Extrathoracic carotid reconstruction: The subclavian-carotid artery bypass

Transcription

1 Extrathracic cartid recnstructin: The subclavian-cartid artery bypass Wtlliam R. Fry, MD, Jhn D. Martin, MD, G. Patrick Clagett, MD, and Wtlliam J. Fry, MD, Dallas) Texas Althugh the predminant lcatin fsymptmatic cartid artery cclusive disease is the cartid b~catin, prximal cmmn cartid artery lesins cause similar symptms. Cmmn cartid artery lesins ccur as islated disease r in tandem with cartid bulb disease. Restratin fcartid arteryinflw frm subclavian based extraanatmic bypasses shuld prvide adequate recnstructin f these lesins. T evaluate subclavian-cartid artery bypass, a retrspective review' fall patients Wlderging this prcedure frm Jan., 977, t Feb. 0, 989, was perfrmed. Twenty patients (4 men, 6 wmen) with a mean age f 60 years were treated. Fifteen patients (75%) were admitted with transient ischemic attacks. Five (5%) had nnfcal symptms (e.g., dizziness, syncpe). Arterigraphicevaluatindemnstratedsevere prximal cclusivedisease fthe cmmncartid artery in all cases. Recnstructin bypasses were perfrmed t the cartid bulb (45%), internal cartid artery (0%), and external cartid artery (5%). Fur patients Wlderwent endarterectmyfthe internal cartid arteryincnjunctin with subclavian-cartid artery bypass. Bypass cnduits included saphenus vein (75%) and prsthetic grafts (5%). Asymptmatic phrenic nerve neurpraxia was identified by pstperative chest radigraphyin fur cases, with n resultant respiratry disease. N periperative strkes ccurred.. One pstperative death (5%) resulted frm a mycardial infarctin. Lng-term results were available fr 8 patients (90%), with 'a meanfllw-up f50 mnths (range, t mnths). Fur patients have died f causes tmrelated t cartid vascular disease. Serial. duplex scans have dcumented graft patency in all 8 patients. A single patient returned with fcal neurlgic symptms as a result f a psterir circulatin infarct. This experience dcuments that subclavian-t-cartid artery bypass appears t be a safe, durable, and well-tlerated prcedure fr the recnstructin f symptmatic prximal cartid artery stensis when the subclavian artery is an apprpriate inflw surce. Fr this prcedure saphenus vein appears t be a suitable cnduit. Lng-term fllw-up demnstrates excellent patency and prtectin against further anterir circulatin neurlgic events. (J VASe SURG 99;5:8-9.) The effect f extracranial cartid artery cclusive disease n the prductin f cerebral ischemia has undergne extensive experimental and clinical investigatin. Cmmn cartid artery (CCA) bifurcatin lesins dminate clinical practice; thus mst studies have centered arund cclusive lesins at this lca ~n. Less frequently, CCA cclusive disease alner m cmbinatin with bifurcatin invlvement can cause the same spectrum f cerebral symptms. Frm the DepamnentfSurgery, UniversityfTexas Suthwestern Medical Center and Dallas Veterans Administratin Hspital. P~nted at the Thirty-ninth Scientific Meeting f the Internabnal Sciety fr Cardivascular Surgery, Nrth American Ch.apter, Bstn, Mass., June -4, 99. lepn~lt re.quests: William R. Fry, MD, Department f Surgery, Ullverslty f Califrnia - Davis East Bay, 4 E. st St., ')~~akand) Ca ~6/97 Presumably, cartid bifurcatin and CCA cclusive lesins prduce ischemic symptms by analgus mechanisms (e.g., emblizatin f athersclertic plaque r platelet aggregates, hyppeffusin). If the mechanisms causing cerebral ischemia are similar fr bth lesins, then restratin f CCA inflw shuld alleviate ischemic symptms. Prcedures perfrmed n the CCA frm art extrathracic apprach include endarterectmy, retrgrade thrmbectmy, cartcartid bypass, axillary-cartid bypass, and subclavian-cartid bypass.. The purpse f this study is t determine the utility and durability f subclavian-cartid bypass in the treatment f CCA cclusive disease. PATIENTS AND METHODS T evaluate subclavian-cartid bypass fr the treatment f CCA cclusive disease, a retrspective 8

