High-intensity Transient Signals Counts Research Articles

High-intensity transient signals during transcatheter aortic valve implantation assessed by ultrasonic carotid artery blood-flow monitoring: A single center prospective observational study

BackgroundNo reports to date have assessed the procedural patterns of high-intensity transient signals (HITS) by monitoring blood flow in cervical arteries. The aim of this study was to examine the sequential distribution of HITS in each procedural phase and predictive factors for HITS during transcatheter aortic valve implantation (TAVI) by monitoring blood flow in the common carotid artery. MethodsThis prospective observational study included 73 patients who underwent TAVI via the transfemoral artery approach. We continuously evaluated and analyzed HITS from administration of heparin to valve implantation. ResultsHITS peaked during balloon valvuloplasty (BAV), amounting to almost 30% of the total HITS count, followed by valve implantation [BAV 141 (73–186) and valve implantation 86 (64–126), respectively]. In univariate and multivariate analysis, the Agatston score of the aortic valve and low-density lipoprotein were confirmed as independent predictors of HITS frequency with logarithmically converted coefficients of 0.00015 (p < 0.001) and 0.0032 (p = 0.027), respectively. ConclusionsThese results provide the first evidence that micro-emboli deriving from calcified burden were scattered primally during BAV, followed by valve implantation. The Agatston score may be a predictor for the amount of HITS.

Most High-Intensity Transient Signals Are Not Associated With Specific Surgical Maneuvers.

Mortality after congenital heart defect surgery has dropped dramatically in the last few decades. Current research on long-term outcomes has focused on preventing secondary neurological sequelae, for which embolic burden is suspected. In children, little is known of the correlation between specific surgical maneuvers and embolic burden. Transcranial Doppler ultrasound is highly useful for detecting emboli but has not been widely used with infants and children. Bilateral middle cerebral artery blood flow was continuously monitored from sternal incision to chest closure in 20 infants undergoing congenital heart defect repair or palliative surgery. Embolus counts for specific maneuvers were recorded using widely accepted criteria for identifying emboli via high-intensity transient signals (HITS). An average of only 13% of all HITS detected during an operation were correlated with any of the surgical maneuvers of interest. The highest mean number of HITS associated with a specific maneuver occurred during cross-clamp removal. Cross-clamp placement also had elevated HITS counts that significantly differed from other maneuvers. In this study of infants undergoing cardiac surgery with cardiopulmonary bypass, the great majority of HITS detected are not definitively associated with a specific subset of surgical maneuvers. Among the measured maneuvers, removal of the aortic cross-clamp was associated with the greatest occurrence of HITS. Future recommended research efforts include identifying and confirming other sources for emboli and longitudinal outcome studies to determine if limiting embolic burden affects long-term neurological outcomes.

The self-expanding Symetis Acurate does not increase cerebral microembolic load when compared to the balloon-expandable Edwards Sapien prosthesis: a transcranial Doppler study in patients undergoing transapical aortic valve implantation.

ObjectivesThe aim of this study was to quantify potential differences in count, frequency and pattern of high-intensity transient signals (HITS) during transapical transcatheter aortic valve implantation (TA-TAVI), by comparing the Symetis Acurate TA (SA) with the balloon-expandable Edwards Sapien XT (ES) system.BackgroundRecently, the Symetis Acurate TA revalving system has been introduced for TA-TAVI. The Symetis Acurate TA aortic bioprosthesis is self-expanding and is deployed by a specific two-step implantation technique. Whether this novel method increases the load of intraprocedural emboli, detected by transcranial Doppler ultrasound (TCD) as HITS, or not is not clear.MethodsTwenty-two patients (n = 11 in each study arm, median logistic EuroScore 20%, median STS score 7%) displayed continuous TCD signals of good quality throughout the entire TA-TAVI procedure and were included in the final analysis. Data are presented as median with interquartile ranges.ResultsNo significant differences were detected in total procedural or interval-related HITS load (SA: 303 [200; 594], ES: 499 [285; 941]; p = 0.16). With both devices, HITS peaked during prosthesis deployment (PD), whereas significantly fewer HITS occurred during instrumentation (SA: p = 0.002; ES: <0.001) or post-implantation PI (SA: p = 0.007; ES: <0.001). PD-associated HITS amounted to almost half of the total HITS load. One patient suffered new disabling stroke at 30 days. Thirty-day mortality amounted to 13.6% (3 of 22 patients).ConclusionsSimplified transapical delivery using the self-expanding SA device does not increase HITS, despite of a two-step deployment technique with more interactions with the native aortic valve, when compared to the balloon-expandable ES valve. The similarity in HITS count, frequency and pattern with the two systems suggests a common mechanism for the release of cerebral microemboli.

