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INTRODUCTION

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Echocardiography plays an important role in cardiac surgery by defining myocardial structure, function, and intracardiac blood flow velocities. Preoperatively, transthoracic and transesophageal echocardiography with color and spectral Doppler identify, quantify, and characterize cardiac disease and support decision making in terms of surgical timing and choices. Intraoperative transesophageal echocardiography (TEE) provides high-fidelity assessment of underlying pathophysiology, guides beating heart procedures in real time, supports surgical planning, and, allows for timely assessment of the results of surgical procedures. Furthermore, TEE can be critical in the early postoperative period to elucidate various etiologies of perioperative hemodynamic instability, allowing surgeons and intensivists to identify and manage complications accurately and efficiently. Lastly, transthoracic echocardiography (TTE) is often employed to evaluate and monitor long-term surgical results due to its noninvasive nature.

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It is important that surgeons appreciate the potential and the limitations of perioperative ultrasound to provide case-specific predictors and intraoperative procedural guidance to improve surgical outcomes and facilitate incorporation of new technologies into current practice.

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The goals of this chapter are to provide a framework for understanding the technique, and its indications for use. We summarize American Society of Echocardiography/Society of Cardiovascular Anesthiologists (ASE/SCA) guidelines for the surgical use of epicardial ultrasound, which can supplement or substitute for intraoperative TEE when TEE is contraindicated. Finally, we outline expectations that surgeons should have for intraoperative TEE images and interpretations.

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BASIC PRINCIPLES

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Echocardiographic images are constructed by transmitting high-frequency sound waves into the chest from a transducer composed of piezo-electric crystals. These waves reflect off cardiac structures, and the returning signals are received by the same transducer. By knowing when the signal was sent, the speed of the sound in the tissue, and the time it takes for the reflected signal to return to the transducer, the position of the structure responsible for the reflection can be calculated. An image from these signals can thus be created. The quality of the image relies on many factors, including the media through which the sound is traveling, the orientation of the structures in relation to the ultrasound beam, and the composition of the structure. Sound travels incredibly well through water and blood, reasonably well through tissue, but poorly through air. Therefore, the media through which the sound travels will determine the strength of the returning signal. When the ultrasound beam reflects off various portions of the heart, the signal is scattered in various directions such that some never return to the transducer. For this reason, structures that are perpendicular to the ultrasound beam and reflect stronger signals back to the transducer produce images of the most accuracy. On the other hand, strong reflectors such as calcified valvular leaflets will result in a bright picture but they also inevitably create imaging artifacts. The fact that sound transmitted from a TEE transducer has less distance to travel (which means less signal lost to scatter) and mainly travels through muscle and ...

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