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Intraoperative duplex sonography during renal artery reconstruction
Intraoperative duplex sonography during renal artery reconstruction Kimberley J. Hansen, M D , Elizabeth A. O'Neil, M D , Scott W. Reavis, RVT, T i m o t h y E. Craven, M S P H , George W. Plonk, Jr., M D , and Richard H . Dean, M D , Winston Salem, N.C. To assess renal duplex sonography as an intraoperative study to detect technical defects during repair, 57 renal artery reconstructions in 35 patients were studied. Sixteen men and 19 women (mean age, 62 years) underwent unilateral (13 patients) or bilateral (22 patients) renal artery repair to 57 kidneys. Methods of repair included aortorenal bypass grafting in 29 cases (20 saphenous vein, 5 polytetrafluoroethylene, 4 Dacron), reimplantation in 7, transrenal thromboendarterectomy with patch angioplasty in 13, and transaortic extraction thromboendarterectomy in 8. Branch renal artery repair was required in six cases (five in vivo, one ex vivo). Fourteen patients had combined aortic replacement (11 patients: 8 abdominal aortic aneurysms, 3 aortic occlusions) or visceral artery reconstruction (three patients: three superior mesenteric artery thromboendarterectomies, one inferior mesenteric artery thromboendarterectomy). Intraoperative renal duplex sonography (mean scan time, 4.5 minutes) was complete in 56 of 57 repairs (98%), and renal duplex sonography was normal in 44 repairs (77%). Overall, B-scan defects were present in 13 repairs (23%). Six of these (11%) were defined as major B-scan defects by Doppler spectra with focal increases in peak systolic velocity _>2.0 meters/sec (major defect, mean renal artery peak systolic velocity, 3.1 m/sec), which prompted immediate operative revision. Seven B-scan defects were defined as minor by Doppler spectra (minor defect, mean renal artery, peak systolic velocity, 0.7 m/sec) and were not revised. Postoperative evaluation (range, 1 to 22 months; mean follow-up, 12.4 months) of 55 renal artery repairs in 34 operative survivors (surface renal duplex sonography, 33 patients; renal angiography, 9 patients) demonstrated 42/43 renal artery repairs with normal intraoperative renal duplex sonography, and 6/6 repairs with minor B-scan defects were patent and free of critical stenosis. Of the 6 renal artery revisions prompted by major B-scan defects, 4 remained patent, 1 stenosed, and 1 occluded. Our experience suggests that intraoperative renal duplex sonography during renal artery repair provides valuable anatomic and physiologic information. Renal artery repairs with normal renal duplex sonography and minor B-scan defects without Doppler spectral changes demonstrated 98% patency without critical stenosis at 12.4 months of mean follow-up. However, major B-scan defects defined by a focal increase in renal artery peak systolic velocity should be considered for immediate correction. (J VAsc SvR~ 1991;14:364-74.)
Despite advances in surgical materials and techniques, postoperative failure (stenosis and occlusion) of renovascular repairs continues to occur. Serial angiographic studies have demonstrated early thrombosis in 3% to 14% and critical stenosis in 1% to 7% From the Divisionof SurgicalSciencesand Departmentof Public Health Sciences, Bowman Gray School of Medicine of Wake Forest University,Winston-Salem. Presented at the Fifteenth Annual Meeting of the Southern Association for Vascular Surgery, Palm Springs, Calif., Jan. 23-26, 1991. Reprint requests: KimberleyJ. Hansen, MD, AssistantProfessor of Surgery,BowmanGray Schoolof Medicineof Wake Forest University,300 S. HawthorneRd., Winston-Salem,NC 27103. 24/6/30142 364
of aortorenal bypass grafts.~-3 Although infrequent in most contemporary series, the cost of these failures in the current population admitted for treatment is high-unrelieved hypertension and potential loss of functioning renal mass in a patient group already at high risk for major cardiovascular events and renal insufficiency.4 The high flow rate and the short length of renovascular repairs favor their prolonged patency rather than occlusion. Therefore the technical aspects of repair and the consequences of technical error play a dominant role in determining operative success. 1'2's The impact of unrecognized technical error is emphasized by the fact that we have observed no late
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failures of autogenous renovascular reconstructions free of disease at I year. 3 Technical error after completion of most peripheral artery reconstructions has been defined by intraoperative angiography. 6-8 This method has serious limitations, however, when applied to renovascular reconstructions. At this location intraoperative angiography requires temporary suprarenal aortic occlusion and provides purely anatomic evaluation in only one projection. Branch renal artery and intraparenchymal arteriolar vasospasm in response to high contrast injection may falsely suggest an intrarenal vascular catastrophe. Finally, one half of our patients with hypertension submitted to renovascular reconstruction have renal insufficiency, increasing the risk of contrast nephropathy superimposed on changes associated with reperfusion of chronic renal ischemia. 4,9 !Previous reports suggest that intraoperative duplex sonography is free of the limitations and potential complications associated with angiography. 1°~3 B-scan images provide excellent anatomic detail sensitive to small ( _ i ram) anatomic defects) 2 Imaged defects can be viewed in a multitude of sagittal and transverse projections with no adverse effect on renal blood flow or excretory function. Pulsed-Doppler spectral analysis proximal and distal to an imaged defect provide potentially important hemodynamic information regarding associated flow disturbance) 4 Freedom from limited anatomic projections, the absence of renal toxicity, and the addition of hemodynamic data make intraoperafive renal duplex sonography (RDS) an attractive method to assess the technical aspects ofrenovascular repair, is,16 This report reviews our recent 25-month experience with intraoperative RDS to determine its ability to define technical defects after renovascular repair and to determine the influence of these defects on subsequent renal artery patency as defined by postoperative angiography and surface RDS. In addition, the following validation analyses are made: (1) intraoperative RDS velocity criteria were examined by comparison of prerepair intraoperative RDS with preoperative angiography; (2) retrospectively defined surface RDS velocity criteria were examined prospectively by comparison with preoperative and postoperative angiography. MATERIAL AND METHODS Patient material During the 25-month period from Oct. 1, 1988, through Oct. 31, 1990, 41 patients had renovascular
reconstruction at the Bowman Gray School of Medicine of Wake Forest University and were studied with intraoperative RDS. Our experience with 35 of these patients with follow-up tests of renal artery patency constitutes the basis of this report. Participants included 16 men and 19 women (ages, 27 to 72 years; mean age, 62 years). Significant hypertension was present in all but one patient treated for a renal artery aneurysm. In the remaining 34 patients hypertension ranged from 246/140 m m H g to 172/94 m m Hg (mean, 193 __+27/103 _+ 17 m m Hg). Hypertension treatment regimens included one to five drugs (mean, 2.7 _+ 1.2 drugs). In addition to hypertension, additional atherosclerotic risk factors included tobacco use (31 patients), diabetes mellims (9 patients), and hypercholesterolemia (11 patients). Based on preoperative sermn creatinine values after cessation of angiotensin converting enzyme inhibitors and high-dose diuretics, 15 patients (43%) had renal insufficiency (range, 2.0 to 8.8 mg/dl; mean, 3.3 mg/dl). Two patients were recently dependent on hemodialysis. Operative management After our routine preoperative evaluation, which has been detailed elsewhere, 35 patients had renovascular repair to 57 kidneys. Twelve patients underwent unilateral repair, 22 patients underwent bilateral repair, and 1 patient had a unilateral repair with contralateral nephrectomy. No patient who had unilateral reconstruction had significant contralateral renal artery disease recognized. Renal artery reconstruction was accomplished by aortorenal bypass grafting in 29 instances (Table I). Autogenous saphenous vein was used in 20 of these, including one ex vivo and five in vivo branch renal artery repairs. Six millimeter polytetrafluoroethylene (PTFE) was used in five, and knitted Dacron was used in four aortorenal reconstructions. Distal anastomoses were constructed in an end-to-side fashion in 4 grafts and end-to-end in the remaining 25. Renal artery reimplantation was used for 7 vessels and renal artery thromboendarterectomy was used in 21. Thirteen renal artery thromboendarterectomies were accomplished by transrenal technique with transverse aortorenal patch angioplasty by use of either PTFE (eight repairs) or aurogenous saphenous vein (five repairs). The remaining eight thromboendarterectomies were performed with rransaortic extraction technique as described by Stoney et al.17 After arterial reconstruction by these methods, intraoperative RDS was performed according to the techniques described below.
