period. DR CALDARONE: The 2 patients you are talking about did not have permanent paralysis? DR FIORE: I think we said temporary paresis.