Transcranial Doppler Monitoring Of Microembolic Signals Research Articles

Superb Microvascular Imaging Ultrasound for Cervical Carotid Artery Stenosis for Prediction of the Development of Microembolic Signals on Transcranial Doppler during Carotid Exposure in Endarterectomy

Introduction: During exposure of the carotid arteries, embolism from the surgical site is recognized as a primary cause of neurological deficits or new cerebral ischemic lesions following carotid endarterectomy (CEA), and associations have been reported between histological neovascularization in the carotid plaque and both plaque vulnerability and the development of artery-to-artery embolism. Superb microvascular imaging (SMI) enables accurate visualization of neovessels in the carotid plaque without the use of intravenous contrast. This study aimed to determine whether preoperative SMI ultrasound for cervical carotid artery stenosis predicts the development of microembolic signals (MES) on transcranial Doppler (TCD) during exposure of the carotid arteries in CEA. Methods: Preoperative cervical carotid artery SMI ultrasound followed by CEA under TCD monitoring of MES in the ipsilateral middle cerebral artery was conducted in 70 patients previously diagnosed with internal carotid artery stenosis (defined as ≥70%). First, observers visually identified intraplaque microvascular flow (IMVF) signals as moving enhancements located near the surface of the carotid plaque within the plaque on SMI ultrasonograms. Next, regions of interest (ROI) were manually placed at the identified IMVF signals (or at arbitrary places within the plaque when no IMVF signals were identified within the carotid plaque) and the carotid lumen, and time-intensity curves of the IMVF signal and lumen ROI were generated. Ten heartbeat cycles of both time-intensity curves were segmented into each heartbeat cycle based on gated electrocardiogram findings and averaged with respect to the IMVF signal and lumen ROI. The difference between the maximum and minimum intensities (ID) was calculated based on the averaged IMVF signal (ID_IMVF) and lumen (ID_l) curves. Finally, the ratio of ID_IMVF to ID_l was calculated. Results: MES during exposure of the carotid arteries were detected in 17 patients (24%). The incidence of identification of IMVF signals was significantly greater in patients with MES (94%) than in those without (57%; p = 0.0067). The ID_IMVF/ID_l ratio was significantly greater in patients with MES (0.108 ± 0.120) than in those without (0.017 ± 0.042; p < 0.0001). The specificity and positive predictive value for the ID_IMVF/ID_l ratio for prediction of the development of MES were significantly higher than those for the identification of IMVF signals. Logistic regression analysis revealed that only the ID_IMVF/ID_l ratio was significantly associated with the development of MES (95% CI 101.1–3,628.9; p = 0.0048). Conclusion: Preoperative cervical carotid artery SMI ultrasound predicts the development of MES on TCD during exposure of the carotid arteries in CEA.

Transcranial Doppler to Detect Right to Left Communication: Evaluation Versus Transesophageal Echocardiography in Real Life.

We compared transcranial Doppler (TCD) with transesophageal echocardiography (TEE) and transthoracic echocardiography (TTE) for the detection of right to left communication (RLC) in the heart. All patients explored from 2013 to 2016 in a vascular medicine unit to detect RLC by TCD were included. Right to left communication was detected by TCD monitoring for microembolic signals after intravenous injection of agitated 5% glucose and air. One hundred one patients were explored for RLC by TCD, 64 by TEE (not possible in 10, bubble injection in 51), and 93 by TTE because of unexplained stroke or arterial thrombosis (51 males, 50 females, age 51.0 ± 15.8 years) (bubble injection in 35). Fifty-three patients were positive after TCD (TEE: 4 negative, TTE: 7 negative). Of the negative patients after TCD, none was positive for TEE and 1 was positive for TTE with no evidence of patent foramen ovale. Transcranial Doppler was sensitive to detect RLC, even in patients with negative TTE or TTE. A negative TEE did not exclude RLC demonstrated by TCD. Transcranial Doppler might be proposed as first line to detect RLC.

Preoperative cervical carotid artery contrast-enhanced ultrasound findings are associated with development of microembolic signals on transcranial Doppler during carotid exposure in endarterectomy

Background and aimsEmboli from the surgical site during exposure of the carotid arteries cause new cerebral ischemic lesions or neurological deficits after carotid endarterectomy (CEA). The purpose of the present study was to determine whether preoperative contrast-enhanced ultrasound findings of the cervical carotid arteries are associated with the development of microembolic signals (MES) on transcranial Doppler, during exposure of the arteries in CEA, and to compare the predictive accuracy of contrast-enhanced ultrasound findings with that of gray-scale median (GSM). MethodsSeventy patients with internal carotid artery stenosis (≥70%) underwent preoperative cervical carotid artery ultrasound and CEA under transcranial Doppler monitoring of MES in the ipsilateral middle cerebral artery. Maximally enhanced intensities on the intraplaque and lumen time-intensity curves, respectively, were obtained from contrast-enhanced ultrasonography data, and the ratio of the maximal intensity (EIp) of the intraplaque curve to that (EIl) of the lumen curve was calculated. The GSM value of the plaque was also measured. ResultsThe area under the receiver operating characteristic curve to discriminate between the presence and absence of MES during exposure of the carotid arteries was significantly greater for EIp/EIl than for GSM (p = 0.0108). Multivariate statistical analysis demonstrated that only EIp/EIl was significantly associated with the development of MES during exposure of the carotid arteries (p = 0.0002). ConclusionsPreoperative contrast-enhanced ultrasound findings of the cervical carotid arteries are associated with development of MES on transcranial Doppler during exposure of the arteries in CEA, and the predictive accuracy of contrast-enhanced ultrasound is greater than that of GSM.

