Ultrasound has potential in stroke treatment

The EKOS Micro-Infusion Catheter is guided to the site of the clot (Figure 1). Once positioning is verified (Figure 2), the ultrasound in the catheter tip is activated (Figure 3).

Photo courtesy of EKOS Corporation.

The use of ultrasound to augment drug treatment may improve outcomes in acute stroke.

Tissue plasminogen activator (tPA) is a drug used to treat acute ischemic stroke – stroke associated with a clot causing blockage of blood flow to the brain. Continuous transcranial ultrasound monitoring of an occluded (or blocked) artery induces changes in the structure of the clot, resulting in faster penetration of tPA and enhanced clot breakdown (thrombolysis).[1]

Other approaches to augment tPA treatment include micro-bubble administration with transcranial ultrasound [2,3] and a catheter with an ultrasound transducer.[4]

How it Works

SonoLysis® therapy (ImaRx Therapeutics, Inc., Tucson, AZ) uses micro-bubbles – composed of a lipid shell and an inert, biocompatible gas – which are injected intravenously, with or without a thrombolytic drug. SonoLysis bubbles penetrate the clot, and transcranial ultrasound causes them to expand and contract. It is thought that this mechanical energy helps break up the clot.

The EKOS® Micro-Infusion Catheter (EKOS® Corporation, Bothell, WA) is a disposable infusion/ultrasound catheter with an ultrasound transducer at the tip. The ultrasound energy transmitted by the catheter helps to loosen the fibrin matrix and drive tPA into the blood clot for faster thrombolysis.

Who Might Benefit

These technologies have the potential to benefit persons diagnosed with acute ischemic stroke. In 2004 to 2005, there were 19,197 “new stroke episodes” in Canada, 88% of which involved ischemic stroke.[5]

Regulatory Approval

The SonoLysis system has not yet received approval from any regulatory body. Though not approved in Canada, the EKOS Micro-Infusion System has approval from the US Food and Drug Administration for regional infusion of contrast materials into selected vessels in the neurovasculature.[6]

Evidence

A non-randomized trial compared patients treated with tPA, ultrasound and galactose-based micro-bubbles to patients who received only tPA and ultrasound, and those who received only tPA.[3] The complete recanalization rate (re-opening of blocked brain arteries) was significantly higher in patients treated with micro-bubbles than those in the other groups (54.5% versus 40.8% and 23.9%, p=0.038).

SonoLysis therapy is being evaluated for the treatment of acute ischemic stroke in a Phase I-II study.[7]

In a Phase II study, the EKOS Micro-Infusion Catheter was used in 34 of 52 patients who had a visible, treatable clot. The recanalization rate was higher than that found in an earlier Phase I study, which did not use ultrasound catheters (69% versus 55.6%).[8] A 40-centre Phase III trial will provide further evidence on the efficacy of the EKOS Micro-Infusion Catheter in the treatment of ischemic stroke.[8]

Cost

The cost of these devices is unknown.

References

[1] Alexandrov AV, et al. N Engl J Med 2004;351(21):2170-8.

[2] SonoLysis© bubbles. In: ImaRx Therapeutics [Web page]. Tucson (AZ): ImaRx Therapeutics; 2006. Available: http://www.imarx.com/ImaRx/products3_2

[3] Molina CA, et al. Stroke 2006;37(2):425-9. Available: http://stroke.ahajournals.org/cgi/reprint/37/2/425

[4] About EKOS© Micro-Infusion System. In: EKOS Corporation [Web page]. Bothell (WA): EKOS Corporation; 2006. Available: http://www.ekoscorp.com/pdMi_intl.html

[5] Health Care in Canada. Ottawa (ON): Canadian Institute for Health Information; 2006. Available: http://secure.cihi.ca/cihiweb/dispPage.jsp?cw_page=AR_43_E

[6] Special 510(k) notification: EKOS Micro-Infusion system. In: U.S. Food and Drug Administration [Web page]. Rockville (MD): U.S. Food and Drug Administration; 2006. Available: http://www.fda.gov/cdrh/pdf5/K053437.pdf

[7] Clinical trials. In: ImaRx Therapeutics [Web page]. Tucson (AZ): ImaRx Therapeutics; 2006. Available: http://www.imarx.com/ImaRx/clinical_trials5_0