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Biomedical subjects

R M Zwolak

Publications and source records attributed to R M Zwolak.

At least 19 recordsLinked to original sources
PubMed2001

Coding and billing issues in the vascular laboratory.

Noninvasive vascular testing grew from a need for a safe, accurate, and inexpensive alternative to contrast injection venography and arteriography. The ultrasound studies performed to evaluate vascular disease today meet all expectations for safety and accuracy, and cost thousands of dollars less than their contrast counterparts, yet few sectors in medicine have been challenged so regularly by the Health Care Financing Administration (HCFA). Tests performed on duplex ultrasound instruments have prevented innumerable arterial and venous injuries and episodes of renal failure caused by contrast injection. Despite those laudable accomplishments, the financing agencies continue to reduce payments, threaten inappropriate supervisory requirements, and belittle the overall importance of the examinations. This report reviews the last decade of payment issues involving the vascular laboratory, pointing out inequities and problems that threaten not the quantity, but the quality, of this technology. The discussion focuses on Medicare Part B payments because they represent the majority of payments for noninvasive studies across the United States. The topics include payment denials, supervision issues, and problems associated with the zero work pool. In addition, the method by which HCFA calculates relative value unit (RVU) payments for procedures is included.

Centers for Medicare and Medicaid Services, U.S.↗
PubMed2001

Early results of infragenicular revascularization based solely on duplex arteriography.

PURPOSE: Recent reports have both advocated and questioned the utility of duplex arteriography (DA) as the sole preoperative imaging modality for planning infragenicular revascularization. This study compares the outcome of patients with critical limb ischemia who underwent infragenicular vein grafts on the basis of DA alone versus conventional preoperative contrast arteriography (CA). METHODS: The study group is composed of 23 consecutive patients who underwent infragenicular vein bypass grafting solely on the basis of preoperative DA from 1998 to 1999. They were compared with 50 consecutive patients who underwent infragenicular vein bypass grafting after CA from 1996 to 1998. Peak systolic velocity and end-diastolic velocity of potential target arteries were recorded during DA studies. In situ saphenous vein grafts were used preferentially, and technical adequacy of all grafts was assessed with completion duplex or arteriography. RESULTS: DA and CA groups were comparable on the basis of age and risk factors. In one limb (4%), the target artery selected by DA was abandoned because of dense calcification. No other revision in target or inflow artery was required on the basis of intraoperative completion studies. At 1 year, primary graft patency (78% vs 70%, P =.72) and limb salvage (70% vs 81%, P =.21) were comparable between the two groups. In the DA group, mean preoperative target artery peak systolic velocity in patent versus failed grafts was 49 +/- 18 cm/s versus 31 +/- 9 cm/s (P =.04), whereas mean end-diastolic velocity was 22 +/- 7 cm/s versus 14 +/- 8 cm/s (P =.08). CONCLUSION: Infragenicular revascularization directed by DA alone provides early graft patency and limb salvage rates comparable to similar procedures that are based on CA. Preoperative DA target artery velocities may predict outcome and improve target selection. These initial results justify further clinical testing of DA as the primary imaging modality for planning infragenicular vein grafts.

Angiography↗
PubMed2001

Results of endovascular superficial femoral endarterectomy.

