Abstract
Myocardial contrast echocardiography has been used for assessing myocardial perfusion. Some concerns regarding its safety still remain, mainly regarding the induction of microvascular alterations. We sought to determine the bioeffects of microbubbles and real-time myocardial contrast echocardiography (RTMCE) in a closed-chest canine model. Eighteen mongrel dogs were randomly assigned to two groups. Nine were submitted to continuous intravenous infusion of perfluorocarbon-exposed sonicated dextrose albumin (PESDA) plus continuous imaging using power pulse inversion RTMCE for 180 min, associated with manually deflagrated high-mechanical index impulses. The control group consisted of 3 dogs submitted to continuous imaging using RTMCE without PESDA, 3 dogs received PESDA alone, and 3 dogs were sham-operated. Hemodynamics and cardiac rhythm were monitored continuously. Histological analysis was performed on cardiac and pulmonary tissues. No hemodynamic changes or cardiac arrhythmias were observed in any group. Normal left ventricular ejection fraction and myocardial perfusion were maintained throughout the protocol. Frequency of mild and focal microhemorrhage areas in myocardial and pulmonary tissue was similar in PESDA plus RTMCE and control groups. The percentages of positive microscopical fields in the myocardium were 0.4 and 0.7% (P = NS) in the PESDA plus RTMCE and control groups, respectively, and in the lungs they were 2.1 and 1.1%, respectively (P = NS). In this canine model, myocardial perfusion imaging obtained with PESDA and RTMCE was safe, with no alteration in cardiac rhythm or left ventricular function. Mild and focal myocardial and pulmonary microhemorrhages were observed in both groups, and may be attributed to surgical tissue manipulation.
Highlights
The assessment of myocardial perfusion by echocardiography following intravenous injection of ultrasound contrast agents has proved to be feasible [1]
Intravenous infusion of perfluorocarbon-exposed sonicated dextrose albumin (PESDA) microbubbles permitted the analysis of myocardial perfusion and left ventricular function in all dogs during the protocol
One from the PESDA plus real-time myocardial contrast echocardiography (RTMCE) group and the other from the PESDA group because of hemodynamic instability before the beginning of microbubble infusion, which was attributed to the effects of anesthesia and hypovolemia
Summary
The assessment of myocardial perfusion by echocardiography following intravenous injection of ultrasound contrast agents has proved to be feasible [1]. The development of low-mechanical index imaging techniques that cause minimal microbubble destruction has permitted simultaneous analysis of myocardial perfusion and function in real time [2]. Investigations of the interaction of ultrasound and contrast agents in vivo are scarce, some effects have been reported in the literature [10] such as capillary damage in organs that contain air such as the lungs [7], damage to the microvasculature [11], and limited capillary ruptures in the heart [12]. Simultaneous exposure of isolated rabbit hearts to ultrasound and a contrast agent has been found to result in transient depression of left ventricular contractile function, an increase in coronary perfusion pressure and in lactate production, and in limited mechanical index-dependent capillary rupture [12]. The clinical importance of these effects has not been established [13]
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