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Table I. Methods of renal artery reconstruction (N = 57) Aortorenal bypass grafting Saphenous vein PTFE Dacron RA Reimplantation RA TEA No TEA RA TEA Transrenal with patch PTFE 8 Saphenous vein 5 Transaortic
29 20 5 4 7 5 2 21 13 8
PTFE, Polytetrafluorothylene; RA, renal artery; TEA, thromboendarterectomy
T E C H N I Q U E OF R E N A L DUPLEX S O N O G R A P H Y Surface RDS (preoperative and postoperative) and intraoperative RDS were performed by use of either an Ultramark 8 or Ultramark 9 ultrasound system (Advanced Technology Laboratories, Bothell, Wash.). Surface studies were performed with either a 3.0 MHz. mechanical long-focus probe or a 2.25 MHz. phased-array probe with Doppler colorflow capability. Intraoperative studies were performed with a 10 MHz. mechanical probe with 5 MHz. pulsed Doppler, providing 0.4 m m B-scan resolution within the i to 4 cm probe focal zone and 1.5 m m 3 minimal Doppler sample volume at the 1.6 cm focal point. Intraoperative renal duplex sonography Renal duplex sonography studies were obtained 10 to 15 minutes after arterial reconstruction. The 10 MHz mechanical probe head was placed in a sterile, plastic sheath containing acoustic gel. The operative field was flooded with warm, normal saline solution, and B-scan images were first obtained from the perirenal aorta in sagittal and transverse planes to exclude unrecognized aortic defects. The renal artery was then imaged in longitudinal projection with care to visualize the renal artery origin, endarterectomy segments, endarterectomy end points, and perianastomic areas. All defects detected in longitudinal projection were imaged in transverse projection to confirm their anatomic presence and to estimate the degree of luminal narrowing. Centerstream Dopplershifted signals were obtained in longitudinal projection at all imaged defects and at positions immediately proximal and distal to all defects. Doppler insonating angles were maintained at 60 degrees or less. Renal artery peak systolic velocity (RA-PSV)
and renal artery end-diastolic velocity were calculated from real-me, fast-Fourier transform analysis of the Doppler-shifted signals. B-scan images and spectra from the fast-Fourier transform spectrum analyzer were recorded on videotape and hard copy processor. From the sagittal and transverse B-scan image, defects were described according to type (residual disease, intimal flap, thrombus) and location (endarterectomy segment, endarterectomy end point, perianastomic area). B-scan defects were designated as major (requiring revision) or minor (not requiring revision) by their hemodynamic significance determined by Doppler velocity criteria in Table II. In summary, these criteria are: (1) minor defect ( < 60% diameter-reducing stenosis) indicated by an RA-PSV of < 2.0 meters/see (m/see); (2) major defect ( _>60% diameter-reducing stenosis) indicated by focal RAPSV of >_2.0 m/see and distal turbulent velocity waveform; (3) occlusion indicated by no Dopplershifted signal from the renal artery B-scan image; (4) technically inadequate study for interpretation indicated by failure to obtain B-scan images and Doppler samples from the entire main renal artery. Arteries in patients with postrepair major B-scan defects ( ___60% diameter-reducing stenosis or occlusion) had immediate operative revision. Arteries in patients with normal postrepair B-scan studies or minor B-scan defects did not undergo revision. In an attempt to validate these intraoperative Doppler criteria, we compared intraoperative RDS performed before renal artery repair with preoperative angiography in 20 of 35 patients. Surface renal duplex sonography-preoperative and postoperative studies Preoperative and postoperative surface RDS studies were obtained by methods and techniques reported previously. 17 Surface RDS criteria for presence of < 60% or ---60% diameter-reducing renal artery stenosis or occlusion were identical to intraoperative RDS criteria (Table II), except no B-scan image was required for a technically adequate surface study.
Postoperative studies were obtained within 1 month of operation and serially when return patient evaluation permitted. Patients with intraoperative RDS but without postoperative surface RDS or angiography confirming the status of renal artery repair were excluded from study. Although our methods and results of surface RDS have been previously reported, 18 the Doppler velocity criteria for a < 60% or >_60% diameterreducing stenosis used in the present study were
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Intraoperative duplex sonography during renal artery repair 367
defined by retrospective comparison with conventional angiograms. In an attempt to validate these Doppler criteria prospectively, we compared preoperative surface RDS with preoperative angiography performed within 3 weeks of the duplex study.
Angiography The presence of renal artery stenosis was determined from preoperative (35 patients) and postoperative (9 patients) conventional cut-film angiograms by two independent observers without knowledge of the RDS results. Atherosclerotic lesions were estimated in 5% diameter-reducing increments. When the estimated degree of renal artery reduction differed by more than 15% between two independent observers, the dianleter-reduction was determined by a third independent observer. Statistical analysis Patient demographic data, RDS results, and angiographic interpretations were analyzed by use of the following techniques. Descriptive statistics (such as means and standard deviations of continuous data; frequencies and relative frequencies of categorical data) were computed, and the data were checked to verify that assumptions of statistical tests were met. Relationships between RDS data and angiographic data were assessed by means of Pearson correlations and scattergrams. Correlations between RDS measurements across time and between RDS data and percent renal artery stenosis were computed by analyzing their residual output from a general linear model with a subject effect to control for withinsubject correlation. Confidence limits for comparative analysis estimates (e.g., sensitivity, specificity) were found by use of standard errors that were adjusted for within-subject correlations. Relationships between RDS data and functional and hypertension responses were assessed by use of Spearman rank correlations. Changes in blood pressures and number of medications before and after operation were assessed by paired t tests.
RESULTS OF STUDIES Intraoperative renal duplex sonography Intraoperative RDS performed after renal artery reconstruction provided technically satisfactory studies in 56 of 57 repairs (98%). The technically inadequate study failed to image completely an endarterectomy end point; pulsed-Doppler spectral analysis in this patient did not suggest a major defect. Renal duplex sonography scan time after repair
Table II. Doppler velocity criteria for B-scan defects Defect
Criteria
Minor ( < 60% diameterreducing RA defect) Major ( ->60% diameterreducing RA defect)
RA-PSV from entire RA < 2.0 m/sec Focal RA-PSV ->2.0 m/sec and distal turbulent velocity
Occlusion
No Doppler-shifted signal from RA B-scan image Failure to obtain B-scan images and Doppler samples from entire main RA
waveform
Inadequate study for interpretation
RA, Renal artery; RA-PSV, renal artery peak systolic velocity.
averaged 4.5 minutes, and no complications were recognized relative to the technique. Of the 56 technically adequate intraoperative studies, B-scan defects occurred in 13 (23%) renal artery repairs (Table III). These 13 defects occurred in five autogenous saphenous vein grafts, one renal artery reimplantation, and seven thromboendarterectomies- five transrenal (two PTFE, three saphenous vein patches) and two transaortic thromboendarterectomies. Vein graft defects were considered perianastomic in three (two distal, one proximal anastomosis), one sclerotic venous valve, and one midgraft stenosis as a result of graft suture repair. Of the defects associated with thromboendarterectomies, five were intimal flaps within the thromboendarterectomy segment, one was residual disease at a transaortic extraction thromboendarterectomy end point, and one was a misoriented venous valve as part of a vein patch. A single perianastomotic intimal flap was present in the renal artery reimplantation. Seven of the eight intimal flaps and venous valves were considered 2 mm or less in length. Estimation of diameter reduction from flaps and valves was difficult because of their motion, but seven of these eight defects were felt to reduce lumen diameter by < 20% (Fig. 1). Two of the three perianastomotic defects were likewise considered < 20% diameter reducing, however, one distal perianastomotic defect was felt to reduce lumen diameter by 40%. The midgraft defect within a saphenous vein bypass graft, residual disease at a thromboendarterectomy end point, and an intimal-medial flap were each considered to reduce lumen diameter by 50%. Doppler-derived RA-PSV from these 13 B-scan defects demonstrated six that met criteria for a major defect creating a _ 60% diameter-reducing stenosis (RA-PSV range, 3.0 to 3.3 m/sec; mean, 3.1 m/see)
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Table III. Summary of major and minor B-scan defects Patient age (2VffF) 70 (M) 68 (F)
62 (M) 51 (M) 59 (F)
BIL TEA R-RABG L-TEA BIL TEA R-RABG L-TEA R-RABG R-RABG L-REIMP L-RABG R-TEA BIL TEA, AFBG
44 (F)
BIL RABG
27 (F)
R-RABG
68 (F) 66 (F) 53 (F) 69 (F)
2~Iajor/minor
RA-PSV (m/sec)
Follow-Up (mo)
Minor Minor
0.73 0.60
13 mo
Patent Operative death
L-IF L-valve
Minor Minor
0.60 0.72
18 mo 22 mo
Patent Patent
Proximal anastomosis L-IF
Minor Minor
0.70 0.60
16 mo 5 mo
Patent Patent
L-valve R-RD R-IF L-IF R-distal anastomosis L-midgraft Distal anastomosis
Minor Major Major Major Major Major Major
1.00 3.10 3.30 3.20 3,00 3,00 3,00
4 mo 13 mo 10 mo 10 mo 10 mo 10 mo 3 mo
Patent Patent L-patent R-RAS R-occluded L-patent Patent
Procedure
Deficit ,~ L-IF L-IF
Outcome
R, Right; L, left; BIL, bilateral; TEA, thromboendarterectomy; RAB, renal artery bypass graft; AFBG, aortobifemoral bypass graft; IF, Intimal flap; RD, residual disease; RAS, renal artery stenosis.