BACKGROUND: Endovascular superficial femoral artery (SFA) endarterectomy with a ring stripper/cutter and distal stenting has been suggested to have a patency comparable with above-knee bypass surgery. We report our initial experience with this technique. METHODS: Seventeen patients (13 men and 4 women; mean age, 64 years) with SFA occlusion and above-knee popliteal reconstitution underwent attempted remote endarterectomy with a ring cutter system combined with primary stenting of the distal end point. Analysis was performed in a prospective manner with patency rates determined by Kaplan-Meier life-table analysis. RESULTS: The indication for operation was claudication in 8 patients, rest pain in 6, and tissue loss in 3. Initial technical success was achieved in 11 patients (65%). Reasons for technical failure included SFA perforation (4), inability to traverse a calcified/diseased segment (1), and inability to retract/remove the ring cutter (1). Life-table analysis of all patients revealed a primary patency at 1 year of 26% +/- 11%. Primary-assisted patency was 38% +/- 12% at 1 year, with 59% of patients ultimately requiring surgical bypass grafting. In patients in whom initial technical success was achieved, the 1-year primary and primary-assisted patency rates were 40% and 59%, respectively. There were four reocclusions requiring surgical revascularization with below-knee popliteal (2) or tibial (2) bypass grafting, 1 symptomatic restenosis requiring repeat angioplasty, and 1 symptomatic restenosis treated conservatively. CONCLUSION: The results of endovascular SFA endarterectomy were disappointing, with technical success in less than two thirds of patients and a 1-year primary patency of only 26%. Remote SFA endarterectomy appears less effective than above-knee femoropopliteal bypass grafting, and after early failure, patients may require more distal revascularization for limb salvage.

Angioplasty↗
PubMed2001

Danazol and limb-threatening arterial thrombosis: two case reports.

Danazol is a synthetic androgenic steroid used clinically for the treatment of a wide variety of disorders. Although there is no extensive evidence that androgens are thrombogenic in humans, there are case reports of cerebral, coronary, and peripheral arterial thrombosis in young male athletes abusing anabolic-androgenic steroids. There are also two reported cases of arterial and venous thrombotic events attributed to danazol therapy. We report two additional cases of limb-threatening arterial thrombosis in patients undergoing danazol therapy, and suggest the possibility that danazol may be an independent risk factor for arterial thrombosis.

Acute Disease↗
PubMed2000

Pedal branch artery bypass: a viable limb salvage option.

PURPOSE: We reviewed our experience with pedal branch artery (PBA) bypass to confirm the role of these target arteries for limb salvage and to identify patient and technical factors that may be associated with graft patency and limb salvage. METHODS: In this retrospective study we analyzed 24 vein grafts to PBAs performed from 1988 to 1998 for limb salvage in 23 patients who had no suitable tibial, peroneal, or dorsal pedal target arteries. These PBA grafts were compared with 133 perimalleolar posterior tibial, defined at or below the ankle, or dorsalis pedis bypass grafts performed contemporaneously; the Kaplan-Meier life table was used in the analysis of graft patency and limb salvage. Life table analyses and logistic regression analysis of prognostic patient variables were also performed. RESULTS: The PBA bypass represented 3% of infrainguinal revascularizations for chronic critical limb ischemia at our institution over the study period. Patients who received PBA bypasses were more likely to be male (92% vs. 69%, P =.02) with lower incidences of overt coronary artery disease (33% vs. 50%, P =.12) and stroke (0% vs 15%, P =.04), and a higher incidence of end-stage renal disease (21% vs 8%, P =.06) than those undergoing perimalleolar bypass. Seventeen percent of PBA bypasses were performed with the anterior lateral malleolar artery, a vessel not previously described as a common bypass target. Two-year primary patency and limb salvage for PBA versus perimalleolar bypass was 70% versus 80% (P =.16) and 78% versus 91% (P = .28), respectively. Patency and limb salvage rates were no different in bypasses with above-knee or below-knee inflow arteries. CONCLUSION: An autogenous vein bypass to the PBA, though rarely required, provides acceptable primary patency and limb salvage when compared with perimalleolar tibial artery bypass when no suitable, more proximal target arteries are available. The PBA bypass should be considered before major amputation is undertaken.

Aged↗
PubMed1999

Can duplex ultrasound replace arteriography in screening for mesenteric ischemia?

