Subclavian artery stenosis masquerading as prosthetic aortic stenosis: a potential source of confusion in Doppler evaluation of aortic valve disease.

In this case report we describe a patient with a prosthetic aortic valve in whom a high-velocity signal from a right subclavian artery stenosis initially was mistaken for the aortic jet signal. Differences in the shapes of the jets obtained from an apical and right supraclavicular position suggested different origins of these two high-velocity systolic signals. Correct identification of the origin of each signal was possible with pulsed Doppler recordings of the subclavian artery and high pulse-repetition-frequency pulsed Doppler interrogation of the aortic valve.

Flow separation in the carotid bulb: prognostic significance.

It has been previously shown that boundary layer or flow separation occurring in the carotid bulb and detected by duplex scanning denotes minimal or no carotid atherosclerotic disease as demonstrated by angiography and reliably predicts aetiology other than carotid artery disease in symptomatic patients. To evaluate outcome at long-term follow-up we prospectively studied 94 patients (48 males, 46 females) who demonstrated bilateral flow separation. Mean age was 61.2 years (27 to 86 years). Mean follow-up was 57 months (5 to 113 months). There was one death during follow-up at 69 months. It was stroke related. Using age and sex specific death rates for the general population 14.3 deaths would be expected for the same average period. By life table analysis, survival was 98.7% at five years compared to a general population expected 5 year survival of 85.9%. There were no strokes at 5 years of follow-up. (Age and sex specific stroke-free survival for Rochester, MN 1970-1974 is 98% at 5 years). TIA-free survival was 99% at one year (n = 87) and 96% at five years (n = 46). It is concluded that the presence of boundary layer separation in the carotid bulb not only indicates absent or minimal atherosclerotic disease, but is predictive of a favourable long-term outcome with respect to mortality and neurological events.

Pseudocolor B-mode arterial images to quantify-echogenicity of atherosclerotic plaque.

Based on the differences between tissue impedances in atherosclerotic plaques and on the scattering of ultrasound from blood, colors were assigned to the echo strength scale, replacing the usual gray scale in 2-D B-mode ultrasound images. Using a "green tag" indicating -55 dB to mark blood, other echo strength values from atherosclerotic plaque were assigned specific colors, creating a B-mode color ultrasound display that highlights selected echogenicities. The color scale permits the use of a wider dynamic range in the B-mode image, and allows the instrument gains to be set reproducibly.

In vivo ultrasonic measurement of tissue vibration at a stenosis: a case study.

It is known that bruits often can be heard downstream from stenoses. They are thought to be produced by disturbed blood flow and vessel wall vibrations. Our understanding of bruits has been limited, though, to analysis of sounds heard at the level of the skin. For direct measurements from the stenosis site, we developed an ultrasonic pulse-echo multigate system using quadrature phase demodulation. The system simultaneously measures tissue displacements and blood velocities at multiple depths. This paper presents a case study of a severe stenosis in a human infrainguinal vein bypass graft. During systole, nearly sinusoidal vessel wall vibrations were detected. Solid tissue vibration amplitudes measured up to 2 microm, with temporal durations of 100 ms and frequencies of roughly 145 Hz and its harmonics. Cross-axial oscillations were also found in the lumen that correlate with the wall vibrations, suggesting coupling between wall vibration and blood velocity oscillation.

Serial measurement of cross-sectional area in peripheral vein grafts using three-dimensional ultrasound.

Frequent surveillance of bypass grafts placed in the lower limbs can provide early detection of stenoses. A three-dimensional (3-D) ultrasound (US) imaging system has been used to produce serial surface reconstructions of regions of interest in vein grafts in the lower extremities. Using anatomical reference points, data sets from serial studies are registered in a common 3-D coordinate system. Cross-sectional area measurements are extracted from the surface reconstructions in planes normal to the vessel center axis. These measurements are compared at matched sites over time to track changes in the vessel configuration. The quantitative measurements are paired with surface displays of the vessels for a complete depiction of the changing geometry. Example studies from three patients are shown, for time periods up to 38 weeks. The cross-sectional area measurements highlight regions of remodeling and developing stenoses within the grafts.

Noninvasive assessment of normal carotid bifurcation hemodynamics with color-flow ultrasound imaging.