(Table III). These six defects occurred in three autogenous saphenous vein grafts and three thromboendarterectomies. Vein graft defects were perianastomic in two (both distal) and midgraft at the site of suture repair in the third. Of the three defects associated with thromboendarterectomies, two were flaps in the endarterectomy segment (Figs. 1 and 2), and one reflected residual disease at the distal endarterectomy end point. Three of these defects (one distal perianastomotic, two flaps in endarterectomy segments) were considered <20% diameter reducing by B-scan image alone. The six B-scan defects with abnormal Doppler findings were immediately revised with vein patch angioplasty (three saphenous vein grafts) or completion thromboendarterectomy (three thromboendarterectomies) (Fig. 2). In each case the presence of a defect reducing the luminal diameter by at least 60% was confirmed during revision. Intraoperative RDS was repeated after four of the six revisions. After each revision no defect was recognized on B-scan image, and RA-PSV was decreased (RA-PSV range, 1.0 to 1.8 m/sec; mean, 1.3 m/sec). Considering all i3 B-scan defects, the presence of a defect was associated with a significant increase in RA-PSV compared to repairs without B-scan defects (Spearman rank correlation, r = 0.3029;p = 0.03). However, RA-PSV from the seven repairs with defects that were defined as minor by Doppler criteria did not differ significantly from the 43 renal artery repairs with no B-scan defect (mean RA-PSV, 0.7 + 0.3 versus 0.8 +__0.3 m/sec). In these seven minor defects no revision was performed.
To test the validity of our Doppler criteria when applied during operation, intraoperative RDS performed before renal artery repair was compared with preoperative angiography in 20 of the 35 patients. Intraoperative prerepair RDS was performed unilaterally in three patients, providing comparative anatomy to 37 kidneys. Intraoperative prerepair RDS correctly identified five of five kidneys with normal or <60% renal artery stenosis (mean RA-PSV, 0.9 _ 0.4 m/sec), 25 of 26 kidneys with __.60% to 99% stenosis (mean RA-PSV, 3.2 +_ 1.3 m/sec), and six of six renal artery occlusions. By comparison with preoperative angiography, intraoperative prerepair RDS was 96% sensitive and 100% specific, with a 99% overall accuracy. Postoperative surface renal duplex sonography and angiography In 33 of 34 patients surviving renal artery reconstruction, the status of 54 repairs was defined by 57 postoperative surface RDS studies. Four postoperative RDS studies (7%)were tectmically inadequate for interpretation, however, each study was repeated and was technically satisfactory 1 to 3 months later. Surface RDS studies at the time of last follow-up (mean, 12.4 months) found 51 of 54 repairs patent with < 60% diameter-reducing stenosis (mean RA-PSV, 1.3 _ 0.3 m/sec). One repair demonstrated _>60% stenosis on follow-up examinations 1, 3, and 10 months after surgery (RA-PSV, 3.4 m/sec). Two repairs were occluded on RDS examination I week after surgery. One occlusion led to eventual nephrectomy, and one kidney was sal-
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Intraoperative duplex sonography during renal artery repair 369
Fig. 1. (A, B, and C). Saggital (A) and transverse (B) images of a minor B-scan defect. This intimal flap within the endarterectomy segment (heavy arrows) had normal Doppler spectral analysis (C). This minor defect was not revised. vaged by a second bypass procedure, which remains patent and free ofstenosis at last follow-up. The renal artery stenosis and two renal artery occlusions were confirmed by postoperative angiography. One contralateral unrepaired renal artery developed significant stenosis by RDS examination at 6 months follow-up, and this disease was also confirmed by angiography. Thirteen conventional angiograms were performed in nine patients with 13 renal artery repairs 1 week to 20 months after surgery (mean, 8.9 months). Six patients (five unilateral, one bilateral repair) had one angiogram after surgery, two patients (bilateral repair) had two angiograms, and a single patient (bilateral repair) had three angiograms defining renal artery anatomy to 21 renal reconstructions. By angiography, 16 renal reconstructions were considered normal or had < 60% diameter-reducing stenosis, 3 arteries had _>60% to 99% dianleter-reducing stenosis, and 2 repaired renal arteries were occluded.
The clinical response to surgery supports the 96% follow-up patency rate. Applying a previously described algorithm for blood pressure and renal function response,* hypertension was considered cured in 5 patients, improved in 26, and unchanged in 2 patients. Postoperative systolic and diastolic blood pressures and number of antihypertensive medications (mean _ SD, 137 + 12/75 _+ 10 mm Hg; 1.6 _+ 1.2 medications) were significantly decreased when compared with preoperative values (paired t test; p < 0.001). Among the 15 patients with preoperative serum creatinine of __.2.0 mg/dl, renal function was considered improved in 12 patients (two patients removed from dialysis), not changed in two patients, and worsened in one patient.
Comparison with postoperative studies Thirty-four of 35 patients survived renovascular reconstruction providing comparison between intra-
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Fig. 2. (A, B, C, and D). Sagittal image (A) of a major B-scan defect (heavy arrow). This intimal flap at the proximal anastomosis (B) demonstrated a focal increase in RA-PSV (3.1 m/sec). After revision RA-PSV (C) was decreased (1.1 m/sec) and follow-up angiogram (D) demonstrated a widely patent anastomosis. This patient was cured of hypertension.
operativc RDS and the status of renal artery repair determined by either postoperative surface RDS (33 patients) or postoperative angiography (9 patients) or both. Of renal artery repairs with normal intraoperative RDS demonstrating neither B-scan or Doppler abnormalities, 42 of 43 (98%) were patent without recurrent stenosis at last follow-up (42 by surface RDS and 4 by angiography). An ex vivo branch renal artery repair for fibromusca~lar dysplasia occluded within 1 week of surgery. This occlusion was confirmed by both surface RIDS and angiography. A nephrectomy was ultimately required in this patient.
At the time of reexploration, the failure of reconstruction was thought to be a result of a technical complication at the renal vein to vena cava anastomosis. Review of this patient's intraoperative RDS revealed no B-scan defect with RA-PSV of 0.7 m/sec uniformly from aorta to renal hilum. The venous anastomosis, however, was not studied at surgery. Of the seven minor defects without Doppler abnormality, six of seven survivors demonstrated six patent renal artery repairs without stenosis on follow-up examination (six by surface RDS and two by angiography). One patient who died in the perioperative period demonstrated a flap within the
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Intraoperative duplex sonography during renal artery repair 371
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20
30
40
50
60
70
80
90
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Fig. 3. Scatter plot ofrenal artery peak systolicvelocity (RA-PSV in m/sec) versus percent renal
artery stenosis defined by angiography. endarterectomy segment without Doppler criteria for significance. At autopsy I week later, the renal artery repair was found to be patent. Of the six renal reconstructions in four patients (two unilateral, two bilateral) with major defects defined by B-scan and Doppler criteria, four of the revised repairs remained patent without stenosis (four by surface RDS and one by angiogram), one repair demonstrated early (or unrelieved) ___60% stenosis, and one repair occluded. Renal artery stenosis detected by surface RDS and confirmed by angiography occurred after completion endarterectomy was performed for a significant flap (RA-PSV 3.0 m/see) in the endarterectomy segment. Postrevision intraoperative RIDS was not performed. An autogenous saphenous vein bypass occluded (seen on angiogram) after patch angioplasty of a significant stenosis at the distal anastomosis (RA-PSV 3.0 m/sec). Postrevision RDS was normal (normal B-scan; RA-PSV 1.0 m/sec). This kidney was salvaged by successful reoperation, at which time an apparent atheroembolus was occluding the distal vein bypass. If the six major defects are considered true positives and the renal artery occlusion among the 49 normal (43 RDS) and minor defects (6 RDS) is
considered to be the single false negative, intraoperative RDS was 86% sensitive and 100% specific for technical defects associated with significant postoperative stenosis and occlusion of renovascular repair. To validate our Doppler criteria for surface RDS prospectively, preoperative surface RDS was compared with preoperative angiography in 33 of the 35 patients (65 kidneys). Surface RDS was technically inadequate to 3 kidneys (4.6%) yielding renal artery anatomy to 62 kidneys for comparison (Fig. 3). Surface RDS correctly identified 10 of 11 kidneys with normal and < 60% diameter reducing stenosis (mean RA-PSV, 1.3 + 0.25 m/sec), 50 of 51 kidneys with _>_>60% stenosis (mean RA-PSV, 3.6 _+ 1.8 m/see), including nine of nine occlusions, providing 98% sensitivity, 91% specificity, and a 97% overall accuracy (Table IV). DISCUSSION
Our experience with intraoperative RDS after renovascular repair indicates that RDS is both sensitive (86%) and specific (100%) for technical defects contributing to postoperative failure. Renal artery repairs with normal and minor B-scan defects by RDS demonstrated 98% patency free of critical stenosis at 1-year follow-up. This degree of anatomic
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Table IV. Surface RDS versus cut-film angiography; comparative analysis parameter estimates and their 95% confidence intervals (N = 62 kidneys) Method
Estimate
Sensitivity Specificity PPV NPV Accuracy
0.98 0.91 0.98 0.91 0.97
95% Confidence interval
(0.94, (0.82, (0.94, (0.81, (0.92,
1.00) 0.99) 1.00) 1.00) 1.00)
RDS, Renal duplex sonography; PPV, positive predictive value; NPV, negative predictive value.
