The chest x-ray provides information about heart size, the pulmonary circulation (with characteristic signs suggesting both pulmonary artery or pulmonary venous hypertension), primary pulmonary disease, and aortic abnormalities. The echocardiogram provides much more reliable information about chamber size, hypertrophy, pericardial effusions, valvular abnormalities, and congenital abnormalities and has replaced the x-ray for evaluation of cardiac disease. The electrocardiogram (ECG) indicates cardiac rhythm, reveals conduction abnormalities, and provides evidence of ventricular hypertrophy, myocardial infarction, or ischemia. Nonspecific ST segment and T wave changes may reflect these processes but are also noted with electrolyte imbalance, drug effects, and many other conditions. Routine x-rays and ECGs are not recommended to screen for heart disease and have a limited role in the follow-up of patients with known heart disease. However, a baseline ECG is helpful in older patients.

Noninvasive diagnostic testing
Noninvasive diagnostic procedures are growing in number and application. However, they are frequently overutilized. The clinician should carefully consider what question is being asked and how the results will alter patient management before ordering these tests. They have limited applicability in screening for asymptomatic disease and should not be substituted for a careful clinical evaluation.

The most versatile and generally informative noninvasive technique is echocardiography, which plays a crucial role in the evaluation of patients with most cardiac symptoms and conditions, including congenital, valvular, coronary, and cardiomyopathic heart disease. An overview of echocardiography and its applications is presented below, as is a brief discussion of the evolving role of cardiac MRI. Other specialized noninvasive cardiac testing procedures, such as stress testing, ambulatory electrocardiography, cardiac nuclear medicine tests, and cardiac computed tomography are discussed in conjunction with their major applications.

Echocardiography
Echocardiography provides measurements of left ventricular size, function, and thickness. Left ventricular regional wall motion can be assessed, and the size of all four cardiac chambers can be determined. The morphology of the heart valves can be examined. Hypertrophic cardiomyopathy, pericardial effusion, mitral valve prolapse, valvular vegetations, and cardiac tumors may all be diagnosed. Doppler ultrasound provides a quantitative or qualitative estimation of transvalvular gradients, pulmonary artery pressure, valvular regurgitation, and intraventricular shunts. Doppler measurements, especially of mitral valve inflow patterns, are also frequently used to evaluate diastolic function, but changes related to aging and the effects of heart rate, blood pressure, and valvular regurgitation often make these measurements unreliable. Color Doppler visually demonstrates patterns and directionality of flow; it has been particularly useful in evaluating congenital heart disease. However, Doppler studies frequently detect clinically insignificant valvular regurgitation; care should be taken not to overinterpret those findings.

Transesophageal echocardiography is used to improve the quality of echocardiograms, to derive information about posterior structures (especially the atria and atrioventricular valves) and prosthetic valves, and to monitor patients during surgery. It is superior to surface echocardiography in diagnosing left atrial thrombi, valvular vegetations, and eccentric mitral regurgitant jets (especially with prosthetic valves). The absence of atrial thrombi identifies patients in atrial fibrillation at low risk for embolization, thus facilitating early cardioversion. It is also quite sensitive in detecting aortic dissection and severe atherosclerosis of the ascending aorta, which may be the source for transient ischemic attacks or embolic strokes.

Stress echocardiography is used to enhance the information available from ECGs and as an alternative to nuclear medicine procedures. Echocardiograms may be performed during or immediately following exercise. Transient depression of segmental wall motion during or following stress suggests ischemia. Improvement in wall motion during low-dose dobutamine infusions is an indicator of myocardial viability. Dobutamine infusions can also be utilized as a form of stress testing in patients unable to exercise.

Goldman ME et al: Echocardiography in search of a cardioembolic source. Curr Probl Cardiol 2002;27:342.
Gottdiener JS: Overview of stress echocardiography: uses, advantages, and limitations. Prog Cardiovasc Dis 2001;43:315.
Stewart WJ et al: Echocardiography in emergency medicine: a policy statement by the American Society of Echocardiography and the American College of Cardiology. Task Force on Echocardiography in Emergency Medicine of the American Society of Echocardiography and the Echocardiography and Technology and Practice Executive Committees of the American College of Cardiology. J Am Coll Cardiol 1999;33:586.

Magnetic Resonance Imaging (MRI)
Cardiac MRI continues to evolve rapidly. Currently available systems provide high-quality and high-resolution images of cardiac and adjacent vascular structures, making this a preferred technique to evaluate many cardiac conditions, including pericardial and congenital abnormalities. MRI also provides excellent images that can be used to quantify cardiac function and structure. With the use of gadolinium contrast agents, MRI has been used to assess myocardial perfusion and viability.

Botnar RM et al: Coronary magnetic resonance angiography. Cardiol Rev 2001;9:77.