The combination of a B-mode imaging system and a single range-gate pulsed Doppler flow velocity detector (duplex scanner) has become the standard noninvasive method for assessing the extracranial carotid artery. However, a significant limitation of this approach is the small area of vessel lumen that can be evaluated at any one time. This report describes a new duplex instrument that displays blood flow as colors superimposed on a real-time B-mode image. Returning echoes from a linear array of transducers are continuously processed for amplitude and phase. Changes in phase are produced by tissue motion and are used to calculate Doppler shift frequency. This results in a color assignment: red and blue indicate direction of flow with respect to the ultrasound beam, and lighter shades represent higher velocities. The carotid bifurcations of 10 normal subjects were studied. Changes in flow velocities across the arterial lumen were clearly visualized as varying shades of red or blue during the cardiac cycle. A region of flow separation was observed in all proximal internal carotids as a blue area located along the outer wall of the bulb. Thus, it is possible to detect the localized flow patterns that characterize normal carotid arteries. Other advantages of color-flow imaging include the ability to rapidly identify the carotid bifurcation branches and any associated anatomic variations.

Vein graft surveillance with scanhead tracking duplex ultrasound imaging: a preliminary report.

A severe arterial occlusion in the leg usually is bypassed by implanting a saphenous vein harvested from the limb. Once implanted, the vein functions well but over time may develop stenoses that may lead to occlusion. In order to detect and correct the stenoses that may lead to graft failure, frequent surveillance of the vein graft is required. A new ultrasound imaging method was developed to display the panoramic view of the vein graft in combination with its blood flow velocity waveform for surveillance. The panoramic view is the projection (ray-casting) image of multiple B-mode images with sequential longitudinal view of the vein graft. The velocity waveform also is recorded along the vessel with pulsed Doppler ultrasound. The acquired images and waveforms from the ultrasound scanner are registered individually in three-dimensional space with an electromagnet-based position and orientation sensor located on the scanhead. A prominent point on the scar from the surgery is used as the fiducial mark for spatial registration, so that the same lesion in the vein graft can be tracked automatically at each visit for retrospective study.

Echolucent regions in carotid plaque: preliminary analysis comparing three-dimensional histologic reconstructions to sonographic findings.

This study compares sonographic and histologic findings within defined spatial regions in carotid artery plaque, using computer generated three-dimensional reconstructions. Twenty-four patients (14 asymptomatic, 10 symptomatic) with angiographically documented 70% to 99% carotid artery stenosis were examined with ultrasonic B-mode imaging prior to endarterectomy. Using a standardized protocol for instrument set-up and scanning technique, echolucent regions in the plaque were identified. After endarterectomy, each plaque was sectioned at 0.5 to 1.0 millimeter increments throughout its length. Sites containing intraplaque hemorrhage, cholesterol clefts, foam cells, necrotic cores, dense calcification and speckled calcification were identified. These areas were outlined on a template, digitized and imported into a computer program that created three-dimensional reconstructions of the histologic findings. Each carotid plaque was divided into quadrants for analysis: (1) lateral wall proximal to the common carotid bifurcation (flow divider); (2) medial wall proximal to the flow divider; (3) lateral wall distal to the flow divider; and (4) medial wall distal to the flow divider. The odds of finding intraplaque hemorrhage, foam cells, necrotic cores and speckled calcification were significantly higher in quadrants with an echolucent region identified by ultrasonography (odds ratio (95% confidence interval) for intraplaque hemorrhage = 3.5 (1.4-8.6); foam cells = 4.0 (1.6-9.9); necrotic cores = 3.2 (1.2-8.4); speckled calcification = 4.0 (1.6-9.8). This preliminary analysis demonstrates the potential of these newly developed techniques for comparing ultrasonic imaging to histology.

Clinical outcome in patients with mild and moderate carotid artery stenosis.

PURPOSE: The natural history of incidentally discovered asymptomatic mild (< 50%) and moderate (50% to 79%) carotid artery stenosis is not known. The carotid artery duplex ultrasound surveillance program at the University of Washington Department of Vascular Surgery has serially evaluated patients with carotid artery disease for more than a decade and provides data on the progress and management of this disease. METHODS: Patients with asymptomatic carotid artery bruits who had carotid artery disease causing less than 80% lumen diameter narrowing at their initial visit were identified. At each return visit (6 months, 1 year, and annually thereafter) a clinical questionnaire was completed, and bilateral carotid artery duplex sonography was performed. RESULTS: Two hundred thirty-two patients (136 men and 96 women) were monitored for up to 10 years with sufficient data for a 7-year life-table analysis. Progression in the degree of stenosis was noted in 23% of patients during follow-up, and nearly half of these progressed to severe stenosis (80% to 99%) or occlusion. The risk of progression to severe stenosis and occlusion was significantly greater for those patients with moderate initial stenosis than mild initial stenosis (p < 0.01). The cumulative stroke risk for patients with mild initial stenosis (6%) was half of that for patients with moderate initial stenosis (11%) after 7 years. Carotid endarterectomy was performed in 27 patients during follow-up; in 13 the indication was an event ipsilateral to the stenosis, and in 14 there was asymptomatic progression to high-grade stenosis. CONCLUSIONS: Regular monitoring of mild to moderate carotid artery stenosis shows how these lesions progress over time, permitting a realistic appraisal of their potential for producing an ischemic cerebrovascular event.