success determined by surface RDS (in 97%) and renal angiography (in 26%) was supported by the clinical results of operative intervention- a favorable hypertension response was observed in 94% of patients, whereas global renal fimction improved in 80% of patients with preexisting renal insufficiency. The 23% incidence of defects in this study is similar to previous reports of other methods of ultrasonography at different anatomic sites, n'12'~9-2~ Experimental and clinical experience have suggested that B-mode ultrasonography is more sensitive to the presence ofintimal-medial defects than is completion angiography) 2'16'22'~3 Similar studies with highfrequency pulsed-Doppler spectral analysis have detected subtle disturbances in laminar flow in the absence of distal pressure/flow reduction. 24'2S Although these methods would appear quite sensitive to technical errors, they lack the necessary specificity to guide intraoperative management. To eliminate the potential risks of unnecessary exploration, most authors have advised that subsequent intraoperative angiography determine the need for surgical revision. Used in this manner, the ultrasound study serves as a screening test to avoid routine completion angiography. 26 As a completion study for renal artery reconstruction, however, ultrasonography alone must demonstrate sensitivity and specificity sufficient to guide operative revision, In this respect, we believe that the combination of B-scan imaging with realtime Doppler spectral analysis provides more useful clinical information than either modality used alone. B-scan image defines the presence, location, and type of defect, whereas Doppler spectral analysis defines its hemodynamic significance. By revising only major B-scan defects defined by velocity criteria, unnecessary operative revision of minor B-scan defects is eliminated. Okuhn et al) 1 have reported similar results from
intraoperative RDS after 83 renal reconstructions. In their study major defects indicating the need for immediate revision were defined by B-scan defects reducing luminal area by > 50% or a "markedly abnormal flow signal." These authors assessed Doppler signals audibly at surgery and by off-line spectral analysis at a later time. Intravenous digital subtraction angiography defined early (7- to 10-day) postoperative patency. By these duplex criteria, defects were present in 31% of repairs. Four major defects were recognized-three occlusions and one floating thrombus. Each occlusion was defined by the absence of Doppler-shifted signal despite a normal B-scan appearance. These investigators found that velocity waveforms defined by off-line spectral analysis provided no additional information as compared with subjective audible assessment. B-scan defects that were not associated with "obviously abnormal Doppler signal" with normal confirmatory studies were considered to be false positives, yielding 85% sensitivity and 75% specificity for 77 renal artery repairs. Our experience supports these previously reported results, however, our methodology and criteria for revision differ. Although audible analysis of the Doppler-shifted signal can easily detect severe flow disturbance (occlusion, high-grade stenosis), 16'2°'27 we think that on-line spectral analysis of the Doppler signal contributes valuable objective hemodynamic assessment of an imaged lesion. Audible features of the Doppler-shifted signals from renal artery endarterectomy and renal artery branch repairs contain qualities that can be confused with poststenotic turbulence. We feel that on-line spectral analysis with velocity estimation has proved very useful in these reconstructions. This study and the study of Okuhn et al. 11 suffer from a similar and potentially serious limitationintraoperative RDS examinations were compared with renal artery patency defined by several postoperative tests of varying sensitivity and specificity. In our study we have compared intraoperative RDS with three different assessments after renal reconstruction-gross findings at operative revision, postoperative cut-film renal angiography, and postoperative surface RDS. Probably the most controversial of these is the use of surface RDS for follow-up of repair status. 2*'29 Although the criteria resulting from retrospective comparative analysis between surface RDS and angiography has been confirmed prospectively in this study (sensitivity 98%, specificity 91%), other potential limitations of surface RDS exist. One potential limitation is that a reason-
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Intraoperative duplex sonography during renal artery repair
able estimate of stenosis or occlusion of renal artery repairs (< 10%) differs markedly from the actual prevalence within the group examined retrospectively (44%) and prospectively (82%) for validity analysis. In this instance one might expect a high false-positive rate from postoperative RDS. However, in the eight patients in whom both angiography and surface RDS were obtained after operation, including all positive surface RDS studies, there was perfect agreement. Another limitation of surface RDS is that it accurately defines only the presence or absence of a critical stenosis (___60% diameter reduction) or occlusion of the renal artery; definition of lesser degrees of stenosis is not provided by the surface technique.18 Unrepaired minor defects could conceivably favor subendothelial fibroblastic proliferation or neoatherogenesis causing progressive stenosis and late graft failure, s'13'25 In this regard, most autogenous renal artery reconstructions that fail do so within the first year, and our period of mean follow-up (12.4 months) should detect these. 13 Despite these limitations, we believe the advantages of an inexpensive, serial postoperative study free of any recognized risk and proved highly correlated with hemodynamic renal artery disease supports the use of surface RDS as a useful method of follow-up and comparison. Finally, the interaction between surgeon and vascular technologist during intraoperative RDS deserves comment. Both visual and spectral data acquired during the performance of intraoperative RDS are enhanced by the participation of the vascular technologist. Although the surgeon is responsible for manipulating the probe head to acquire optimal B-mode images and Doppler spectra of the vascular repair at likely sites of technical error, the power and time gain adjustments (which minimize potential artifact) are made best by an experienced technologist. Close cooperation is likewise required to obtain c.omplete pulsed-Doppler sampling associated with any B-scan defect. Last, knowledge of the surgical anatomy through participation in intraoperative studies enhances the technologist's ability to obtain satisfactory surface RDS images during follow-up. ha conclusion, our experience with intraoperativ~ RDS as a completion study after renal artery repair suggests that intraoperative RDS is a rapid examination with a high rate of technical success. The designation of B:scan defects as minor or major according to Doppler velocity waveform criteria provides the sensitivity and specificity necessary to guide decisions regarding intraoperative revisions.
373
REFERENCES
1. Dean RH, Wilson Jr', Burko H, Foster JH. Saphenous vein aortorenal bypass grafts: serial angiographic study. Ann Surg 1974;180:469-78. 2. Stanley JC, Ernst CB, Fry WJ. Fate of 100 aortorenal vein grafts: characteristics of late graft expansion, aneurysmal dilatation, and stenosis. Surgery 1973;74:931-44. 3. Dean RH, Krueger TC, Whiteneck 1M, et al. Operative management of renovascula( hypertension. J VASC SURG 1984;1:234-42. 4. Hansen KJ, Ditesheim JA, Metropol SH, et al. Management ofrenovascular hypertension in the elderly population. J VAse SURG 1989;10:266-73. 5. Dean RH. Complications of renal revascularization. In: Bernhard VM, Towne JB, eds. Complications in vascular surgery, 2nd ed. Orlando: Grune & Stratton, 1985:229-46. 6. Plecha FR, Pories WJ. Intraoperative angiography in the immediate assessment of arterial reconstruction. Arch Surg 1972;105:902-7. 7. Rosental JJ, Gaspar MR, Marius HJ. Intraoperative arteriography in carotid thromboendarterectomy. Arch Surg 1977; 106:806-8. 8. Courbier R, Jausseran JM, Reggi M. Detection complications of direct arterial surgery. Arch Surg 1977;112:1115-8. 9. Metropol SH, Hansen KJ, Holmes RP, Iskandar SS, Strandhoy ]W, Dean RH. Reperfusion changes after relief of sustained renal isehemia. Surg Forum 1989;XL:300-1. 10. Okuhn SP, Reilly LM, Bennett JB, et al. Intraoperative assessment of renal and visceral artery reconstruction: the r01e of duplex scanning and spectral analysis. J VAsc Sr:RG 1987;5:137-47. 11. Schwartz RA, Peterson G], Noland KA, Hower JF, Nannheim KS. Intraoperative duplex scanning after carotid artery reconstruction: a valuable tool. ] VAsc SUV,G 1988;7:620-4. 12. Cato RF, Seabrook GR, Bandyk DF, Moldenhaner PI~ Schmitt DD, Towne JB. Intraoperative duplex scanning following carotid artery reconstruction. J Vasc Tech 1989; XIII:31-6. 13. Reilly LM, Okuhn SP, Rapp ]H, et al. Recurrent carotid stenosis: a consequence of local or systemic factors? The influence of unrepaired technical defects. J VASC SURe 1990;11:448-60. 14. Rutherford RB, Jones DN, Lowenstein D, Fleming P. The effects of changes in lumen and flow on the arterial velocity waveform. J Surg Res 1982;32:110-20. 15. Goldstone J. Intraoperative assessment of renal and visceral arterial reconstruction using Doppler and duplex imaging. In: Ernst CB, Stanley JC, eds. Current therapyin vascular surgery, 2nd ed. Philadelphia: BC Decker, 1991:872-5. 16. Bandyk DF. Intraoperative assessment of arterial reconstructions utilizing ultrasound. Semin Vasc Surg 1989;2: 75 -84. 17. Stoney RJ, Skioldebrand CG, Qvarfordt PG, Reilly LM, Ehrenfeld WK. Juxtarenal aortic atherosclerosis. Surgical experience and functional result. Ann Surg 1984;200:345-54. 18. Hansen I(J, Tribble RW, Reavis SW, et al. Renal duplex sonography: evaluation of clinical utility. J VAsc SURG 1990;12:227-36. 19. Seifert KB, Blackshear WM. Continuous-wave Doppler in the intraoperative assessment of carotid endarterectomy. J VASC S~:v~G1985;2:817-20. 20. Barnes RW. Intraoperative monitoring in vascular surgery. Ultrasound Med Biol 1986;12:919-26.
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21. Zierler RE, Bandyk DF, Thiele BL. Intraoperative assessment of carotid endarterectomy. J VAsc SURG 1984;1:73-83. 22. Coelho JCU, Sigel B, Flanigan DP, et al. An experimental evaluation of arteriography and imaging ultrasonography in detecting arterial defects at operation. J Surg Res 1982;32: 130-7. 23. Sawchuk AP, Flanigan DP, Machi J, Schuler II, Sigel B. The fate of unrepaired minor technical defects detected by intraoperative ultrasonography during carotid endarterectomy. J VAse SUING1989;9:671-6. 24. Bandyk DF, Zierler RD, Berui GA, Thiele BL. Pulsed Doppler velocity patterns produced by arterial anastomoses. Ultrasound Med Biol 1983;9:79-87. 25. Bandyk DF, Kaebnick HW, Adams MB, Towne lB. Turbulence occurring after carotid bifurcation endarterectomy: a harbinger of residual and recurrent carotid stenosis. J Vase StJRG 1988;7:261-74.
