Valsalva maneuver in detection of right-to-left shunt by transcranial Doppler

Abstract

979Opinion Sir: We read with great interest the study by Lange et al (Arq Neuropsiquiatr 2010;68:410-3) regarding the effect of valsalva maneuver (VM) in right-to-left shunt (RLS) detection by transcranial Doppler (TCD). We wish to highlight some relevant issues.Trans-esophageal echocardiography (TEE) is considered the gold-standard for diagnosing RLS. Although, TEE provides anatomical details of RLS, the real-time travel of a thrombus has been observed rarely 1 . Limitations of TEE include the need of an expert echocardiographer, poor tolerance by patients and often insufficient VM due to sedation and endoscope in the throat. In contrast, TCD is reliable, performed without sedation and carries high sensitivity and specificity as compared to TEE 2 . We disagree with the finding that the timing of VM does not influence the diagnosis of RLS. Considerable variations exist in the methodology for RLS detection, especially the timing of VM during the test performance. While VM has been performed simultaneously with the contrast injection in some studies 3 , others initiated it after a delay of 3-5 seconds 2 . Substantial hemodynamic changes occur during the "Strain-phase" (amplifies inter-atrial leftto-right pressure-gradient and counteracts RLS) as well as the "release-phase" (reverses pressure gradient with sudden increase in venous return and right atrial pressure that facilitate RLS) 4 . Furthermore, VM causes considerable reduction, and even complete stoppage, of flow in proximal large veins. Thus, the injection of saline-air contrast mixture during VM into a proximal vein (with elevated pressure and near-stagnant flow) does not seem logical. Injection during VM theoretically seems counterproductive since the high venous-pressure might destroy some of the "microbubbles" in "saline-air" contrast mixture. This assumes further significance as the microbubbles created during the vigorous shaking of the contrast mixture survive only for a short time. We believe that although, the timing of VM may not affect the detection of RLS, it might influence the functional grading of the shunt.Body position during the diagnosis of RLS needs special consideration. TEE, usually performed with patient lying in left-lateral position, is met with an adverse environment for air microbubbles -to travel from right atrium (at higher level) into the left atrium (at lower level) -thus challenging the basic physical fundamentals! We have demonstrated previously that multiple injections of contrast mixture during TCD are safe and "functional-grades" of RLS varies with body positions as larger number of microbubbles are detected in sitting position 5 . Larger studies with controlled conditions for various confounding factors are needed to develop a standardized protocol for RLS detection.

A Comparison of Transthroracic Echocardiograpy and Transcranial Doppler With Contrast Agent for Detection of Patent Foramen Ovale With or Without the Valsalva Maneuver

“…14 Another limitation is that TEE requires an excellent echocardiographer, patients cannot tolerant the test, and patients often failed to perform VM properly owing to sedation and endoscope in the throat. 15 These disadvantages limit the routine application of TEE. RLS across PFO can be detected with contrast agent with other 2 different modalities: contrast-transthoracic echocardiography (TTE) and contrast-transcranial Doppler sonography (c-TCD).…”

“…Because the functional grading of the cardiac shunt might influenced by VM. 15 A previous standardized c-TCD study reported that the VM increases the positive results 45% by increasing the right atrial pressure (RAP) to cause or reveal flow inversion through PFO. 16 We investigated the ability of TTE with or without VM to detect RLSs compared with TCD in patients suspected of PFO.…”

Influence of the Valsalva maneuver on cardiac hemodynamics and right to left shunt in patients with patent foramen ovale

“…At rest, the left atrial pressure exceeded right atrial pressure, and the left to right shunt via patent foramen ovale generally occurred. Right to left shunt did not occur at the strain phase of the Valsalva maneuver, but after the release phase of the Valsalva maneuver, when the patent foramen instantaneous opened19 (Fig. 5).…”