Duplex examination of the mesenteric vasculature is not a widely performed examination, but the published literature documents the ability of this test to accurately identify chronic atherosclerotic occlusive disease. The test is a recent addition to the armamentarium of noninvasive duplex technology, with studies of adequate size for statistical analysis appearing only since 1991. Two primary sets of diagnostic threshold values for significant stenoses of the superior mesenteric artery (SMA) and the celiac artery have been published and subsequently tested for accuracy. One of these recommends use of peak systolic velocity (PSV), whereas end diastolic velocity (EDV) was found to be most accurate in the other. Both sets of criteria identify overall accuracy of greater than 90% for identification of SMA stenosis, and greater than 80% for diagnosis of celiac stenosis. Identification of celiac disease may be aided by analysis of blood flow direction in the common hepatic artery. The finding of retrograde hepatic flow is virtually diagnostic of severe celiac stenosis or complete occlusion. Duplex also has been shown capable of identifying anatomic anomalies of the mesenteric vessel origins, a situation that occurs in approximately 20% of the population. Finally, mesenteric duplex has utility in a variety of less common abdominal visceral disorders, but statistical analysis of accuracy and adequate identification of quantitative velocity thresholds have not been performed. Skilled technologists who have access to appropriate training and equipment can master this test. There is little doubt that it can replace angiography as a screening tool in the setting of suspected chronic mesenteric ischemia.

Acute Disease↗
PubMed1998

Mesenteric and celiac duplex scanning: a validation study.

PURPOSE: To validate the accuracy of previously established duplex ultrasound criteria for > or =50% superior mesenteric artery (SMA) and celiac artery (CA) stenosis by comparison with arteriography. METHODS: Duplex criteria established retrospectively in our laboratory in 1991 identified an end-diastolic velocity (EDV) > or =45 cm/sec, or no flow signal, as highly sensitive (100%) and specific (92%) indicators for SMA stenosis > or =50% or occlusion. EDV was more accurate (95%) than peak systolic velocity (PSV), which had a maximal accuracy of 86% at a PSV > or =300 cm/sec, with low sensitivity (62%), but high specificity (100%). For CA, accurate velocity thresholds were not identified, but we subsequently noted that retrograde common hepatic artery flow direction from SMA collateral was highly predictive of severe CA stenosis or occlusion. Since publication of those findings, 243 mesenteric duplex scans were performed for clinical evaluation of suspected chronic mesenteric ischemia. Angiographic confirmation was available for a subset of 46. SMA and CA diameters were measured on lateral aortograms by observers blinded to the duplex results, and the original duplex diagnostic criteria were tested for accuracy. In addition, receiver operator characteristic curve analysis was performed on the velocity data to identify the most accurate velocity thresholds in the new data. RESULTS: Duplex was technically adequate in 98% of SMA, 96% of CA, and 89% of hepatic arteries, and arteriograms were adequate in 100% of SMA and 98% of CA. For the SMA, EDV > or =45 cm/sec again provided the best sensitivity (90%), specificity (91%), positive predictive value (90%), negative predictive value (91%), and overall accuracy (91%). As in the retrospective study, PSV > or =300 cm/sec provided low overall accuracy (81%), low sensitivity (60%), but high specificity (100%). Lowering the PSV threshold improved sensitivity but reduced accuracy. For CA, retrograde common hepatic artery flow direction was 100% predictive of severe CA stenosis or occlusion. Velocity data in CA provided accuracy not found in the original study. EDV > or =55 cm/sec or no flow signal had best overall accuracy (95%) with high sensitivity (93%) and specificity (100%). PSV > or =200 cm/sec or no signal also had excellent accuracy (93%), sensitivity (93%), and specificity (94%). In addition, three of four anatomic anomalies were correctly identified by duplex. These included one right hepatic and one common hepatic artery originating from the SMA, and one common celiacomesenteric trunk. CONCLUSION: This validation analysis confirms that duplex velocity criteria are accurate in the identification of mesenteric occlusive disease. Retrograde common hepatic artery flow direction correctly predicts severe CA stenosis or occlusion. Duplex ultrasound may also identify mesenteric anatomic variants that can influence study interpretation.

Aged↗
PubMed1998

Fate of the contralateral leg after infrainguinal bypass.

