Transcranial Doppler detection of microemboli in prosthetic heart valve patients: dependency upon valve type

ASNM and ASN joint guidelines for transcranial Doppler ultrasonic monitoring: An update

Today, it seems prudent to reconsider how ultrasound technology can be used for providing intraoperative neurophysiologic monitoring that will result in better patient outcomes and decreased length and cost of hospitalization. An extensive and rapidly growing literature suggests that the essential hemodynamic information provided by transcranial Doppler (TCD) ultrasonography neuromonitoring (TCDNM) would provide effective monitoring modality for improving outcomes after different types of vascular, neurosurgical, orthopedic, cardiovascular, and cardiothoracic surgeries and some endovascular interventional or diagnostic procedures, like cardiac catheterization or cerebral angiography. Understanding, avoiding, and preventing peri- or postoperative complications, including neurological deficits following abovementioned surgeries, endovascular intervention, or diagnostic procedures, represents an area of great public and economic benefit for society, especially considering the aging population. The American Society of Neurophysiologic Monitoring and American Society of Neuroimaging Guidelines Committees formed a joint task force and developed updated guidelines to assist in the use of TCDNM in the surgical and intensive care settings. Specifically, these guidelines define (1) the objectives of TCD monitoring; (2) the responsibilities and behaviors of the neurosonographer during monitoring; (3) instrumentation and acquisition parameters; (4) safety considerations; (5) contemporary rationale for TCDNM; (6) TCDNM perspectives; and (7) major recommendations.

A Mathematical Representation of the Wheatley Heart Valve

Starting from a hand-drawn contour plot, this note develops a set of intersecting and contiguous circles whose perimeter, upon extending appropriately to three dimensions, can be seen to be a natural mathematical representation of the Wheatley heart valve.

Association of homocysteine and smoking with cerebral microemboli in patients with mechanical heart valves: a transcranial Doppler study

Objectives

Microembolic signals (MES) on transcranial Doppler (TCD) predict stroke and cognitive decline. Plasma levels of total homocysteine (tHcy), a prothrombotic factor, are higher in patients with microemboli in carotid stenosis and in patients with paradoxical embolism. In this study we assessed the association between the level of tHcy and the number of MES in patients with mechanical heart valves (MHVs).

Methods

TCD monitoring was performed to detect MES before and after breathing 100% oxygen and repeated every 2-4 weeks up to six times.

Results

Twenty-five patients with MHVs (mean age: 63.60±10.15 years) participated in this study; 15 were men (66.47±7.25 years) and 10 were women (59.30±12.60 years). In total, there were 126 study visits. In multiple regression, higher tHcy was associated with more MES in both preoxygenation (OR 1.34 (95% CI 1.07 to 1.68, P=0.009)) and postoxygenation (OR 1.40 (95% CI 1.07 to 1.83, P=0.01)) phases. Current smoking and the length of time between the operation and monitoring also correlated with a higher number of MES before and after breathing oxygen, particularly in women.

Conclusions

Higher tHcy and smoking were associated with a higher MES count in both preoxygenation and postoxygenation phases. Because smoking can be stopped and hyperhomocysteinaemia is treatable, these are clinically important findings.

Microemboli in aortic valve replacement

Microembolic signals (MES) can be detected in many recipients of mechanical aortic valve prostheses by transcranial Doppler ultrasound. The nature and etiology of these MES have remained unclear for a long time. The solid and gaseous nature of MES are discussed, as well as whether or not MES may reflect artifacts. Recently, the gaseous nature of these MES has been widely established. To understand the physics of bubble formation related to mechanical heart valve prostheses, it is necessary to discuss the different types of cavitation occurring at the prostheses and the conditions leading to the degassing of blood. We describe the history of transcranial Doppler ultrasound-techniques and the current techniques in the measurement of these signals. Furthermore, the possible clinical impact of MES, as well as strategies for the design of new prostheses and surgical alternatives to diminish their load are discussed.

