Characterization of ultrasound-detected cerebral microemboli in patients undergoing cardiac catheterization using an in vitro middle cerebral artery model.

Cerebral embolization has been documented as one of the complications of diagnostic heart catheterization by transcranial Doppler (TCD). This study aimed to evaluate our hypothesis that the nature of embolic signals involved in different stages of catheter manipulation may be distinct. TCD-detected cerebral emboli occurring at different phases of cardiac catheterization were registered and differentiated by comparing their acoustic signatures with the Doppler signals generated from clinically frequently encountered embolic materials in an in vitro middle cerebral artery model. We found that there was a significant difference in embolic signal intensity and duration between different phases of cardiac catheterization. Our data suggest that different types of emboli may be involved in different phases of the catheterization. Cathet Cardiovasc Intervent 2001;53:323-330.     

Cerebral Embolism as a Cause of Stroke and Transient Ischemic Attack

The most frequent cause of stroke and transient ischemic attacks is cerebral embolism. Cardiogenic cerebral embolization is common among patients with any cause of atrial fibrillation (AF) but particularly in AF resulting from rheumatic and arteriosclerotic heart disease. Rare causes of cerebral embolism include fat entering the bloodstream after trauma, tumor cells arising from atrial myxomata, and gas embolism. Cerebral embolic infarctions and their sources of origin can now be confirmed during life by many invasive (I) and noninvasive (NI) procedures including computerized tomography (CT) scanning (NI), magnetic resonance imaging (MR) (NI), contrast angiography (I), digital subtraction angiography (I), magnetic resonance angiography (NI), carotid Doppler and transcranial Doppler (NI), and echocardiography (NI) without and with contrast. These tests visualize the following: embolic occlusions of small and large cerebral arteries, resultant cerebral infarctions in appropriate vascular territories, plaques within the aorta, subclavian, vertebral, and carotid arteries, and mural thrombi located within the heart and aortocephalic arteries. Transcranial Doppler monitoring of the middle cerebral artery detects both small (asymptomatic) and large (symptomatic) cerebral emboli, as well as transseptal cardiac shunting, which is a cause of paradoxical embolization. Holter monitoring detects episodic cardiac dysrhythmias not apparent during routine ECG. CT or MRI identify cerebral infarctions resulting from virtually all large cerebral emboli. Early recognition and identification of types of cerebral embolism are important because of the availability of effective prophylactic therapies.     

Detection of Embolism with Doppler Ultrasound: A Review

Doppler detection of venous and arterial gas emboli has been recognized since 1968. The technology has been applied using 5-MHz ultrasound to study decompression sickness and monitor cardiopulmonary bypass and intracranial surgery. Since the advent of transcranial Doppler, which requires the use of lower ultrasonic carrier frequencies to penetrate the temporal bone, the detection of particulates moving in the bloodstream has been available. Using 2 MHz, microembolic signals have been detected in a variety of clinical situations, including cardiac conditions known to have high probabilities to produce embolic stroke. The basic features of a Doppler embolic signal have been clarified, and many investigators are applying the technology to determine the clinical significance of the detected emboli and their use in diagnosis and medical and surgical treatments. The basis for automatic sizing, counting, and characterizing the emboli is under development. The applications of Doppler detection of emboli will range from diagnosis and localization of embolic sources to improvement in surgical techniques and adjustments in medical treatments.     

Detection of embolic particles with the Doppler guide wire during coronary intervention in patients with acute myocardial infarction: efficacy of distal protection device

OBJECTIVES: We investigated whether embolic particles could be detected as high-intensity transient signals (HITS) with a Doppler guide wire during percutaneous coronary intervention (PCI) in patients with acute myocardial infarction (AMI) We also assessed whether these signals could be reduced using a distal protection (DP) device. BACKGROUND: Embolization of thrombi and plaque components to the microcirculation is a major complication of PCI in patients with AMI. Embolic particles running in the cerebral artery are detected as HITS by transcranial Doppler ultrasound. METHODS: We prospectively studied 16 consecutive patients with AMI who underwent direct PCI within 24 h after the onset of symptoms. A PercuSurge GuardWire (MedtronicAVE, Santa Rosa, California) was used as the DP device. Eight patients were randomly assigned to the non-DP group, and the remaining eight were assigned to the DP group. Coronary flow velocity was recorded continuously from before the first balloon inflation to after balloon deflation. RESULTS: All patients in the non-DP group had HITS detected (12 +/- 9 counts) within five consecutive beats (4 +/- 1 beat) after balloon deflation, but none were detected in any of the patients in the DP group. CONCLUSIONS: The Doppler guide wire can be used to visually detect and count emboli as HITS, and the DP device is effective for prevention of distal embolization.     