PURPOSE: To identify variables predictive of the need for future vascular intervention in a leg contralateral to one currently undergoing infrainguinal bypass. METHODS: We reviewed the records of 450 consecutively treated patients undergoing infrainguinal bypass for occlusive disease to examine the outcome of a previously untreated contralateral leg. Patients with coexistent contralateral limb-threatening ischemia at the time of initial ipsilateral operation were excluded, as were patients with bilateral disease who underwent a staged contralateral procedure within 3 months of the ipsilateral operation. This yielded a study cohort of 383 patients with no anticipated intervention in the contralateral leg who were followed for a mean value of 38 months. Patient survival and subsequent intervention in the contralateral leg were examined with life-table and regression analysis. RESULTS: Mean age of the patients was 68 years; 60% were men; 54% had diabetes; and 50% had coronary artery disease. The initial ipsilateral operation was performed for limb threat in 90% of instances. Twenty percent of patients subsequently needed intervention in the contralateral leg (infrainguinal bypass 83%, primary major amputation 17%). According to life-table analysis, 30% of patients needed intervention at 5 years, and the overall survival rate was 51% at 5 years. Multivariate analysis indicated that the need for future contralateral intervention was independently predicted with the following four risk factors: diabetes (relative risk [RR] 2.4x), coronary artery disease (RR 1.8x), lower initial ankle-brachial index (RR 2.1x with ankle-brachial index less than 0.7), and younger age (RR 2.2x if age less than 70 years). Regression models predicted the need for contralateral intervention for only 8% of patients at 5 years when none of these risk factors was present but for 67% when all risk factors were present. CONCLUSION: The fate of the contralateral leg after infrainguinal bypass is affected by diabetes, coronary artery disease, contralateral ankle-brachial index, and age at initial ipsilateral bypass. The effect of these risk factors is additive in prediction of the likelihood of future intervention. Knowledge of these factors may help identify instances in which the contralateral greater saphenous vein will be important for future limb salvage and also determine which patients need more careful follow-up care.

Adult↗
PubMed1997

Longitudinal comparison of dialysis access methods: risk factors for failure.

PURPOSE: To compare dialysis access patency rates and identify risk factors for failure. METHODS: All access procedures at our institution from 1987 to 1996 were reviewed. Primary procedures were surgically implanted dual-lumen central venous hemodialysis catheters (SIHCs), peritoneal dialysis catheters (PDCs), arteriovenous fistulas (AVFs), and prosthetic shunts (PTFEs). RESULTS: Five hundred eighty-five primary procedures (236 PTFEs, 87 AVFs, 112 SIHCs, and 150 PDCs) and 259 secondary procedures (215 PTFEs, 14 AVFs, 0 SIHCs, and 30 PDCs) were performed on 350 patients. By life table analysis, SIHCs exhibited the lowest primary patency rate (9% at 1 year; p < 0.0001), whereas PDCs had the highest primary patency rate (57% at 1 year; p < 0.02). The primary patency rates of AVFs and PTFEs was similar, with 43% and 41% 1-year patency rates, respectively (p = 0.70). Less-stringent reporting methods would have increased apparent 1-year patency rates by 9% to 41%. With regard to secondary patency, there was no significant difference between PTFEs and PDCs, with 1-year patency rates of 59% and 70%, respectively (p = 0.62), but PTFEs were more frequently revised. In addition, there was no significant difference between AVF and PTFE secondary patency rates, with 1-year patency rates of 46% and 59%, respectively. Early differences in patency rates for AVFs, PTFEs, and PDCs diminished over time, and at 4 years AVFs had the best secondary patency rate (p = 0.6). The most common reasons for access failure were: PTFEs, thrombosis; AVFs, thrombosis and failure to mature; SIHCs, inadequate dialysis; PDCs, infection and inadequate exchange. By regression analysis, a history of a previous unsalvageable PTFE was the only significant risk factor for failure of a subsequent PTFE (p < 0.01), and the risk of graft failure increased exponentially with the number of previous PTFE shunts. Diabetes was the only significant risk factor for failure of PDCs (p < 0.02; odds ratio, 2.0). CONCLUSIONS: The patency rate for PTFEs is similar to that for AVFs, but AVFs require fewer revisions. When replacing a failed access graft, the risk of PTFE failure increases with the number of prior unsalvageable PTFE shunts. PDCs have excellent patency rates, but failure rates are doubled in patients with diabetes. Because of poor patency rates and inadequate dialysis flow rates, SIHCs should be avoided when possible. Reporting methods dramatically affect apparent patency rates, and reporting standards are needed to allow meaningful comparisons in the dialysis access literature.