Relationship between exercise-induced heart rate increase and the formation of microbubbles and high-intensity transient signals in mechanical heart valve implanted patients.

IntroductionThe formation and collapse of vapor-filled bubbles near a mechanical heart valve is called cavitation. Microbubbles can be detected in vivo by doppler ultrasonography (USG) as HITS (high intensity transient signals) in cranial circulation. We investigated the relationship between exercise induced heart rate increase and HITS formation in cranial circulation.Material and methodsThirty-nine mechanical heart valve implanted (8 aortic valve replacement (AVR) + mitral valve replacement (MVR), 9 AVR, 22 MVR) patients aged 18-80 years old were included in our study. Microbubbles were counted in the left ventricular cavity via transthoracic echocardiography at rest per cardiac cycle. Afterwards transcranial Doppler USG was performed and HITS were counted in each patient's middle cerebral artery at 5 min duration. Subsequently an exercise test according to the Bruce protocol was performed. After achieving maximal heart rate, microbubbles in the left ventricle and HITS were counted again.ResultsMicrobubbles in the left ventricle and transcranial HITS increased after exercise significantly compared to resting values (15.79 ±10.91 microbubbles/beat vs. 26.51 ±18.00 microbubbles/beat, p < 0.001; 6.13 ±8.07 HITS/5 min vs. 13.15 ±15.87 HITS/5 min, p = 0.001). There was a significant correlation between microbubbles and HITS counts after peak exercise (r = 0.55, p < 0.001).ConclusionsIn our study, we found that the microbubbles were increasing as the heart rate increased and more HITS were propelled to the cerebral circulation. As previously shown, HITS can alter cognitive functions. Therefore heart rate control is essential in mechanical heart valve patients to protect neurocognitive functions.

Cerebral Emboli Detected by Transcranial Doppler During Cardiopulmonary Bypass Are Not Correlated With Postoperative Cognitive Deficits

High-intensity transient signals (HITS) are the transcranial Doppler representation of both air and solid cerebral emboli. We studied the frequency of HITS associated with different surgical maneuvers during cardiopulmonary bypass for coronary artery bypass graft surgery and their association with postoperative cognitive dysfunction (POCD). We combined 356 patients undergoing coronary artery bypass graft from 2 clinical trials who had both neuropsychological testing (before, 1 week and 3 months after surgery) and transcranial Doppler during cardiopulmonary bypass. HITS were grouped into periods that included: cannulation, cardiopulmonary bypass onset, aortic crossclamp-on, aortic crossclamp-off, side clamp-on, side clamp-off, and decannulation. POCD was defined by a decreased combined Z-score of at least 2.0 or reduction in Z-scores of at least 2.0 in 20% of the individual tests. Incidence of POCD was 47.3% and 6.3% at 1 week and 3 months after surgery. There was no association between cardiopulmonary bypass counts of HITS and POCD at 1 week (P=0.617) and 3 months (P=0.110). No differences in HITS counts were identified at any of the surgical periods between patients with and without POCD. Factors affecting HITS counts were surgical period (P<0.0001), blood flow velocity (P=0.012), cardiopulmonary bypass duration (P=0.040), and clinical study (P=0.048). Although cerebral microemboli have been implicated in the pathogenesis of POCD, in this study that included low-risk patients undergoing coronary artery bypass surgery, there was no demonstrable correlation between the counts of HITS and POCD.