Ultrasonic techniques for assessing wall vibrations in stenosed arteries.

Arterial stenoses are often associated with audible bruits. Quantitative analysis of the bruit spectrum has been successfully used to predict the residual lumen diameter in carotid stenoses. Arterial wall vibrations occurring due to turbulent pressure fluctuations in the post-stenotic jet are known to be the source of the bruits. We present novel signal processing techniques that enable the detailed noninvasive assessment of these vibrations in real time using color-Doppler and pulsed-wave Doppler ultrasound. A color-Doppler-based two-dimensional vibration imaging technique can be used to locate the source of the bruits relative to the underlying anatomy. Subsequently, a pulsed-wave Doppler-based technique can be used to analyze the bruit spectrum quantitatively. Experiments in ex vivo arteries indicate that these techniques can predict the location of the bruit as well as its spectral content. Case studies on human subjects with stenosed vein grafts are presented and the clinical applicability of this technique is discussed.

A clinical marker for arterial wall healing: the double line.

PURPOSE: B-mode imaging of a normal arterial wall shows two echo-dense lines separated by an echolucent zone. Immediately after carotid endarterectomy, this double-line pattern is no longer detectable, but it subsequently reappears in some patients. The objective of this study was to test the hypothesis that the postoperative double line is associated with a lower incidence of carotid restenosis. METHODS: Carotid arteries were serially studied with B-mode ultrasound imaging at 2 weeks and 1, 2, 3, 6, 9, 12, 18, and 24 months after carotid endarterectomy. The wall of the common carotid artery 1 to 2 cm distal to the proximal endarterectomized shelf was analyzed for the presence, quality, and thickness of double lines. All hemodynamically significant stenoses (> or = 50% diameter reducing) were documented with standard duplex scanning criteria. RESULTS: Twenty-four carotid arteries in 23 patients were studied for a mean of 14.7 months (range, 3 to 24 months). A double line developed in 21 common carotid arteries (87.5%) at a mean time of 3.2 months (range, 0.5 to 9.0 months) after surgery with a mean thickness of 0.65 mm (SD = 0.17 mm) at the time of initial detection. A single hemodynamically significant stenosis developed in this group. All three of the remaining arteries that did not form the double-line pattern developed hemodynamically significant stenoses. Carotid restenosis was more likely to occur in arteries that did not form double lines (p < 0.05, Fisher's exact test). CONCLUSIONS: The majority of carotid arteries re-form a double line after endarterectomy. These arteries are less likely to develop restenotic lesions caused by myointimal hyperplasia.

Noninvasive testing vs clinical evaluation of arterial disease. A prospective study.

In a prospective clinical study involving 458 diabetic patients, the results of noninvasive testing procedures were compared with the findings obtained by clinical evaluation. The results of the study showed that nearly one third of the patients who gave no history of intermittent claudication were found to have arterial disease when tested. One fifth of the patients with what were considered normal physical examination results had abnormal results by noninvasive testing. When history and physical examination prove ineffective for obtaining a diagnosis of arterial disease, the use of noninvasive devices effectively rules out or confirms the presence of hemodynamically significant arterial obstruction. Not only can simple, noninvasive testing methods greatly increase the accuracy of clinical diagnosis for the presence of arterial disease, but the baseline data obtained can serve as objective indexes to follow the natural history of the disease.

Carotid artery occlusion: natural history.

