cardiovascular disorders
Echocardiography
Methodology
Two-dimensional echocardiographyis most commonly used; contrast, Doppler and other echocardiography modalities provide additional information. Contrast echocardiographyis a 2-dimensional echocardiogram done while agitated saline (or another ultrasonographic contrast agent) is rapidly injected into the cardiac circulation. Agitated saline develops microbubbles, which produce a cloud of echoes in the right cardiac chambers and which, if a septal defect is present, appear on the left side of the heart. Usually, the microbubbles do not traverse the pulmonary capillary bed; however, one agent, sonicatedalbuminmicrobubbles, can do so and can enter left heart structures after IV injection and can therefore be used to delineate the heart chambers, especially the left ventricle. Spectral Doppler echocardiographycan record velocity, direction, and type of blood flow. This technique is useful for detecting abnormal blood flow (eg, due to regurgitant lesions) or velocity (eg, due to stenotic lesions). Spectral Doppler echocardiography does not provide spatial information about the size or shape of the heart or its structures. Color Doppler echocardiographycombines 2-dimensional and spectral Doppler echocardiography to provide information about the size and shape of the heart and its structures as well as the velocity of and direction of blood flow around the valves and outflow tracts. Color is used to code blood flow information; by convention, red is toward and blue away from the transducer. Tissue Doppler imaginguses Doppler techniques to measure the velocity of myocardial tissue contraction (rather than of blood flow). Myocardial tissue movement can also be evaluated withspeckle-tracking echocardiography, which uses algorithms to track myocardial echo speckles (characteristic reverberations from the myocardium during an ultrasonography) from frame to frame.Strain imaginguses these data to calculate myocardial strain (percentage change in length between contraction and relaxation) and myocardial strain rate (rate of change in length). Strain and strain rate measurements can help assess systolic and diastolic function and identify ischemia during stress testing. Three-dimensional echocardiographyis increasingly used; special transducers can obtain a real-time, 3-­dimensional image of cardiac structures. Three-dimensional echocardiography is particularly useful in evaluating the mitral valve apparatus for surgical correction. It is also increasingly being used to quantify right ventricular volumes, because the crescent shape of the right ventricle limits evaluation by 2-dimensional echocardiography, and during interventional procedures such as transcatheter edge-to-edge repair of the mitral valve. Use of 3-­dimensional echocardiography continues to evolve. 