A modified Valsalva maneuver increases the detection rate of patent foramen ovale in transcranial sonography

Aim : Patent foramen ovale (PFO) is discussed as a source of paradoxical embolism in cryptogenic stroke. In clinical routine, PFO can be diagnosed either by echocardiography or by transcranial ultrasound after application of an ultrasonic contrast agent. It is commonly recommended to start the Valsalva maneuver (VM) 10s after injection of the contrast agent in the right antecubital vein. The observation that in patients with known PFO microbubbles occur mainly a few seconds after the release of the VM and only sparsely during the maneuver itself, induced this study, in which we compared the rate of detected PFOs after performing the recommended VM to a modified technique. Methods: In 15 patients with cryptogenic stroke and already known PFO (diagnosed by echocardiography), the PFO test with transcranial ultrasound was performed in two ways consecutively: 1) recommended test (Widder et al., 2005): 5ml of ultrasound contrast agent (Echovist, Schering, Berlin) was injected in the right antecubital vein. After 10s the patients was requested to perform a VM for 5s. 2) modified test: Injection of Echovist was performed simultaneously with the onset of VM. The patients was requested to release the VM 5s after Echovist injection was completed. Results: In both versions of the PFO test, microbubbles occurred mainly after the release of the VM. With the modified version the count of high intensive transient signals (HITS) was higher then with the established method. In some of the patients HITS were only detectable, when the test was performed in the modified version. Discussion : We demonstrate that the right-to-left interatrial shunt is effective mainly during the release phase of the VM and not during the strain phase. This is in accordance to studies that used indicator dilution techniques to detect shunt flow via PFO (Cheng, 2005). Increased intrathoracical pressure during VM reduces the venous backflow and therefore increases the concentration of the contrast agent in the right atrium. We propose to use this modified test in those patients in whom the conventional technique fails to demonstrate a PFO.