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Ann Thorac Surg 2009;88:253-257. doi:10.1016/j.athoracsur.2009.01.058
© 2009 The Society of Thoracic Surgeons
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New Technology

The EmBlocker: Efficiency of a New Ultrasonic Embolic Protection Device Adjunctive to Heart Valve Surgery

Loes D. Sauren, Msc*, Mark la Meir, MD, Gil Bolotin, MD, PhD, Frederik H. van der Veen, PhD, John H. Heijmans, MD, PhD, Werner H. Mess, MD, PhD, Jos G. Maessen, MD, PhD

Departments of Cardiothoracic Surgery and Clinical Neurophysiology, Academic Hospital Maastricht, Maastricht, the Netherlands

Accepted for publication January 22, 2009.

* Address correspondence to Dr Sauren, Department of Cardiothoracic Surgery, Academic Hospital Maastricht, P. Debyelaan 25, Maastricht, 6229HX, the Netherlands (Email: l.sauren{at}ctc.unimaas.nl).


Dr Bolotin discloses that he has a financial relationship with Neurosonix Ltd.

 

   Abstract
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Purpose: Perioperative cerebral microemboli in cardiac surgery are associated with postoperative neurologic complications. The EmBlocker (Neurosonix Ltd, Rehovot, Israel), a newly developed device should be positioned against the ascending aorta, and it produces an ultrasonic force expected to divert microemboli away from the cerebral vasculature and reduce cerebral emboli.

Description: Twenty-one consecutive patients, undergoing a valve procedure, were enrolled into this nonrandomized pilot study. The EmBlocker (Neurosonix Ltd) was positioned in 11 consecutive patients and activated for 1 minute (1.5 W/cm2) during seven selected aortic manipulations and for 10 minutes (0.5 W/cm2) intermittently after cross-clamp removal. Transcranial Doppler-based quantification of microembolic signals was performed in all patients.

Evaluation: The use of the EmBlocker showed a significant overall reduction of the cerebral microembolic signals of 53%.

Conclusions: The use of the EmBlocker during valve surgeries is associated with a reduction of perioperative cerebral microembolic signals. This new technology holds the potential to lower the risk of postoperative neurologic complications.


   Technology
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Cardiac surgery is associated with the occurrence of intraoperative cerebral emboli, which are suggested to be correlated with the postoperative neurologic complications, such as cognitive decline, transient ischemic attack, and stroke [1, 2]. The EmBlocker (Neurosonix Ltd, Rehovot, Israel) is a novel, ultrasonic cerebral embolic protection transducer.


   Technique
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The EmBlocker (Neurosonix Ltd) should be positioned on the ascending aorta after sternotomy. The emitted ultrasonic forces deflect emboli in the aortic arch away from the innominate and left common carotid arteries downstream to the descending aorta. In this pilot study, the effectiveness of the EmBlocker was evaluated during valve surgery by means of detection of cerebral microembolic signals (MES).


   Clinical Experience
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Material and Methods
EmBlocker
The mechanism of the EmBlocker is based on the principle that an object with a different acoustic impedance partly absorbs ultrasound energy. This energy is the acoustic radiation force and is able to move an object or change the direction of its path [3–5]. By virtue of this acoustic radiation force, emboli flowing in the ascending aorta and aortic arch may be re-routed downstream to the descending aorta away from the innominate artery and left common carotid artery to avoid their passage into the cerebral vasculature. Because the difference in acoustic impedance between red and white blood cells and its surroundings is very small, the EmBlocker activations are unlikely to affect these cells.

The disposable transducer The EmBlocker (Neurosonix Ltd) has an oval shape (maximum, 15.8 mm x 25 mm x 14 mm) and has only transmitting capacity. No additional incision was required for the placement of the EmBlocker, and all surgical maneuvers were not affected by the presence of the EmBlocker. A biocompatible dome filled with saline is placed over the transducer for cooling and also to prevent the presence of air between the transducer and the tissue (Fig 1). A temperature sensor monitors the temperature of the transducer, and this will shut down the activation when the temperature reaches a level that correlates with a tissue temperature of 43°C. The EmBlocker was kept in position using an ESTECH stabilizer (ESTECH, San Ramon, CA) as shown in Figures 1 and 2.Go


Figure 1
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  		Fig 1. EmBlocker connected to ESTECH arm.

 

Figure 2
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  		Fig 2. Schematic view of the EmBlocker placement. Locations of (A) the cardioplegia needle, (B) the cross clamp, and (C) the aortic cannula.