The Relationship Between Coronary Plaque Characteristics and Small Embolic Particles During Coronary Stent Implantation

We investigated the relationship between coronary plaque components and small embolic particles during stenting and examined the influence on the coronary microcirculation. In vivo tissue characterization of atherosclerotic plaques was introduced by the Virtual Histology intravascular ultrasound (VH-IVUS) system (Volcano Therapeutics, Inc., Rancho Cordova, California). The study consisted of 44 patients who underwent elective coronary stenting. Plaque characteristics were identified with VH-IVUS, and small embolic particles liberated during stenting were detected as high-intensity transient signals (HITS) with a Doppler guidewire. Coronary flow velocity reserve (CFVR) was also measured before and after stenting. Patients were divided into the tertiles according to the HITS counts: the lowest, HITS <5 (n = 16); the middle, 5 to 12 (n = 15); and the highest, >12 (n = 13). Dense calcium and necrotic core area identified with VH-IVUS were significantly larger in the highest tertile (lowest vs. middle vs. highest; dense calcium: 0.2 +/- 0.3 mm2 vs. 0.3 +/- 0.6 mm2 vs. 0.8 +/- 0.7 mm2, p = 0.007; necrotic core: 0.5 +/- 0.4 mm2 vs. 0.9 +/- 0.9 mm2 vs. 1.8 +/- 1.0 mm2, p < 0.001, respectively). Multivariate logistic regression analysis revealed only necrotic core area was an independent predictor of high HITS counts (odds ratio 4.41, p = 0.045). Furthermore, there was a significant negative correlation between the HITS count and CFVR after stenting (r = -0.35, p = 0.017). The necrotic core component identified with VH-IVUS is related to liberation of small embolic particles during coronary stenting, which results in the poorer recovery of CFVR.

Comparison of two different extracorporeal circuits on cerebral embolization during cardiopulmonary bypass in children

To compare the effect of two different extracorporeal circuits on the counts of high-intensity transient signals (HITS) during pediatric cardiopulmonary bypass (CPB). Transcranial Doppler was used to detect HITS associated with extracorporeal sources during the period of aortic crossclamping in the middle cerebral artery of children undergoing CPB. Based on body size, children were assigned one of two extracorporeal circuits (A or B). Circuit A included a D-705 oxygenator and associated reservoir, and circuit B included a Lilliput oxygenator and reservoir. Patients were further classified into two groups according to the complexity of surgical repair: single simple lesions or multiple complex lesions. We studied 109 pediatric patients. Surgery for multiple complex lesions was associated with longer periods of aortic crossclamping and CPB (p < 0.0001). The median count of extracorporeal HITS was 12 (25th, 75th percentiles: 3, 51). The type of extracorporeal circuit (p = 0.012) and the complexity of surgical repair (p < 0.0001) had an effect on the HITS counts. The use of circuit A was associated with higher HITS counts during surgery for multiple complex lesions compared to single simple lesions (p < 0.0001). Conversely, no differences were found with the use of circuit B between these two surgical groups (p > 0.25). During surgery for multiple complex lesions, patients treated with circuit A showed higher HITS counts than those with circuit B (p < 0.01), but there were no circuit-related differences in HITS counts (p = 0.30) during single simple lesions. Variations in the design characteristics of extracorporeal circuits can increase cerebral emboli during CPB in children. This may be related to the reduced ability of some circuits to remove emboli during long periods of CPB for complex congenital heart-surgery.

