Effect of mild hypothermia on the thrombolytic efficacy of 120 kHz ultrasound enhanced thrombolysis in an in-vitro human clot model.

INTRODUCTION: Ischemic stroke causes substantial death and disability. Currently, recombinant tissue plasminogen activator (rt-PA) is the only FDA approved therapy. However, there are dangerous side effects and therapy must start within 3 h of onset. Therefore, there is interest in adjunctive therapies such as ultrasound enhanced thrombolysis (UET) and hypothermia. Recently, transcranial ultrasound during rt-PA therapy was shown to improve vessel recanalization. Also hypothermia (32-34 degrees C) was shown to be safe and possibly improve outcome. This suggests combining UET and hypothermia to treat ischemic stroke. Little is known about the effects of hypothermia on UET, and in-vitro rt-PA efficacy is reduced for T<37 degrees C. Here, the effects of hypothermia on UET in in-vitro human clot are presented. It is hypothesized that UET efficacy at 33 degrees C is less than at 37 degrees C.
MATERIALS AND METHODS: Whole blood was drawn from volunteers. Clots were made, incubated at 37 degrees C and aged for 2 days for maximal lytic resistance. Clots were exposed to human fresh-frozen plasma (control), hFFP and rt-PA ([rt-PA]=3.2 microg/ml), hFFP and 120 kHz ultrasound (US), and hFFP, rt-PA and ultrasound (UET) at 33 degrees C and 37 degrees C. Clot percent mass loss (Deltam) was measured to determine thrombolytic efficacy. Data were analyzed using mixed-model analysis of variance. RESULTS AND
CONCLUSIONS: US and rt-PA independently increased Deltam (3.5+/-1.0% and 5.1+/-0.9% respectively; p<0.01) over control. UET increased Deltam an additional 8.1+/-1.3% (p=0.026) The effect of temperature on Deltam (-1.6+/-0.7%) was not significant (p=0.09). Hypothermia did not reduce UET efficacy in this in-vitro model.