 
Due to different acoustical properties of gaseous and solid emboli, gaseous emboli experience a higher radiation force than solid emboli. Thus, lower energy levels can be applied when gaseous emboli are to be excepted and result in an equivalent diverting effect. Therefore two intensity levels of the 2.2-Mhz EmBlocker were determined; for the air removal phase, a level of 0.5 W/cm2 was determined, and for the aortic interventions, a level of 1.5 W/cm2. Both intensity levels stayed within temperature safety ranges of all underlying tissues in animals experiments. For efficacy purposes, 0.5W/cm2 and 1.5W/cm2 energy levels proved to be efficient during injections of a mixture of air and saline (1:9) and injections of polystyrene particles (500 µm to 750 µm), respectively [5].

The EmBlocker was activated by a trained physician at selected manipulations for 60 seconds: cannulation, cardioplegia needle placement, bypass on, cross-clamp placement, cross-clamp removal, bypass off, and de-cannulation, and for 10 minutes, the air removal phase (10 minutes after cross-clamp removal).

Transcranial doppler
In both groups, transcranial Doppler (TCD) (Embodop DWL, Singen, Germany) examination was performed by bilateral insonation of the middle cerebral arteries. The moments of EmBlocker activation (or imitation activations in the control group) were marked and analyzed offline. Two blinded physicians manually, independently counted, according to the established consensus criteria [6]. All interventions were divided in 200 ms segments. Each segment was categorized for the presence or absence of a MES by each observer. Only when an agreement of both observers was achieved, it was considered a MES.

The nature (gaseous or solid) and size of cerebral emboli is currently not possible to determine with the use of transcranial Doppler [7].

Study design
This single-center nonrandomized, blinded trial was conducted from February 2006 until August 2007. A total of 21 patients were enrolled; 10 consecutive patients in the control group and 11 consecutive patients in the EmBlocker group.

Patient selection
Eligible patients for this study were men and women between the age of 50 and 75 years undergoing a valve procedure with or without coronary artery bypass grafting. The exclusion criteria for this study were a carotid atheroma higher than grade II, protruding ascending aortic atheroma (atheroma grade > III), previous cardiac operation, uncontrolled diabetes (ie, fasting glucose > 250 mg/dL), risk for surgery, Euroscore > 8, left ventricular ejection fraction < 40% (35% for aortic stenosis), history of stroke, abnormal clotting activation with a prothrombin time > 60%, and partial thromboplastin time > 2 than the normal, emergency procedure, and life-threatening disease other than cardiac.

Study procedure
The TCD transducers were positioned on the head just after placement of the central venous pressure line. In the EmBlocker group, the EmBlocker was placed on the ascending aorta just proximal of the origin of the innominate artery after sternotomy (Fig 2). EmBlocker activations and de-activations were marked on the TCD recording. No EmBlocker was placed in the control group, but the console of the EmBlocker was present to imitate EmBlocker activations. Each manipulation resulted in 1 minute of TCD recording, except the removal of air phase, which was a 1- minute TCD recording.

EmBlocker procedure
In 11 patients the EmBlocker transducer was positioned as shown in Figure 2. Placement of the EmBlocker did not have any impact on the valve procedure, and it was performed according to the standard protocol.

The EmBlocker was activated for 60 seconds (intensity, 1.5 W/cm2) during the selected aortic manipulations. The start of activation of the EmBlocker and applying a marker in the TCD recording was synchronized with the surgeon and perfusionist. In the air removal phase the EmBlocker was activated for 90 seconds and switched off for 30 seconds (intensity, 0.5 W/cm2). This sequence was repeated successively 5 times. Immediately after de-cannulation, the EmBlocker was removed.

Statistical analysis
Statistical comparisons (Mann-Whitney U signed-rank test; two-tailed comparisons) were made between the number of detected cerebral MES during the selected interventions in the control group and in the EmBlocker group. A p value < 0.05 was considered statistically significant.

The investigation was approved by the Human Research and Ethics Committees of the Academic Hospital Maastricht in the Netherlands. All participating patients gave written informed consent


   Results
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One patient from the EmBlocker group was excluded from the efficacy study due to technical problems with the EmBlocker device. The temperature algorithm did terminate all the activations within 2 seconds, which appeared postoperatively, caused by a leaking biocompatible dome placed over the EmBlocker.

Table 1 represents the patient's characteristics of both groups (n = 20). Table 2 represents the number of cerebral MES in the left and right middle cerebral arteries in the control and EmBlocker group during the selected manipulations.


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  		Table 1 Patient Demographics and Intraoperative Characteristics
 

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  		Table 2 The Number of Cerebral Microembolic Signals Measured in the Left and Right Middle Cerebral Artery in the Control Group and in the EmBlocker Group in All Selected Manipulations
 
Efficacy
In all selected manipulations, the number of cerebral MES was lower in the EmBlocker group compared with the control group. A significant reduction of 63% of cerebral MES during the selected aortic manipulations was accomplished by use of the EmBlocker. Due to activation of the EmBlocker, the overall number of cerebral MES was significantly reduced by 53%. No significant differences were found between the number of MES detected in the left and right middle cerebral artery in both groups.


