Incidence of transcranial Doppler-detected cerebral microemboli in patients referred for echocardiography

Atrial fibrillation: villain or bystander in vascular brain injury

Atrial fibrillation (AF) and stroke are inextricably connected, with classical Virchow pathophysiology explaining thromboembolism through blood stasis in the fibrillating left atrium. This conceptualization has been reinforced by the remarkable efficacy of oral anticoagulant (OAC) for stroke prevention in AF. A number of observations showing that the presence of AF is neither necessary nor sufficient for stroke, cast doubt on the causal role of AF as a villain in vascular brain injury (VBI). The requirement for additional risk factors before AF increases stroke risk; temporal disconnect of AF from a stroke in patients with no AF for months before stroke during continuous ECG monitoring but manifesting AF only after stroke; and increasing recognition of the role of atrial cardiomyopathy and atrial substrate in AF-related stroke, and also stroke without AF, have led to rethinking the pathogenetic model of cardioembolic stroke. This is quite separate from recognition that in AF, shared cardiovascular risk factors can lead both to non-embolic stroke, or emboli from the aorta and carotid arteries. Meanwhile, VBI is now expanded to include dementia and cognitive decline: research is required to see if reduced by OAC. A changed conceptual model with less focus on the arrhythmia, and more on atrial substrate/cardiomyopathy causing VBI both in the presence or absence of AF, is required to allow us to better prevent AF-related VBI. It could direct focus towards prevention of the atrial cardiomyopathy though much work is required to better define this entity before the balance between AF as villain or bystander can be determined.

Carotid atherosclerotic plaque instability and cognition determined by ultrasound-measured plaque strain in asymptomatic patients with significant stenosis

OBJECTIVE This article describes the use of ultrasound measurements of physical strain within carotid atherosclerotic plaques as a measure of instability and the potential for vascular cognitive decline, microemboli, and white matter changes. METHODS Asymptomatic patients with significant (> 60%) carotid artery stenosis were studied for dynamic measures of plaque instability, presence of microemboli, white matter changes, and vascular cognitive decline in comparison with normative controls and premorbid state. RESULTS Although classically asymptomatic, these patients showed vascular cognitive decline. The degree of strain instability measured within the atherosclerotic plaque directly predicted vascular cognitive decline in these patients thought previously to be asymptomatic according to classic criteria. Furthermore, 26% of patients showed microemboli, and patients had twice as much white matter hyperintensity as controls. CONCLUSIONS These data show that physical measures of plaque instability are possible through interpretation of ultrasound strain data during pulsation, which may be more clinically relevant than solely measuring degree of stenosis. The data also highlight the importance of understanding that the definition of symptoms should not be limited to motor, speech, and vision function but underscore the role of vascular cognitive decline in the pathophysiology of carotid atherosclerotic disease. Clinical trial registration no.: NCT02476396 (clinicaltrials.gov).

Cerebral microembolism in patients with segmental left ventricular wall motion abnormalities

BACKGROUND AND PURPOSE

The significance of segmental heart wall motion abnormalities for stroke is unknown. The aims of the study included (1) comparison of the frequency and type of embolic signals in the middle cerebral artery in patients with segmental left ventricular wall hypokinesis due to coronary heart disease with and without stroke, and (2) determination of the relationship between inflammatory parameters, fibrinogen level, dyslipidemia and microembolic signals in the middle cerebral artery in patients with segmental heart hypokinesis.

MATERIAL AND METHODS

The study included 68 patients with segmental heart hypokinesis (33 without stroke [group I] and 35 with stroke [group II]), as well as 37 healthy volunteers and a reference group of 30 patients. Echocardiography and carotid/transcranial Doppler with detection of microembolic signals were performed. Patients from group I and II had erythrocyte sedimentation rate, leucocyte count, triglycerides, total cholesterol, HDL, and LDL examined.

