Therapeutic Use of Ultrasound Associated to Microbubbles in Acute Myocardial Infarction

Abstract

with participation of Dr. Thomas Richard Porter, from the University of Nebraska. It is a pilot study that aimed to evaluate the effectiveness of intravenous microbubbles (MB) and ultrasound (US), a procedure known as sonothrombolysis on the initial rates of recanalization of coronary arteries in patients with acute ST segment elevation myocardial infarction (STEMI). This study brings an auspicious message: the possibility of a therapeutic option that assists in the recanalization of coronary artery and consequent myocardial preservation in patients with STEMI.The use of contrast agents in echocardiography (CAE) has shown significant progress. Microbubbles suspension created by manual agitation was initially used. 2 These microbubbles, however, were large and unstable. In the evolution of the process, more stable microbubbles were created. These could pass through the pulmonary capillaries and reach the left heart chambers with a high degree of safety, reliability and diagnostic efficiency. 3,4 In these days, the use of CAE is not limited to diagnosis, but also includes therapeutic support in many segments of medicine, including as an auxiliary therapy to thrombolysis. 5,6 The mechanism by which the use of MB associated to US causes thrombolysis appears to be multifactorial. The most accepted one is the mechanical action. Specific ultrasonic pulses issued during off-the-shelf MB infusion cause the growth and collapse of microbubbles in the course of insonation, an effect known as cavitation. This transformation in the shape of microbubbles culminates in their rupture. This process causes shear stress in the areas surrounding the microbubbles. If this occurs in an area with thrombus, it will be achieved and eventually dissolved. 7,8 Another mechanism of improved ischemia appears to be associated with the release of nitric oxide. Specific ultrasonic pulses, when applied to the heart during infusion of MB, causes the release of nitric oxide, which improves microvascular flow in ischemic regions and enhances the effects of thrombus dissolution caused by cavitation. 9,10 Studies have shown that use of MB associated with US induces acceleration of thrombolysis during acute stroke, causing a more complete recanalization and a tendency to improve short and long-term outcomes in humans. 5 Xie F. et al. showed that MB associated with US improves microvascular flow in the peri-infarcted region in pigs with STEMI. 11 In the study by Tavares et al., 1 the authors studied 24 patients in the acute phase of STEMI. These were randomized to three groups: the first one used MB, in continuous infusion, associated with US with mechanical index (MI) and high pulse duration between 4 and 20 μseg (N = 7); the second one, MB + US with repetitive pulses of high MI with pulse duration <2 μseg (n = 8). All patients underwent coronary angioplasty (PCI). In both groups, patients received therapy before and immediately after PCI for a total period of 50 to 60 minutes. Pre-PCI sonothrombolysis was conducted while the patient was waiting to b...