Brian L. Thiele

Indium-111 platelet imaging for detection of platelet deposition in abdominal aneurysms and prosthetic arterial grafts

Thirty-four platelet imaging studies were performed in 23 patients to determine whether platelet deposition could be detected in patients with vascular aneurysms (18 patients) or in patients in whom Dacron prosthetic grafts had been place (5 patients). In patients in whom abnormal platelet deposition was detected, the effect of administration of platelet-active drugs on platelet deposition was examined. Of the 18 patients with an aneurysm, 12 had positive studies on initial imaging and 2 had equivocally positive images. Of five patients with Dacron arterial grafts in place, four had diffuse platelet deposition in the grafts; the fifth patient had platelet deposition only in a pseudoaneurysm. Eight patients with an abdominal aneurysm and positive or equivocally positive baseline images were restudied during platelet-active drug therapy either with aspirin plus dipyridamole (seven patients) or with sulfinpyrazone (four patients). No patient studied during treatment with aspirin plus dipyridamole had detectably decreased platelet deposition compared with baseline determinations. In contrast, two of four patients studied while receiving sulfinpyrazone showed decreased platelet deposition. Thus, platelet imaging may be of value for studying platelet physiology in vivo and for assessing platelet-active drugs and the thrombogenicity of prosthetic graft materials in human beings.

Intraoperative assessment of carotid endarterectomy

The use of operative arteriography during carotid endarterectomy facilitates identification and correction of technical errors. Although arteriography is the standard for assessing surgical results, it prolongs the operation and may increase the overall risk. The purpose of this study was to evaluate pulsed Doppler spectral analysis and arteriography as methods of intraoperative assessment. Operative arteriography was performed in 150 consecutive carotid endarterectomies. In 50 of these cases a sterile 20 MHz pulsed Doppler probe and real-time spectrum analyzer were used to evaluate internal carotid velocity patterns before and after endarterectomy. Operative arteriograms were normal in 127 cases, whereas abnormalities were noted in 16 internal and seven external carotid arteries. Thirteen of the arteriographic defects were considered minor and accepted. Major defects requiring immediate repair occurred in eight (5%) internal and two external carotid arteries. In the 50 cases assessed by both techniques, seven internal carotid arteries had mild flow disturbances both before and after endarterectomy, whereas 38 of the remaining 43 arteries showed improvement in spectral characteristics after endarterectomy. In two patients who failed to show improvement on the initial postendarterectomy evaluation, operative arteriography demonstrated residual defects that required immediate repair. No other technical errors were encountered, and there were no perioperative deaths or neurologic complications in the 150 operations. Intraoperative assessment by pulsed Doppler spectral analysis is a safe, rapid, and accurate method for detecting technical errors during carotid endarterectomy. The high sensitivity of this method (no false negative assessments) makes it an ideal screening test to be used for selection of patients for operative arteriography. By indicating when a technical error is most likely, this approach precludes the need for routine operative arteriography.

Natural history of platelet deposition on Dacron aortic bifurcation grafts in the first year after implantation

This study defined the dynamics of platelet deposition on Dacron arterial grafts up to 1 year after implantation in human subjects. Indium-111 platelet imaging was performed on 8 men 1 to 2 weeks after graft implantation and on 5 of these patients at a mean of 31 weeks (range 28 to 34) and again at 55 weeks (range 50 to 62). Serial imaging was performed at 24 to 96 hours after platelet labeling and injection in each study. Quantitative analysis was performed using a graft/blood ratio that compared background-corrected indium-111 platelet activity in the graft region to whole-blood indium-111 platelet activity. Additionally, blinded qualitative visual analysis of the images compared graft activity with the activity in adjacent native arteries. The mean of all graft/blood ratios (24, 48, 72, and 96 hours) progressively decreased from 4.4 +/- 2.1 (+/- 1 standard deviation) at 1 to 2 weeks to 3.0 +/- 1.8 at 31 weeks (p = 0.002). There was no further decrease at 55 weeks (2.8 +/- 2.0). For comparison, 12 normal subjects without grafts had a mean ratio of 1.8 +/- 0.7. Visual analysis detected platelet deposition in 7 of 8 grafts at 1 to 2 weeks, 4 of 5 at 31 weeks, and 4 of 5 at 55 weeks. Deposition decreased qualitatively in 2 of 5 patients at late study. It is concluded that there is consistent, early platelet deposition on Dacron grafts in man. Although deposition decreases over 31 weeks, it remains readily detectable in most patients at 1 year. These findings suggest absent or incomplete endothelialization of the graft flow surface in humans in the first year after implantation.

Importance of noninvasive ultrasonic-Doppler testing in the evaluation of patients with asymptomatic carotid bruits

An ultrasonic Duplex scanner was used to estimate the site and degree of extracranial arterial disease in two groups of patients with asymptomatic bruits. In the first 100 patients only the extent of disease was assessed with 37% of the sides with bruits having high-grade stenoses (greater than 50% diameter reduction) and one-half having lesions which narrowed the internal carotid artery by less than 50%. Seven percent were found to be normal. The remaining 6% had occlusion of the internal carotid artery. In a second group of 81 patients, the effect of the reported findings of the Duplex scan on patient management was reviewed. Only 13 patients underwent angiography and 11 of these were in patients with high-grade stenoses. Five carotid endarterectomies were performed and in each case, the patient had bilateral high-grade lesions. The implications of this diagnostic approach are discussed as well as the need for prospective studies of patients who present with an asymptomatic bruit.

