Original article
A Critical Review of Patent Foramen Ovale Detection Using Saline Contrast Echocardiography: When Bubbles Lie

https://doi.org/10.1016/j.echo.2005.09.023Get rights and content

Saline and indocyanine green dye were the first agents noted to produce a contrast effect when injected peripherally during M-mode echocardiographic imaging, although it was subsequently found that almost any type of injected solution would have this effect. These first-generation contrast agents were limited to opacification of right heart structures, and they prompted subsequent development of agents that traverse pulmonary circulation. Although opacification limited to right heart structures is considered a limitation of these first-generation agents, this is an advantage when attempting to identify the presence of right-to-left shunt. First-generation air contrast is considered the gold standard for identification of patent foramen ovale (PFO). However, PFO investigators have used varying criteria to define abnormal contrast studies. There are also multiple mechanisms by which saline contrast studies may produce both false-positive and false-negative results for presence of PFO. There is mounting experimental evidence that PFO is associated with cerebral ischemia and migraine headache, with a resulting evolution of devices for percutaneous closure of these shunts. Echocardiographic physicians must be aware of potential pitfalls of the air contrast technique to avoid exposing patients to unnecessary risk of closure devices, and missing the potential benefit of shunt closure in appropriately selected patients.

Section snippets

Microbubble Origin

Early investigators like Kremkau et al5 were among those whose in vitro experiments with distilled water, saline, and sucrose solution suggested that microbubble formation is caused by cavitation. When fluids are rapidly injected through a catheter, the hydrostatic pressure at the tip of the catheter is reduced, allowing dissolved gas to come out of solution to form transient microbubbles. It was demonstrated in subsequent experiments by Ziskin et al6 that almost any fluid, if rapidly injected

Clinical use of saline contrast in identification of shunt

Saline contrast use has been described for identification of cardiac structures,3 evaluation of complex congenital heart disease,13 enhancement of intracardiac Doppler signals,14 and needle localization during percutaneous drainage of pericardial effusion.15 Its most common use, however, has been in the detection of intracardiac shunt. With evolving interest in percutaneous closure of intracardiac defects, there is increasing reliance on the use of saline contrast echocardiography in clinical

What Quantity of Left Heart Contrast is Abnormal?

Since the origin of the 3-beat rule, there has been wide variation among investigators as to what quantity of LA contrast must appear before diagnosing the presence of a PFO. In 1994, when describing the use of TEE for identification of PFO, Homma et al30 defined as little as one microbubble in the LA to be abnormal during a saline contrast study. Mas et al,21 from the PFO and Atrial Septal Aneurysm Study Group, and Martin et al,31 studying the effects of PFO closure, required the presence of

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