26. Bandyk DF, Zierier RE, Thiele BL. Detection of technical error during arterial surgery by pulsed Doppler spectral analysis. Arch Surg 1984;119:421-8. 27. Barnes RW, Nix ML, Nichols BT, Wingo IP. Recurrent versus residual carotid stenosis. Ann Surg 1986;203:65260. 28. Eidt IF, Fry RE, Clagett GP, Fisher DF, Alway C, Fry WJ. Postoperative follow-up of renal artery reconstruction with duplex ultrasound. J VAsc SURG 1988;8:667-73. 29. Sandager G, Flinn WR, McCarthy WJ, Yao JST, Bergan JJ. Assessment of visceral arterial reconstruction using duplex scan. J Vase Tech 1987;XI:13-6.
Submitted Feb. 2, 1991; accepted Apr. 11, 1991.
Despite advances in surgical materials and techniques, postoperative failure (stenosis and occlusion) of renovascular repairs continues to occur. Serial angiographic studies have demonstrated early thrombosis in 3% to 14% and critical stenosis in 1% to 7% From the Divisionof SurgicalSciencesand Departmentof Public Health Sciences, Bowman Gray School of Medicine of Wake Forest University,Winston-Salem. Presented at the Fifteenth Annual Meeting of the Southern Association for Vascular Surgery, Palm Springs, Calif., Jan. 23-26, 1991. Reprint requests: KimberleyJ. Hansen, MD, AssistantProfessor of Surgery,BowmanGray Schoolof Medicineof Wake Forest University,300 S. HawthorneRd., Winston-Salem,NC 27103. 24/6/30142 364
of aortorenal bypass grafts.~-3 Although infrequent in most contemporary series, the cost of these failures in the current population admitted for treatment is high-unrelieved hypertension and potential loss of functioning renal mass in a patient group already at high risk for major cardiovascular events and renal insufficiency.4 The high flow rate and the short length of renovascular repairs favor their prolonged patency rather than occlusion. Therefore the technical aspects of repair and the consequences of technical error play a dominant role in determining operative success. 1'2's The impact of unrecognized technical error is emphasized by the fact that we have observed no late
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Intraoperative duplex sonography during renal artery repair 365
failures of autogenous renovascular reconstructions free of disease at I year. 3 Technical error after completion of most peripheral artery reconstructions has been defined by intraoperative angiography. 6-8 This method has serious limitations, however, when applied to renovascular reconstructions. At this location intraoperative angiography requires temporary suprarenal aortic occlusion and provides purely anatomic evaluation in only one projection. Branch renal artery and intraparenchymal arteriolar vasospasm in response to high contrast injection may falsely suggest an intrarenal vascular catastrophe. Finally, one half of our patients with hypertension submitted to renovascular reconstruction have renal insufficiency, increasing the risk of contrast nephropathy superimposed on changes associated with reperfusion of chronic renal ischemia. 4,9 !Previous reports suggest that intraoperative duplex sonography is free of the limitations and potential complications associated with angiography. 1°~3 B-scan images provide excellent anatomic detail sensitive to small ( _ i ram) anatomic defects) 2 Imaged defects can be viewed in a multitude of sagittal and transverse projections with no adverse effect on renal blood flow or excretory function. Pulsed-Doppler spectral analysis proximal and distal to an imaged defect provide potentially important hemodynamic information regarding associated flow disturbance) 4 Freedom from limited anatomic projections, the absence of renal toxicity, and the addition of hemodynamic data make intraoperafive renal duplex sonography (RDS) an attractive method to assess the technical aspects ofrenovascular repair, is,16 This report reviews our recent 25-month experience with intraoperative RDS to determine its ability to define technical defects after renovascular repair and to determine the influence of these defects on subsequent renal artery patency as defined by postoperative angiography and surface RDS. In addition, the following validation analyses are made: (1) intraoperative RDS velocity criteria were examined by comparison of prerepair intraoperative RDS with preoperative angiography; (2) retrospectively defined surface RDS velocity criteria were examined prospectively by comparison with preoperative and postoperative angiography. MATERIAL AND METHODS Patient material During the 25-month period from Oct. 1, 1988, through Oct. 31, 1990, 41 patients had renovascular
reconstruction at the Bowman Gray School of Medicine of Wake Forest University and were studied with intraoperative RDS. Our experience with 35 of these patients with follow-up tests of renal artery patency constitutes the basis of this report. Participants included 16 men and 19 women (ages, 27 to 72 years; mean age, 62 years). Significant hypertension was present in all but one patient treated for a renal artery aneurysm. In the remaining 34 patients hypertension ranged from 246/140 m m H g to 172/94 m m Hg (mean, 193 __+27/103 _+ 17 m m Hg). Hypertension treatment regimens included one to five drugs (mean, 2.7 _+ 1.2 drugs). In addition to hypertension, additional atherosclerotic risk factors included tobacco use (31 patients), diabetes mellims (9 patients), and hypercholesterolemia (11 patients). Based on preoperative sermn creatinine values after cessation of angiotensin converting enzyme inhibitors and high-dose diuretics, 15 patients (43%) had renal insufficiency (range, 2.0 to 8.8 mg/dl; mean, 3.3 mg/dl). Two patients were recently dependent on hemodialysis. Operative management After our routine preoperative evaluation, which has been detailed elsewhere, 35 patients had renovascular repair to 57 kidneys. Twelve patients underwent unilateral repair, 22 patients underwent bilateral repair, and 1 patient had a unilateral repair with contralateral nephrectomy. No patient who had unilateral reconstruction had significant contralateral renal artery disease recognized. Renal artery reconstruction was accomplished by aortorenal bypass grafting in 29 instances (Table I). Autogenous saphenous vein was used in 20 of these, including one ex vivo and five in vivo branch renal artery repairs. Six millimeter polytetrafluoroethylene (PTFE) was used in five, and knitted Dacron was used in four aortorenal reconstructions. Distal anastomoses were constructed in an end-to-side fashion in 4 grafts and end-to-end in the remaining 25. Renal artery reimplantation was used for 7 vessels and renal artery thromboendarterectomy was used in 21. Thirteen renal artery thromboendarterectomies were accomplished by transrenal technique with transverse aortorenal patch angioplasty by use of either PTFE (eight repairs) or aurogenous saphenous vein (five repairs). The remaining eight thromboendarterectomies were performed with rransaortic extraction technique as described by Stoney et al.17 After arterial reconstruction by these methods, intraoperative RDS was performed according to the techniques described below.
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Table I. Methods of renal artery reconstruction (N = 57) Aortorenal bypass grafting Saphenous vein PTFE Dacron RA Reimplantation RA TEA No TEA RA TEA Transrenal with patch PTFE 8 Saphenous vein 5 Transaortic
29 20 5 4 7 5 2 21 13 8
PTFE, Polytetrafluorothylene; RA, renal artery; TEA, thromboendarterectomy
T E C H N I Q U E OF R E N A L DUPLEX S O N O G R A P H Y Surface RDS (preoperative and postoperative) and intraoperative RDS were performed by use of either an Ultramark 8 or Ultramark 9 ultrasound system (Advanced Technology Laboratories, Bothell, Wash.). Surface studies were performed with either a 3.0 MHz. mechanical long-focus probe or a 2.25 MHz. phased-array probe with Doppler colorflow capability. Intraoperative studies were performed with a 10 MHz. mechanical probe with 5 MHz. pulsed Doppler, providing 0.4 m m B-scan resolution within the i to 4 cm probe focal zone and 1.5 m m 3 minimal Doppler sample volume at the 1.6 cm focal point. Intraoperative renal duplex sonography Renal duplex sonography studies were obtained 10 to 15 minutes after arterial reconstruction. The 10 MHz mechanical probe head was placed in a sterile, plastic sheath containing acoustic gel. The operative field was flooded with warm, normal saline solution, and B-scan images were first obtained from the perirenal aorta in sagittal and transverse planes to exclude unrecognized aortic defects. The renal artery was then imaged in longitudinal projection with care to visualize the renal artery origin, endarterectomy segments, endarterectomy end points, and perianastomic areas. All defects detected in longitudinal projection were imaged in transverse projection to confirm their anatomic presence and to estimate the degree of luminal narrowing. Centerstream Dopplershifted signals were obtained in longitudinal projection at all imaged defects and at positions immediately proximal and distal to all defects. Doppler insonating angles were maintained at 60 degrees or less. Renal artery peak systolic velocity (RA-PSV)
and renal artery end-diastolic velocity were calculated from real-me, fast-Fourier transform analysis of the Doppler-shifted signals. B-scan images and spectra from the fast-Fourier transform spectrum analyzer were recorded on videotape and hard copy processor. From the sagittal and transverse B-scan image, defects were described according to type (residual disease, intimal flap, thrombus) and location (endarterectomy segment, endarterectomy end point, perianastomic area). B-scan defects were designated as major (requiring revision) or minor (not requiring revision) by their hemodynamic significance determined by Doppler velocity criteria in Table II. In summary, these criteria are: (1) minor defect ( < 60% diameter-reducing stenosis) indicated by an RA-PSV of < 2.0 meters/see (m/see); (2) major defect ( _>60% diameter-reducing stenosis) indicated by focal RAPSV of >_2.0 m/see and distal turbulent velocity waveform; (3) occlusion indicated by no Dopplershifted signal from the renal artery B-scan image; (4) technically inadequate study for interpretation indicated by failure to obtain B-scan images and Doppler samples from the entire main renal artery. Arteries in patients with postrepair major B-scan defects ( ___60% diameter-reducing stenosis or occlusion) had immediate operative revision. Arteries in patients with normal postrepair B-scan studies or minor B-scan defects did not undergo revision. In an attempt to validate these intraoperative Doppler criteria, we compared intraoperative RDS performed before renal artery repair with preoperative angiography in 20 of 35 patients. Surface renal duplex sonography-preoperative and postoperative studies Preoperative and postoperative surface RDS studies were obtained by methods and techniques reported previously. 17 Surface RDS criteria for presence of < 60% or ---60% diameter-reducing renal artery stenosis or occlusion were identical to intraoperative RDS criteria (Table II), except no B-scan image was required for a technically adequate surface study.