INTRAOPERATIVE PULSED DOPPLER ASSESSMENT OF CAROTID ENDARTERECTOMY

A 20 MHz pulsed Doppler velocimeter and fast Fourier transform spectrum analyzer were used at operation to assess the velocity patterns just prior to and immediately following carotid endarterectomy (TEA). In all 45 sides studied, the status of the endarterectomized segment was verified by operative arteriography. Corresponding Pre-TEA and Post-TEA internal carotid artery spectra were compared to each other and classified according to criteria developed using the ultrasonic Duplex scanner. Of 39 arteries with significant Pre-TEA flow disturbances, improvement in Post-TEA spectral characteristics was observed in 35, and 4 were not changed. Six arteries had only minimal flow disturbances both before and after endarterectomy. In one case the initial Post-TEA spectrum showed a worsening of the flow disturbance which was found on operative arteriography to be due to a stenosis secondary to a technical error. After vein patch angioplasty, the spectrum and repeat arteriogram were both improved. No other significant technical problems were encountered. Although the velocity patterns were improved by endarterectomy in most cases, some residual flow disturbance often remained. Technical factors were not a major cause of the Post-TEA flow disturbances. Lack of improvement or deterioration in the spectra after closure of the arteriotomy may be useful in selecting patients for operative arteriography. Intraoperative spectra also provide important baseline data for long term followup studies.

Pulsed Doppler velocity patterns produced by arterial anastomoses

Centerstream velocity waveforms produced by end-to-end and end-to-side anastomoses constructed in the dog illeofemoral arterial system were studied with a 20 MHz pulsed Doppler velocimeter combined with spectral analysis. Flow disturbance was identified by changes in spectral width during the systolic phase of the cardiac cycle. Measurement of the maximum frequency and the spectral width at peak systole was used to quantify the magnitude of flow disturbance at varying locations proximal and distal to the anastomoses. Disruption of the normal laminar flow pattern observed in the unoperated dog artery was evident distal to both anastomotic configurations. An increase in spectral width reflecting disturbed flow was maximal during the deceleration phase of systole. Flow disturbance was localized to a zone within one diameter distal to the anastomosis and dissipated rapidly downstream. The velocity spectrum changes observed downstream of an anastomosis resemble the flow disturbances produced by low grade, nonpressure reducing arterial stenoses. This study suggests that spectral analysis of pulsed Doppler waveforms is a potentially useful method of anastomosis assessment both to rule out major flow disruption produced by technical error, and to provide insight into the role of turbulence in the development of anastomotic intimal hyperplasia.

Effect of carbon dioxide on flow patterns in normal extracranial arteries

Abstract To evaluate the velocity pattern changes in the extracranial carotid arteries, five normal subjects were studied with a 5-MHz pulse Doppler device combined with spectral analysis prior to and during breathing 6.8% carbon dioxide. Changes in flow were quantified by features derived from the velocity waveform of the common, internal and external carotid arteries. An increase in velocities during diastole correlated well with the expected increase in total blood flow induced by breathing 6.8% carbon dioxide. Increases in spectral width reflected the development of flow disturbances not apparent under basal conditions. These studies suggest that marked increases in flow produced by intracranial vasodilatation can dramatically alter the velocity patterns normally observed.

Noninvasive Detection of Internal Carotid Artery Occlusion

Flow in the common carotid artery is normally quasisteady with flow never approaching zero during diastole. With total occlusion of the internal carotid artery, flow in the common carotid assumes the pattern observed in the external carotid, which supplies a relatively high-resistance vascular bed. In 34 instances of total internal carotid obstruction, flow went to zero in diastole in 33 cases and also demonstrated flow reversal in 22. In addition, there was a significant reduction in peak systolic velocity when the low-resistance internal carotid was obstructed. These observations, which are simple to determine using an ultrasonic duplex scanner, are of value in suspecting total occlusion of the internal carotid artery, thus obviating the need for arteriography in some cases.

The influence of limb elevation, examination technique, and outflow system design on venous plethysmography.

The effect of limb elevation and the design of the thigh cuff outflow system on venous capacitance and venous outflow, as determined by strain gauge plethysmography, was reviewed in a group of normal limbs without evidence of deep venous thrombosis. We improved the reliability of plethysmography in evaluating venous outflow, particularly in the early period after cuff deflation, by using uniform leg elevation, large diameter outflow tubing, and single rather than simultaneous limb examinations. Based on this experience, an optimum technique of examination empha sizing precise limb elevation, sequential limb examination and proper design of the cuff outflow system was used to evaluate 21 patients with acute venous thrombosis. The results obtained were compared with previously reported re sults of strain gauge plethysmography in patients with acute venous throm bosis. This technique significantly reduced the incidence of false-positive re sults.

Changing Etiology of Anastomotic Aneurysms

Anastomotic aneurysms in patients at the Seattle Veterans Administration Medical Center between 1974-1979 were analyzed to determine their etiol ogy. Thirty-nine aneurysms occurred in 29 patients with 19 aneurysms presenting in 15 patients who had vascular reconstruction at our institution. The site most commonly involved was the femoral anastomosis (5%/anas tomosis) followed by the iliac (2%) and the aortic (0.5%) anastomoses. Mechanical forces appear to be the most common cause (76%) followed by graft infection (23%) with suture failure being very uncommon (2%) Histo logic examination of the aneurysms thought to be produced by mechanical forces disclosed normal host artery wall in 1 group and aneurysmal degen erative change in the remainder. The generation of disruptive forces at anastomoses between compliant and stiff materials and their role in produc ing anastomotic disease is discussed. A disturbing feature is the incidence of commensal infections seen previously in other prosthetic surgery.