Cerebral protection systems for distal emboli during carotid artery interventions

Carotid angioplasty and stenting is associated with liberation of cerebral emboli that can cause periprocedural stroke. There are currently three classes of emboli protection devices (EPDs) that are undergoing feasibility studies and one randomized clinical trial. Preliminary data from a small series appear to be promising, and there appears to be attenuation of embolic signals on a cerebral Doppler exam with EPD use. However, rare strokes and patient intolerance due to imposed ischemia have been observed. The advantages and disadvantages of each EPD class and the issues involving clinical trials and surrogate end points in this area of study are discussed.     

Carotid artery stenting: utility of cerebral protection devices

Neurologic deficits secondary to embolic events have been the most significant concern regarding carotid bifurcation stenting. Experimental studies utilizing human carotid plaques have shown that embolic particles were released from all specimens. In addition, transcranial Doppler studies have confirmed the fact that multiple emboli are released during each case. Preliminary experiences with the use of cerebral protection devices for carotid stenting have shown encouraging results with embolic particles recovered from each case, although these experiences have also revealed some of the down sides of its use. The present article provides the rationale for routine use of these protection devices and also reviews various protection devices, some of which are currently undergoing clinical trials.     

Doppler Microembolic Signals for Diagnosis of Ulcerated Carotid Artery Plaques

Background: Finding the pathological meaning of Doppler microembolic signals is important to developing the clinical applications of this new technology. Methods: Two hundred eighty-four plaques, removed at carotid endarterectomy, were examined by the surgeon and pathologist for evidence of ulceration. The ipsilateral middle cerebral artery was monitored, with 2-MHz pulsed Doppler, preoperatively and during surgical mobilization of the carotid arteries. Associated Doppler embolic signals representing formed element emboli (FEE) were sought for 15–273 (mean 60) minutes. The embolization rate was calculated in FEE/hour. Results: Preoperatively, 21% of patients demonstrated FEEs. During surgical mobilization of the carotid arteries, 51% demonstrated FEEs. A 79% prevalence of plaque ulceration was found. Analysis demonstrated 61% sensitivity and specificity, and an 86% positive predictive value. The positive predictive value increased progressively with higher FEE rates, up to 100% for patients with > 60 FEE/hour. Conclusions: FEEs detected in the middle cerebral artery ipsilateral to carotid artery stenosis are diagnostic of plaque ulceration or luminal thrombus formation. Other embolic sources may be ruled out by monitoring the contralateral carotid artery system and the ipsilateral carotid arteries. There is no significant relationship between the number and prevalence of FEEs and the severity of stenosis or preoperative symptoms. Postoperative cerebral complications of stroke were associated with more FEEs than were postoperative transient ischemic attacks.     

经颅多普勒超声检测老年人糖尿病脑血管病变

目的为了解老年人高血压和糖尿病对脑血管病变的影响，探讨老年人糖尿病脑血管病变经颅多普勒超声的诊断方法。方法对老年人糖尿病并存高血压、糖尿病或高血压患者及健康对照组共１０５０条、老年前期各组共１３９５条脑血管进行了经颅多普勒超声检查及对照分析。结果老年患者中以糖尿病并高血压组呈现血流缓慢供血不足型异常最多见，占该组受检血管的８．９％；老年前期组中糖尿病并高血压组及单纯糖尿病组的发生率也较单纯高血压组为高，三者分别为４．６％、６．０％和０．７％。结论老年人高血压、糖尿病并存时脑血管血流缓慢供血不足病变最常见，对发生脑梗塞的患者进行经颅多普勒超声动态观察殊为必要。     

Transcranial Doppler with contrast injection for the detection of patent foramen ovale in stroke patients

