Cardiovascular imaging plays an essential role in the practice of cardiology. Two-dimensional (2D) echocardiography is able to visualize the heart directly in real time using ultrasound, providing instantaneous assessment of the myocardium, cardiac chambers, valves, pericardium, and great vessels. Doppler echocardiography measures the velocity of moving red blood cells and has become a noninvasive alternative to cardiac catheterization for assessment of hemodynamics. Transesophageal echocardiography (TEE) provides a unique window for high-resolution imaging of posterior structures of the heart, particularly the left atrium, mitral valve, and aorta. Nuclear cardiology uses radioactive tracers to provide assessment of myocardial perfusion and metabolism, along with ventricular function, and is applied primarily to the evaluation of patients with ischemic heart disease. Cardiac MRI and CT can delineate cardiac structure and function with high resolution. They are particularly useful in the examination of cardiac masses, the pericardium, the great vessels, and ventricular function and perfusion. Gadolinium enhancement during cardiac MRI adds information on myocardial perfusion. Detection of coronary calcification by CT as well as direct visualization of coronary arteries by CT angiography (CTA) may be useful in selected patients with suspected coronary artery disease (CAD). This chapter provides an overview of the basic concepts of these cardiac imaging modalities as well as the clinical indications for each procedure.
2D echocardiography uses the principle of ultrasound reflection off cardiac structures to produce images of the heart (Table 229-1). For a transthoracic echocardiogram (TTE), the imaging is performed with a handheld transducer placed directly on the chest wall. In selected patients, a TEE may be performed, in which an ultrasound transducer is mounted on the tip of an endoscope placed in the esophagus and directed toward the cardiac structures.
Table 229–1. Clinical Uses of Echocardiography
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Table 229–1. Clinical Uses of Echocardiography
|Left ventricular hypertrophy|
|Regional wall motion abnormalities|
|Morphology and motion|
|Intracardiac pressures |
|Inadequate transthoracic images|
|Aortic disease Infective endocarditis|
|Source of embolism|
Current echocardiographic machines are portable and can be wheeled directly to the patient's bedside. Thus, a major advantage of echocardiography over other imaging modalities is the ability to obtain instantaneous images of the cardiac structures for immediate interpretation. Thus, echocardiography has become an ideal imaging modality for cardiac emergencies. A limitation of TTE is the inability to obtain high-quality images in all patients, especially those with a thick chest wall or severe lung disease, as ultrasound waves are poorly transmitted through lung parenchyma. Technology such as harmonic imaging and IV contrast agents (which traverse the pulmonary circulation) can be used to enhance endocardial borders in patients with poor acoustic windows.
Chamber Size and Function
2D echocardiography is an ideal imaging modality for assessing left ventricular (LV) size and function (Fig. 229-1). A qualitative assessment of the ventricular cavity and systolic function can be made directly from the 2D image by experienced observers. 2D echocardiography is useful in the diagnosis of LV hypertrophy and is the imaging modality of choice for the diagnosis of hypertrophic cardiomyopathy. Other chamber sizes are assessed by visual analysis, including the left atrium and right-sided chambers.
Two-dimensional echocardiographic still-frame images from a normal patient with a normal heart. Upper: Parasternal long-axis view during systole and diastole (left) and systole (right). During systole, there is thickening of the myocardium and reduction in the size of the left ventricle (LV). The valve leaflets are thin and open widely. Lower: Parasternal short-axis view during diastole (left) and systole (right) demonstrating a decrease in the left ventricular cavity size during systole as well as an increase in wall thickening. LA, left atrium; RV, right ventricle; Ao, aorta.
2D echocardiography is the "gold standard" for imaging valve morphology and motion. Leaflet thickness and mobility, valve calcification, and the appearance of subvalvular and supravalvular structures can be assessed. Valve stenosis is reliably diagnosed by the thickening and decreased mobility of the valve. 2D echocardiography is also the gold standard for the diagnosis of mitral stenosis, which produces typical tethering and diastolic doming, and the severity of the stenosis can be ascertained from a direct planimetry measurement of the mitral valve orifice. The presence and often the etiology of stenosis of the semilunar valves can be made by 2D echocardiography (Fig. 229-2), but evaluation of the severity of the stenosis requires Doppler echocardiography (see below). The diagnosis of valvular regurgitation must be made by Doppler echocardiography, but 2D echocardiography is valuable for determining the etiology of the regurgitation, as well as its effects on ventricular dimensions, shape, and function.
Two-dimensional echocardiographic still-frame images from a patient with aortic stenosis. Parasternal long-axis view shows a heavily calcified aortic valve. RV, right ventricle; LV, left ventricle; AO, aorta; LA, left atrium.
2D echocardiography is the imaging modality of choice for the detection of pericardial effusion, which is easily visualized as a black echolucent ovoid structure surrounding the heart (Fig. 229-3). In the hemodynamically unstable patient with pericardial tamponade, typical echo findings include a dilated inferior vena cava, right atrial collapse, and then right ventricular collapse. Echocardiographically guided pericardiocentesis has now become a standard of care.
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