2 84 Fry et al. Jurnal '-~f VASCULAR SURGERY A Stentic cmmn cartid a. Occluded cmmn cartid a. Dacrn grafts Fig.. A, Patterns f stensis and cclusin f the CCA with a patent nndiseased cartid bifurcatin. B, Recnstructin f the lesins demnstrated with Dacrn cnduits. Table I. Preperative symptms as related t cartid artery recnstructin Transient ischemic attack Amaursis fugax Dizziness/syncpe Cerebral infarct Asymptmatic Sme patients had mre than ne symptm. CCA lca ECA. Ttal study was undertaken f all patients underging su~lavian-cartid bypass fr the treatment fsymptmatic CCAcclusive disease at Parkland Memrial Hspital and the Dallas Veterans Hspital frm Jan., 977, t Feb., 989. Risk factr analysis, symptms, arterigraphic findings, and details fthe perative prcedure'were reviewed. Operative results and 0-day mrtality rates were recrded. This review als included lng-term fllw-up including graft patency, symptm relief, and lng-term survival. Bypass patency was dcumented by duplex examinatin. RESULTS Twenty patients Wlderwent subclavian-cartid artery bypass during the study perid. Furteen men and six wmen with a mean age f 60 years (range, t 8 years) were studied. Preperative risk factrs included hypertensin in patients un.. derging six CCA bypasses, three internal cartid artery bypasses (ICA), and ne external cartid artery (ECA) bypass. All patients had a histry f.tbacc use. Preperative symptms are tabulated in Table I by type f cartid artery recnstructin. Many patients suffered frm multiple symptms, mst frequendy transient ischemic attacks and amaursis fugax. Eleven patients had recnstructins f the right cartid artery, with nine patients underging left cartid artery recnstructin. Arterigraphic eval.. uatin revealed fur types f cclusive patterns (Figs., A and, A): () Significant CCA stensis alne; () Cmmn cartid artery cclusin with a patent bifurcatin; () Cmmn cartid artery c.. elusin with tandem stentic internal cartid artery r small diameter lea, and (4) Cmmn cartid artery and ICA cclusin with a patent external cartid artery. OPERATIVE TECHNIQUE Expsure f the subclavian artery was accm" plished thrugh a transverse cervical incisin apprx" imately cm abve the clavicle ver the clavicular

3 'Vl\l'le 5 Number January 99 Subclavian-cartid bypass 85 A B Stentic internal cartid a. Occluded.cmmn cartid 8. Occluded internal and cmmn cartid aa. Vein grafts Fig.. A, Patterns fcclusin fthe CCAwith-leAstensis r cclusin. B, Recnstructin f the lesins demnstrated with greater saphenus vein cnduits. head f the sterncleidmastid muscle. After divisin f the platysma and clavicular head f the sterncleidmastid muscle, the anterir scalene fat pad was carefully dissected frm the anterir scalene muscle. The vasculature fthis fat padcan be avided by en blc mbilizatin frm a lateral t medial directin. This expses the phrenic nerve, which is mbilized with a rim f the fat pad and anterir scalene muscle t avid nerve devascularizatin. By dividing the anterir scalene muscle, the subclavian artery can be identified and islated distal t the vertebral artery rigin. Expsure f the cartid bifurcatin was accmplished thrugh eithera transverse cervical incisin r an incisin n the anterir brder f the sterncleidmastid muscle. The usual precautins t avid cranial nerve injuries and minimize emblizatin by careful dissectin were bserved. Once bth vessels are islated the bypass graft is first anastmsed t the subclavian artery endt side. Care shuld be taken t assure the ptimum angle frm the subclavian artery t the area f intended cartid artery anastmsis. The graft is passed under the sterncleidmastid muscle t the cartid artery. Transectin f the cartid artery at the level f anastmsis is perfrmed next. Ifendarterectmy f the lea is planned, the psterir aspect f the ICA is spatulated t facilitate this step. Recnstructins fr the varius types f lesins encuntered are included in Figs., B and, B. Cartid artery shunting was nt used. Intraperative evaluatin f the recnstructin was perfrmed by use f a cntinuus-wave Dppler. Operative interventin included subclaviancartid artery bypass t the CCA belw r at the cartid bulb in nine patients (45%), t the cartid bulb with an ICA patch angiplasty in six (0%), and the external cartid artery in five patients (5%). Fur patients underwent simultaneus lea endarterectmywith the bypass fashined t create a patch angiplasty at the site f endarterectmy. The cnduit used included the greater saphenus vein in 5 patients (75%) and prsthetic grafts in 5 (5%) (three Dacrn and tw plytetrab.urethylene). In the immediate pstperative perid, fur asymptmatic phrenic nerve neurpraxias were identified by chest radigraphy. N respiratryabnrmalities resulted, with all patients recvering dia... phragmatic functin in the periperative perid. N pstperative strkes ccurred. One pstperative death (5%) resulted frm mycardial infarctin cmplicated by respiratry failure. The duratin ffllw up ranged frm t mnths, with a mean f50 mnths. One patient was