Postoperative studies were obtained within 1 month of operation and serially when return patient evaluation permitted. Patients with intraoperative RDS but without postoperative surface RDS or angiography confirming the status of renal artery repair were excluded from study. Although our methods and results of surface RDS have been previously reported, 18 the Doppler velocity criteria for a < 60% or >_60% diameterreducing stenosis used in the present study were
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Intraoperative duplex sonography during renal artery repair 367
defined by retrospective comparison with conventional angiograms. In an attempt to validate these Doppler criteria prospectively, we compared preoperative surface RDS with preoperative angiography performed within 3 weeks of the duplex study.
Angiography The presence of renal artery stenosis was determined from preoperative (35 patients) and postoperative (9 patients) conventional cut-film angiograms by two independent observers without knowledge of the RDS results. Atherosclerotic lesions were estimated in 5% diameter-reducing increments. When the estimated degree of renal artery reduction differed by more than 15% between two independent observers, the dianleter-reduction was determined by a third independent observer. Statistical analysis Patient demographic data, RDS results, and angiographic interpretations were analyzed by use of the following techniques. Descriptive statistics (such as means and standard deviations of continuous data; frequencies and relative frequencies of categorical data) were computed, and the data were checked to verify that assumptions of statistical tests were met. Relationships between RDS data and angiographic data were assessed by means of Pearson correlations and scattergrams. Correlations between RDS measurements across time and between RDS data and percent renal artery stenosis were computed by analyzing their residual output from a general linear model with a subject effect to control for withinsubject correlation. Confidence limits for comparative analysis estimates (e.g., sensitivity, specificity) were found by use of standard errors that were adjusted for within-subject correlations. Relationships between RDS data and functional and hypertension responses were assessed by use of Spearman rank correlations. Changes in blood pressures and number of medications before and after operation were assessed by paired t tests.
RESULTS OF STUDIES Intraoperative renal duplex sonography Intraoperative RDS performed after renal artery reconstruction provided technically satisfactory studies in 56 of 57 repairs (98%). The technically inadequate study failed to image completely an endarterectomy end point; pulsed-Doppler spectral analysis in this patient did not suggest a major defect. Renal duplex sonography scan time after repair
Table II. Doppler velocity criteria for B-scan defects Defect
Criteria
Minor ( < 60% diameterreducing RA defect) Major ( ->60% diameterreducing RA defect)
RA-PSV from entire RA < 2.0 m/sec Focal RA-PSV ->2.0 m/sec and distal turbulent velocity
Occlusion
No Doppler-shifted signal from RA B-scan image Failure to obtain B-scan images and Doppler samples from entire main RA
waveform
Inadequate study for interpretation
RA, Renal artery; RA-PSV, renal artery peak systolic velocity.
averaged 4.5 minutes, and no complications were recognized relative to the technique. Of the 56 technically adequate intraoperative studies, B-scan defects occurred in 13 (23%) renal artery repairs (Table III). These 13 defects occurred in five autogenous saphenous vein grafts, one renal artery reimplantation, and seven thromboendarterectomies- five transrenal (two PTFE, three saphenous vein patches) and two transaortic thromboendarterectomies. Vein graft defects were considered perianastomic in three (two distal, one proximal anastomosis), one sclerotic venous valve, and one midgraft stenosis as a result of graft suture repair. Of the defects associated with thromboendarterectomies, five were intimal flaps within the thromboendarterectomy segment, one was residual disease at a transaortic extraction thromboendarterectomy end point, and one was a misoriented venous valve as part of a vein patch. A single perianastomotic intimal flap was present in the renal artery reimplantation. Seven of the eight intimal flaps and venous valves were considered 2 mm or less in length. Estimation of diameter reduction from flaps and valves was difficult because of their motion, but seven of these eight defects were felt to reduce lumen diameter by < 20% (Fig. 1). Two of the three perianastomotic defects were likewise considered < 20% diameter reducing, however, one distal perianastomotic defect was felt to reduce lumen diameter by 40%. The midgraft defect within a saphenous vein bypass graft, residual disease at a thromboendarterectomy end point, and an intimal-medial flap were each considered to reduce lumen diameter by 50%. Doppler-derived RA-PSV from these 13 B-scan defects demonstrated six that met criteria for a major defect creating a _ 60% diameter-reducing stenosis (RA-PSV range, 3.0 to 3.3 m/sec; mean, 3.1 m/see)
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Table III. Summary of major and minor B-scan defects Patient age (2VffF) 70 (M) 68 (F)
62 (M) 51 (M) 59 (F)
BIL TEA R-RABG L-TEA BIL TEA R-RABG L-TEA R-RABG R-RABG L-REIMP L-RABG R-TEA BIL TEA, AFBG
44 (F)
BIL RABG
27 (F)
R-RABG
68 (F) 66 (F) 53 (F) 69 (F)
2~Iajor/minor
RA-PSV (m/sec)
Follow-Up (mo)
Minor Minor
0.73 0.60
13 mo
Patent Operative death
L-IF L-valve
Minor Minor
0.60 0.72
18 mo 22 mo
Patent Patent
Proximal anastomosis L-IF
Minor Minor
0.70 0.60
16 mo 5 mo
Patent Patent
L-valve R-RD R-IF L-IF R-distal anastomosis L-midgraft Distal anastomosis
Minor Major Major Major Major Major Major
1.00 3.10 3.30 3.20 3,00 3,00 3,00
4 mo 13 mo 10 mo 10 mo 10 mo 10 mo 3 mo
Patent Patent L-patent R-RAS R-occluded L-patent Patent
Procedure
Deficit ,~ L-IF L-IF
Outcome
R, Right; L, left; BIL, bilateral; TEA, thromboendarterectomy; RAB, renal artery bypass graft; AFBG, aortobifemoral bypass graft; IF, Intimal flap; RD, residual disease; RAS, renal artery stenosis.
(Table III). These six defects occurred in three autogenous saphenous vein grafts and three thromboendarterectomies. Vein graft defects were perianastomic in two (both distal) and midgraft at the site of suture repair in the third. Of the three defects associated with thromboendarterectomies, two were flaps in the endarterectomy segment (Figs. 1 and 2), and one reflected residual disease at the distal endarterectomy end point. Three of these defects (one distal perianastomotic, two flaps in endarterectomy segments) were considered <20% diameter reducing by B-scan image alone. The six B-scan defects with abnormal Doppler findings were immediately revised with vein patch angioplasty (three saphenous vein grafts) or completion thromboendarterectomy (three thromboendarterectomies) (Fig. 2). In each case the presence of a defect reducing the luminal diameter by at least 60% was confirmed during revision. Intraoperative RDS was repeated after four of the six revisions. After each revision no defect was recognized on B-scan image, and RA-PSV was decreased (RA-PSV range, 1.0 to 1.8 m/sec; mean, 1.3 m/sec). Considering all i3 B-scan defects, the presence of a defect was associated with a significant increase in RA-PSV compared to repairs without B-scan defects (Spearman rank correlation, r = 0.3029;p = 0.03). However, RA-PSV from the seven repairs with defects that were defined as minor by Doppler criteria did not differ significantly from the 43 renal artery repairs with no B-scan defect (mean RA-PSV, 0.7 + 0.3 versus 0.8 +__0.3 m/sec). In these seven minor defects no revision was performed.