Sources of Variability in the Detection of Cerebral Emboli with Transcranial Doppler During Cardiac Surgery

The application of intensity thresholds for embolus detection with transcranial Doppler (TCD) can exclude from analysis an unrecognized proportion of high-intensity transient signals (HITS))whose intensities are below the threshold. The lack of consistent threshold criteria between clinical trials may explain part of the discrepancy in the reported HITS counts. We investigated the effect of choosing different thresholds on the sensitivity and specificity of detecting HITS during cardiopulmonary bypass (CPB). Two observers independently analyzed TCD recordings from 8 patients under CPB. Doppler signals were classified as true HITS, equivocal HITS, artifacts, and Doppler speckles according to preestablished criteria. The relative intensity of Doppler signals was measured by two different methods (TCD software vs manual). Receiver Operating Characteristic curves determined the optimal threshold for each of the two intensity methods. Reviewers achieved agreement in 96% of 2190 Doppler signals (kappa = 0.90). Relative intensities calculated with the TCD-software method were 3 dB (95% CI: 3.0-3.4) higher than the manual method. The optimal threshold was found at 10 dB (sensitivity: 99%; specificity: 90.8%) with the software method and at 7 dB with the manual method (sensitivity: 96%; specificity: 83%). The use of an intensity threshold 2 dB higher than the optimal increased the rejection of true HITS by 8% and 14%, respectively. Using intensity thresholds higher than the optimal for embolus detection decreases HITS counts. Choosing a threshold depends on the type of method used for measuring the signal intensity. Uniform threshold criteria and comparative studies between different Doppler devices are necessary for making clinical trials more comparable.

Residual air in the venous cannula increases cerebral embolization at the onset of cardiopulmonary bypass

When the right atrium (RA) cannula is connected to the venous return line of the cardiopulmonary bypass (CPB) circuit, air is often introduced. Air in the venous cannula may increase cerebral air embolization at initiation of CPB despite the arterial line filter. We measured the volume of air present in the venous cannula after cannulation of the RA. Transcranial Doppler quantified emboli as high-intensity transient-signals (HITS) in both middle-cerebral arteries (MCA) at the beginning of CPB. After RA cannulation, the air column in the venous line was measured and the total volume calculated using the known lumen diameter. CPB onset was defined as the instant when the CPB machine started moving the patient's blood from the RA into the venous reservoir. Starting from CPB onset, HITS were counted: (a) until completion of the first minute on CPB (1-min count) and (b) until aortic cross clamping (pre-clamping count). We studied 135 patients during coronary artery bypass surgery operated on by 10 cardiac surgeons. HITS during onset of CPB were detected in 95% of patients. Median counts were 10 HITS (25th, 75th percentiles: 3, 26) at 1-min and 21 HITS (8, 51) during pre-clamping. A significant correlation was found between the volume of air in the venous cannula and the HITS counts (r=0.524, p<0.0001). Absence of retained air was associated with lower HITS counts [3 HITS (1, 11)] compared with any amount of air [13 HITS (4, 29), p=0.002)]. The volume of air in the venous cannula, the MCA mean blood flow velocity and the pre-clamping time were the only independent predictors of the pre-clamping HITS counts (p<0.001). Air in the venous cannula can result in HITS in the MCA. Minimizing the volume of air introduced into the venous cannula after cannulation of the RA can decrease cerebral air embolization at the beginning of CPB.

Effect of perfusionist technique on cerebral embolization during cardiopulmonary bypass

To determine the association between high-intensity transient signals (HITS) and perfusionist interventions, purging techniques, pump flows and venous reservoir blood volume levels during cardiopulmonary bypass. Transcranial Doppler was used to detect HITS in the middle cerebral artery during the period of aortic crossclamping in patients undergoing coronary artery bypass grafting. Perfusionist-related interventions were recorded and included blood sampling (including the number of times that the oxygenator sampling manifold was purged), drug bolus injections and infusions (vasopressors, crystalloid and mannitol). Pump flows and venous reservoir volume levels were also documented. There were 534 interventions in 90 patients [median number of interventions per patient: 6 (quartiles: 4, 8)]. The median total HITS count from all interventions was 17 (5, 37). This represented 38% of the total HITS counts during aortic crossclamping. Factors contributing to differences in the HITS count included type of intervention (p <0.0001) and perfusionist (p =0.0012). Blood sampling (p<0.001) and drug bolus injections (p=0.06) had higher HITS counts per patient than infusions. Repetitive purging significantly increased HITS counts (r=0.74; p <0.001). Purging perfusionists (purging: 1-10 times) had higher HITS counts per patient [5 HITS (1, 15) than nonpurgers [0 HITS (0, 1) p <0.0001]. HITS counts were significantly correlated with reservoir volumes (r= -0.20, p=0.017) and pump flow rates (r=0.21, p =0.008). Reservoir volume levels < or =800 mL were associated with higher HITS counts per intervention [11 HITS (2, 27)] during blood sampling compared with higher volume levels [3 HITS (1, 10), p =0.001]. Cerebral emboli associated with perfusionist interventions can be minimized by not purging the sampling manifold, using continuous infusions rather than bolus injections, and maintaining high blood-volume levels (>800mL) in the venous reservoir.

