Abstract 10749: Optimizing the Mechanical Index and Pulse Duration for Transthoracic Ultrasound Induced Microvascular Thrombolysis in Acute Myocardial Infarction
Background: During an intravenous microbubble infusion, guided high mechanical index (MI) impulses from a diagnostic transducer that induce inertial cavitation (IC) can dissolve vascular and microvascular thrombi.
Objectives: Since IC is the presumptive mechanism for thrombolysis enhancement, we hypothesized that measures which sustain a high intensity of IC (longer impulse duration at a higher mechanical index (MI)) may more effectively restore both coronary and microvascular flow and reduce infarct size in acute myocardial infarction (STEMI).
Methods: We compared angiographic and microvascular outcomes in 27 hyperlipidemic atherosclerotic pigs with acute ST segment elevation myocardial infarction (STEMI) due to a thrombosed left anterior descending artery. In addition to low dose (0.5 mg/kg) tissue plasminogen activator (TPA), pigs received transthoracic guided high MI impulses that would sustain a high intensity of IC (1.3 MI 20usec duration ;1.9 MHz M5S-D; GE), or sustain a lower intensity of IC (1.0 MI 20 usec duration;1.6 MHz S5-1, Philips). Outcomes were compared with the use of TPA alone. All high MI impulses were applied to the risk area microvasculature during a 3% lipid encapsulated microbubble infusion. Infarct artery recanalization rates and % residual stenosis (RS) at 30, 60, and 90 minutes, and 17-segment analysis of microvascular obstruction (MVO) with delayed enhancement magnetic resonance imaging (DE-MRI) at 48 hours post infarction were analyzed.
Results: Epicardial recanalization rates were 70% in both groups that received guided ultrasound 20 usec impulses (p<0.05 compared to TPA alone). However, %RS was less with higher MI 20usec impulses (21±12% versus 69±12% for lower MI 20 usec impulses). Furthermore, the degree of microvascular obstruction at 48 hours post infarction was lowest with the higher 1.3 MI 20usec impulses (median 0.5 segments versus 2.0 segments for lower intensity 1.0 MI 20usec impulses and 2.5 segments for TPA alone; p=0.02).
Conclusions: Therapeutic impulses which sustain a high intensity of IC produce both improved epicardial recanalization and microvascular outcome in acute STEMI.
- © 2013 by American Heart Association, Inc.