Chapter 27: Echocardiography

INTRODUCTION

Echocardiography is a widely used cardiac imaging modality that is often the first-choice test for assessing cardiac structure and function. It provides a detailed structural assessment of the myocardium, valves, pericardium, and portions of the surrounding vasculature, which includes the thoracic aorta, pulmonary artery, pulmonary veins, inferior vena cava, and superior vena cava. With real-time evaluation, echocardiography provides an assessment of the systolic and diastolic function of the myocardium, as well as a measurement of intracardiac hemodynamics and the severity of valvular disease. Compared to other cardiac imaging modalities, echocardiography is relatively less expensive, does not expose the patient to ionizing radiation, and is generally well tolerated by the patient.

The two primary echocardiographic techniques include transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE). With TTE, the ultrasound probe is placed on the patient's chest and several views of the heart are obtained from various angles. In TEE, a flexible ultrasound transducer is introduced into the esophagus and can be rotated or flexed at varying levels in the esophagus to allow for imaging of the cardiac structures. Compared to TTE, TEE has better image quality for posterior cardiac structures due to the closer proximity of the transducer to the heart. TEE is especially useful in the evaluation of endocarditis, valvular dysfunction, and interatrial septal defects.¹ Since its introduction to clinical medicine, echocardiograpjy has undergone significant technological advances. As a result, echocardiography is an essential imaging tool in clinical medicine.

Echocardiographic images are obtained with an ultrasound transducer which emits sound waves that are transmitted through the internal structures and then reflected back to the transducer to create an image.² In standard TTE, the available modalities include M mode, two-dimensional (2D), and three-dimensional (3D). M mode is the most basic method which evaluates cardiac structures in a one-dimensional (1D) view along a single-scan line, which places depth on the y-axis and time on the x-axis. This is ideal for making fine linear measurements. M mode also has excellent temporal and spatial resolution and is thus useful to assess motion and timing.² 2D is the most utilized echocardiographic modality, and produces cross-sectional images of the heart by emitting numerous signals that are repeatedly generated to create moving images in real time. The most common standard 2D views are the parasternal long-axis, parasternal short-axis, and the apical and subcostal views (Fig. 27-1). Off-axis imaging may then be necessary to evaluate more complex structures. Newer machines are also able to generate 3D images of the cardiac structures through the use of matrix-array transducers to provide detailed structural assessments.³ Compared to 2D echocardiography, 3D imaging provides more accurate quantification of ventricular volumes (Fig. 27-2), generates unique views of valve structures (Fig. 27-3), and demonstrates improved visualization of spatial relationships between cardiac structures.³