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Eur J Cardiothorac Surg 2007;32:274-280. doi:10.1016/j.ejcts.2007.02.033
Copyright © 2007, European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved

New ultrasonic radiation reduces cerebral emboli during extracorporeal circulation

^a Cardiovascular Research Institute Maastricht, Department of Cardiothoracic Surgery, Academic Hospital Maastricht, The Netherlands
^b Cardiovascular Research Institute Maastricht, Department of Clinical Neurophysiology, Academic Hospital Maastricht, The Netherlands

Received 11 October 2006; received in revised form 15 February 2007; accepted 16 February 2007.

^_* Corresponding author. Address: Department of Cardiothoracic Surgery, Academic Hospital Maastricht, P. Debyelaan 25, 6229HX Maastricht, The Netherlands. Tel.: +31 43 3875070; fax: +31 43 3875993.

Objective: Cardiac surgery is associated with intraoperative cerebral emboli, which can result in postoperative neurological complications. A new ultrasonic transducer (EmBlocker^TM) can be positioned on the ascending aorta and activation of the EmBlocker^TM is expected to divert emboli to the descending aorta, thereby decreasing emboli in the cerebral arteries. In this preliminary animal study, safety and efficiency of this technology were examined. Methods: In 14 pigs (±70 kg), a median sternotomy was performed and the EmBlocker^TM was positioned on the aorta ascendens at the level of the bifurcation of the aorta and the innominate artery. In one animal temperature measurements were performed. During these measurements, the EmBlocker^TM was activated for four periods of 120 s of high power (1.5 W/cm²) and for four periods of 600 s of low power (0.5 W/cm²). In the safety study (n = 6), the EmBlocker^TM was activated twice the expected clinical duration (eight periods of 120 s of high power and, subsequently, one period of 20 min of low power). Tissue samples (control and sonicated) were collected after 1 week for histopathological evaluation (aorta, trachea, esophagus, vagus nerves). In the efficiency study (n = 7), extracorporeal circulation was installed. Emboli (air and solid (1200, size 500 µm–750 µm)) were introduced in the proximal ascending aorta and the EmBlocker^TM was alternately activated with high power for solid emboli injections and low power for air emboli injections. Transcranial Doppler (TCD) was used to analyse middle cerebral artery blood flow for occurrence of embolic signals, which were manually counted offline. Results: Histopathology revealed no difference between control and sonicated tissue. There is a rise in temperature during EmBlocker^TM activation, but in all measured tissues it was within limits; less then 42 °C for 2 min in the aorta wall directly under the EmBlocker^TM. Use of the EmBlocker^TM significantly reduced emboli in the cerebral arteries in an animal model; air emboli with 65% (left) and 69% (right) and solid emboli with 49% (left) and 50% (right). Conclusions: The new ultrasound technology can safely be applied and is capable of reducing emboli in the cerebral arteries during extracorporeal circulation. Use of the EmBlocker^TM in cardiac surgery bears the potential to lower the risk of postoperative neurological complications. Clinical feasibility studies are in progress.

Key Words: Cerebral emboli • Transcranial Doppler • Cardiac surgery • Ultrasound