To the Editor:
We thank Professor Naqvi for her positive comments about our papers regarding the diagnosis of patent foramen ovale (PFO). We share her wish to optimize examining technique and to minimize the number of injections during contrast transesophageal echocardiography (TEE) in clinical practice.
In the original study, we used a multitude of injections because the study was designed to explore mechanisms. The results indicate that it is possible to increase the accuracy of PFO detection by optimizing injection technique and that adequate PFO diagnosis is possible with fewer injections.
The suggested technique includes several Valsalva maneuvers during TEE. The initial Valsalva maneuver should be performed without contrast injection to ensure that the maneuver really causes the interatrial septum to bulge toward the left atrium. The bulging of the atrial septum and opening of PFO is often best visualized in about 60°.
We used agitated polygeline as a contrast agent, because this agent creates dense contrast, which is beneficial for PFO detection. Two milliliters of polygeline was agitated with 0.2 mL of air and the solution rapidly injected together with a flush of 5 mL of saline. Our experience is that this small amount of contrast solution creates more intense contrast than 9 mL of saline agitated with 1 mL of air. The use of polygeline also makes it possible to reduce the amount of injected air, which may increase patient safety in the presence of a right-to-left shunt.
The suggested technique includes repeated contrast injections when (1) no right-to-left shunt is seen and (2) the echocardiographic image reveals characteristics of false-negative injections: the absence of leftward bulging of the atrial septum at the same moment as dense contrast filling of the right atrium adjacent to the septum occurs. On the other hand, when the atrial septum demonstrates leftward bulging at the same moment as dense contrast filling of the right atrium (adjacent to the atrial septum) occurs, our opinion is that two such injections will be enough to exclude the presence of a PFO.
In the presence of a PFO, the association with cryptogenic stroke is stronger when shunting occurs also during normal respiration at rest. Besides visual contrast passage, resting shunt through an existing PFO may be inferred when the interatrial septum bulges (intermittently) toward the left. Injection during resting respiration may also help distinguish interatrial shunting from a (concomitant) intrapulmonary shunt, as an intrapulmonary shunt is not dependent on pressure changes during the respiratory cycle and is present both at rest and also during the Valsalva maneuver.
Because there are a variety of techniques for contrast TEE, we share Professor Naqvi’s opinion that there is a great need for international guidelines regarding PFO detection with contrast TEE.