The "Bubble Study" For PFO

echocardiogram
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A bubble study is a noninvasive test that allows physicians to assess the flow of blood through the heart. It is typically used in conjunction with an echocardiogram or a transcranial Doppler study (TCD). A bubble study is often performed when a patent foramen ovale (PFO) is suspected.

How A Bubble Study Is Done

In a bubble study, a saline solution is shaken vigorously to produce tiny bubbles and is then injected into a vein.

As the bubbles travel through the vein and into the right side of the heart, an echocardiogram allows the physician to watch the bubbles move through the cardiac chambers.

Normally, the bubbles will be seen entering the right atrium, then the right ventricle, then out the pulmonary artery and into the lungs, where they are filtered out of the circulation.

However, if the bubbles are seen entering the left side of the heart, this indicates that there is an abnormal opening between the two sides of the heart- a so-called intracardiac shunt.

Such an intracardiac shunt can be produced, for instance, by a PFO, an atrial septal defect, or a ventricular septal defect.

Bubble Studies For Patent Foramen Ovale

The most common reason for performing a bubble study is to look for a PFO. In these studies, while the bubbles are being injected into the vein, the patient is asked to perform a valsalva maneuver (that is, bearing down as if having a bowel movement).

The valsalva maneuver transiently raises the pressures in the right side of the heart, so that if a PFO is present, the bubbles can often be seen entering the left atrium. Bubbles appearing in the left atrium confirm the presence of a PFO.

The main reason doctors worry about PFOs is the possibility that they might allow blood clots to cross into the left side if the heart, where the might enter the circulation of the brain and produce an embolic stroke.

Fortunately, while PFOs are quite common (occurring in up to 25% of adults), they lead to stroke only rarely. So, while a positive bubble study might confirm the presence of a PFO, it does not tell the doctor much about the likelihood of stroke.

Recent evidence suggests that a better way to assess whether a PFO is likely to produce a stroke is to perform a TCD in conjunction with a bubble study.

The TCD study can detect whether the bubbles injected into a vein are actually entering the brain circulation. If so, the PFO appears to be more likely to increase the risk of stroke, and the doctor will be more likely to recommend anticoagulation therapy, or, if a stroke has already occurred, possibly surgical closure of the PFO.

Sources:

Mulvagh SL, Rakowski H, Vannan MA, et al. American Society of Echocardiography Consensus Statement on the Clinical Applications of Ultrasonic Contrast Agents in Echocardiography. J Am Soc Echocardiogr 2008; 21:1179.

Romero JR, Frey JL, Schwamm LH, et al. Cerebral ischemic events associated with 'bubble study' for identification of right to left shunts. Stroke 2009; 40:2343.

Parker JM, Weller MW, Feinstein LM, et al. Safety of ultrasound contrast agents in patients with known or suspected cardiac shunts. Am J Cardiol 2013; 112:1039.

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