During a 5-year period, 212 patients (170 men and 42 women, median age 65 and 64 years, respectively) were diagnosed as having internal carotid artery occlusion. Mean follow-up was 24.9 months. Five-year cumulative survival and stroke-free rates by life-table analysis were 62% and 75%, respectively. Deaths were due to stroke in 7 of 40 patients (17%) and were of cardiac origin in 22 of 40 patients (55%). The strokes were ipsilateral in 20 of 31 patients (65%). No statistically significant difference between the sexes could be demonstrated for either death or stroke, nor was age correlated with stroke during follow-up. Diabetes and hypertension increased the risk of stroke, whereas gender and aspirin consumption had no discernible effect. Endarterectomy of the opposite carotid artery did not significantly affect the natural history but did reduce the stroke rate in the territory of the operated artery. Presenting symptoms were useful for estimating prognosis. Twenty-two of 111 patients referred for stroke (20%) suffered a further stroke and 21 of 111 patients (19%) died (three were stroke-related), whereas of those patients referred for transient ischemic attack (TIA), only 2 of 42 patients (5%) suffered a stroke and none died. TIAs occurred in 23 patients (11%) during follow-up, and these were premonitory for stroke in three cases (13%). The limited value of TIA in predicting stroke and the high mortality rate unrelated to stroke in this group are important considerations when therapy is considered for these patients.

Carotid endarterectomy. Relationship of outcome to early restenosis.

The results following carotid endarterectomy were prospectively evaluated in 134 patients (145 sides) by repeat ultrasonic duplex scanning and clinical evaluation extending for a period of 4 years. There were 107 men and 27 women in the study group. The perioperative stroke rate was 1.3% and the mortality rate, 0.7%. There were 9 late deaths, of which two were stroke related (1.4%). Focal symptoms occurred in 12 patients on the ipsilateral side, six of which were strokes (one lacunar). The remaining symptoms developed in the presence of moderate degrees of carotid stenosis (less than 50%). There were seven patients who had transient ischemic attacks (TIAs) referable to the operated side, but only two of these were associated with a recurrent high-grade stenosis. During follow-up 32 (22%) patients had recurrent high-grade stenosis. Restenosis regressed in seven, giving a persistent rate of 17.1%. The incidence of restenosis was significantly higher in women (p less than 0.01). By life-table analysis, restenosis occurred early, the majority within 24 months. There was no consistent association between the development of symptoms and the occurrence of restenosis. Therefore, it is concluded that there is no justification for reoperation based on the degree of narrowing observed to prevent subsequent TIAs and strokes.

Fate of the carotid artery contralateral to endarterectomy.

The management of internal carotid artery disease contralateral to endarterectomy is highly controversial. At our institution we have adopted an approach by which patients are followed with serial duplex scanning after unilateral carotid endarterectomy. Surgery on the contralateral carotid artery is recommended for patients who exhibit ischemic neurologic symptoms or develop an 80% to 99% carotid stenosis. This strategy is based on previous reports that have documented an increased incidence of strokes in these two groups of patients. As a result, 40 patients among a study population of 200 underwent carotid endarterectomy on the originally unoperated side. The current study reviews the natural history of the patients who were followed without or before operation of the contralateral carotid artery in an attempt to identify other cohorts at increased risk for stroke. Patients were followed for up to 126 months after unilateral carotid endarterectomy (mean, 54 months). Six patients were lost to follow-up (3.0%). By life-table analysis the estimated mean annual rate of progression to greater than or equal to 50% diameter reduction was 3.9% and 1.2% for progression to greater than or equal to 80% stenosis. Only two patients went on to occlusion during follow-up. Neurologic events referable to the contralateral carotid distribution were infrequent. The estimated mean annual rate was 2.9% for transient ischemic attacks and less than 0.8% for strokes. Case history review of the six patients who had strokes during follow-up suggested that only one patient may have benefited from carotid endarterectomy. Conservative management with serial duplex scanning of the unoperated, contralateral carotid artery appears appropriate.(ABSTRACT TRUNCATED AT 250 WORDS)

Color Doppler imaging of infrainguinal arterial occlusive disease.

Few reports in the literature validate the use of color Doppler imaging (CDI) for the evaluation of lower extremity arterial occlusive disease, particularly in the tibial and peroneal arteries. This prospective, blinded study compares CDI to arteriography to address the following questions: (1) how well does CDI visualize arterial segments, including those below the knee? and (2) can CDI alone accurately classify the degree of occlusive disease? Twenty-nine men undergoing arteriography before a lower extremity arterial reconstructive procedure were studied with a color ultrasound scanner from the level of the inguinal ligament to the ankle. Color images were examined for the presence or absence of triphasic flow, poststenotic turbulence, color bruits, and collateral vessels. Among 636 arterial segments adequately visualized by arteriography, > or = 90% were identified with color Doppler imaging, including the tibial and peroneal arteries. With color criteria only, specificity was > or = 92% for distinguishing < 50% from > = 50% lesions and > or = 93% for differentiating patent from occluded arteries. Sensitivity for detecting an occlusion was > or = 97% in the superficial femoral (SFA) and popliteal arteries and 83% in the tibial vessels. For identifying a > or = 50% stenosis, sensitivity was > or = 85% in the SFA and popliteal arteries but only 79% and 86% in the posterior and anterior tibial arteries, respectively. CDI reliably identifies vessel location from the level of the groin to the ankle. For the detection of occlusions, CDI is an accurate screening tool in the SFA and popliteal arteries but is less accurate in the tibial vessels.(ABSTRACT TRUNCATED AT 250 WORDS)

A new method for studying plaque morphology.