High-intensity transient signals due to prosthetic valve obstruction: diagnostic and therapeutic implications

Background High-intensity transient signals (HITS) can be detected by transcranial Doppler ultrasonography (TCD) in patients carrying a mechanical prosthetic valve. The HITS counts and a frequency analysis were evaluated in patients with prosthetic valve obstruction in the aortic position. Methods Simultaneous echocardiographic, cineradiographic, and TCD evaluations for a St. Jude Medical valve were performed in 108 patients. All patients were asymptomatic and had no significant stenosis of the carotid artery. The HITS were identified according to criteria established by consensus of the International Cerebral Hemodynamics Symposium. Results The HITS counts in 69 patients with normal prosthetic valve function were 2.2 ± 4.4, and the counts in 39 patients with prosthetic valve obstruction (group D) were 8.3 ± 10.8. This difference was significant ( p = 0.0002). In 2 patients of group D who had a greater rate of less than 400 Hz HITS, which were produced by solid microemboli, thrombolysis resulted in a mitigation of restricted leaflet movement equal to or greater than 10 o. The total number of HITS decreased and the rate of less than 400 Hz HITS also markedly decreased after thrombolysis in these 2 patients. On the other hand, 4 patients who obtained no improvement of leaflet movement by thrombolysis had lower rates of less than 400 Hz HITS than did the 2 patients. Conclusions These results suggest that measurement of HITS counts is useful for detection of prosthetic valve obstruction, and that a frequency analysis of HITS may be valuable to clarify the cause of the obstructed prosthetic valves.

Platelet Activation During Carotid Endarterectomy And the Antiplatelet effect of Dextran 40

Objective: To determine changes in platelet activation during carotid endarterectomy (CEA) and the antiplatelet effect of Dextran 40. Methods: Prospective study in 40 patients undergoing CEA. Platelet activity was measured by whole blood flow cytometry and platelet aggregometry during CEA. The expression of P-selectin and the PAC-1 antigen were used as markers of platelet activation and aggregation. Patients received aspirin (75-300 mg) preoperatively and 5,000 units unfractionated heparin during surgery. High intensity transient signals (HITS) in the ipsilateral middle cerebral artery were monitored using transcranial Doppler (TCD) perioperatively. Results: P-Selectin expression increased after carotid clamping (P < 0.01) and clamp release (P < 0.05). There was higher expression of PAC-1 after carotid clamping (p < 0.05). Spontaneous and ADP-induced platelet aggregation increased after carotid clamping (P< 0.01) and release (P < 0.01). TCD monitoring showed an increased HITS count from preoperative levels, after clamp release (P < 0.01) and during recovery (P < 0.01). After the operation, patients with more than 50 HITS per 30 min were started on an infusion of dextran 40 (n = 6). P-selectin expression decreased 24 h after dextran 40 (P < 0.01). Conclusion: Significant platelet activation and aggregation occurs during CEA despite the current use of antiplatelet treatment. Dextran 40 had an antiplatelet effect after CEA providing further evidence that it may contribute to reducing thromboembolic complications.

