Abstract 10752: Effect of Guided High Mechanical Index Impulses and Intravenous Microbubbles on Infarct Size and Systolic Function Assessed by Cardiac Magnetic Resonance Imaging Following Acute Myocardial Infarction

Abstract

Background. Guided high mechanical index (MI) impulses from a modified diagnostic ultrasound system during an intravenous microbubble (IV MB) contrast infusion have been shown to improve ST segment resolution and recanalization rates in atherosclerotic pig models with ST elevation acute myocardial infarction (STEMI). Cardiac magnetic resonance imaging (CMRI) with delayed gadolinium enhancement imaging (DE-MRI) allows for quantification of systolic function, infarct size, and microvascular flow in this setting. We hypothesized that this guided high MI impulses and IV MB, utilized with low dose tissue plasminogen activator (TPA), would result in quantitative improvements in these CMRI parameters.

Methods. Twelve pigs with acute STEMI of the left anterior descending artery were treated with low dose TPA alone (0.5 mg/kg over 30 minutes; n=5) or a low dose TPA infusion (n=7) combined IV MB (MRX 801; NuVox) and guided high MI (1.0) impulses (20 usec pulse duration 1.6 MHz S5-1 transducer; Philips Medical), which were applied over the risk area only when simultaneous low MI imaging detected MB within the RA. All treatment times were 30 minutes. Angiographic recanalization rates (ARR), and CMRI segmental assessments of transmural DE-MRI and quantitative left ventricular ejection fraction (LVEF) were made at 48-72 hours post infarction.

Results. ARR was significantly higher in pigs treated with IV MB and guided high MI impulses (5/7 versus 0/5 for low dose TPA alone; p<0.05). In pigs who angiographically recanalized with guided high MI impulses and IV MB, the number of transmural infarct segments by DE MRI were significantly less (median 3 versus median 5; p<0.05). LVEF in pigs treated with guided high MI impulses and IV MB was also significantly higher (53 + 9% versus 44+2% TPA alone; p<0.05).

Conclusion. Guided high MI impulses from a modified diagnostic ultrasound system and IV MB significantly improve the effectiveness of a low dose TPA in producing epicardial recanalization in acute STEMI, which reduces the extent of transmural infarction and improves systolic function in the early post-infarct setting.