RESULTS

Embolic signals were detected in patients with segmental heart hypokinesis significantly more frequently than in the control and reference groups. The high number of embolic signals, signals of high intensity, hypokinesis of the distal part of the intraventricular septum, increased cholesterol levels, LDL and triglycerides were all found more frequently in patients from group II than in group I. Embolic signals were detected more frequently in patients with high fibrinogen levels and leukocytosis.

CONCLUSIONS

Embolic signals in the middle cerebral artery in patients with segmental left ventricular hypokinesis have to be considered as a risk factor of stroke. The following changes are observed in patients with cardiogenic stroke: hypokinetic intraventricular septum, high intensity embolic signals, increased serum fibrinogen levels and leucocyte count. It may indicate the importance of these factors in the aetiology of stroke.

Clinical assessment, neuroimaging and immunomarkers in Chagas disease study (CLINICS): Rationale, study design and preliminary findings

Chagas disease (CD) is an important cause of cardiomyopathy and stroke in Brazil. Brain infarcts and atrophy seem to occur independently of cardiomyopathy severity and cognitive impairment is understudied.

OBJECTIVE

Compare the prevalence of brain magnetic resonance imaging abnormalities between patients with or without CD; determine if inflammatory biomarkers are increased in CD; and determine the efficacy of aspirin in reducing the rate of microembolization in these patients.

METHODS

500 consecutive patients with heart failure will undergo a structured cognitive evaluation, biomarker collection and search for microembolic signals on transcranial Doppler. The first 90 patients are described, evaluated with cognitive tests and brain magnetic resonance imaging to measure N-acetyl aspartate (NAA), choline (Cho), myo-inositol (MI) and creatine (Cr).

RESULTS

Mean age was 55±11 years, 51% female, 38 (42%) with CD. Mean NAA/Cr ratio was lower in patients with CD as compared to other cardiomyopathies. Long-term memory and clock-drawing test were also significantly worse in CD patients. In the multivariable analysis correcting for ejection fraction, age, sex and educational level, reduced NAA/Cr (p=0.006) and cognitive dysfunction (long-term memory, p=0.023; clock-drawing test, p=0.015) remained associated with CD.

CONCLUSION

In this preliminary sample, CD was associated with cognitive impairment and decreased NAA/Cr independently of cardiac function or educational level.

Prevention of cardioembolic stroke

Cardiac causes of ischemic stroke lead to severe neurological deficits from large intracranial artery occlusion compared to small vessel ischemic stroke. The most common cause of cardioembolic stroke is atrial fibrillation (AF), which has an increasing incidence with age. AF stroke trials demonstrate that anti-coagulation is superior to anti-platelet therapy in terms of ischemic stroke prevention. Recently, warfarin was compared with dabigatran, an oral, direct thrombin inhibitor, and was found to be at least equally effective in reducing ischemic stroke with less intracranial bleeding risk. Future research is investigating other direct thrombin inhibitors as potential alternatives to warfarin, which has a narrow therapeutic index, requires frequent blood monitoring, has multiple drug interactions, and a higher rate of intracranial bleeding. Other causes of cardioembolic stroke include myocardial infarction, left ventricular thrombus, reduced ejection fraction, valvular abnormalities, and endocarditis. Patent foramen ovale is a common finding on echocardiograms in patients with and without stroke (up to 20% of the population), and it is a controversial source of cryptogenic stroke. The best way to prevent cardioembolic stroke remains early detection and treatment of AF, and treating the underlying stroke mechanism. Cardiac magnetic resonance imaging is an emerging technology and reveals some sources of cardiac embolism missed by echocardiography, and might provide an additional diagnostic tool in investigating cardioembolic stroke.