Adolescent↗
PubMed1997

Thrombolysis of occluded infrainguinal vein grafts: predictors of outcome.

PURPOSE: The purpose of this study was to identify factors that influence graft patency and limb salvage rates after thrombolysis of occluded infrainguinal vein grafts. METHODS: The records of patients who underwent percutaneous catheter-directed thrombolysis of occluded infrainguinal vein bypass grafts at our institution between 1985 and 1995 were reviewed. Life table analysis was used to determine survival and patency differences. Univariate and multivariate analyses were used to identify the patient-specific factors that affected outcomes. RESULTS: Forty-four patients with 44 thrombosed infrainguinal vein grafts underwent thrombolysis with urokinase. The thrombolysis-related mortality rate was 2%, and nonfatal complications occurred in 16%. Thrombolysis was unable to restore graft patency in 25% of grafts (11 of 44). Of the remaining 33 successfully lysed grafts, 88% required adjunctive surgery or percutaneous transluminal angioplasty after thrombolysis. Overall, the primary graft patency rate was 25% at 1 year and 19% at 2 years after thrombolysis. Considering only successfully lysed grafts, the primary patency rate improved to 34% at 1 year and 25% at 2 years. Multivariate analysis revealed that the graft patency rate was substantially better in patients without diabetes and in vein grafts that had been in place for longer than 12 months (p < 0.01). The limb salvage rate was significantly improved by successful thrombolysis (63% at 2 years vs 31% if lysis failed; p < 0.01). The patient survival rate was high-89% 2 years after thrombolysis. CONCLUSIONS: Even with adjunctive therapy, vein graft thrombolysis is unlikely to yield durable patency overall. However, successful thrombolysis improves limb salvage rates and may be beneficial in patients without diabetes who have mature vein grafts but who do not have options for other autogenous revascularization procedures.

Aged↗
PubMed1997

Vascular surgery and the Resource-based Relative Value Scale five-year review.

PURPOSE: The first 5-year review of the Medicare Resource-based Relative Value Scale (RBRVS) work values (RVUs) began in 1995, and adjustments became effective January 1, 1997. This report summarizes the methods used by The Society for Vascular Surgery (SVS) and the International Society for Cardiovascular Surgery, North American Chapter, (ISCVS-NA) Joint Council Government Relations Committee (GRC) to evaluate vascular surgery work RVUs and the results that were achieved. METHODS: The GRC performed a work study to determine accurate skin-to-skin operative times for typical vascular and nonvascular operations. These were compared with the original Harvard/Hsiao time estimates and intraservice work per unit time (IWPUT) values that had been used to determine work RVUs. For most vascular procedures the current operative times were longer than the original Harvard estimates, resulting in calculated IWPUTs substantially less than the Harvard values. This lack of correspondence was not identified in the nonvascular procedures, where operating room times and IWPUT values were more consistent with Harvard data. These study results were then used to support compelling evidence arguments in a petition to the Health Care Financing Administration (HCFA) that identified vascular surgery as being undervalued in the RBRVS. Nine commonly performed vascular procedures were cited for review in the 5-year update, and five distinct work analysis methods were used to justify each recommended RVU increase. These techniques included a standardized survey from the American Medical Association (AMA)/Specialty Society Relative Value Update Committee (RUC), a work calculation using accurate intraservice times and appropriate IWPUT values, and an evaluation and management (E&M) building-block approach. RESULTS: The RUC met throughout 1995 to assess codes submitted for review, and recommendations were forwarded to HCFA. The Notice of Proposed Rule Making (NPRM), which contained HCFA's preliminary RVU determinations, was released in May 1996. RVU increases from 11.5% to 44.6% were proposed for the nine vascular services cited by the SVS/ISCVS-NA. Also included were two increases and two reductions in less-common vascular operations. Of far greater overall fiscal import, HCFA proposed substantial increases in the work RVU for all E&M except that performed within global surgical packages. The SVS/ISCVS and most other surgical societies appealed HCFA's proposal regarding E&M. The Final Rule for the 1997 Medicare Fee Schedule was published late in 1996. CONCLUSIONS: The Final Rule upheld the 11 vascular work value improvements and the E&M increases that excluded global service packages. Because most surgical E&M is performed within 10- or 90-day global periods, the E&M ruling will produce an estimated annual $2.5 billion shift from surgical to nonsurgical specialties. Because the overall fiscal impact of the 5-year review was mandated to be budget-neutral, HCFA imposed an 8.3% reduction in the work payment of every service in Part B of the Medicare program, primarily to compensate for the increased nonsurgical E&M payments. The net fiscal impact of the 5-year review for vascular surgery has been estimated at +0.5%.

