Brad L. Johnson

A rational algorithm for duplex scan surveillance after carotid endarterectomy

PURPOSE This study was undertaken to determine the appropriate timing and frequency of duplex ultrasound scanning after carotid endarterectomy (CEA) for the detection of high-grade stenosis caused by recurrent carotid stenosis or contralateral atherosclerotic disease progression. METHODS In 221 patients who underwent 242 CEAs, duplex scanning was performed before, during, and after operation (in 3-month to 6-month intervals). High-grade internal carotid artery (ICA) stenosis (peak systolic velocity, >300 cm/s; diastolic velocity, >125 cm/s; ICA/common carotid artery ratio, >4) prompted the recommendation for repair. An average of four postoperative scanning procedures was performed during a mean follow-up period of 27.4 months. RESULTS Intraoperative duplex scan results prompted the immediate revision of 12 repairs (4.9%), and one perioperative stroke (<1%) occurred. Six CEAs (2.7%) had asymptomatic recurrent stenosis (>50% diameter-reduction [DR]; systolic velocity, >125 cm/s) develop. Only one of six patients had >75% DR stenosis develop and underwent reoperation (<1% yield for CEA surveillance). The yield of surveillance of the unoperated ICA was higher (P =.003), and 12% of unoperated sides had progressive stenosis (n = 21) or occlusion (n = 3) develop, which led to seven CEAs for high-grade stenosis. Disease progression to >75% DR stenosis was five times as frequent (P =.002) in patients with >50% DR stenosis initially. All patients but one who required contralateral endarterectomy for disease progression had >50% ICA stenosis when first seen. During the follow-up period, no disabling strokes ipsilateral to an operated carotid artery occurred, but three strokes occurred in the hemisphere of the contralateral unoperated ICA. CONCLUSION The yield of duplex scan surveillance after CEA was low. Only 13 patients (5.9%) had severe disease develop to warrant additional intervention. Progression of contralateral disease rather than restenosis was the most common abnormality that was identified. Duplex scanning at 1-year to 2-year intervals after CEA is adequate when a technically precise repair is achieved and minimal contralateral disease (<50% DR) is present. A policy of duplex scan surveillance and reoperation for high-grade stenosis was associated with a 1.6% incidence rate of disabling stroke during the follow-up period.

Dosimetry of the I‐Plant Model 3500 iodine‐125 brachytherapy source

125I brachytherapy sources have been widely used for interstitial implants for a number of years in several tumor sites, especially the prostate. The design of the new I-Plant Model 3500 iodine source is novel, yet its characteristics are similar to those of two existing designs, Model 6711 and the Symmetra. Dosimetry parameters (including dose rate constant, radial dose function, and anisotropy function, as defined by AAPM Task Group 43) were measured with LiF thermoluminescent dosimeters in water-equivalent plastic phantoms. The dose rate constant was found by direct comparison of calibrated I-Plant Model 3500 and Model 6711 seeds in a solid water phantom, to be 1.01 (cGy/h)/U. The radial dose function and anisotropy function are similar to those of the Model 6711 and Symmetra seeds.

Graft Infectivity of Rifampin and Silver-Bonded Polyester Grafts to MRSA Contamination