4 86 Fry et al. Jurnal f VASCULAR SURGERY Table ll..retrgrade thrmbendarterectmy Authr Cartid IJnny bypflssed N. f'lises Wylie Cmmn + bifurcatin 5 Rbbs 6 Cmmn + bifurcatin Ehrenfeld Cmmn + bifurcatin Rushtn 5 Cmmn + bifurcatin 5 Mre Cmmn + bifurcatin 8 VOgt4 Cmmn NS, Nt specified; MI, mycardial infarctin. Mnths fllw-up NS -6 m up t 8 m -4 m -9 m NS Cmplictltins Nne Prcedure nt selected ut strke, death Nne perative MI, death patient with strke and death thrmbsis-asymptmatic NS lst t fllw-up leaving 8 patients (90%) available fr lng-term fllw-up. Duplex s~anning was perfrmed n all patients. N cclusins r hemdynamically significant stenses were detected. One patient returned with psterir circulatin infarct at 0 mnths after prcedure; hwever, the graft was fund t be patent withut stensis n duplex examinatin. During the sntdy perid, fur additinal patients died (%), all fcauses unrelated t their cartid vascular disease. These deaths ccurred between and 04 mnths after prcedure, and were caused.by cardiac disease. in tw, and malignancy in tw. DISCUSSION Althugh mst patients with athersclertic cartid artery cclusive disease have the primary invlvement in the cartid bulb, a small subset f patients remains wh have mre significant prximal cartid artery invlvement. Multiple surgical prcedures have been described fr thse patienfs with CCA cclusive disease. Retr9grade thrmbendarterectmy invlves blind disblite(atin f the CCA. This prcedure is usually ~ted t the right cartid artery, since surgical cntrl f this artery can be safely gained thrugh a cervical incisin. Cntrl f the cartid rigin must be btained t qllnimize emblizatin t the subclavian rvertebral artery. Thepublishedcases reviewed are summarized in Table II. I - 7 The cmbined mrbidity and mrtality rates ranged frm 0%4-6 t 7.5%. This high cmplicatin rate may be significandy decreasediit current practice because f imprvements in patient selectin and periperative care. Cartid-subclavian artery transpsitin cmbines distal CCA thrmbendartereetmy with transpsitin t the subclavian artery. This prcedure is mst cmmnly perfrmed n the left cartid artery because f the inability t btain cntrl f the left cartid rigin frm a transcervical incisin. In reviewing cartid artery transpsitin,,? n significant mrbidityrmrtality rates were reprted. One wund serma did ccur,7 which emphasizes the pssibility f thracic duct injury with this prcedure, similar t subclavian-t-cartid artery transpsitin cmplicatins., Cartid-cartid artery bypass has received little dcumentatin in the literature.,4,8 In the five cases reviewed, n shrt-term r lng-term cmplicatins were bserved. This prcedure may have a mre imprtant rle in extrathracic revascularizatin f the ccluded innminate artery. Axillary-cartid artery bypass is re~rted bysme authrs t~ be technically less demanding than subclavian-cartid artery bypass. Cmmn, internal, and external cartid arteries have been revascularized by this prcedure. 9 - One pssible advantage fthis technique ver thers may ccur in thse patients with symptmatic cartid artery disease wh have undergne radical neck dissectin r radiatin therapy fr head and neck neplasms r bth. Ruting a bypass graft frm the axillary t cartid artery allws cartid artery recnstructin while minimizing disturbance fsignificandy altered tissue planes caused by previus therapy. In ne reprted case a Dacrn prsthesis erded thrugh the skin. 9 Therefre autgenus tissue shuld be used in this prcedure. Experience with subclavian-cartid artery bypasses has been vershadwed by reprting these prcedures tgether with cartid-subclavian artery bypass fr subclavian artery cclusive disease. Em.. phasis in these reprts has been placed n subclavian artery recnstructin. Separatin f data n subclavian-cartid artery bypasses frm cartid.. subclavian artery bypasses byuse fpublishedreprts becmes difficult because f cmplicatins nt reprtedin a standard fashin t the recipient vessel f a bypass. Befre this reprt, 8 cases fsubclavian~cartid artery bypass with r withut bifurcatin endarterectmy have been reprted.,4,5.- A ~ummary f