Stroke prevention in atrial fibrillation and other major cardiac sources of embolism

The frequency of cardioembolic stroke is expected to rise as the general population ages. Much of the increase may be attributed to atrial fibrillation, the most common cause of cardioembolic stroke and one that plays a substantial role in aging adults. Other sources of cardioembolic stroke may include ventricular thrombus from myocardial infarction, heart failure, structural heart defects such as patent foramen ovale (PFO), atrial septal aneurysm, proximal aortic atheroma, valvular heart disease, and endocarditis. Diagnostic studies, such as neuroimaging, ECG, and echocardiography, are helpful in uncovering cardioembolic sources of stroke. Medical therapy is predicated on the underlying mechanism. For example, warfarin may be indicated in certain patients who have atrial fibrillation, atrial, or ventricular thrombi, and PFO with atrial septal aneurysm and cryptogenic stroke in select young patients to prevent stroke. Newer diagnostic technologies, including multidetector CT and cardiac MRI, may be useful to diagnose cardiac causes of stroke when transesophageal echocardiography is indeterminate or cryptogenic stroke is present.

Heart diseases and stroke

A heterogeneous group of heart diseases, varying by cardiac anatomy and physiology, are responsible for a variety of embolic materials that result in cerebral and systemic embolism. Atrial fibrillation accounts for nearly half of all cardioembolic stroke, particularly in the elderly, but in the young congenital septal abnormalities such as patent foramen ovale play a more important role. Therapeutic strategies include stabilization or treatment of the underlying heart disease and prevention of embolism. Oral anticoagulant therapy is indicated for many but decision making on balancing the benefits versus risks can be difficult. New endovascular therapies and devices have become available and await clinical trials that allow them to be compared with existing medical therapies.

Deterioration of vascular dementia caused by recurrent multiple small emboli from thoracic aortic atheroma

We report a case of a 77-year-old man with deteriorating dementia caused by repeated multiple small cerebral embolisms from a thoracic aortic atheroma. Multiple small embolisms were confirmed by diffusion-weighted magnetic resonance imaging (DWI). The patient ultimately died due to aortic dissection. Pathological examinations revealed that no causative embolic source for multiple embolisms could be detected other than severe atheromatous ulcer in thoracic aorta. This case demonstrates that severe aortic atheroma has the potential to precipitate deterioration of vascular dementia.

Does short-term anticoagulation with heparin increase risk for microemboli patients undergoing transesophageal guided electrical cardioversion for atrial fibrillation? A transcranial Doppler ultrasonography study

BACKGROUND

Electrical cardioversion (ECV) in patients with atrial fibrillation (AF) is known to be associated with an increased peri-procedural risk for thromboembolic events. ECV of AF for at least 3 weeks of effective oral anticoagulation was recently determined to be disassociated with occurrence of cerebral circulating microemboli (ME). Nonetheless, whether ECV in patients undergoing short-term anticoagulation with heparin is concomitant with cerebral ME still remains obscure. The objective of this study was to determine whether or not short-term anticoagulation with heparin helps avoid microemboli before and immediately after cardioversion of AF in patients undergoing transesophageal echocardiography (TEE)-guided ECV.

METHOD

A total of 34 patients (21 women, aged 61+/-12 years) who underwent TEE-guided ECV were enrolled into the study. All the patients underwent treatment with heparin for 3 days for anticoagulation before ECV. Transcranial Doppler ultrasonography (TCD) of the right middle cerebral artery and left middle cerebral artery was simultaneously performed through the temporal skull with a two-channel 2-MHz probe in all patients lasting for 30 min before ECV and 30 min immediately after successive ECV.

RESULTS

No ME were detected in 34 patients during the 30-min period during AF before ECV. Similarly, after ECV no ME were observed during 30-min monitoring in 27 patients who were converted to sinus rhythm. None of the patients presented with clinical signs or symptoms suggestive of manifest cerebral embolism either before or after ECV.

CONCLUSION

TCD monitoring did not disclose any evidence of microemboli in short-term anticoagulated patients with heparin before and immediately after TEE-guided ECV.