Centers for Medicare and Medicaid Services, U.S.↗
PubMed1997

Cost-effectiveness of carotid endarterectomy in asymptomatic patients.

PURPOSE: The purpose of this study was to determine the cost-effectiveness of carotid endarterectomy for treating asymptomatic patients with > or = 60% internal carotid stenosis, based on outcomes reported in the Asymptomatic Carotid Atherosclerosis Study (ACAS). METHODS: A cost-effectiveness analysis was performed using a Markov decision model in which the probabilities for base-case analysis (average age, 67 years; 66% male; perioperative stroke plus death rate, 2.3%; ipsilateral stroke rate during medical management, 2.3% per year) were based on ACAS. The model assumed that patients who had TIAs or minor strokes during medical management crossed over to surgical treatment, and used the NASCET data to model the outcome of these now-symptomatic patients. Average cost of surgery ($8500), major stroke ($34,000 plus $18,000 per year), and other costs were based on local cost determinations plus a review of the published literature. Cost-effectiveness was calculated as the incremental cost of surgery per quality-adjusted life year (QALY) saved when compared with medical treatment, discounting at 5% per year. Sensitivity analysis was performed to determine the impact of key variables on cost-effectiveness. RESULTS: In the base-case analysis, surgical treatment improved quality-adjusted life expectancy from 7.87 to 8.12 QALYs, at an incremental lifetime cost of $2041. This yielded an incremental cost-effectiveness ratio of $8,000 per QALY saved by surgical compared with medical treatment. The high cost of care after major stroke during medical management largely offset the initial cost of endarterectomy in the surgical group. Furthermore, 26% of medically managed patients eventually underwent endarterectomy because of symptom development, which also decreased the cost differential. Sensitivity analysis demonstrated that the relative cost of surgical treatment increased substantially with increasing age, increasing perioperative stroke rate, and decreasing stroke rate during medical management. CONCLUSION: For the typical asymptomatic patient in ACAS with > or = 60% carotid stenosis, our results indicate that carotid endarterectomy is cost-effective when compared with other commonly accepted health care practices. Surgery does not appear cost-effective in very elderly patients, in settings where the operative stroke risk is high, or in patients with very low stroke risk without surgery.

Aged↗
PubMed1997

Resource-Based Relative Value Scale (RBRVS), coding, and Medicare reimbursement.

Many changes occurred during 1996 in the Resource-Based Relative Value Scale that determines physician payment for services to Medicare beneficiaries in 1997. These issues include the 5-year review of physician work values, the Correct Coding Initiative, changes in the surgical Conversion Factor, and a new Medicare payment formula. Likewise, several more changes on the horizon in 1997 will dramatically impact the 1998 Medicare Fee Schedule, primarily the upcoming resource-based Practice Cost Relative Value Scale, and possible elimination of the separate surgical Conversion Factors. There are also several new Current Procedural Terminology codes that will receive Medicare payment in 1997 and 1998. This article summarizes these events and issues from a vascular surgical perspective.

Centers for Medicare and Medicaid Services, U.S.↗
PubMed1996

Carotid duplex criteria for a 60% or greater angiographic stenosis: variation according to equipment.