Brain microembolic counts during extracorporeal circulation depend on aortic cannula position

Thrombofibrinous and gaseous brain microemboli are commonly observed during extracorporeal circulation in patients undergoing cardiac surgery. Recent studies showed a preference of microemboli to the left hemisphere. We hypothesized that placement of the aortic cannula tip within the aorta descendens rather than in the aorta ascendens as commonly used reduces the number of microemboli to the brain and also reduces the side preference. Of 60 patients undergoing elective coronary artery bypass grafting primarily randomized to either a short aortic cannula (aorta ascendens) or an elongated one (aorta descendens), 29 (16 and 13) patients had complete and technically perfect continuous intraoperative transcranial Doppler sonography with embolus detection bilaterally. The number of high-intensity transient signals (HITS) was 994 ± 2118 (mean ± SD) for the short cannula group and was significantly lower with the elongated cannula (223 ± 208; p < 0.02). HITS counts per min also differed significantly in favour of the aorta descendens group ( p < 0.02), but there was an overlap. Thus, elongated cannulas can reduce, but not prevent microembolism to the brain. The side-to-side ratio of microemboli revealed more events in the left hemisphere, but this was similar in both groups. This suggests that individual anatomic factors may be responsible for this hemodynamically-mediated effect. (E-mail:wolfgang.muellges@mail.uni-wuerzburg.de)

Is Cerebral Microembolism in Prosthetic Heart Valves Clinically Relevant?

P138 Background. High intensity transient signals (HITS) are frequently detected by TCD ultrasound in patients with mechanical PHV, but the published data about their clinical relevance is controversial. This study was undertaken to determine whether the presence of HITS is related to clinical and neuropsychological changes in patients with mechanical PHV. Methods. Patients with mechanical PHV had bilateral 30 minute TCD monitoring for microemboli (HITS) detection with and without oxygen (O 2 ) inhalation. Cognitive testing of patients included MMSE, DRS, and Microcog with two measures: General Cognitive Performance (GCP) and General Cognitive Functioning (GCF). Results. We studied 36 patients (20 females, mean age 58±13 years), 20 with mitral, 9 with aortic, and 7 with a combined PHV after median of 1.5 years of valve insertion. HITS were detected in 72% of patients. There was no difference in HITS frequency between 16 symptomatic and 20 asymptomatic patients. HITS counts were significantly decreased after O 2 inhalation (21.7±30.6 vs. 3.3±9.1 s, p=0.009 ). Table shows that no relationship exists between the number of HITS and cognitive scores of patients. Conclusion. Decreased frequency of HITS after oxygen inhalation confirms their gaseous origin. Lack of relationship between the HITS and cognitive performance suggests that cerebral microembolism in PHV is a benign epiphenomenon without any clinical neurological and neuropsychological sequalae.

Is Cerebral Microembolism in Prosthetic Heart Valves Clinically Relevant

P138 Background. High intensity transient signals (HITS) are frequently detected by TCD ultrasound in patients with mechanical PHV, but the published data about their clinical relevance is controversial. This study was undertaken to determine whether the presence of HITS is related to clinical and neuropsychological changes in patients with mechanical PHV. Methods. Patients with mechanical PHV had bilateral 30 minute TCD monitoring for microemboli (HITS) detection with and without oxygen (O 2 ) inhalation. Cognitive testing of patients included MMSE, DRS, and Microcog with two measures: General Cognitive Performance (GCP) and General Cognitive Functioning (GCF). Results. We studied 36 patients (20 females, mean age 58±13 years), 20 with mitral, 9 with aortic, and 7 with a combined PHV after median of 1.5 years of valve insertion. HITS were detected in 72% of patients. There was no difference in HITS frequency between 16 symptomatic and 20 asymptomatic patients. HITS counts were significantly decreased after O 2 inhalation (21.7±30.6 vs. 3.3±9.1 s, p=0.009 ). Table shows that no relationship exists between the number of HITS and cognitive scores of patients. Conclusion. Decreased frequency of HITS after oxygen inhalation confirms their gaseous origin. Lack of relationship between the HITS and cognitive performance suggests that cerebral microembolism in PHV is a benign epiphenomenon without any clinical neurological and neuropsychological sequalae.