Research approaches for studying flow-induced thromboembolic complications in blood recirculating devices

The advent of implantable blood recirculating devices has provided life-saving solutions to patients with severe cardiovascular diseases. Recently it has been reported that ventricular assist devices are superior to drug therapy. The implantable total artificial heart is showing promise as a potential solution to the chronic shortage of available heart transplants. Prosthetic heart valves are routinely used for replacing diseased heart valves. However, all of these devices share a common problem--significant complications such as hemolysis and thromboembolism often arise after their implantation. Elevated flow stresses that are present in the nonphysiologic geometries of blood recirculating devices, enhance their propensity to initiate thromboembolism by chronically activating the blood platelets. This, rather than hemolysis, appears to be the salient aspect of blood trauma in devices. Limitations in characterizing and controlling relevant aspects of the flow-induced mechanical stimuli and the platelet response, hampers our ability to achieve design optimization for these devices. The main objective of this article is to describe state-of-the-art numerical, experimental, and in vivo tools, that facilitate elucidation of flow-induced mechanisms leading to thromboembolism in prosthetic devices. Such techniques are giving rise to an accountable model for flow-induced thrombogenicity, and to a methodology that has the potential to transform current device design and testing practices. It might lead to substantial time and cost savings during the research and development phase, and has the potential to reduce the risks that patients implanted with these devices face, lower the ensuing healthcare costs, and offer viable long-term solutions for these patients.

Doppler ultrasonography-aided early diagnosis of venous thromboembolism after total knee arthroplasty

OBJECTIVES

Postoperative deep venous thrombosis (DVT) is usually asymptomatic but can result in a fatal pulmonary embolism (PE). To assess the ability of transcranial Doppler (TCD) ultrasound apparatus to detect venous emboli in patients who had undergone total knee arthroplasty (TKA).

METHODS

Forty-eight patients undergoing TKA were examined postoperatively by using compression ultrasonography, computed tomographic angiography, and TCD ultrasonography that detected high-intensity transient signals (HITS) in femoral veins. An original scoring system based on both the number of HITS and the locations of DVT was tested for its accuracy in predicting PE development.

RESULTS

Twenty-three of the 48 patients had DVT postoperatively, and 8 had an asymptomatic PE. The sensitivity and specificity of the HITS assessment alone in identifying PE development were 75% and 92.5%, respectively. The scoring system, however, had a sensitivity of 100% and a specificity of 85% and the area under the receiver operating characteristic (ROC) curve (AUC) was 0.96.

CONCLUSIONS

Application of a scoring system based on the detection of both DVT and HITS may be an effective and efficient method of screening for PE after knee arthroplasty.

Solid and gaseous cerebral microembolization after biologic and mechanical aortic valve replacement: investigation with multirange and multifrequency transcranial Doppler ultrasound

OBJECTIVE

Cerebral microembolization is a well-recognized phenomenon after cardiac valve replacement, but the relative proportion of solid and gaseous emboli is uncertain. Particulate microemboli are thought to be the most damaging. With the use of multifrequency transcranial Doppler ultrasound, we compared the number and nature of microemboli in recipients of biologic and mechanical aortic valve prostheses.

METHODS

The middle cerebral arteries of 60 patients were monitored bilaterally with a new-generation transcranial Doppler ultrasound (Embo-Dop, DWL Elektronische Systeme GmbH, Singen, Germany) that rejects artefacts online and automatically discriminates between solid and gaseous microemboli. All recordings were performed during a 30-minute period 1 day before and at a mean of 5 days and 3 months after isolated aortic valve replacement with a biologic (30, group B) or mechanical (30, group M) prosthesis.

RESULTS

The patients in group B were older, with a mean age of 70.6 +/- 9.7 years versus 55.4 +/- 9.4 years (P < .005) in the patients in group M. Biologic prosthesis recipients were all taking aspirin (no warfarin); patients with mechanical valves were well anticoagulated with warfarin both 5 days and 3 months after surgery. None of the patients had solid microemboli preoperatively. Five days postoperatively, the absolute number of cerebral microemboli was 145 and 594 for total microemboli (P = .001) and 41 and 182 for solid microemboli (P = .002) in groups B and M, respectively. At 3 months, the absolute number was 65 and 608 for total microemboli (P < .001) and 10 and 188 for solid microemboli (P < .001) in groups B and M, respectively. Solid microemboli accounted for 16% of the total microembolic load in group B compared with 31% in group M (P = .05) at 3 months.

CONCLUSIONS

Solid cerebral microemboli represent approximately one third of the total cerebral microembolic load after mechanical aortic valve replacement and are detectable in the majority of such patients both 5 days and 3 months after surgery. The neurofunctional consequences of this phenomenon should be carefully assessed.

Occurrence and clinical impact of microembolic signals during or after cardiosurgical procedures

BACKGROUND AND PURPOSE

Microembolic signals (MESs) are detectable within the transcranial Doppler frequency spectrum downstream from vascular atherothrombotic or cardiothrombotic lesions. A frequent occurrence of MESs has also been shown during bypass surgery or after mechanical valve implantation. We sought to compile the knowledge on MES prevalence, the clinical impact of these cardiogenic MESs, and microemboli composition.