The purpose of this study was to evaluate the ability of vascular polyester grafts with antibacterial properties to resist colonization following surface contamination by methicillin-resistant Staphylococcus aureus(MRSA) in an experimental canine model or aortic graft infection. Twenty-four pathogen-free dogs underwent replacement of the infrarenal aorta with either a rifampin-soaked (30 mg/mL) or silver-impregnated (Ag-acetate) woven polyester graft. Following implantation, the external graft surface was inoculated with 2 mL of 107 colonyforming units/mL (CFU) of MRSA. Preoperative antibiotic prophylaxis consisted of a single intravenous dose of 500 mg of sodium cefazolin. Four grafts of each type were explanted at 3, 7, and 14 days after implantation. Quantitative cultures (CFU/specimen) of perigraft fluid (1 mL), graft material (1 cm segment), and adjacent aorta (1 cm segment) were performed. Differences between grafts are expressed as% mean log reduction in recoverable CFU compared to the inoculation solution concentration of 107 CFUs. At 3 days, explanted rifampinsoaked grafts exhibited no MRSA growth (4 of 4 grafts) and a =97% mean log reduction of MRSA CFUs from the adjacent aorta and perigraft fluid (PGF). At 3 days, all silver-bonded grafts exhibited signs of infection and a mean log CFU reduction of MRSA ranging from 68% (absolute range 101–103 recoverable CFU) for the graft, 79% (absolute range 101–103 recoverable CFU) for the aorta, and 86% (absolute range 101–104 recoverable CFU) for PGF. The 7-day rifampin group had an average log reduction in MRSA CFU of 72% (graft), 58% (PGF), 75% (aorta). Quantitative cultures of 14-day rifampin grafted demonstrated continued bacterial growth suppression with mean MRSA CFU log reductions of 82%, graft; 72%, PGF; 89%, aorta. Silver-bonded grafts demonstrated <50% mean CFU reduction in MRSA growth at 7 days (absolute range 105–107 recoverable CFU) and 14 days (absolute range 103–107 recoverable CFU). No animal died from sepsis or anastomotic hemorrhage. Neither rifampin nor silverbonded grafts demonstrated prolonged resistance to surface MRSA contamination. Rifampinsoaked polyester grafts exhibited a marked but transient resistance MRSA colonization likely the result of high antibiotic concentration in the perigraft tissue. While both types of grafts failed to eradicate the MRSA infection future research with silver-bonded grafts that have an additional antibiotic attached may have a place in the treatment of MRSA infection.

Critical Appraisal of Cardiac Risk Stratification Before Elective Vascular Surgery

This study was undertaken to evaluate the efficacy of the cardiac risk stratification protocol proposed by the American College of Cardiology/American Heart Association (ACC/AHA) in predicting cardiac morbidity and mortality associated with elective, major arterial surgery. Cardiac risk stratification using ACC/AHA guidelines was done on 425 consecutive patients before 481 elective cerebrovascular (n=146), aortic/inflow (n=166), or infrainguinal (n=169) procedures at an academic Veterans Affairs Medical Center. Cardiac risk was stratified as low, intermediate, or high based on clinical risk factors, such as, Eagle criteria, history of cardiac intervention, patient functional status, results of noninvasive cardiac stress testing, and coronary angiography with coronary revascularization performed when appropriate. Outcomes (myocardial infarction, unstable angina, congestive heart failure, ventricular arrhythmia, cardiac death, and mortality) within 30 days of surgery were compared between the various risk stratification groups. Univariate and multivariate analyses were used to identify clinically useful prognostic variables from the preoperative cardiac evaluation algorithm. Overall mortality (1.7%), cardiac death (0.4%), and adverse cardiac event (4.8%) rates were low, but cardiac death and morbidity were increased (p<0.05) in high-risk stratified patients (3.4%, 11.9%) compared to intermediate (0%, 2.8%) and low (0%, 4.0%) cardiac risk groups. The presence of 3-vessel angiographic coronary artery occlusive disease was an independent predictor of cardiac morbidity, while inducible ischemia by cardiac stress imaging was not. Previous coronary revascularization was associated with increased mortality as was the development of a non-cardiac complication. Cardiac risk assessment identified 78 (18%) patients with indications for coronary angiography. Angiographic findings resulted in coronary artery intervention (9-angioplasty; 4-bypass grafting) in 13 (3%) patients who experienced no adverse cardiac events after the planned vascular surgery (15 procedures). Cardiac risk stratification using ACC/AHA guidelines can predict adverse cardiac events associated with elective vascular surgery; however, protocol modification by increased reliance on Eagle criteria and less use of cardiac stress testing can improve identification of the “highest risk” patients who may benefit from prophylactic coronary intervention.

Regional antibiotic delivery for the treatment of experimental prosthetic graft infections.