High-Intensity Transient Signals (HITS) as a Parameter for Optimum Orientation of Mechanical Aortic Valves*

In previous studies [1,2], the impact of valve orientation on the hemodynamic performance of mechanical aortic valves has been demonstrated. This study investigates Turbulence (RNS values) and High Intensity Transient Signals (HITS) as a new and objective parameter for hemodynamics in different orientations of Medtronic Hall (MH) and St. Jude Medical (SJM) aortic valves. A rotation device carrying MH or SJM valves was implanted in 4 pigs. The device allowed valve rotation without reopening the aorta. In different orientations, turbulent shear stresses (RNS values) and HITS were measured. RNS and HITS changed for both valve designs in various orientations, with superior results for the MH in the hemodynamically best orientation. Downstream turbulence (RNS) and HITS varied into the same direction, but a one-to-one correlation was not observed. RNS and HITS vary with respect to valve orientation and design with superior results for the tilting disc valve. Both MH and SJM valves showed lower turbulence and HITS counts in their hemodynamically best orientations. HITS were related to downstream turbulence and the hemodynamic performance of the mechanical aortic valves.

High-intensity transient signals indicate a risk of cerebral embolism during left ventricular assist devices

Introduction. Cerebral embolism is still a serious complication during left ventricular assist devices (LVAD). We attempted to elucidate whether high-intensity transient signals (HITS) indicate a risk of cerebral embolism during LVAD in animal model. Methods. LVAD was established with XEMEX (Nippon ZEON) in 10 pigs. Animals were divided into two groups: heparin injection group and no heparin injection group. If HITS count exceeded 1 per 10 minutes, additional heparin was injected. HITS were detected by TC2020 with 2.0-MHz pulsed Doppler at the middle cerebral artery. Results. HITS were significantly reduced by additional heparin (8±3/h to 1±0.7/h, p<0.01). Middle cerebral artery occlusion occurred after rapidly increasing HITS. Issues. HITS can reflect thrombus formation in artificial devices. HITS can indicate a risk of cerebral embolism during LVAD. Monitoring of HITS is useful for preventing cerebral embolism during LVAD.

Association between large aortic arch atheromas and high-intensity transient signals in elderly stroke patients.

Aortic arch atheromas (AAs) have been shown to be a risk factor for ischemic stroke (IS) in the elderly because of their potential for cerebral embolization. However, the association between AAs and the presence of cerebral microemboli has not been clearly established. The aim of this study was to determine whether large AAs are associated with an increased frequency of high-intensity transient signals (HITS) in elderly patients with IS. We performed bitemporal simultaneous HITS monitoring of both middle cerebral arteries in 62 consecutive elderly patients with acute IS (mean age 72.5+/-8.8 years, 65% men). In 16 patients, one or both temporal windows were inadequate; therefore, the analysis of HITS was performed in the remaining 46 patients. All patients underwent omniplane transesophageal echocardiography (TEE), and they had no significant extracranial or intracranial artery disease and no cardiac prosthetic valves. Large AA was defined as > or = 4 mm in thickness. Complex AA was defined as ulcerated or mobile, regardless of plaque thickness. HITS monitoring was performed within 24 hours of TEE and analyzed by an experienced neurologist-sonographer blinded to TEE findings. A 9-dB threshold was chosen to discriminate HITS from background Doppler signal. The HITS counts in the left and in the right middle cerebral arteries were added and reported as a total number of HITS in 30 minutes. HITS were detected in 14 (78%) of 18 patients with large AAs versus 8 (29%) of 28 patients with no or small AAs (odds ratio [OR] 8.8, 95% CI 2.2 to 34.8; P=0. 001). The association was also present in 27 patients with no other cardiac embolic sources, such as atrial fibrillation, patent foramen ovale, spontaneous echo contrast, and thrombus (7 of 10 patients with large AAs versus 3 of 17 patients with small or no AA; OR 10.9, 95% CI 1.7 to 68.5; P=0.013). Complex AAs were associated with a higher frequency of HITS than were noncomplex AAs (6 of 6 patients with complex AAs versus 15 of 39 patients with noncomplex AAs; OR 2. 6, 95% CI 1.7 to 3.9; P=0.005). HITS are significantly associated with large AAs in elderly stroke patients. This observation may support the causal role of large AAs in IS.