SUMMARY OF REVIEW

We performed a systematic MEDLINE search and summarized the currently available literature about MESs during or after cardiosurgical procedures for this state-of-the-art report.

CONCLUSIONS

The nature of cardiogenic MESs is heterogeneous, and their prevalence is highly variable, reflecting their different origin from a broad spectrum of cardiosurgical conditions. The occurrence and number of MESs during cardiac catheterization and percutaneous coronary angioplasty seem to have a clinical impact but need to be explored further. In patients with prosthetic heart valves, in those with left ventricular assist devices, and during cardiac surgery, the occurrence of MESs has an important clinical impact, and MES monitoring has proven its reliability. Although the data encourage intensifying MES detection in cardiac disorders, their heterogeneous nature does not yet allow the use of MESs as a general surrogate parameter for neuronal damage or cardial thromboembolic risk.

Detection of venous emboli using Doppler ultrasound

OBJECTIVES

To detect emboli in the venous system using a Doppler ultrasound device with embolism detecting software.

METHODS

Pulmonary embolism (PE) was induced by injecting thrombus through the iliac vein of castrated swine under general anaesthesia. Data recorded from the Doppler system were analysed for high intensity transient signals (HITS) using receiver operating characteristic curves. Four different thrombi (5 or 10mm long and 3 or 5mm in diameter) were then injected to assess the quantitative analysis.

RESULTS

Thrombus could be detected in the venous system by the Doppler ultrasound device with an embolism detecting function. Appropriate confidence level was 60%. If thrombus were assumed to travel at the maximum flow rate (30 cm/s) in the inferior vena cava, the estimated embolism size was 10.4 S.D. 2.8mm for 3mm and 10.8 S.D. 4.9 mm for 5mm, both of which were close to 10mm.

CONCLUSION

Thrombi could be detected as high intensity transient signals in the venous system. The appropriate confidence level was 60%. The size of emboli can be estimated if they are more than 3mm in diameter when the venous flow rate is 30 cm/s or less. Our results suggest that it may be possible to detect emboli in the subclavian vein, axillary vein or inferior vena cava in clinical cases.

Spontaneous echocardiographic microbubbles associated with prosthetic mitral valves: mechanistic insights from thrombolytic treatment results

The purpose of this study was to determine the prevalence of microbubbles (MBs) in patients with prosthetic mitral valves (PMVs). The clinical and echocardiographic predictors of MB were investigated. We also analyzed the temporal relation between MBs and the thrombolytic treatment of thrombotic PMV dysfunction. The study material comprised 307 transesophageal echocardiography examinations in 279 patients (170 women and 109 men with a mean age of 37.9 +/- 13.3 years) with PMV. The PMV was mechanical in 245 patients (tilting-disk valves in 129, and bileaflet aortic valves in 116) and bioprosthetic mitral valves in 34 patients. Twenty-eight sessions of thrombolytic treatment were performed because of the obstructive (n = 18) and nonobstructive (n = 10) thrombi involving the PMV. No MBs were seen in any of the bioprosthetic valves. The MBs were present in 128 of 227 (56.4%) PMV without obstruction compared with only 1 of 18 (5.5%) valves with thrombotic obstruction (P <.0001). The MB were documented in 75.4% of the normal bileaflet valves compared with 38.5% of the tilting-disk valves (P <.0001). The MB intensity score was also significantly higher in the bileaflet valves (2.0 +/- 0.8 vs 0.7 +/- 0.7, P <.05). The incidence of MBs increased from 5.5% to 68.7% after successful thrombolysis in patients with obstructive PMV thrombi (P <.001). There were no other predictors of MBs in this series. The passage of MBs in the aortic root was not documented in any instances. We conclude that MBs are normal echocardiographic findings depending on the type and function of the mechanical PMVs.

The nature of microemboli in patients with artificial heart valves

Cognitive decline has recently been found to be associated with microemboli in cerebral vessels in patients with artificial heart valves. The authors sought to determine the nature of such microemboli, that is, whether they are gaseous or solid, by comparing their characteristics to those of artificially generated air emboli in patients with patent foramen ovale (PFO). Three hundred and forty-eight microemboli were recorded in 11 patients with artificial valves (all taking coumadin), and 86 microemboli were recorded in response to intravenous injection of saline agitated with air in 8 PFO patients. No difference in intensity, duration, or relative velocity of microemboli was found between groups. The authors conclude that microemboli generated from artificial heart valves are generally gaseous and not solid.

