Echocardiography: The Preeminent Front Line Screening and Diagnostic Tool for Cardiovascular Imaging and Physiological Assessmen

Gregory Gilman, BS, RN, RDCS, FASE, and William H. Hansen, MMS, RDCS, FASE, Rochester, Minnesota
Gregory Gilman, BS, RN, RDCS, FASE, and William H. Hansen, MMS, RDCS, FASE, Rochester, Minnesota
Cardiovascular imaging presents as a landscape of multiple maturing technologies, developed through billions of dollars of research and decades of dedication by both industry and clinicians to create diagnostic tools capable of revealing many of the elusive characteristics of cardiovascular disease. So powerful are these tools that they have become integral in the clinician s diagnostic armamentarium.1-7 For the uninitiated, echocardiography is the utilization of ultrasound to view cardiopulmonary and the major thoraco-abdominal vascular structures and obtain structural, hemodynamic and perfusion parameters of the heart and great vessels. Ultrasound imaging is accomplished by transmitting ultrasound through the tissues and fluids of the body. At the core of this technology is the piezoelectric crystal (crystalline material that converts sound into an electrical signal), which enables the generation, sending and reception of ultrasound waves. The term two-dimensional imaging refers to the computer re-creation of reflected ultrasound waves into an image with height and width dimensions, thus the reference to two dimensions. Three-dimensional echo is in the early stages of clinical application and adds the third plane of depth. A computer-mediated rendition of the reflected signals produce still and moving images, and overlays of color Doppler images depict speed and direction of blood flow. Focused directional ultrasound, referred to as Doppler, enables the unique assessment of dynamic physiological characteristics and cardiovascular hemodynamics yielding a differentiation of etiologies for symptoms of heart failure.8-10 With this in mind, imagine the cardiac ultrasound exam as providing the ability to view thin slices (tomographic planes) of the beating heart. During the cardiac cycle, one can observe the expansion and contraction of the ventricles in concert with the opening and closing of the heart valves, which are driven by the rise and fall of pressures within the cardiac chambers. By selective interpretation of the reflected ultrasound, the speeds at which the structures move within the ultrasound beam are re-created into two- and three-dimensional images. This results in visualization of the relative slower moving tissue and valves, and non-visualization or darkening of areas of the image where blood is moving at a faster speed. In this manner, thrombus formations, changes in myocardial integrity due to myocardial infarction or disease infiltration, and delineation of non-myocardial structures such as tumors and cysts are readily discernable. With increased sophistication of the manipulation of the send/receive functionality of the ultrasound, advances in image quality, and the use of injectable non-radioactive microbubble agents, the imaging capabilities of ultrasound have dramatically advanced the ability to visualize cardiac structures and demonstrate perfusion within the myocardium. By overlaying a broad rather than focused Doppler scan across the imaging field, individually colored packets of information reflecting the direction and speed of motion of small areas within the field can be displayed as blood flow. This is referred to as color-flow Doppler. As blood moves through the valves, the overlaying of the color-flow Doppler on the two-dimensional images enables visualization of normal flow through valves as well as the acceleration of flow as in the case of valvular abnormalities such as stenosis (narrowing of the valve) or regurgitation (leakage of the valve). Color-flow Doppler has resulted in clinically valuable advances into non-invasive calculation of the degree of valvular disease and associated abnormalities. Paralleling the advance of the ultrasound technologies related to the creation and interpretation of cardiovascular imaging has been the refinement of the instrumentation. The ability to miniaturize the footprint of the piezoelectric crystal has enabled them to be engineered into intravascular catheters small enough to be placed within coronary vessels. By providing the interventional cardiologist with direct visualization of atherosclerotic lesions, informed decisions as to the most appropriate interventional procedure can be made. Incrementally larger versions of this design may be placed into the great vessels, enabling real-time visualization of aortic pathologies. These catheters may also be placed within the heart to help guide the electophysiologist during mapping and ablation, as well as for real-time monitoring of increasingly performed non-invasive cardiac interventions such as percutaneous coronary interventions, atrial septal closure devices and valve repairs, and thoracoscopic coronary bypass grafting.11,12 The big brother of the intravascular ultrasound imaging devices is the transesophageal echo (TEE) probe. This remarkable innovation has enjoyed decades of utility in the clinical cardiology and cardiovascular surgery disciplines. The esophagus is positioned immediately adjacent to the left atrium and a significant portion of the great vessels. The antrum of the stomach is positioned adjacent to the inferior aspect of the left ventricle. This affords the cardiologist an opportunity to consistently image the heart and great vessels with remarkable clarity and avail themselves to most of the imaging technologies available by conventional echocardiography. This device has become the diagnostic imaging tool of choice for: detection of intracardiac thrombus in the setting of embolic events, preventing thromboembolic sequelae after cardioversion; delineation of structural specifics of valvular disease, enabling detailed surgical planning; assessment of cardiac function in patients whom have poor image quality by conventional echo; and peri-operative real-time dynamic monitoring of cardiac surgical interventions. Portability and configuration of the imaging platform has been a major focus of ultrasound machine development. Reduced size, improved ergonomic operation, small hand-held devices, ultrasound probes and catheters, and other special adaptations are now commonplace. Armature access of these machines for interventional labs and operating rooms, as well as the reduced cost of smaller imaging systems, will fuel the next decade of the utility of echocardiography in the clinical and research settings. We in the field of echocardiography have been fortunate to benefit from the recognition of the value of this diagnostic modality, and the resulting efforts by research clinicians and industry to advance every aspect of its functionality and clinical application for the betterment of patient care. When we look to the horizon, we can anticipate further surges toward efficient web-based digital image transfer, ubiquitous web-based information access and management, and platform miniaturization. Today s state-of-the-art echocardiography laboratory has evolved from a videotape media to full digitization format of echocardiographic images.13 These developments have facilitated the significant expansion of the mobile outreach echo practice,14 offering echo laboratories an improved efficiency in the image review process. Along these lines, there is a requirement for ready access to patient information. We believe this will best be accomplished through web-based echo imaging and information management systems. These systems must meet the highest standards of secure patient data management, based upon regulatory guidelines, accreditation standards and appropriate testing criteria, while providing workflow management to maximize human and material resource utilization. Additional interpretive logic and automated functions within the application would be helpful to facilitate the necessary documentation of diagnostic findings and streamline the laboratory workflow. In order to be safe, diagnostic testing needs to expose the patient to minimal risk of radiation exposure. In order to be prognostic, research needs to support findings that directly correlate imaging technology with the diagnosis and management of disease. To be cost-effective, testing modalities must be portable and produced with minimal expenditure for instrumentation. Based upon these criteria, in the field of cardiovascular imaging, no other modality competes with echocardiography. Its power to screen for and diagnose cardiopulmonary disease is based upon a foundation of decades of complimentary research efforts and hundreds of platform iterations to arrive at a peerless masterpiece of innovation. Echocardiography is the preeminent front line screening and diagnostic tool for diagnostic screening and physiologic assessment in cardiovascular medicine.