Anticoagulant Agents Reduce High Intensity Transient Signals without Associated Sound during V-A ECMO.

Background and Purpose: With recent transcranial Doppler ultrasonography (TCD) techniques, high intensity transient signals (HITS) can be detected automatically. However, the significance of automatically detected HITS without associated sound is unclear. We attempted to determine whether HITS detected automatically during veno-arterial extracorporeal membrane oxygenation (V-A ECMO) reflect the state of blood coagulability. Methods : In an animal study, V-A ECMO was performed in 11 adult pigs by aortic and pulmonary cangulation using a roller pump and membrane oxygenator. HITS were counted automatically during bypass before and after administration of anticoagulants. In a clinical study of 6 patients with V-A ECMO after cardiac surgery, HITS were detected during and after removal of ECMO. Results: In the animal study, the majority of HITS recorded during V-A ECMO had no associated sound. The HITS count before and after ECMO was 0 and 49±35/10-min (n=11), respectively. The HITS count after administration of heparin was 4±4/10-min (n=5), and that after administration of argatroban was 7±7/10-min (n=6) . HITS counts were significantly reduced after administration of either anticoagulant (p<0.001) . In the clinical study, HITS were detected frequently during ECMO (158±99/15-min (n=6) ), but no HITS were detected after its removal. The HITS count rate was negatively correlated with activated clotting time. Conclusions: Automatically detected HITS without associated sound may reflect the degree of coagulation during V-A ECMO. Therefore, inaudible HITS may be a useful indicator of the level of anticoagulation during V-A ECMO.

ＴＣＤにおけるＨｉｇｈ Ｉｎｔｅｎｓｉｔｙ Ｔｒａｎｓｉｅｎｔ Ｓｉｇｎａｌ（ＨＩＴＳ）の臨床的意義について

High intensity transient signals (HITS) were detected in patients with a high risk of stroke. The signals were detected in the middle cerebral artery for 15-30 min by a TC2020 or Multi-Dop DX4. HITS were never detected in young healthy volunteers (n=20) . The HITS count in patients with cerebral infarction (16-20/30 min, n-42) was significantly higher than that in patients without cerebrovascular disease (0.5±0.7/30 min, n17) (p<0.01) . In the cerebral infarction group, the HITS count in patients without antiplatelet (20±29/30 min, n=20) was significantly higher than that in patients with antiplatelet (9±6/30 min, n=22) (p<0.01) . HITS were frequently detected in patients fitted with mechanical valves (St. Jude Medical valve) (14.3±34.5/15 min, n=51), and the count was significantly higher than that in open heart surgery patients without mechanical valves (0.05+0.08/15 min, n=11) (p<0.01) . In the mechanical valve replacement group, the HITS count in patients with cerebral infarction after surgery (88±66/30 min, n=43) was significantly higher than that in patients without a historyof stroke (7±7, n-8) (p<0.01) . The HITS intensity in the mechanical valve replacement group (15.1+4.3 dB, n=31) was significantly greater than that in the cerebral infarction group (10.8+1.1dB, n-32) (p<0.05) . In the mechanical valve replacement group, the HITS intensity in patients with post-surgical cerebral infarction (18±3.5 dB, n8) was significantly greater than that in patients without a history of stroke (14.5±5.6 dB, n=23) (p<0.0001) . During veno-arterial extracorporeal membrane oxygenation (V-A ECMO), HITS were frequently detected (124±60/15 min, n=6), and the HITS count was negatively correlated with activated coagulation time (ACT) . HITS may therefore reflect the presence of microemboli and indicate the risk of stroke or the state of blood coagulation.