To test the validity of our Doppler criteria when applied during operation, intraoperative RDS performed before renal artery repair was compared with preoperative angiography in 20 of the 35 patients. Intraoperative prerepair RDS was performed unilaterally in three patients, providing comparative anatomy to 37 kidneys. Intraoperative prerepair RDS correctly identified five of five kidneys with normal or <60% renal artery stenosis (mean RA-PSV, 0.9 _ 0.4 m/sec), 25 of 26 kidneys with __.60% to 99% stenosis (mean RA-PSV, 3.2 +_ 1.3 m/sec), and six of six renal artery occlusions. By comparison with preoperative angiography, intraoperative prerepair RDS was 96% sensitive and 100% specific, with a 99% overall accuracy. Postoperative surface renal duplex sonography and angiography In 33 of 34 patients surviving renal artery reconstruction, the status of 54 repairs was defined by 57 postoperative surface RDS studies. Four postoperative RDS studies (7%)were tectmically inadequate for interpretation, however, each study was repeated and was technically satisfactory 1 to 3 months later. Surface RDS studies at the time of last follow-up (mean, 12.4 months) found 51 of 54 repairs patent with < 60% diameter-reducing stenosis (mean RA-PSV, 1.3 _ 0.3 m/sec). One repair demonstrated _>60% stenosis on follow-up examinations 1, 3, and 10 months after surgery (RA-PSV, 3.4 m/sec). Two repairs were occluded on RDS examination I week after surgery. One occlusion led to eventual nephrectomy, and one kidney was sal-
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Intraoperative duplex sonography during renal artery repair 369
Fig. 1. (A, B, and C). Saggital (A) and transverse (B) images of a minor B-scan defect. This intimal flap within the endarterectomy segment (heavy arrows) had normal Doppler spectral analysis (C). This minor defect was not revised. vaged by a second bypass procedure, which remains patent and free ofstenosis at last follow-up. The renal artery stenosis and two renal artery occlusions were confirmed by postoperative angiography. One contralateral unrepaired renal artery developed significant stenosis by RDS examination at 6 months follow-up, and this disease was also confirmed by angiography. Thirteen conventional angiograms were performed in nine patients with 13 renal artery repairs 1 week to 20 months after surgery (mean, 8.9 months). Six patients (five unilateral, one bilateral repair) had one angiogram after surgery, two patients (bilateral repair) had two angiograms, and a single patient (bilateral repair) had three angiograms defining renal artery anatomy to 21 renal reconstructions. By angiography, 16 renal reconstructions were considered normal or had < 60% diameter-reducing stenosis, 3 arteries had _>60% to 99% dianleter-reducing stenosis, and 2 repaired renal arteries were occluded.
The clinical response to surgery supports the 96% follow-up patency rate. Applying a previously described algorithm for blood pressure and renal function response,* hypertension was considered cured in 5 patients, improved in 26, and unchanged in 2 patients. Postoperative systolic and diastolic blood pressures and number of antihypertensive medications (mean _ SD, 137 + 12/75 _+ 10 mm Hg; 1.6 _+ 1.2 medications) were significantly decreased when compared with preoperative values (paired t test; p < 0.001). Among the 15 patients with preoperative serum creatinine of __.2.0 mg/dl, renal function was considered improved in 12 patients (two patients removed from dialysis), not changed in two patients, and worsened in one patient.
Comparison with postoperative studies Thirty-four of 35 patients survived renovascular reconstruction providing comparison between intra-
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Fig. 2. (A, B, C, and D). Sagittal image (A) of a major B-scan defect (heavy arrow). This intimal flap at the proximal anastomosis (B) demonstrated a focal increase in RA-PSV (3.1 m/sec). After revision RA-PSV (C) was decreased (1.1 m/sec) and follow-up angiogram (D) demonstrated a widely patent anastomosis. This patient was cured of hypertension.
operativc RDS and the status of renal artery repair determined by either postoperative surface RDS (33 patients) or postoperative angiography (9 patients) or both. Of renal artery repairs with normal intraoperative RDS demonstrating neither B-scan or Doppler abnormalities, 42 of 43 (98%) were patent without recurrent stenosis at last follow-up (42 by surface RDS and 4 by angiography). An ex vivo branch renal artery repair for fibromusca~lar dysplasia occluded within 1 week of surgery. This occlusion was confirmed by both surface RIDS and angiography. A nephrectomy was ultimately required in this patient.
At the time of reexploration, the failure of reconstruction was thought to be a result of a technical complication at the renal vein to vena cava anastomosis. Review of this patient's intraoperative RDS revealed no B-scan defect with RA-PSV of 0.7 m/sec uniformly from aorta to renal hilum. The venous anastomosis, however, was not studied at surgery. Of the seven minor defects without Doppler abnormality, six of seven survivors demonstrated six patent renal artery repairs without stenosis on follow-up examination (six by surface RDS and two by angiography). One patient who died in the perioperative period demonstrated a flap within the
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Intraoperative duplex sonography during renal artery repair 371
10
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8
7 r = 0.4862 p = 0.0013 [3_
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0 I
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10
20
30
40
50
60
70
80
90
100
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Fig. 3. Scatter plot ofrenal artery peak systolicvelocity (RA-PSV in m/sec) versus percent renal
artery stenosis defined by angiography. endarterectomy segment without Doppler criteria for significance. At autopsy I week later, the renal artery repair was found to be patent. Of the six renal reconstructions in four patients (two unilateral, two bilateral) with major defects defined by B-scan and Doppler criteria, four of the revised repairs remained patent without stenosis (four by surface RDS and one by angiogram), one repair demonstrated early (or unrelieved) ___60% stenosis, and one repair occluded. Renal artery stenosis detected by surface RDS and confirmed by angiography occurred after completion endarterectomy was performed for a significant flap (RA-PSV 3.0 m/see) in the endarterectomy segment. Postrevision intraoperative RIDS was not performed. An autogenous saphenous vein bypass occluded (seen on angiogram) after patch angioplasty of a significant stenosis at the distal anastomosis (RA-PSV 3.0 m/sec). Postrevision RDS was normal (normal B-scan; RA-PSV 1.0 m/sec). This kidney was salvaged by successful reoperation, at which time an apparent atheroembolus was occluding the distal vein bypass. If the six major defects are considered true positives and the renal artery occlusion among the 49 normal (43 RDS) and minor defects (6 RDS) is
considered to be the single false negative, intraoperative RDS was 86% sensitive and 100% specific for technical defects associated with significant postoperative stenosis and occlusion of renovascular repair. To validate our Doppler criteria for surface RDS prospectively, preoperative surface RDS was compared with preoperative angiography in 33 of the 35 patients (65 kidneys). Surface RDS was technically inadequate to 3 kidneys (4.6%) yielding renal artery anatomy to 62 kidneys for comparison (Fig. 3). Surface RDS correctly identified 10 of 11 kidneys with normal and < 60% diameter reducing stenosis (mean RA-PSV, 1.3 + 0.25 m/sec), 50 of 51 kidneys with _>_>60% stenosis (mean RA-PSV, 3.6 _+ 1.8 m/see), including nine of nine occlusions, providing 98% sensitivity, 91% specificity, and a 97% overall accuracy (Table IV). DISCUSSION
Our experience with intraoperative RDS after renovascular repair indicates that RDS is both sensitive (86%) and specific (100%) for technical defects contributing to postoperative failure. Renal artery repairs with normal and minor B-scan defects by RDS demonstrated 98% patency free of critical stenosis at 1-year follow-up. This degree of anatomic
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Table IV. Surface RDS versus cut-film angiography; comparative analysis parameter estimates and their 95% confidence intervals (N = 62 kidneys) Method
Estimate
Sensitivity Specificity PPV NPV Accuracy
0.98 0.91 0.98 0.91 0.97
95% Confidence interval
(0.94, (0.82, (0.94, (0.81, (0.92,
1.00) 0.99) 1.00) 1.00) 1.00)
RDS, Renal duplex sonography; PPV, positive predictive value; NPV, negative predictive value.