5 Vlume 5 Number January 99 Subclavian-cartid bypass 87 Table Ill. Subclavian-cartid artery bypass -- Fllw-up Authr Cartid artery bypassed N. fcases in mnths Cumplicatins Graft ---- Diethrich l Cmmn 5 NS perative MI with recurrent symptms Dacrn Brckenbrugh External 9 Nne GSV Berguer l4 External NS Nne GSV Mre Cmmn 4-9 m NS GSV Dacrn Kzl 5 Cmmn 7m? late cclusin NS Zarins l6 External up t 4 CVA caused by hyptensin GSV VOgt4 Cmmn -89 m patients wjcntinued AF up t GSV 4 cclusins 8- m PTFE Schuler l7 External 5 Nne GSV PTFE Riles l8 Internal, external 9 NS late cclusin (asymptmatic) GSV Hans 9 External NS Nne GSV Rushtn 5 Cmmn, external 5 m Subclavian-subclavian bypass graft ersin Dacrn Zimek O Cmmn 5 6 m-9 year NS GSV Dacrn PTFE McGuiness External m graft failure - successfully repened 4PTFE 5 GSV Current study Cmmn, internal, external 0 50 IMI GSV psterir circulatin CVA Dacrn PTFE NS, Nt specified; GSV, greater saphenus vein; PTFE, plytetraflurethylene; CVA, cerebrvascular accident. these reprts.is presentedintableill. These bypasses have been t the CCA, ICl\ r ECA (Table Ill). Mst cases were recnstructins fr athersclertic cclusive disease, whereas the remainder were recnstructins f the cartid artery after radical neck dissectin with radiatin. All patients in the current study underwent recnstructin fr athersclertic CCAcclusive disease. The small number freprted cases with variable lng-term fllw-up creates difficulty in prviding strng cnclusins abut the durability f this prcedure, the cnduit fchice, and its success in preventing further neurlgic symptms. In additin, frequendy patients are included wh are treated with cartid-subclavian artery bypasses fr subclavian artery disease withut distinct separatin f grups regarding the recnstructed vessel, cmplicatins, and pstperative symptms. We suggest that cartid-subclavian artery bypasses and subclavian-cartid artery bypasses are in fact different prcedures in terms f the symptms, cmplicatins, graft rientatin, and chice fgraft cnduit. An interesting example is in the chice f cnduit. In the literature abut cartid-ta-subclavian artery bypasses Zimek et al. 0 fund that the prsthetic graft ffered better results fr cartid.. subclavian artery bypass. Yet, this was a mixed prcedure grup including bth cartid-subclavian artery and subclavian-cartid artery bypasses. The superirity f prsthetic grafts was explained by the stiffness f the graft resisting lonking better than saphenus vein. In reviewing ur experience with cartid-subclavian artery bypass, we supprt the cncept that prsthetic grafts have greater durability than venus grafts (unpublished data). When subclavian-cartid artery bypass is analyzed, the benefits f prsthetic ver venus cnduits is nt upheld. Our review f the published data and ur wn experience fail t shw increased rates f cclusins with saphenus vein cnduits in subclavian-cartid artery bypass. This maybe because the distal anastmsis in this peratin is typically placed mre distally n the cmmn cartid artery, r n the cartid bulb r ECA. The subclavian-cartid artery bypass des nt take an acute angular curse acrss the base f the neck as in the typical cartid-subclavian artery bypass fr prximal subclavian cclusin. The mre vertically placed subclavian-t-cartid artery bypass runs clsely perpendicular t the frces exerted n the graft with neck rtatin. Increased graftstiffness is ntneeded t resist kinking andgraft cclusin. Thus ne can take advantage f- the pssible benefits f an autgenus tissue recdstruc... tin. Cartid-subclavian artery bypasses typically run almstparallel t the applied frces fneck rtatin. Thus rtatinal frces try t cmpact r kink as well as elngate a bypass cnduit in this psitin. A

