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Non-invasive Cardiac Imaging

Chest X-Ray

The chest X-ray provides information about the size and configuration of the heart and great vessels, as well as pulmonary vasculature, and pleural effusions. Cardiac chamber dilation, rather than wall thickening is generally perceived as an alteration in cardiac silhouette. Routinely posteroanterior (PA) and lateral chest films are obtained. Enlargement of the fight atrium may cause bulging of the heart to the fight on the PA film, while fight ventricular enlargement is generally perceived as a filling of the anterior clear space on the lateral film. Left atrial enlargement may be detected by an upward displacement of the left main-stem bronchus, or posterior displacement of the barium filled esophagus on lateral films. Left ventricular enlargement is the most common finding on chest x-ray, generally results in an increased cardiothoracic ratio (> 0.50). Pericardial effusions may be suspected by an enlarged cardiac silhouette with "water bottle" appearance. Fluoroscopy, more often performed in the cardiac catheterization suite, generally confirms minimal motion of cardiac borders. Fluoroscopy is also more sensitive.


Echocardiography uses ultrasound to image the heart and great vessels. It is widely regarded as the technique of choice for evaluation of suspected valvular heart disease. Its ease of use, high temporal and spatial resolution, and lack of complications also makes it ideal for assessment of cardiac chamber size and systolic function, though comprehensive left ventricular endocardial borders may be difficult to identify in a significant minority (20%) of patients.

Quantitative data regarding left echocardiography ventricular wall thickness and chamber dimensions are generally measured using M-mode methods, a technique which uses very high temporal (>1000 Hz) resolution, while qualitative global and regional left ventricular systolic function is generally best appreciated using 2D methods. Automated endocardial edge-detection techniques have recently been introduced for "real-time" analysis of global systolic indices, but these algorithms make many assumptions regarding the ventricular geometry (symmetry) which may not be applicable to the individual patient. Complications of myocardial infarction such as left ventricular aneurysm or left ventricular apical thrombi are readily identified by 2D transthoracic echocardiography.

Assessment of valvular heart disease is the "bread-and butter" of echocardiography, and the need for confirmatory cardiac catheterization for many of these lesions has recently been questioned. Mitral stenosis, most commonly the result of rheumatic heart disease is characterized by leaflet thickening, calcification, and immobility. Mitral valve area may be assessed either by direct planimetry or Doppler assessment of the pressure half-time, (time needed for the pressure gradient across the mitral valve to decrease by 50 percent). The longer the pressure half-time, or the longer it takes for the gradient across the mitral valve.

Pressure = 4 [velocity]2

In the setting of normal left ventricular systolic function, aortic gradients exceeding 4 cm/sec (pressure gradient > 64 mmHg) indicate severe aortic stenosis (aortic valve area < 0.7 cm2).

In the late-1980's, transesophageal echocardiography (TEE) was commercially introduced in the United States. Due to the proximity of the esophagus to the heart and thoracic aorta, and lack of interposed lung or bone, higher frequency transducers may be used, allowing for superior spatial resolution. Indications for TEE include: inadequate transthoracic studies (especially post-thoracotomy or ventilated patients), suspected aortic dissection, endocarditis with vegetations.

Radionuclide Imaging

Radionuclide ventriculography (RVG) or MUGA uses technetium 99m labeled red cells to delineate cardiac chambers. The first pass technique also allows for identification of intracardiac shunts while the equilibrium method records from at least two views and averages data over several minutes to give an(EF):

The technique is accurate to +5% and is considered the best clinical test for quantitation of global left ventricular ejection fraction.

Radionuclide techniques are more commonly used for assessment of regional myocardial perfusion. For many years, thallium 201, an analog of potassium was the most commonly used agent.