Right-to-left shunt through a patent foramen ovale was searched for in 80 patients with acute ischemic stroke by simultaneously performing transthoracic two-dimensional echocardiography and transcranial Doppler during agitated saline injection. A patent foramen ovale was detected by echocardiography in 14 patients (17.5%). Transcranial Doppler correctly identified all 14 patients, and 7 more patients in whom echocardiographic findings were indeterminate. Prevalence of patent foramen ovale by transcranial Doppler was therefore 26.3% (21 of 80 patients). Concordance between the two tests was 91.3% (73 of 80 patients). The delivery of contrast material to cerebral vessels is therefore demonstrable by transcranial Doppler in all patients diagnosed by contrast echocardiography, suggesting that paradoxical embolization through a patent foramen ovale may be more frequent than previously thought. Transcranial Doppler with contrast injection is a valid alternative in case of poor echocardiographic image quality.     

Cerebral microvascular responses to air embolism-reperfusion in the cat using fluorescence videomicroscopy

Cerebral microvascular changes due to air embolism-reperfusion in the cat were investigated. Air embolism-reperfusion was produced in the cerebral microvessels by an intra-carotid injection of air (0.2-0.3 ml). Air emboli in the cerebral arterioles were observed continuously from the air injection to reperfusion using fluorescence videomicroscopy. Arteriolar diameter was measured based on video images of arterioles filled with rhodamine-B isothiocyanate dextran, and red cell velocity was measured using a dual window technique with FITC-labeled red cells. Air bubbles ceased to move in the arterioles of 20-70 microm diameter and blood flow was almost stopped in distal arterioles. The air emboli were of cylindrical shape in the arterioles, with hemispherical end caps. The emboli progressed slowly at rates of 7-73 microm/sec and then flowed away. The air emboli induced ischemia-reperfusion with the ischemic duration of approximately 1 minute (10 sec-3 min) at the arteriolar level. Cerebral arterioles began to dilate after the formation of the air emboli and significantly dilated by approximately 50% after reperfusion. A transient increase in red cell velocity was observed after reperfusion. Arteriolar dilation and the increase in velocity led to a hyperemic response in arteriolar flow to ischemia-reperfusion.     

经颅多普勒超声微栓子检测技术中分贝阈值的选择

目的　通过采用EMETC 2 0 2 0型PioneerVersion 2 .1检测系统对正常人大脑中动脉进行监测 ,以期获得帮助确定栓子信号分贝 (dB)阈值的参考数据。方法　正常人 50名按年龄分为 3组 (≤ 30岁 1 0名 ;>65岁 2 0名 ;30～ 65岁2 0名 ) ,选用相同技术参数监测大脑中动脉 30min。结果　 30min内总的信号数及不同dB值信号 (3～ 6dB)的频率之间 ,3组比较差异无显著性意义 ;30min内未出现 7dB值以上的信号 ;不同dB值信号的出现频率分别为 :3dB 87.0 7%(1 0 1 / 1min) ,4dB 1 1 .64 % (1 2 / 30min) ,5dB 1 .1 8% (1 / 30min) ,6dB 0 .1 0 % (0 .1 / 30min)。结论　采用EMETC 2 0 2 0型TCD仪作循环中微栓子检测时 ,栓子的信号阈值应≥ 5dB     

经颅多普勒超声对糖尿病患者脑血管病变的诊断价值

应用经颅多普勒（ｔｒａｎｓｃｒａｎｉａｌＤｏｐｐｌｅｒ，ＴＣＤ）超声波仪检查３４例糖尿病患者３７４条脑血管。结果显示６８条血管呈现血流加速狭窄型改变，７２条血管呈现血流缓慢供血不足型改变。提示ＴＣＤ超声检查可以较明确反映糖尿病脑血管病变的部位、范围和性质。     

Detection of embolic signals using Doppler ultrasound: a new approach to cardiac embolism

Cerebral embolism from cardiac, aortic or carotid cause can be detected by Doppler examination of carotid arteries or transcranial Doppler with long-duration recordings. The signals detected called HITS (high intensity transient signals), which have been described in vitro and in vivo, have specific physical characteristics. This novel technique is considered promising in establishing the relationship between the discovery of embolic heart disease and its clinical neurological manifestations. In the evaluation of a stroke, the detection of HITS could provide evidence in support of an embolic cause. The areas of application of this new technique are many: screening for asymptomatic embolism in patients with an embolic cardiac disorder, and effects of antiplatelet and anticoagulant medications or surgical treatments.     