OBJECTIVES To evaluate the efficacy of antibiotic-impregnated polymethylmethacrylate (PMMA) beads in eradication of an arterial prosthetic graft methicillin-resistant Staphylococcus aureus (MRSA) biofilm in an experimental animal model. METHODS Forty rats underwent subcutaneous implantation of a MRSA-colonized arterial polytetrafluoroethylene (PTFE) 1 x 1 cm wafer on the back. The effect of regional antibiosis produced by antibiotic PMMA bead placement adjacent to the infected PTFE wafer was determined using four 10-animal study groups: control (no antibiotic), PMMA bead with no antibiotic, PMMA bead with 10% vancomycin, and PMMA bead with 10% daptomycin. After 3 d, the PTFE wafers were explanted and quantitative biofilm cultures, expressed as colony-forming units (CFU) per graft wafer, performed using real-time polymerase chain reaction to assess MRSA eradication. No systemic antibiotic was administered. Bioassays of antibiotic bead bacteriocidal were performed by measuring zone of inhibition diameters on MRSA colonized agar culture plates prior to and following graft explantation. RESULTS All animal tolerated implantation of the MRSA-infected PTFE wafer and survived the 3 d until graft explantation. Quantitative biofilm cultures demonstrated a significant decrease (P < 0.01) in MRSA CFUs present on the PTFE wafer surfaces in the presence of both the vancomycin- and daptomycin-impregnated beads compared to controls and plain PMMA beads. Both vancomycin and daptomycin PMMA beads retained antibacterial activity after 3 d of implantation with decrease in zones of inhibition of 15% and 45%, respectively. CONCLUSIONS Regional antibiotic delivery using an antibiotic-impregnated PMMA bead reduced the bacterial biofilm concentration in experimental subcutaneous pocket model of vascular surgical site infection. The delivery of antibiotics via a PMMA bead may be a useful adjunct in the treatment of vascular surgical site infection.

Anatomic patterns of carotid endarterectomy healing

BACKGROUND Restenosis after carotid endarterectomy is a dynamic process likely influenced by surgical technique as well as by anatomic, hemodynamic, and patient factors. METHODS To characterize the healing of carotid endarterectomy sites, intraoperative and serial postoperative color duplex scans were performed in 126 patients (136 repairs). Vessel-wall imaging, midstream spectral analysis, and measurements of diameter and cross-sectional area from common carotid artery (CCA) and internal carotid artery (ICA) segments were compared (at 3, 6, 15, and 30 months) and severity of lumen stenosis was determined. RESULTS After primary closure (n = 15), patch angioplasty (n = 121), or intraoperative revision based on duplex scanning (n = 5), 12 repairs had mild residual flow abnormalities and 1 repair had a moderate flow abnormality. Mean ICA bulb diameter was greater in patched repairs (0.81 cm, range 0.6 to 1.1 cm) than primary closed repairs (0.7 cm, range 0.45 to 0.8 cm). No ICA occluded during follow-up (mean 24 months), and three repairs, two in the ICA and one in the CCA, demonstrated 50% to 75% diameter reduction at 9 months. Lumen cross-sectional area of vein-patched repairs increased 0.6 cm2 to 0.76 cm2 (P < 0.01) in the ICA and 0.69 cm2 to 1.1 cm2 (P < 0.01) in the CCA segments by 3 months compared with intraoperative measurement. Four patients with progressive dilatation of the patch segment to a mean of 1.77 cm2 developed asymptomatic posterior wall mural thrombus. Postoperative blood flow velocities measured through the repair were similar to intraoperative values. Minor intraoperative hemodynamic abnormalities were not associated with the development of restenosis, and changes in repair site anatomy occurred within 3 months with little change thereafter. CONCLUSIONS We have found intraoperative scanning useful for detection of anatomic defects and associated turbulence, lesions that should be immediately corrected. Surgical technique that achieves normal intraoperative carotid flow hemodynamics and B-mode ultrasonic vessel wall appearance should predict an endarterectomized segment free of significant residual plaques and neointimal hyperplasia. Tailoring of the vein patches to achieve lumen diameters < 1 cm is recommended because of the dilataton likely to develop after surgery that may lead to vessel wall mural thrombus.

The Application of Duplex Surveillance After Carotid Intervention

Carotid duplex ultrasound testing provides a safe and accurate method to detect and grade the severity of atherosclerotic internal carotid artery stenosis both before and following carotid intervention. Testing after surgical endarterectomy or stent angioplasty allows assessment of the technical success by excluding residual stenosis. The focus of duplex surveillance after carotid intervention is to identify recurrent stenosis, repair site occlusion, and progression of contralateral internal carotid artery disease. Patients who develop a neurologic event or a duplex-detected >75% diameter-reducing internal carotid artery stenosis with a peak systolic velocity >300 cm/s and end-diastolic velocity >125 cm/s should be further evaluated by angiographic imaging and should be considered for reintervention if an appropriate lesion is confirmed. Duplex surveillance allows the vascular surgeon to evaluate patency of the rendered intervention, its stenosis-free durability, and its effectiveness in stroke prevention.