PURPOSE: The purpose of this study was to evaluate the carotid duplex criteria for a > or = 60% angiographic internal carotid artery (ICA) stenosis and the degree of variation among duplex scanners. METHODS: Carotid duplex criteria for a > or = 60% angiographic stenosis were evaluated in two ICAVL-accredited vascular laboratories with different brands of duplex scanners (Siemens-Quantum and Diasonics in Laboratory A, ATL and Diasonics in Laboratory B). Analysis was performed for 360 carotid bifurcations in 180 consecutive patients who had concurrent angiographic and duplex evaluation. Blinded angiogram evaluation was performed with precision electronic calipers on magnified views, with stenosis calculated by criteria of the Asymptomatic Carotid Atherosclerosis Study and the North American Symptomatic Carotid Endarterectomy Trial. Duplex data included internal carotid artery peak systolic velocity (ICA PSV), ICA end-diastolic velocity, and the ratio of ICA PSV to common carotid artery (CCA) PSV (ICA/CCA ratio). RESULTS: The most accurate determination of a > or = 60% ICA stenosis was obtained with ICA/CCA ratio and ICA PSV, but the optimal threshold differed for all four scanners. The optimal ICA/CCA ratio varied from 2.6 to 3.3, and the optimal ICA PSV varied from 190 to 240 cm/sec. All four scanners produced criteria that give a positive predictive value > 90% while maintaining accuracy at > or = 90%. Logarithmic transformation of duplex variables created a linear relationship between duplex values and angiographic stenosis, allowing statistical evaluation of scanner operating characteristics by linear regression analysis and analysis of covariance. This analysis revealed that the mathematic equation relating duplex values with angiographic percent stenosis was statistically different for one of the four scanners (p < 0.05). Scanner differences did not appear to be due to technologists, because the regression lines were nearly identical for the two Diasonics scanners despite use by different technologists. Ignoring the significant difference in operating characteristics for one of the four scanners would result in a mean error for predicting a 60% stenosis of 14% to 18% (equating a 46% or 78% stenosis with a 60% stenosis). CONCLUSIONS: We conclude that the correlation of duplex data with angiographic percent stenosis and the duplex criteria for a > or = 60% stenosis are machine-specific. Regression analysis can determine whether apparent differences are due to chance or significant differences in scanner characteristics. Future studies should include regression analysis according to equipment type.

Aged↗
PubMed1994

Preoperative evaluation of the right internal thoracic artery for coronary surgery.

In general, the right internal thoracic artery (ITA) is used less frequently as a graft than the left ITA in coronary artery bypass grafting. To determine whether there is an anatomic or hemodynamic rationale for the underuse of the right ITA, noninvasive measurements of right and left ITAs were performed in 171 patients before the bypass procedure. Transthoracic visualization of both vessels was accomplished using a color-flow duplex scanner (5.0-MHz probe) through the third intercostal space. The diameter (in millimeters), peak systolic velocity (in centimeters per second), and end-diastolic velocity (in centimeters per second) were measured in all but 2 patients. The mean right ITA diameter was 2.7 +/- 0.6 mm, the mean peak systolic velocity was 100 +/- 29 cm/s, and the mean end-diastolic velocity was 6 +/- 5 cm/s. Diameter and flow velocity measurements for the right and left ITA were similar in all patients (p = not significant). The measured values for both sites were independent of age and sex, or the presence of hypertension or diabetes mellitus (p = not significant). We conclude that no morphologic or physiologic differences exist between the right and left ITAs. The findings from this study indicate that color-flow duplex ultrasound imaging is a safe and reliable noninvasive technique in the preoperative assessment of the anatomic and functional characteristics of the right ITA before coronary artery bypass grafting.

Adult↗
PubMed1994

Femorofemoral versus aortobifemoral bypass: outcome and hemodynamic results.