success determined by surface RDS (in 97%) and renal angiography (in 26%) was supported by the clinical results of operative intervention- a favorable hypertension response was observed in 94% of patients, whereas global renal fimction improved in 80% of patients with preexisting renal insufficiency. The 23% incidence of defects in this study is similar to previous reports of other methods of ultrasonography at different anatomic sites, n'12'~9-2~ Experimental and clinical experience have suggested that B-mode ultrasonography is more sensitive to the presence ofintimal-medial defects than is completion angiography) 2'16'22'~3 Similar studies with highfrequency pulsed-Doppler spectral analysis have detected subtle disturbances in laminar flow in the absence of distal pressure/flow reduction. 24'2S Although these methods would appear quite sensitive to technical errors, they lack the necessary specificity to guide intraoperative management. To eliminate the potential risks of unnecessary exploration, most authors have advised that subsequent intraoperative angiography determine the need for surgical revision. Used in this manner, the ultrasound study serves as a screening test to avoid routine completion angiography. 26 As a completion study for renal artery reconstruction, however, ultrasonography alone must demonstrate sensitivity and specificity sufficient to guide operative revision, In this respect, we believe that the combination of B-scan imaging with realtime Doppler spectral analysis provides more useful clinical information than either modality used alone. B-scan image defines the presence, location, and type of defect, whereas Doppler spectral analysis defines its hemodynamic significance. By revising only major B-scan defects defined by velocity criteria, unnecessary operative revision of minor B-scan defects is eliminated. Okuhn et al) 1 have reported similar results from
intraoperative RDS after 83 renal reconstructions. In their study major defects indicating the need for immediate revision were defined by B-scan defects reducing luminal area by > 50% or a "markedly abnormal flow signal." These authors assessed Doppler signals audibly at surgery and by off-line spectral analysis at a later time. Intravenous digital subtraction angiography defined early (7- to 10-day) postoperative patency. By these duplex criteria, defects were present in 31% of repairs. Four major defects were recognized-three occlusions and one floating thrombus. Each occlusion was defined by the absence of Doppler-shifted signal despite a normal B-scan appearance. These investigators found that velocity waveforms defined by off-line spectral analysis provided no additional information as compared with subjective audible assessment. B-scan defects that were not associated with "obviously abnormal Doppler signal" with normal confirmatory studies were considered to be false positives, yielding 85% sensitivity and 75% specificity for 77 renal artery repairs. Our experience supports these previously reported results, however, our methodology and criteria for revision differ. Although audible analysis of the Doppler-shifted signal can easily detect severe flow disturbance (occlusion, high-grade stenosis), 16'2°'27 we think that on-line spectral analysis of the Doppler signal contributes valuable objective hemodynamic assessment of an imaged lesion. Audible features of the Doppler-shifted signals from renal artery endarterectomy and renal artery branch repairs contain qualities that can be confused with poststenotic turbulence. We feel that on-line spectral analysis with velocity estimation has proved very useful in these reconstructions. This study and the study of Okuhn et al. 11 suffer from a similar and potentially serious limitationintraoperative RDS examinations were compared with renal artery patency defined by several postoperative tests of varying sensitivity and specificity. In our study we have compared intraoperative RDS with three different assessments after renal reconstruction-gross findings at operative revision, postoperative cut-film renal angiography, and postoperative surface RDS. Probably the most controversial of these is the use of surface RDS for follow-up of repair status. 2*'29 Although the criteria resulting from retrospective comparative analysis between surface RDS and angiography has been confirmed prospectively in this study (sensitivity 98%, specificity 91%), other potential limitations of surface RDS exist. One potential limitation is that a reason-
Volume 14 Nlunber 3 September 1991
Intraoperative duplex sonography during renal artery repair
able estimate of stenosis or occlusion of renal artery repairs (< 10%) differs markedly from the actual prevalence within the group examined retrospectively (44%) and prospectively (82%) for validity analysis. In this instance one might expect a high false-positive rate from postoperative RDS. However, in the eight patients in whom both angiography and surface RDS were obtained after operation, including all positive surface RDS studies, there was perfect agreement. Another limitation of surface RDS is that it accurately defines only the presence or absence of a critical stenosis (___60% diameter reduction) or occlusion of the renal artery; definition of lesser degrees of stenosis is not provided by the surface technique.18 Unrepaired minor defects could conceivably favor subendothelial fibroblastic proliferation or neoatherogenesis causing progressive stenosis and late graft failure, s'13'25 In this regard, most autogenous renal artery reconstructions that fail do so within the first year, and our period of mean follow-up (12.4 months) should detect these. 13 Despite these limitations, we believe the advantages of an inexpensive, serial postoperative study free of any recognized risk and proved highly correlated with hemodynamic renal artery disease supports the use of surface RDS as a useful method of follow-up and comparison. Finally, the interaction between surgeon and vascular technologist during intraoperative RDS deserves comment. Both visual and spectral data acquired during the performance of intraoperative RDS are enhanced by the participation of the vascular technologist. Although the surgeon is responsible for manipulating the probe head to acquire optimal B-mode images and Doppler spectra of the vascular repair at likely sites of technical error, the power and time gain adjustments (which minimize potential artifact) are made best by an experienced technologist. Close cooperation is likewise required to obtain c.omplete pulsed-Doppler sampling associated with any B-scan defect. Last, knowledge of the surgical anatomy through participation in intraoperative studies enhances the technologist's ability to obtain satisfactory surface RDS images during follow-up. ha conclusion, our experience with intraoperativ~ RDS as a completion study after renal artery repair suggests that intraoperative RDS is a rapid examination with a high rate of technical success. The designation of B:scan defects as minor or major according to Doppler velocity waveform criteria provides the sensitivity and specificity necessary to guide decisions regarding intraoperative revisions.
373
REFERENCES
1. Dean RH, Wilson Jr', Burko H, Foster JH. Saphenous vein aortorenal bypass grafts: serial angiographic study. Ann Surg 1974;180:469-78. 2. Stanley JC, Ernst CB, Fry WJ. Fate of 100 aortorenal vein grafts: characteristics of late graft expansion, aneurysmal dilatation, and stenosis. Surgery 1973;74:931-44. 3. Dean RH, Krueger TC, Whiteneck 1M, et al. Operative management of renovascula( hypertension. J VASC SURG 1984;1:234-42. 4. Hansen KJ, Ditesheim JA, Metropol SH, et al. Management ofrenovascular hypertension in the elderly population. J VAse SURG 1989;10:266-73. 5. Dean RH. Complications of renal revascularization. In: Bernhard VM, Towne JB, eds. Complications in vascular surgery, 2nd ed. Orlando: Grune & Stratton, 1985:229-46. 6. Plecha FR, Pories WJ. Intraoperative angiography in the immediate assessment of arterial reconstruction. Arch Surg 1972;105:902-7. 7. Rosental JJ, Gaspar MR, Marius HJ. Intraoperative arteriography in carotid thromboendarterectomy. Arch Surg 1977; 106:806-8. 8. Courbier R, Jausseran JM, Reggi M. Detection complications of direct arterial surgery. Arch Surg 1977;112:1115-8. 9. Metropol SH, Hansen KJ, Holmes RP, Iskandar SS, Strandhoy ]W, Dean RH. Reperfusion changes after relief of sustained renal isehemia. Surg Forum 1989;XL:300-1. 10. Okuhn SP, Reilly LM, Bennett JB, et al. Intraoperative assessment of renal and visceral artery reconstruction: the r01e of duplex scanning and spectral analysis. J VAsc Sr:RG 1987;5:137-47. 11. Schwartz RA, Peterson G], Noland KA, Hower JF, Nannheim KS. Intraoperative duplex scanning after carotid artery reconstruction: a valuable tool. ] VAsc SUV,G 1988;7:620-4. 12. Cato RF, Seabrook GR, Bandyk DF, Moldenhaner PI~ Schmitt DD, Towne JB. Intraoperative duplex scanning following carotid artery reconstruction. J Vasc Tech 1989; XIII:31-6. 13. Reilly LM, Okuhn SP, Rapp ]H, et al. Recurrent carotid stenosis: a consequence of local or systemic factors? The influence of unrepaired technical defects. J VASC SURe 1990;11:448-60. 14. Rutherford RB, Jones DN, Lowenstein D, Fleming P. The effects of changes in lumen and flow on the arterial velocity waveform. J Surg Res 1982;32:110-20. 15. Goldstone J. Intraoperative assessment of renal and visceral arterial reconstruction using Doppler and duplex imaging. In: Ernst CB, Stanley JC, eds. Current therapyin vascular surgery, 2nd ed. Philadelphia: BC Decker, 1991:872-5. 16. Bandyk DF. Intraoperative assessment of arterial reconstructions utilizing ultrasound. Semin Vasc Surg 1989;2: 75 -84. 17. Stoney RJ, Skioldebrand CG, Qvarfordt PG, Reilly LM, Ehrenfeld WK. Juxtarenal aortic atherosclerosis. Surgical experience and functional result. Ann Surg 1984;200:345-54. 18. Hansen I(J, Tribble RW, Reavis SW, et al. Renal duplex sonography: evaluation of clinical utility. J VAsc SURG 1990;12:227-36. 19. Seifert KB, Blackshear WM. Continuous-wave Doppler in the intraoperative assessment of carotid endarterectomy. J VASC S~:v~G1985;2:817-20. 20. Barnes RW. Intraoperative monitoring in vascular surgery. Ultrasound Med Biol 1986;12:919-26.
374
Journal of VASCULAR SURGERY
H a n s e n et al.
21. Zierler RE, Bandyk DF, Thiele BL. Intraoperative assessment of carotid endarterectomy. J VAsc SURG 1984;1:73-83. 22. Coelho JCU, Sigel B, Flanigan DP, et al. An experimental evaluation of arteriography and imaging ultrasonography in detecting arterial defects at operation. J Surg Res 1982;32: 130-7. 23. Sawchuk AP, Flanigan DP, Machi J, Schuler II, Sigel B. The fate of unrepaired minor technical defects detected by intraoperative ultrasonography during carotid endarterectomy. J VAse SUING1989;9:671-6. 24. Bandyk DF, Zierler RD, Berui GA, Thiele BL. Pulsed Doppler velocity patterns produced by arterial anastomoses. Ultrasound Med Biol 1983;9:79-87. 25. Bandyk DF, Kaebnick HW, Adams MB, Towne lB. Turbulence occurring after carotid bifurcation endarterectomy: a harbinger of residual and recurrent carotid stenosis. J Vase StJRG 1988;7:261-74.
26. Bandyk DF, Zierier RE, Thiele BL. Detection of technical error during arterial surgery by pulsed Doppler spectral analysis. Arch Surg 1984;119:421-8. 27. Barnes RW, Nix ML, Nichols BT, Wingo IP. Recurrent versus residual carotid stenosis. Ann Surg 1986;203:65260. 28. Eidt IF, Fry RE, Clagett GP, Fisher DF, Alway C, Fry WJ. Postoperative follow-up of renal artery reconstruction with duplex ultrasound. J VAsc SURG 1988;8:667-73. 29. Sandager G, Flinn WR, McCarthy WJ, Yao JST, Bergan JJ. Assessment of visceral arterial reconstruction using duplex scan. J Vase Tech 1987;XI:13-6.
Submitted Feb. 2, 1991; accepted Apr. 11, 1991.