   Comment
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This study has demonstrated that the use of the EmBlocker is associated with a significant perioperative reduction in cerebral MES. No difference in operation time, no difference in intensive care unit time, and no difference in creatinine levels were caused to document between the control and EmBlocker group.

Efficacy
The lower number of cerebral MES demonstrated in the air removal phase of the EmBlocker group was not statistically significant, which could be due to the high standard deviation and the emboli counting method. The high standard deviation in the number of cerebral MES in the air removal phase in both groups could be originated from the variation in the time period between release of the cross clamp and de-cannulation. This time period difference could cause a variation of dissolving capability of the remaining air in the heart, which may contribute to a difference in number of MES entering the systemic circulation and explain the high standard deviation in the air removal phase. The cerebral MES counting method chosen in this study is a highly reproducible and reliable method, but the choice for segments of 200 ms restricts the counted number of MES in 1 second to 5 MES. A new developed algorithm could not be implemented yet, due to a maximum recording period of 3 seconds [8]. Underestimation of the counted MES will occur when the density of emboli is high, and this could underestimate the difference between the number of cerebral MES between both groups in the air removal phase.

No significant differences were found in the number of cerebral MES measured in the left and right middle cerebral artery. A slightly higher reduction of MES was demonstrated in the right middle cerebral artery (54%) versus the left middle cerebral artery (49%) by the use of the EmBlocker, which could be an indication that some microemboli are diverted away from the innominate artery, which will end up in the left common carotid artery.

Limitations
In this preliminary study a surrogate marker (number of cerebral MES) was used to examine the efficacy of the EmBlocker, but no brain magnetic resonance imaging has been performed to examine the cerebral damage of the cerebral emboli.

No monitoring device is available to quantify the microemboli in the ascending or descending aorta. Therefore, no quantification of the generated or diverted emboli could be made in this study.

Although the physicians are blinded for the TCD data, the surgeons were not blinded due to no EmBlocker placements in the control group. The activation (or imitation activation) was in both groups synchronized with the surgeon to limit the bias introduced by the nonblinded operator.

Summary
In this pilot, clinical study, the activation of the Emblocker during selected interventions that are prone for embolization (ie, cannulation, cardioplegia needle placement, bypass on, cross-clamp placement, cross-clamp removal, 10 minutes after cross-clamp removal [the air removal phase] bypass off, and de-cannulation) resulted in a significant reduction of cerebral MES averaging 53%. Cerebral MES can be considered a surrogate marker for postoperative neurologic complications. Therefore, these results suggest that the EmBlocker technology holds the potential to diminish the risk of the postoperative neurologic complications.


   Disclosures and Freedom of Investigation
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The clinical trial agreement is between the Academic Hospital Maastricht and Neurosonix Ltd, whereby Neurosonix has the rights to the EmBlocker system and desired the Academic Hospital Maastricht and the principle investigator (JGM) to conduct the clinical study. The authors state that they had full control of the design of the study, methods used, outcome measurements, analysis of data, and production of the written report. Bolotin was a member of the advising board of Neurosonix in 2007, and he was also a consultant for Neurosonix in 2007 with payment in stock options of the company.


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Disclaimer The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.


   References
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  1. Pugsley W, Klinger L, Paschalis C, et al. The impact of microemboli during cardiopulmonary bypass on neuropsychological functioning Stroke 1994;25:1393-1399.[Abstract/Free Full Text]
  2. Abu-Omar Y, Cifelli A, Matthews PM, Taggart DP. The role of microembolisation in cerebral injury as defined by functional magnetic resonance imaging Eur J Cardiothorac Surg 2004;26:586-591.[Abstract/Free Full Text]
  3. Palanchon P, Tortoli P, Bouakaz A, Versluis M, de Jong N. Optical observations of acoustical radiation force effects on individual air bubbles IEEE Trans Ultrason Ferroelectr Freq Control 2005;52:104-110.[Medline]
  4. Michishita K, Hasegawa H, Kanai H. Ultrasonic measurement of minute displacement of object cyclically actuated by acoustic radiation force Jpn J Appl Phys 2003;42:4608-4612.
  5. Sauren LD, la Meir M, Palmen M, et al. New ultrasonic radiation reduces cerebral emboli during extracorporeal circulation Eur J Cardiothorac Surg 2007;32:274-280.[Abstract/Free Full Text]
  6. Ringelstein EB, Droste DW, Babikian VL, et al. Consensus on microembolus detection by TCD. International Consensus Group on Microembolus Detection. Stroke 1998;29:725-729.[Abstract/Free Full Text]
  7. Evans DH. Embolus differentiation using multifrequency transcranial Doppler Stroke 2006;37:1641.[Free Full Text]
  8. Lipperts MG, Sauren LD, Maessen JG, Hoeks AP, Mess WH. Quantification of embolic showers using radio-frequency based TCD analysis Ultrasound Med Biol 2009;35:395-402.[Medline]



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