A histologic method was developed for three-dimensional (3-D) analysis of atherosclerotic plaques removed from the carotid bifurcation during endarterectomy. By sectioning the plaque at frequent intervals (0.5 to 1.0 mm), it is possible to obtain important information on plaque constituents with regard to their volume and distribution within the lesion. These data from each section are combined with those from other sections and displayed in a 3-D format for the entire length of the lesion. The tissues making up each of the 10 carotid plaques were outlined and digitized for each histologic section by position along the lesion. From the areas outlined a 3-D model was created by a computer-aided design program. Quantitative information on tissue distribution within the plaque was measured. Fibrous tissue constituted between 35% and 70% of plaque volume; loose necrosis from 0.5% to 30% of the plaque and thrombus occupied, at a maximum, 10% even though if was present in six of the 10 plaques. To investigate the distribution of constituents about the long axis, measurements were also made from each of the four quadrants of each section. The reproducibility of the measurements of three sets of sections at 10-mm separation showed that estimates of the amount of some constituents were very reproducible whereas others had considerable variation related to the small volume they occupied within the lesion. By generating a complete 3-D reproduction of the contents of atherosclerotic plaques, it may be possible to identify those features of the plaque that are most responsible for the development of ischemic events.

Long-term follow-up and clinical outcome of carotid restenosis.

The efficacy of carotid endarterectomy is dependent on the inherent ability of the operation to prevent stroke as well as the incidence of restenosis and associated symptoms. To examine the long-term effects of restenosis, 301 patients having carotid endarterectomy were followed by serial duplex scanning for an average of 4 years. Carotid restenosis, defined as 50% or greater diameter reduction by duplex scanning, occurred after 78 of the endarterectomies; regression of recurrent stenosis occurred in 20 arteries. By life-table analysis the cumulative incidence of restenosis at 7 years was 31%, and the cumulative incidence of regression was 10%. Thus the prevalence of recurrent stenosis at 7 years was 21%. Restenosis developed in women more frequently than men (p = 0.01). Transient ischemic attack occurred in 12% of patients with restenosis, and stroke occurred in 3%; however, the cumulative incidence of stroke or transient ischemic attack was not statistically different in those patients with and without restenosis. Similarly, cumulative survival at 7 years was no different. Carotid restenosis usually occurs early in the postoperative period and tends to regress or remain stable during long-term follow-up. A conservative approach to treatment appears justified, since transient ischemic attacks and stroke were rarely associated with restenosis.

Diagnostic significance of flow separation in the carotid bulb.

Pulsatile blood flow within the normal carotid sinus involves at least two distinct components. That near the flow divider is laminar and antegrade, whereas a boundary layer separation zone in the posterolateral aspect exhibits transient blood flow reversal. It is now possible to document these flow velocity components using pulsed Doppler ultrasound methods. When atherosclerosis develops, it preferentially involves the posterolateral bulb region, obliterating the normal configuration of the sinus with consequent loss of the flow separation zone. It was therefore hypothesized that if flow separation could be detected, it should be predictive of a normal angiogram. To assess this, we evaluated 20 symptomatic patients and two with only bruits found by duplex scanning to have flow separation in either one or both carotid bulbs and who also underwent cerebral angiography. Initial diagnoses were stroke in seven, reversible ischemic neurologic deficit in one, transient ischemic attack in 12, and bruit in two. Flow separation was bilateral in 13 patients (59%). There were 15 patients with symptoms in the territory of a carotid bulb exhibiting flow separation. By angiography, of the 35 bulbs with boundary layer separation, 27 (77%) were normal, with the remainder showing lesions that reduced the diameter of the vessel by 20% or less. Final diagnoses of the 15 patients with symptoms ipsilateral to a carotid sinus exhibiting flow separation were fibromuscular disease in two, lacunar stroke in three, dissection in two, subclavian steal in one, cardiogenic embolus in three, migraine in one, hyperventilation syndrome in one, kink of the mid-internal carotid artery in one, and no diagnosis in one.(ABSTRACT TRUNCATED AT 250 WORDS)