Transthoracic Echocardiography

A comprehensive transthoracic echocardiographic examination (TTE) includes the acquisition of standard two-dimensional (2D) and M-mode views of the intrathoracic structures complemented by continuous- and pulsed-wave spectral Doppler data and color flow Doppler imaging. Commercial echocardiographic imaging systems also have tissue harmonic imaging capability, and this technique is now routinely applied in most laboratories to enhance endocardial definition in patients with technically difficult TTE examinations. In addition, many laboratories routinely utilize tissue Doppler imaging (TDI) as part of standard TTE examination protocol. TDI, analogous to pulsed-wave Doppler assessment of blood flow velocity, is used to measure longitudinal myocardial motion. When combined with a comprehensive TTE examination, TDI can yield clinically useful information regarding diastolic ventricular function and cardiac filling pressures. Small, lightweight, and highly portable ultrasound systems are also available for bedside TTE imaging. Commonly referred to as “handheld” TTE devices, these instruments possess limited capability as compared with standard echocardiographic equipment, but advances have made this technology easier to use while simultaneously incorporating a wider range of imaging features; some of these models can perform many functions of a larger system.

Transthoracic 2D echocardiography is the foundation of the clinical echocardiographic examination. Tomographic images from multiple locations on the chest wall, defined by the transducer position and image plane (Fig. 6-1), provide a reliable, portable, and reproducible evaluation of cardiac chamber sizes, myocardial thickness, ventricular contractile performance, valvular structure and function, the pericardium, and great vessels. Doppler echocardiographic assessment of the direction and velocity of blood flow within the heart and great vessels is valuable in the detection and quantification of obstructive lesions and valvular regurgitation (Fig. 6-2). Transthoracic 2D directed M-mode echocardiography is especially valuable in the evaluation of mitral and aortic valve motion in dynamic and fixed left ventricular outflow obstruction, in the timing of mitral valve closure in aortic regurgitation, and in the assessment of pericardial disease. This technique also provides a precise measurement of cardiac chamber sizes and wall thickness throughout the cardiac cycle allowing accurate estimates of overall left ventricular contractile performance and ejection fraction, provided there are no segmental wall motion abnormalities.

Figure 6-1 Transducer positions in echocardiographic examination.

Figure 6-2 Principles of Doppler echocardiography.

Although coronary arteries cannot be reliably imaged by TTE, the method is nevertheless valuable in the assessment of known or suspected coronary artery disease (CAD). Echocardiographic evidence of segmental ventricular contractile dysfunction can be used to screen for acute or chronic ischemic myocardial injury or infarction, secondary to CAD. However, the diagnosis of CAD is not absolute, because segmental wall motion abnormalities can also be caused by cardiac trauma, myocarditis, and infiltrative myocardial diseases. In addition, multivessel CAD can cause globally decreased ventricular contraction without segmental wall motion abnormalities, a circumstance generally necessitating further evaluation.

TTE is the most reliable and reproducible clinical laboratory method for the initial diagnostic evaluation and follow-up of patients with congenital and valvular heart disease, including the evaluation of right ventricular systolic pressure and pulmonary arterial hypertension. Anatomic information about the nature of a congenital defect and its hemodynamic consequences, including the direction and magnitude of intracardiac shunts and estimation of pulmonary and systemic blood flow, can be estimated by 2D and Doppler techniques.

In stenotic valvular lesions, M-mode techniques can be useful in assessing valvular thickness and motion, ventricular chamber sizes, ventricular wall thickness, and atrial chamber dimensions. This information is valuable in estimating the hemodynamic effects of a stenotic valve abnormality. Transthoracic 2D echocardiography shows a more complete picture of the valvular, subvalvular, and annular structures, and when 2D echocardiography is combined with Doppler ultrasound techniques, obstructive gradients can be accurately measured and cross-sectional valve area can be estimated. Regurgitant valvular lesions can be accurately quantified by color flow Doppler imaging. Clinical decisions regarding medical therapy and operative intervention for patients with valvular disease are usually based on TTE 2D and Doppler echocardiographic data, supplemented by information from cardiac catheterization.

TTE is the primary tool for evaluating the presence and hemodynamic consequences of pericardial effusion. 2D imaging and a comprehensive Doppler examination can reliably identify patients with pericardial effusion and tamponade pathophysiology. TTE-guided pericardiocentesis, either at the bedside or in the cardiac catheterization laboratory, can reduce procedural complications and improve therapeutic results. A thickened pericardium and typical hemodynamic alterations can alert the clinician to the diagnosis of pericardial constriction, but magnetic resonance imaging and catheterization are usually needed for full evaluation. Analysis of Doppler-measured ventricular inflow velocities and TDI can be useful in differentiating between pericardial constriction and infiltrative cardiomyopathy.

“Handheld” ultrasound imaging devices are most widely utilized for the rapid triage of patients in emergency department and intensive care unit settings. This technology can provide accurate assessment for pericardial effusion, left and right ventricular contractile performance, and segmental wall motion abnormalities. Although these devices can also detect valve disease, dilation of the aorta, and structural defects in patients with congenital heart disease, comprehensive echocardiographic evaluation of patients with these conditions and complete assessment of diastolic ventricular function usually require a standard TTE imaging system.

Transesophageal Echocardiography

A transesophageal echocardiographic examination (TEE) requires that an ultrasound probe be passed into the esophagus, posterior to the heart. Because of decreased distance between the transducer and the heart, as well as the absence of interference from bone and lung tissue, the signal-to-noise ratio is more favorable than with TTE, and higher-frequency transducers can be used to improve resolution. Therefore, TEE image quality is generally superior to that of TTE, particularly for posterior structures including the pulmonary veins, left atrium, interatrial septum, and mitral valve.

Stay updated, free articles. Join our Telegram channel

Join