Transcranial Doppler Microembolic Signal Monitoring is Useful in Diagnosis and Treatment of Carotid Artery Dissection: Two Case Reports

Arterial dissection is the underlying stroke mechanism in approximately 2.5% of all strokes and the second leading cause of stroke in patients younger than 45 years of age. Controversy exists regarding the medical management of carotid dissection. Both anticoagulants and antiplatelet agents have been used with no compelling data supporting one therapy over the other. Transcranial Doppler (TCD) emboli monitoring may help in establishing the diagnosis and guide the treatment by measuring the frequency of microembolic signals (MES). We present two cases of carotid dissection where TCD monitoring for MES helped in establishing the diagnosis and proved useful in identifying that standard anticoagulation treatment was not preventing emboli. Both cases were also monitored for emboli count reduction with subsequent antiplatelet therapy.

Evaluation of Cerebral Microembolic Signals in Patients with Mechanical Aortic Valves

Background and Purpose: Microembolic Signals (MES) are frequently observed in Transcranial Doppler (TCD) recordings of patients with Mechanical Heart Valve (MHV).We hypothesized that number of MES produced by MHV could be reduced with oxygen inhalation, if gaseous bubbles are the underlying cause. Methods: All consecutive patients with St Jude aortic valves visiting the cardiology clinic were refered to the neurosonology unit, Valie Asr Hospital, Khorasan during August 2003 to August 2004. TCD monitoring of MES was performed with an ultrasound device (Vingmed 800 Oslo,Norway) and a 2 MHz probe. The MES counts were recorded during 30 minutes breathing room air and thereafter 30 minutes breathing through a facial mask with reservior bag (6 liter O2 per minute). The criteria of MES detection were characteristic chrip sound, unidirectional signal, random appearance within cardiac cycle and intensity increase 3dB above background. The MES counts in two periods of monitoring were compared with paired T test and significance was declared at P < 0.05. Results: Twelve patients (8 females and 4 males) were investigated. Oxygen ventilation caused a significant decrease of MES counts in the patients in comarison to breathing room air, P = 0.001. Thus MES in patients with MHV are mainly gaseous bubbles caused by blood agitation with MHV. Conclusion: The quantity of MES in patients with MHV is not related to the risk of thromboembolic complications in these patients.

Embolism in acute middle cerebral artery stenosis.

To investigate the frequency of middle cerebral artery (MCA) stenosis in a series of nonselected patients and the coexistence of microembolic signals with stenosis. MCA stenosis was sought by transcranial Doppler (TCD) in 387 patients admitted consecutively with acute ischemic cerebrovascular disease within the first 48 hours of the onset of symptoms and again at 6 months. TCD monitoring for microembolic signals was performed on all patients with MCA stenosis. MCA stenoses were found in 29 patients (7%), although in only 20 patients (5%) was the stenosis symptomatic. Microembolic signals were detected in five of 14 symptomatic stenoses (36%) monitored at the acute phase, but none were found in the chronic phase or in asymptomatic stenosis. Despite one third of symptomatic patients having had a further source of emboli, microembolic signals were detected only distally to the MCA stenosis. In the symptomatic group, 25% of stenoses had completely disappeared 6 months after stroke. Microembolic signal detection at the acute phase was associated with the subsequent disappearance of the stenosis. The frequency of symptomatic MCA stenosis in acute ischemic stroke was 5% in the population studied. Many stenoses are transient, and microembolic signals are often detectable at the poststenotic segment in the acute phase. The origin of at least 25% of symptomatic acute MCA stenoses may be embolic rather than atherosclerotic.

Clinical correlations of Doppler microembolic signals in patients with prosthetic cardiac valves: analysis of 580 cases.

The clinical relevance of Doppler microembolic signals (MES) in patients with prosthetic cardiac valves was evaluated by merging and statistically reanalyzing patient data from four research institutions (Departments of Neurology, Universities of Aachen, Halle, and Münster, Germany; Department of Medicine and Therapeutics, University of Glasgow, Scotland, and Department of Cardiothoracic Surgery, Western Infirmary, Glasgow, Scotland). Transcranial Doppler monitoring for MES was performed over the middle cerebral arteries for 30 to 60 minutes per patient. Prevalence of neurological complications was evaluated with a standard neurological questionnaire in patients carrying the valve implant longer than 3 months (n=369). Significant differences in MES prevalence and counts were noted among the 580 patients depending on valve type (presented with medians and [95% confidence intervals]): St Jude Medical, n=200, 72%, 4 [3 to 6]; Björk Shiley Monostrut, n=99, 92%, 133 [93 to 181]; Medtronic Hall, n=80, 47%, 1 [2 to 5]; ATS, n=61, 52%, 3 [2 to 5]; Tecna, n=38, 71%, 2 [1 to 4]; Carbomedics, n=37, 81%, 8 [5 to 13]; Carpentier-Edwards supraannular, n=54, 39%, 1 [0 to 3]; Sorin biological, n=11, 9%, 0 [0 to 0]. No relation between MES counts and valve size, international normalized ratio, patients' age, cardiac rhythm, or implant duration was noted. No significant differences in MES counts or prevalence (22 [3 to 68] versus 5 [3 to 6] and 63% versus 69%, both P>.05), in valve duration, valve position, valve type, patients' age, sex, cardiac rhythm, or international normalized ratio were evident between neurologically symptomatic (n=42) and asymptomatic patients. MES in patients with prosthetic cardiac valves depend on the type and, in certain valve types, the position of the valve implant and possess no direct clinical significance.