6 88 Fry et al. Jurnal f VASCULAR SURGERY cnduit that resists kinking in this psitin shuld have the advantage flnger patency rates. Althugh statistically significant cnclusins regarding lng-term prtectin frm neurlgic events cannt be made n the basis f this reprt, it is ntewrthy that n patients suffered ipsilateral anterir circulatin ischemic symptms during this fllw-up perid. In additin, duplex examinatin dcumented sustained graft patency, substantiating the durability f this prcedure. A high percentage fperiperative and lng-term deaths ccur frm cardiac causes with all types f cartid recnstructins. In ur series mycardial ischemia accunted fr a 5% verall mrtality rate. Based n this, an in depth cardiac evaluatin is warranted fr patients with CCA cclusive disease. Based n ur review, subclavian-cartid artery bypass with either saphenus vein r prsthetic cnduits is an excellent surgical ptin fr symptmatic CCA stensis r cclusin. The prcedure is assciated with lw mrbidity and mrtality rates and prvides lng-term reductin f significant ipsilateral neurlgic events. REFERENCES. Ehrenfeld WK, Chapman RD, Wylie ES. Management f cclusive lesins f the branches f the artic arch. Am J Surg 969;"8: Mre WS, Malne JM, Gldstne J. Extrathracic repair f branch cclusins f the artic arch. Am J Surg 976;: Wylie EJ, Effeney DJ. Surgery fthe artic arch branches and vertebral arteries. Surg Clin Nrth Am 979;59: Vgt DP, Hertzer NR, O'Hara PJ, Beven EG. Brachicephalic arterial recnstructin. Ann Surg 98;96:54-5~ 5. Rushtn FW Jr, Kukra JS. Surgical management f the ccluded cartid artery. Surgery 984;96: Rbbs IV, Human RR, Rajamthnam P. Extracranial arterial recnstructin fr chrnic cerebral ischemia. S Afr Med J 986;70: Gee W, Oiler DW, Schwartz JE. An alternative apprach t lesins inthe prximal segments fthe brachicephalic arterial system. Surg Gynecl Obstet 977;44: Zelenck GB, Crnenwett JL, Graham LM, et al. Brachicephalic arterial cclusins and stenses. Arch Surg 985;0: ' 9. Thmpsn BW, Read RC, Carnpbell GS. Operative crrec tin f prximal blcks f the subclavian r innminate arteries. J Cardivasc Surg 980;: Carabasi RA Ill, DeLaurentis DA. Axilla-internal cartid artery bypass in the treatment f neck metastases. J VASC SURG 985;: Archie JP Jr. Cerebral revascularizatin by axillary-cartid bypass. J Cardivasc Surg 989;0: Diethrich EB, Garrett HE, Ameris J, Crawfrd ES, EI Bayar M, DeBakey ME. Occlusive disease f the cmmn cartid and subclavian arteries treated by cartid-subclavian bypass. Am J Surg 967;4: Brckenbrugh EC. Subclavian - external cartid bypass graft fr cerebrvascularinsufficiency. Am J Surg97;4: Berguer R, Bauer RH. Subclavian artery t external cartid artery bypass graft. Arch Surg 976;:89-6. IS. Kkzl RA, Bredenberg CB. Alternatives in the management f athersclertic cclusive disease f artic arch branches. Arch Surg 98;6: Zarins CK, DelBeccr EJ, Jhns L, Turctte JK, Dhrmann GJ. Increased cerebral bld flw after external cartid artery revascuiarizatin. Surgery 98;89: Schuler IT, Flanigan DP, DeBrd JR, Ryan TJ, Castrnuv JJ, Lim LT. The treatment f cerebral ischemia by external cartid artery revascularizatin. Arch Surg 98;8: Riles TS, Imparat AM, Psner MP, Eikelbm BC. Cmmn cartid cclusin: assessment f the distal vessels. Ann Surg 984;99: Hans SS. Subclavian - external cartid bypass. J Cardivasc Surg 984;5: Zimek S, Quinnes-Baldrich W}, Busuttil RW, Baker ID, Machleder Ill, Mre WS. The superirity f synthetic arterial grafts ver autlgus veins in cartid-subclavian bypass. J VASC SURG 986;: McGuiness CL, Shrt DH, Kersrein MD. Subclavian-external cartid bypass fr symptmatic severe cerebral ischemiafrm cmmn and internal cartid artery cclusin. Am.J Surg 988;55: Submitted June 0, 99; accepted Aug., 99. DISCUSSION Dr. WesleyMre (Ls Angeles, Calif.). The authrs have reviewed experience with this peratin in ver a...year interval, described their experience with 0 patients underging right and nine left bypass prcedures. The distal anastmsis was t the cartid bulb in nine, t the ICA in six, and t the ECA in five. The greater saphenus vein was used as the cnduit in 5, and prsthetic grafts were used in five. One pstperative death ccurred fr a mrtality rate f 5%. N pstperative strkes ccurred, and there were fur phrenic nerve palsies, which are flittle cnsequence. Therefre the authrs have demnstrated that this is indeed a safe prcedure. Furthermre, they have demnstrated excellent efficacy in thatduringfllw-up thatrangedfrm I t mnths with a mean f 50 mnths, 8 f their riginal patients underging duplex scanning had patent grafts at the time f fllw-up. Furthermre, n patient experienced an anterir circulatin strke during that fllw-up interval. Therefre, it is certainly nt pssible t fault the chice f peratin in this grup fpatients with an apparent 00%