PURPOSE: Femorofemoral bypass (FFB) is used in selected patients when aortobifemoral bypass (AFB) is believed to be inappropriate because of high operative risk or predominantly unilateral iliac artery occlusive disease. We examined concurrent patients who underwent either FFB or AFB to better understand the appropriate use of FFB. METHODS: The characteristics and outcomes of patients who underwent FFB and AFB during 1986 to 1991 at our institution were retrospectively reviewed. Primary measures of outcome included patient survival, graft patency, limb salvage, and hemodynamic performance of FFB and AFB. Further analysis was performed after substratification for low versus high risk and claudication versus limb threat as the indication for surgery. RESULTS: FFB was performed in older patients with more medical comorbidities when compared with AFB. Long-term graft patency was inferior after FFB compared with AFB (60% vs 85% at 3 years, p < 0.01). However, both FFB and AFB achieved limb salvage in more than 85% of patients at 3 years. When patients at low risk undergoing nonemergency AFB were compared with patients at low risk who underwent FFB and who had no contraindication to AFB, FFB proved inferior to AFB as measured by graft patency (primary patency 61% vs 87% at 3 years, p < 0.03) and hemodynamic performance (predicted ankle-brachial index with perfect outflow 0.82 after FFB vs 1.03 after AFB). On the basis of a detailed analysis of patient and graft risk factors, we could not explain the inferior patency rate of FFB, although our analysis suggested that inadequate inflow may contribute. CONCLUSIONS: FFB is inferior to AFB as measured by patency and hemodynamic function. This inferior performance is independent of indications for FFB. AFB should remain the standard therapy for patients at low risk with iliac occlusive disease, but FFB provides adequate function and limb salvage in patients at high risk.

Adult↗
PubMed1994

Vein adaptation to the hemodynamic environment of infrainguinal grafts.

PURPOSE: Although arteries appear to remodel in response to changes in hemodynamic parameters such as shear stress, little is known about functioning human vein grafts. This study was designed to explore diameter changes in human saphenous vein grafts after infrainguinal bypass. METHODS: We used duplex ultrasonography to measure hemodynamic variables that might affect the diameter of 48 in situ saphenous vein grafts during the first year after infrainguinal arterial bypass. Volumetric flow rate, average velocity, peak systolic velocity, and vein diameter in the proximal and distal thirds of these grafts were each measured at 1 week and at 3, 6, and 12 months after operation. Veins were divided into three groups based on initial size (1 week after bypass) in the below-knee segment: small, < 3.5 mm diameter; medium, 3.5 to 4 mm diameter; and large, > 4 mm diameter. RESULTS: Distal vein diameters at 1 week for small, medium, and large grafts were 2.9 +/- 0.1, 3.7 +/- 0.1, and 4.3 +/- 0.1 mm, respectively (p < 0.001), but by 12 months these diameters were 3.6 +/- 0.2, 3.8 +/- 0.2, and 3.9 +/- 0.2 mm, respectively (p = 0.54). Large veins decreased in diameter, whereas small veins increased in diameter, as confirmed by linear regression of percent change in diameter versus initial vein graft diameter (r = -0.62, p < 0.001). Volumetric flow rate, peak systolic velocity, and shear stress also tended to approach uniform values over time. Of the hemodynamic variables studied, the best predictor of diameter change was shear stress (linear regression of percent change in diameter vs shear stress, r = 0.67, p < 0.001). Veins with a diameter increase greater than 10% over time had significantly higher initial shear stress than veins with a diameter decrease greater than 10% over time (28.6 +/- 3.8 vs 13.1 +/- 1.8 dynes/cm2, p < 0.01), whereas initial volumetric flow rates in these two groups were similar (135 +/- 23 vs 130 +/- 15 ml/min). CONCLUSIONS: Infrainguinal in situ vein graft diameter, volume flow rate, peak systolic velocity, and shear stress all tend to stabilize at uniform values regardless of the initial vein graft diameter. Of the hemodynamic variables studied, shear stress is most strongly associated with the change in diameter over time. Thus human saphenous vein appears to be capable of adapting to its hemodynamic environment after arterial grafting by modulating diameter to normalize shear stress.

Adaptation, Physiological↗