Microembolism in Carotid Artery Disease

Abnormal high intensity transient signals detectable with transcranial Doppler (TCD) sonography have been associated with formed cerebral microembolism. Using long-term TCD monitoring, these clinically silent microembolic events can be observed in patients with cerebrovascular disease. Downstream of high grade internal carotid artery (ICA) stenosis, they occur significantly more frequently in neurologically symptomatic than in asymptomatic patients. Although the occurrence ofmicroemboli is random, the individual rate underlies circadian fluctuations and seems to decline within the first weeks after an ischemic event. Pathoanatomic work suggests that luminal ulcer and thrombosis of the stenosed ICA are the major sources of microemboli. Thus, by tapping into an important pathomechanism, the detection of clinically silent cerebral microembolism appears to provide paraclinical evidence of "unstable carotid artery disease" and may help to evaluate more specific treatment strategies.     

小儿脑性瘫痪脑血流动力学的研究

目的研究小儿脑性瘫痪(脑瘫)脑血流动力学的变化规律.方法应用经颅多普勒超声对347例脑瘫患儿与30例正常健康儿脑血流动力学参数进行对照检测.结果脑瘫患儿的大脑前动脉、大脑中动脉、大脑后动脉的平均血流较同年龄段的正常小儿显著下降(P＜0.05),而脑血管阻力指数则显著增高(P＜0.05).小于1岁年龄组的平均流速下降及脑血管阻力指数增高较其他年龄组更显著(P＜0.05).结论脑瘫患儿存在脑血流动力学的高阻力、低灌注障碍,早期应用改善脑微循环治疗对于小儿脑瘫的治疗有重要意义.     

Spurious scintiphotographic recurrence of pulmonary emboli

Pulmonary perfusion scintiphotographs in patients with acute, extensive pulmonary embolism have disclosed instances in which Scintiphotographic changes thought to indicate embolic recurrence were not substantiated by clinical-angiographic observations. These spurious Scintiphotographic recurrences reflected changes in the regional distribution of pulmonary vascular resistance secondary to different rates of embolic resolution or distal migration of emboli. To document the influence of changes in vascular resistance upon perfusion scintiphotographs, studies were performed in animals subjected to various sequences of pulmonary arterial obstruction by balloon catheters. Scintiphotographic changes mimicking, but not representing, recurrence of embolism were produced. Observations in both animals and man indicate that the diagnosis of embolic recurrence based on Scintiphotographic changes alone should be made with caution, particularly in patients with multiple emboli and pulmonary hypertension.     

Retrograde embolism from the descending thoracic aorta causing stroke: An underappreciated clinical condition

The mechanism of retrograde aortic blood flow is a complex and underreported clinical phenomenon. Complex plaques of the aortic arch are considered high-risk sources of cerebral emboli.¹ Aortic plaques situated in the descending thoracic aorta are however often overlooked and in fact can be more frequent potential sources of cerebral embolism through the mechanism of retrograde aortic blood flow. We present the case of an elderly Caucasian female who experienced recurrent posterior circulation embolic strokes where the only possible underlying etiology was found to be an atheroma in the descending thoracic aorta, possibly showering retrograde emboli.     

Transesophageal echocardiographic detection of cardiac embolic source in cor triatriatum complicated by aortic saddle emboli

Transesophageal echocardiographic findings are described in a case of cor triatriatum with atrial fibrillation complicated with cerebral and aortic saddle emboli. A spontaneous echo contrast confined to the dilated proximal chamber of the left atrium was noted and was presumed to be the embolic source in cor triatriatum.     

Anticoagulants in the prevention of embolic stroke. Part I

Cardiac lesions among those at high risk of cerebral emboli include: atrial fibrillation, rheumatic mitral valve disease, acute myocardial infarction, prosthetic heart valves, and idiopathic dilated cardiomyopathy. Many of these patients can be protected from cerebral infarction by anticoagulants. Following a cardiac embolic stroke, CT scans are critical in deciding for whom and at what time anticoagulation should be considered. From studies of CT and cerebrovascular pathology, it has become clear that it is the cerebral infarct rather than the arterial occlusion that provides the key piece of information in deciding whether and when anticoagulants should be considered for the secondary prevention of cardiac emboli among patients who present with a clinical stroke.