Contrast echocardiography: clinical applications

Abstract

Echocardiography is a highly effective method for study of cardiac anatomy and function. Since blood has fewer reflective characteristics than the myocardium, the cardiac chambers are seen as echo-free areas and no information about events in the bloodstream is obtained. Injection of a biologically compatible solution into the bloodstream, either in a peripheral vein or directly into the heart via a catheter, can make the blood “echogenic”, so it can be followed through the cardiac chambers. The effect is a result of the fact that with each injection a small amount of microbubbles of air with strong ultrasound reflective properties is introduced (10). These stream along with the blood and allow its visualization during echocardiographic studies. The microbubbles are entirely removed from the blood by the “sieve” action of the peripheral or pulmonary capillary bed (9). The echocardiographic contrast effect was first described by Gramiak and co-workers in 1968 and they used this method for identification of cardiac structures on M-mode echocardiograms (3). Originally they used direct catheter injections and indocyanine green as the contrast agent. It soon became apparent that contrast effect could also be obtained after peripheral injections of different agents, such as physiologic saline, 5% dextrose solution, the patient’s own blood aspirated into the syringe and directly re-injected. Dextrose and saline solutions are currently the most commonly employed contrast agents because they lack toxicity and are inexpensive. In most patients they yield adequate contrast intensity after both peripheral and central injections. If this is not the case, indocyanine green dye solution, freshly prepared and agitated, may improve the contrast yield since indocyanine green is a surfactant stabilizing the microbubbles of air in the solution (10). If this is still insufficient, a 0.5 to 2 ml of 100% carbon dioxide followed by a 5 to 8 ml “chaser” of 5% dextrose solution will provide adequate contrast (13).

Clinician-Scientist Awardee of the American Heart Association