A. Echocardiography is frequently performed in critically ill patients. The major advantages of this diagnostic technique are its portability, lack of patient exposure to ionizing radiation and iodinated contrast, ability to provide real-time structural and functional (hemodynamic) information, and suitability for serial performance.

B. Structural and functional information is provided by transmitting ultrasound (US) energy (2 to 10 MHz) from the echocardiograph and receiving signals returning from the cardiac structures to create real-time two- (2D) and three-dimensional (3D) images of the heart.

C. Using the Doppler principle, reflected US energy is used to determine the velocity and direction of flowing blood in the heart and great vessels providing information about the hemodynamic effects of stenotic and regurgitant valve lesions. In addition, Doppler echocardiography provides information about filling pressures, stroke volumes, and pulmonary artery systolic pressures. Peak instantaneous pressure gradients (P) are estimated by measuring the peak flow velocity (V) and application of the modified Bernoulli equation, P = 4V². Color-flow Doppler provides a spatial velocity map of abnormal flow within the heart and great vessels; it is most useful to estimate the degree of valvular regurgitation and identifying turbulent blood flow. Tissue Doppler imaging adds to the ability to estimate left heart filling pressures.

D. A complete examination includes information provided by the 2D, Doppler, color-flow, and M-mode modalities. 3D echocardiography may add important structural and spatial information in selected cases.

E. Echocardiography methods.

1. Transducer placed directly on the patient’s chest (transthoracic echocardiography [TTE]).

2. Transducer mounted on a gastroscope passed into the patient’s esophagus and stomach (transesophageal echocardiography [TEE]).

A. Evaluation of left ventricular (LV) and right ventricular structure and function.

1. Estimation of ejection fraction and assessment of parameters such as wall thickness, chamber sizes, regional wall motion abnormalities, and diastolic dysfunction.

2. Doppler echocardiography can provide an accurate assessment of LV filling pressures and stroke volumes.

B. Evaluation of hypotension/shock (Tables 20-1 and 20-2).

C. Evaluation of cardiac valves.

1. Assessment of valvular stenosis or regurgitation requires a comprehensive echocardiographic examination utilizing the 2D, pulsed-wave and continuous-wave Doppler, and color-flow Doppler modalities.

2. Suspected infective endocarditis (IE).

a. TTE has a sensitivity of 44% to 80% to identify valvular vegetations. TTE is relatively insensitive to diagnose myocardial or aortic root abscesses and infection of prosthetic valves.

b. TEE has a sensitivity approaching 100% for vegetations as small as 2 mm. TEE can detect complications of IE, such as fistulous tracts, perforation, and abscess formation, in 90% to 95% of cases. It is the modality of choice with suspected prosthetic valve endocarditis or with suspected IE with highly invasive organisms like Staphylococcus aureus.

D. Evaluation of the aorta and great vessels.

1. Aortic dissection.

a. Detection of a mobile intimal flap, aortic regurgitation, pericardial effusion, and aortic rupture.

b. TEE has higher sensitivity and specificity than TTE and equivalent diagnostic accuracy compared to CT angiography or magnetic resonance imaging.

2. Intramural hematomas and penetrating ulcers and variants of aortic dissection, which can cause acute aortic syndromes.

3. Deceleration injury to aorta/aortic trauma/valvular injuries.

E. Evaluation of hypoxemia.

1. Acute pulmonary embolism: Echocardiography is not a first-line test. It can be helpful for determining RV structure and function for purposes of risk stratification and for emergent evaluation when other testing is not practical.

2. Right-to-left shunting through a patent foramen ovale or via pulmonary arteriovenous malformations (bubble test).

3. Congenital heart lesions.

F. Evaluation of cardiac source of embolism.

G. Evaluation of difficulty to wean from mechanical ventilation.

H. Monitoring of therapeutic procedures (such as pericardiocentesis).

A. A standard TTE examination is performed by placing an US transducer on the chest and imaging from a variety of areas.

1. In approximately 30% of critically ill patients, the image quality of TTE may be inadequate to obtain necessary diagnostic information. Administration of a microbubble contrast agent may improve the diagnostic utility of bedside TTE in this situation. When image quality


remains an issue or a more detailed evaluation is needed, a TEE will often be required.