7 Vlume 5 Number January 99 Subclavian-cartid bypass 89 late patency rate. Hwever, it shuld be kept in mind that patients with this cnditin and peratin n supraartic trunks are relatively few in number, and therefre any individual series, including this ne, is ging t be relatively small, and therefre statistical analysis is smewhat limited. We have had experience with 6 patients underging cartid-subclavian artery bypass grafting fr lesins fthe subclavian artery. In a 5-year fllw-up we have demnstrated a marked superirity f prsthetic grafts ver the saphenus vein. We had a remarkably high thrmbsis rate, with saphenus vein grafts ccurring between the first year and 8 mnths. We pstulated that a cmbinatin ftissue cmpressin and neck mtin may cmpress the relatively small vein graft inducing a larger thrmbsis rate in cntrast t the largerdiameterfprsthetic graft, which is stiffer and mre likely t resist these extrinsic frces. Indeed, review f an additinal eight series in the literature demnstrated an average patencyf75% fr vein grafts and 97% fr prstheses. The authrs in their discussin pintutthatthe behavirand patencyfgrafts fr these peratins may be different when the indicatin is a bypass t the CCA rather than t the subclavian artery. They pint ut that the bliquityfthe anastmsis, when a vein graft is taken frm the subclavian t an area f the cartid bifurcatin, is less than when it is taken the shrt distance between the subclavianand CCAin the base fthe neck. This may well be true; hwever, I wuld like t prpse a simpler and mre direct alternative fr the management fthe prximal CCA lesin; ne, in fact, that the authrs mentined in their list. This is a simple transpsitin f the CCA t the subclavian artery after transectin lw in the neck. This accmplishes a direct revascularizatin with use f autgenus artery with ne anastmsis as a ppsed t translcating the saphenus vein with tw anastmses and perhaps a questinable furre. Even in the instance f CCA thrmbsis, retrgrade thrmbectmy r thrmbendarterectmy with a transeeted artery can be carriedut befre its transpsitin. Shuld bifurcatin endarterectmy be required, this is dne in the usual fashin. I ask the authrs t cmment n this particular alternative surgical apprach with respect t its applicability in their patient series and ask them what peratin they wuld use when faced with a patient admitted with a CCA lesin next week. Dr. Jhn Martin. We agree with many f the cnclusins that yu bviusly have summarized fr us. We t enjy using the cartid-subclavian artery transpsitin, but use it in selective cases. We find it particularly suitable. fr patients with prximal CCA stensis alne with a patent cmmn cartid artery. Althugh it can be used in cmbinatin with endarterectmy fr the ttally ccluded artery, we have nt been as satisfied with the results and the ease in endarterectmy in these chrnically ccluded arteries. We have had sme difficulty in establishing a gd plane and it smetimes can be mre difficult than a simple direct bypass alne. In ur hands we have fund the bypass has wrked better. It als avids the ccasinal ccurrence f early thrmbsis in these extensive endarterectmies, but we wuld agree whleheartedly with yu that there are sme patients in which this is an excellent ptin, particularly thse with prximal stensis alne. Dr.llbert Rutherfrd (Denver, Cl.). I wuld like t ask.dr. Martin, in his cnsideratin f the differences between the subclavian-t-cartid and the cartid-tsubclavian artery bypasses, whether pssibly a mre imprtant difference is the fact that the subclavian-t~ cartid artery bypass has a much lwer resistance and apprximately three times the flw rate f ~e cartid-tsubclavian bypass. I think this may be much mte imprtantthan kinking and graft chice in determining the demnstrated difference in patency.. Dr. Martin. I think these suggestins are imprtant. Obviusly flw dynamics are very imprtant when assessing why ne graft stays pen and the ther. des nt. Obviusly, the resistant beds are different and, as we suggested befre in ur additinal answers, I think the utflwbedhas a lttdwith thefact thatsaphenus vein grafts did stay pen in this study. I wuld agree whleheartedly.