[Turbulence and high intensity transient signals (HITS) as a parameter for optimum orientation of mechanical heart valves]

BACKGROUND

In previous studies, 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 various orientations of Medtronic Hall (MH) and St. Jude Medical (SJM) aortic valves.

METHODS

Rotation devices carrying a MH or SJM valve were implanted into four pigs. The device allowed valve rotation without reopening the aorta. In various orientations, turbulent shear stresses (RNS values) and HITS were measured.

RESULTS

RNS and HITS changed for both valve designs in the different orientations, with superior results for the MH in the hemodynamically best orientation. Downstream turbulence (RNS) and HITS varied in the same direction, but a one to one correlation was not observed.

CONCLUSIONS

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.

Blood biocompatibility analysis in the setting of ventricular assist devices

Ventricular assist devices (VADs) are increasingly applied to support patients with advanced cardiac failure. While the benefit of VADs in supporting this patient group is clear, substantial morbidity and mortality occur during the VAD implant period due to thromboembolic and infective complications. Efforts at the University of Pittsburgh aimed at evaluating the blood biocompatibility of VADs in the clinical, animal, and in vitro setting over the past decade are summarized. Emphasis is placed on understanding the mechanisms of thrombosis and thromboembolism associated with these devices.

Doppler microembolic signals in patients with two different types of bileaflet valves

OBJECTIVES

This study was performed to evaluate the prevalence and counts of Doppler microembolic signals in patients with St Jude Medical valves (St Jude Medical, Inc, St Paul, Minn) and patients with ATS valves (ATS Medical, Inc, Minneapolis, Minn) and their relation to clinical parameters.

METHODS

A total of 179 outpatients of the department of cardiothoracic surgery were examined. They included 98 men and 81 women, aged 61 +/- 11 years, with ATS (n = 91) or St Jude Medical (n = 88) valves in the aortic (n = 110), mitral (n = 39), or both positions (n = 30). Neurologic examination was followed by transcranial Doppler monitoring for microembolic signals. Monitoring was performed bilaterally over the middle cerebral arteries for 1 hour per session.

RESULTS

Microembolic signal counts and prevalence were significantly higher in patients with St Jude Medical as compared with ATS valves. Valve type and presence of diabetes mellitus were the only predictors of microembolic signal prevalence on multivariate analysis. No influence of microembolic signals on cerebral embolic complications was established. Additionally, patients with a postoperative history of cerebral embolic complications did not have a higher number of microembolic signals than remaining patients. Interobserver variability was satisfactory.

CONCLUSIONS

Patients with St Jude Medical valves were shown to have significantly higher microembolic signal counts than patients with ATS valves. However, our results suggest that microembolic signal counts cannot be used to predict cerebral embolic complications. Their relation to neuropsychologic deficits remains to be evaluated.

Downstream turbulence and high intensity transient signals (HITS) following aortic valve replacement with Medtronic Hall or St. Jude Medical valve substitutes

OBJECTIVE

High intensity transient signals (HITS) representing microembolization to the brain have been found to contribute to cognitive impairment and psychoneurological dysfunction in patients carrying a mechanical aortic valve. It is unknown, whether HITS represent gaseous or solid emboli. This animal study evaluates the impact of valve orientation on HITS for two different mechanical valves with both valves implanted in their best and worst orientation, which has been defined in previous studies with respect to downstream turbulence.

METHODS

In four pigs a rotation device carrying either a Medtronic Hall (MH) or St. Jude Medical (SJM) valve size 23 mm was implanted. The device allowed rotation of the implanted valves without reopening of the aorta. Approximately 30 min after weaning from extracorporeal circulation, a Doppler probe was placed on both common carotid arteries. In different orientations of the implanted valves (best and worst position), HITS were detected by the Doppler probe and recorded for ten min by a transcranial Doppler sonography device (Medilab Inc., Estenfeld, Germany).

RESULTS

HITS showed significant change with rotation for both valve designs. With the major orifice of the MH oriented towards the non-coronary leaflet (optimum position) very low HITS-counts (0.8-1.7/min) were observed. In the worst orientation HITS rose to 43-66/min. For the SJM the HITS count in the optimum position was 23.4-24/min and in the worst orientation 38-48/min.

CONCLUSIONS

Valve orientation has an important impact on microembolization to the brain. In the optimum orientation (large orifice facing the non-coronary leaflet) the Medtronic Hall valve showed negligible incidence of HITS. The St. Jude Medical bileaflet valve showed less variation but demonstrated significant HITS counts at any orientation. As the MH in the worst position shows significantly higher turbulent stresses than the SJM but no higher incidence of HITS, a strong correlation between turbulence and HITS was not demonstrated by this study.