Microembolus detection by transcranial doppler sonography

Microembolic signals can be detected by transcranial ultrasound as signals of high intensity and short duration. These signals represent circulating gaseous or solid particles. To optimize the differentiation from artefacts and the background signal and to facilitate the clinical use, several attempts have been made to automatize the detection of microemboli. Microemboli occur spontaneously in various clinical situations but their clinical impact and possible therapeutical implications are still under debate. This article provides a review of the actual literature concerning the current state of technical and clinical aspects of microembolus detection.

Asymptomatic embolisation in non-valvular atrial fibrillation and its relationship to anticoagulation therapy

OBJECTIVE

A prospective study to determine the prevalence of embolic signals (ES) detected with transcranial Doppler ultrasound (TCD) in subjects with non-valvular atrial fibrillation (NVAF) who were and were not taking anticoagulants.

METHODS

Sixty-eight subjects with NVAF taking warfarin and sixty-three NVAF subjects not taking warfarin were recruited from the cardiology department. No patients had suffered a previous stroke or clinical systemic embolisation. Thirty subjects in sinus rhythm were recruited as controls. TCD recordings were performed bilaterally from the middle cerebral arteries for 1 h. In 126 subjects (96%) the recording was repeated 1 week later. All Doppler recordings were reviewed blindly by an observer for ES.

RESULTS

After one recording ES were detected in one warfarin NVAF subject (1.5%), four non-warfarin NVAF subjects (6.3%) and no sinus rhythm controls. Following both recordings ES were detected in one warfarin NVAF subject (1.5%) and seven non-warfarin NVAF subjects (11.9%) P = 0.017.

CONCLUSIONS

Asymptomatic ES can be detected in a minority of subjects with NVAF. These signals were significantly less common in NVAF subjects taking warfarin, and this is consistent with asymptomatic ES having clinical significance in this disease. TCD detection of ES may have application in patients with NVAF for risk stratification, and assessment of the efficacy of new anti-platelet and anti-thrombotic regimens in the condition. Further large prospective studies are required to determine whether ES predict stroke risk in this patient group.

Transcranial Doppler assessment of cerebral embolic disorders

Transcranial Doppler ultrasound allows noninvasive monitoring of the large intracranial vessels. Microembolic signals (MES) have been observed under a variety of circumstances, especially in symptomatic carotid stenosis, high-risk cardiac conditions, and surgical procedures (such as carotid endarterectomy and cardiopulmonary bypass surgery). Technical considerations have presented numerous challenges to the interpretation of these signals, many of which appear to represent small emboli traveling in the blood flow. The technical aspects of these MES are discussed and their significance in relation to cerebral ischemia and its prevention are examined in some detail.

Carotid Doppler high-intensity transient signals in dilated cardiomyopathy

BACKGROUND

Thromboembolism is an infrequent but serious complication in dilated cardiomyopathy (DCM), and the role of primary preventive antithrombotic or anticoagulation therapy is undetermined. High-intensity transient signals (HITS) by Doppler ultrasound representing microemboli have been described in various clinical settings associated with increased risk of stroke. This study assessed the feasibility, reproducibility, and prevalence of HITS in patients with DCM.

METHODS

Thirty patients with severely reduced left ventricular ejection fraction (< or = 35%, mean 25%) and New York Heart Association class II to III who were not receiving antithrombotic or anticoagulant therapy and 20 age-matched normal subjects were prospectively examined. Patients with atrial fibrillation, significant cardiac valvular heart disease, a history of cerebrovascular disease, and those who otherwise required antithrombotic or anticoagulation therapy were excluded. One-hour pulsed-wave Doppler recordings over the common carotid artery (CCA) were performed on 3 separate days in each subject by a single, experienced, blinded sonographer with a 4-MHz probe (TC-2000, Nicolet/EME) with a specially designed probe holder. Studies were read in a blinded, random fashion by 2 independent, experienced HITS Doppler recording readers.

