Q: On agitated saline contrast echocardiography, appearance of bubbles in the left heart within how many beats after contrast opacification of the right atrium is highly suggestive of intracardiac shunt, mostly PFOs? (Read suggestive not diagnostic)

A)  There is no correlation
B)  At least 3 beats
C) At least 5 beats
D) At least 7 beats 
E) Requires full one minute of wait


Answer: B

The Objective of above question is to emphasize the importance of timing of the appearance of agitated saline contrast, popularly called bubbles, in the left heart on echocardiography. Early contrast appearance in the left heart - within three beats of contrast appearance in the right heart - suggests intracardiac shunting like PFO or ASD. But if it takes more than 3 beats for contrast to appear in the left heart after a contrast opacification of the right atrium is more suggestive of  pulmonary arteriovenous shunting. Please note, this is just a rule of thumb, as there have been reports in the literature of failure of this 3 beats rule.  All ECHOs should be strongly read in correlation with other data and clinical scenarios.




References: 

Woods TD, Patel A. A critical review of patent foramen ovale detection using saline contrast echocardiography: when bubbles lie. J Am Soc Echocardiogr 2006; 19:215. 

Freeman JA, Woods TD. Use of saline contrast echo timing to distinguish intracardiac and extracardiac shunts: failure of the 3- to 5-beat rule. Echocardiography 2008; 25:1127.