Ultrasound Augmentation of Intravenous Thrombolysis in Stroke
Introduction to Ultrasound Augmentation
- The American Heart Association recommends the use of ultrasound augmentation of IV thrombolysis as a technique to enhance clot breakdown and accelerate recanalization in patients with stroke, using continuous transcranial Doppler (TCD) ultrasound applied to the occluded cerebral artery during IV tissue plasminogen activator (tPA) administration 1, 2
Mechanism of Action and Methods of Delivery
- There are three primary approaches to ultrasound-enhanced thrombolysis, including transcranial Doppler (TCD) monitoring, unfocused low-frequency ultrasound, and intra-arterial catheter delivery, such as the EKOS catheter system, which delivers ultrasound directly at the clot site 1, 2, 3
Clinical Evidence
- The CLOTBUST trial demonstrated significant benefits of ultrasound augmentation, including complete recanalization in 49% of patients with TCD + IV tPA versus 30% with IV tPA alone, and any recanalization in 83% of patients with TCD + IV tPA versus 50% with IV tPA alone within 2 hours 1, 2, 4
- The trial also showed a safety profile with symptomatic intracranial hemorrhage rate identical at 3.8% in both groups 1, 2
Critical Safety Considerations
- Low-frequency ultrasound (kilohertz range) is contraindicated due to unacceptable hemorrhage risk, whereas diagnostic-range ultrasound (2 MHz megahertz frequency) has demonstrated acceptable safety 1, 2, 6
Current Clinical Status and Practical Limitations
- Ultrasound augmentation remains investigational, with ongoing trials of diagnostic ultrasound enhancement, and phase II studies evaluating 2 MHz TCD with perflutren-lipid microspheres (ultrasound contrast agents) 1, 2
- The technique requires appropriate temporal bone windows for TCD penetration, and several factors limit widespread implementation, including temporal bone window adequacy, operator dependence, vessel visualization, and technical expertise 5, 6