RESULTS

HITS in the CCA were detected in 6 (20%) of 30 patients with DCM and in 3 (15%) of 20 volunteers. This difference was not statistically significant. Intrareader and interreader reproducibility were high (kappa = 0.91 and 0.84, respectively; P <.001), whereas intrasubject reproducibility over the 3 visits was moderate to low (kappa = 0.22). There was no significant difference between HITS characteristics, that is, intensity and duration, in patients versus controls.

CONCLUSIONS

The prevalence of CCA HITS in patients with clinically stable heart failure who are not receiving anticoagulation/antithrombotic therapy and are not in atrial fibrillation is low and not significantly different from normal patients. These data suggest that HITS monitoring is not a viable surrogate marker for increased thromboembolic risk in such patients with DCM.

A bovine model for detecting high intensity transient signals originating from mechanical heart valves

In patients with mechanical heart valves (MHVs), transcranial Doppler methods commonly detect high intensity transient signals (HITS) representing microemboli. These microemboli, which are presumably gaseous, may cause stroke and cognitive deterioration. A bovine model was therefore developed for studying the relationship between mitral MHV induced HITS and potential etiogenic factors. We placed an 18 mm, 4 MHz Doppler probe in the brachiocephalic artery to detect MHV induced microbubbles at baseline (rest) and under 9 other conditions. To elucidate the gas composition (CO2 or N2) of the microbubbles, we administered 1%, 3%, and 5% CO2, and 100% O2. To determine effect of the heart rate, we paced the heart at 120, 160, and 180 bpm. To alter the myocardial contractility, we gave dobutamine and esmolol. Two independent, blinded observers counted the HITS from recorded doppler spectra. HITS were defined by an initial unidirectional spectral deviation, a signal power of >8 dB relative to the background power, and lack of a cyclic appearance. The electrocardiogram, aortic and LV pressures, and LV dP/dt were obtained telemetrically. The calves were studied 4 to 6, 8 to 10, and 12 to 14 weeks postoperatively, after which the animals were sacrificed at an approximate 4 month study duration, and a postmortem evaluation of the heart and the main viscera was performed. In all, 27 HITS recordings were made in 10 calves. Myocardial contractility was the only factor to significantly affect HITS frequency; the heart rate and blood gas concentrations had minimal effect on HITS frequency. Our bovine model will be useful for assessing valve designs, as well as the mechanism of HITS, the composition of the microemboli, and their possible pathophysiologic effects on the kidneys and brain.

Can cerebrovascular microemboli induce cognitive impairment in patients with prosthetic heart valves?

Doppler ultrasonography can be used to detect the presence of emboli in the cerebral arterial circulation. Emboli can be produced by different sources and can be of different nature: solid elements as thrombi, platelet aggregates or atheromatous material, or gaseous when they are produced during the decompression phase of diving or during extracorporeal circulation (ECC) procedures. A more recent source of emboli has been found in the mechanical prostheic heart valves (MHV). The emboli generated by MHV are likely of gaseous nature and are found in the middle cerebral artery blood flow at a variable rate, where they are detected by transcranial Doppler sonography. The mechanism of production of these microbubbles may be related to the rapid leaflet motion especially at closure when very high local pressure gradients appear, which may be able to provoke a release of the disolved blood gas. Solid element emboli constitute a major cause of cerebrovascular disease and particularly stroke. Conversely, gaseous emboli coming from ECC or MHV are considered as clinically silent. Nevertheless, cognitive alterations have been reported after ECC. As the MHV carriers are chronically submitted to embolic events, it can be assumed that cognitive impairments may occur also in these patients. A preliminary study was designed to inpatients attention and memory in patients with normally functioning MHV and microemboli, with biological prosthesis and in normal subjects. In the two groups of patients, episodic memory was significantly altered relatively to the control group. In the MHV carriers group, a significant decrease in working memory performance was observed relatively to the two other groups. These results confirm a long term effect of the microembolization occuring during ECC and point out the effect of the chronic exposition to microemboli.

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.

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. (ECHOCARDIOGRAPHY, Volume 13, September 1996)