Non-invasive Cardiac Imaging

Janet Wong, M.D.

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 for detection of cardiac valve calcium as well as epicardial calcium (see cine CT). The chest x-ray is also helpful to demonstrate upper zone redistribution, pleural effusions, and Kerley B-lines indicative of congestive heart failure.

Echocardiography
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. Three general types of studies may be performed, M-mode echocardiography, two-dimensional (2D) echocardiography, and Doppler echocardiography. M-mode and 2D imaging are useful for quantifying chamber sizes, ventricular systolic function, wall thickness, and valvular morphology while Doppler echocardiography, which measures blood flow velocity and includes pulsed wave, continuous wave and color Doppler methods, is most valuable for assessing valvular function.

Quantitative data regarding left 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. The crescent shaped right ventricle is more difficult to assess, and only qualitative analyses from 2D data are generally used. Left atrial chamber size may also be quantified by 2D transthoracic echocardiography. While left ventricular thrombi are easily appreciated from transthoracic approaches, left atrial thrombi are best visualized using The physical examination provides a tremendous amount of information we get from that. Just the general appearance of our patients. Is there evidence of peripheral cyanosis? Are they dyspneic? Is there evidence of exophthalmus, the fundi? Again, in patients with hypertension especially diabetes. Looking at jugular venous distension. Examining the carotid pulse. Is it delayed, is there a bi-fib pulse - the bi-fib pulse being suggestive of a hypertrophic obstructive cardiomyopathy? Examining the lungs for rales, effusions. The heart for PMI as well as murmurs. It is important in your patients to have the patients turn in the left lateral decubitus position to hear mitral murmurs and if you are concerned about aortic insufficiency, certainly have them sit up and forward with an exhalation examination. Finally, the abdominal examination - ascites, organomegaly and the extremities.
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