Measurement of hemostatic indexes in conjunction with transcranial doppler sonography in patients with ventricular assist devices

BACKGROUND AND PURPOSE

Clinical thromboembolism (TE) remains an impediment to the chronic application of ventricular assist devices (VADs). Microembolic signals (MES) have been detected by transcranial Doppler ultrasound (TCD) in patients with VADs, although their origin and relation to TE remain undefined. We have investigated the hypothesis that hemostatic alterations are related to MES and that MES are associated with TE in a group of 27 VAD patients.

METHODS

Indexes of coagulation, fibrinolysis, and cellular activation and aggregation were measured before and during the VAD implantation period in conjunction with TCD. Groups were defined on the basis of presence of MES, degree of MES showering, and incidence of TE.

RESULTS

MES were observed in 67 (58%) of 115 of individual postoperative TCD measurements and in 21 (78%) of 27 patients. Of patients with TE, 10 (83%) of 12 had detectable MES compared with 11 (73%) of 15 patients without TE (P=0.66). MES were significantly associated with elevated thrombin generation during the implantation period, as reflected by plasma prothrombin fragment F1.2. Elevations in indexes of coagulation, platelet activation, and fibrinolysis relative to normal control subjects were found for patients with VADs with and without detected MES.

CONCLUSIONS

Although no significant relation between MES and TE in VAD patients was found, the data support the hypothesis that MES are related to increased hemostatic activity in this patient group despite aggressive anticoagulant therapy.

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

BACKGROUND

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).

METHODS

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).

RESULTS

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.

CONCLUSIONS

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.

Influence of oxygen ventilation on Doppler microemboli signals in patients with artificial heart valves

BACKGROUND AND PURPOSE

The purpose of this study was to evaluate the influence of inhalation of 100% oxygen on microembolic signal (MES) counts in patients with artificial cardiac valves.

METHODS

A total of 134 outpatients were examined. Transcranial Doppler baseline monitoring (45-minute duration) was performed in all patients under resting conditions. The first 30 patients subsequently underwent transcranial Doppler monitoring for at least 20 minutes under noninvasive positive pressure ventilation with 100% oxygen and for an additional 30 minutes under resting conditions. The same protocol was applied to all following patients with a baseline MES count > or = 10, while the examination was discontinued in the remaining patients.

RESULTS

Baseline MES counts < 10, which remained unchanged during oxygen inhalation and the subsequent resting period, were observed in 26 of 30 initial patients. A total of 46 patients with MES counts > or = 10 were identified. Oxygen application was feasible in 43 patients. An exponential MES decrease was noted in 42 patients during oxygen inhalation (statistically significant in 38 patients), followed by a subsequent increase in 38 of 43 patients (statistically significant in 25 patients) under resting conditions.

CONCLUSIONS

The exponential reduction of MES counts observed in this study corresponds to blood denitrogenation, thus strongly arguing for nitrogen bubbles as underlying embolic material in prosthetic valve carriers.

Circulating microemboli in patients after aortic valve replacement with pulmonary autografts and mechanical valve prostheses

BACKGROUND

The pulmonary autograft procedure (Ross) is now considered the gold standard for aortic valve replacement. One of its advantages is the freedom from macroemboli without anticoagulation. Whether this holds true for circulating microemboli, detectable as high-intensity transient Doppler signals (HITS), has not yet been verified.

METHODS AND RESULTS

We investigated 8 patients (2 women, 6 men; mean age, 50.6+/-17.9 years) after the Ross procedure, 9 patients (3 women, 6 men; mean age, 67.2+/-9.46 years) after aortic valve replacement with a mechanical valve prosthesis, and 12 young healthy volunteers by unilateral 1-hour recording of the middle cerebral artery on digital audio tape. Patients with extracranial carotid artery disease were excluded by color duplex sonography. During the off-line evaluation, the investigator was not aware of any patient details. No HITS were detected in healthy volunteers (95% confidence interval [CI], 0% to 26.46%). After the Ross procedure, 1 patient had 11 and 1 patient had 1 HITS (95% CI, 3.19% to 65.09%). All recipients of mechanical valves had HITS, ranging from 2 to 84 per hour (95% CI, 66.7% to 100%). Significantly more recipients of mechanical valves exhibited HITS than recipients of pulmonary autografts (P<.05) or control subjects (P<.05).

CONCLUSIONS

In contrast to mechanical valves, pulmonary autografts are seldom the source of microemboli, confirming the pulmonary autograft as the superior substitute for aortic valve replacement.