Effects of patient position on right-to-left shunt detection by contrast transcranial Doppler

The Role of Transcranial Doppler in Detecting Patent Foramen Ovale

Air embolic signals detected in the intracranial arteries using transcranial Doppler after intravenous injection of agitated saline bubbles indicate right-to-left cardiac shunting. They prove that emboli from venous sites can bypass the lungs and flow to the intracranial arteries. The Valsalva maneuver immediately after an intravenous injection of agitated saline bubbles helps the air bubbles pass through the shunt. If the air embolic signal appears in the intracranial arteries without the Valsalva maneuver, the shunting is highly significant to the etiology of embolism. Transcranial Doppler to detect air embolic signals after intravenous injection of agitated saline bubbles may not be mandatory to diagnose and treat patent foramen ovale; however, as with echocardiography, transcranial Doppler is considered a noninvasive, convenient, and low-cost investigation. The test should be helpful to confirm the significance of the corresponding patent foramen ovale.

Comparison of Unilateral Middle Cerebral Artery and Bilateral Middle Cerebral Artery Monitoring for Right-to-Left Shunt Detection by Contrast-Enhanced Transcranial Doppler

Introduction

Contrast-enhanced transcranial Doppler (c-TCD) is a noninvasive test with high sensitivity for the detection of a right-to-left shunt (RLS). Currently, there are no reports on the outcomes of unilateral versus bilateral middle cerebral artery (MCA) monitoring. This study compared the positivity rate of bilateral MCA monitoring with unilateral MCA monitoring for RLS using c-TCD.

Methods

We enrolled 239 patients (86 women and 153 men) with a mean age of 48.54 ± 13.25 years (range, 14–79 years), who underwent c-TCD examination in the Department of Transcranial Doppler Ultrasound of our hospital between February 2018 and February 2021, due to suspicion of RLS. Bilateral MCA monitoring of 239 patients was performed using dual-channel and dual-depth c-TCD. The positive rate and shunt classification of RLS were calculated for left, right, and bilateral MCA monitoring. The differences in RLS detected by c-TCD monitoring of the left, right and bilateral MCA were compared.

Results

In the left middle cerebral artery (LMCA) monitoring, 35.56% (85 of 239) had a positive RLS result, 38 cases were permanent (44.70%), and 47 cases were latent (55.30%). In the right middle cerebral artery (RMCA) monitoring, 36.82% (88 of 239) had a positive RLS result, 38 cases were permanent (43.18%), and 50 cases were latent (56.82%). In the bilateral MCA group, 43.09% (103 of 239) had a positive RLS result, 50 cases were permanent (48.54%) and 53 were latent (51.46%). The positive rate of bilateral MCA monitoring was higher than that of LMCA and RMCA (43.09, 35.56, and 36.82%, respectively), and the difference was not statistically significant (P = 0.193). The positive rate of bilateral MCA monitoring was higher than that of LMCA and RMCA for mild and moderate shunts, but the difference was not statistically significant. The positive rate of bilateral MCA monitoring was equal to that of RMCA, but higher than that of LMCA, with no statistical significance. LMCA monitoring revealed 85 patients with RLS. The sensitivity was 82.52% (85/103). The specificity was 100%. The RMCA monitoring results showed 88 cases with RLS. The sensitivity was 85.44% (88/103). The specificity was 100%.

Conclusions

There was no significant difference in the RLS detection rate between unilateral and bilateral MCA monitoring using c-TCD. Bilateral MCA monitoring may be more advantageous for mild RLS detection.

Simultaneous monitoring of the middle cerebral and basilar arteries to detect right-to-left shunts using transcranial Doppler by agitated saline administration

Transcranial Doppler (TCD) is an easy, non-invasive, and real-time monitoring device for detecting right-to-left shunts (RLS). Nonetheless, it has limited benefits in patients with poor temporal windows. Therefore, we aimed to investigate whether the basilar artery (BA) window was as effective as the middle cerebral artery (MCA) in detecting RLS during TCD monitoring. Overall, we enrolled 344 patients with stroke, transient ischemic attack, headache, or dizziness. MCA and BA were monitored using a modified headset. To investigate the feasibility of the suboccipital window in detecting RLS, we instituted an evaluation tool with three tiers to evaluate microembolic signals (MESs) during TCD monitoring. Tier 1: TCD monitoring of the MCA (bilaterally) in the resting state, tier 2: TCD monitoring of the MCA (bilaterally) while performing the Valsalva maneuver, and tier 3: TCD monitoring of the index MCA and BA while performing the Valsalva maneuver. In tiers 2 and 3, a high agreement rate of 0.808 and 0.809 (p < 0.001), respectively, on the weighted kappa index, and a high intra-class correlation coefficient of 0.982 and 0.986 (p < 0.001), respectively, were observed on detecting MESs. Our data suggests that the BA window is as effective as the MCA window for detecting RLS on TCD.

Comparison of Different Methods of Valsalva Maneuver for Right-to-left Shunt Detection by Contrast-Enhanced Transcranial Doppler

We evaluated 298 patients for right-to-left shunt (RLS) detection by contrast-enhanced transcranial Doppler at rest state (RS), during the conventional Valsalva maneuver (CM), and during the modified Valsalva maneuver (BM: blowing into the connecting tube of a sphygmomanometer at 40 mm Hg for 10 s) in random order, and the degree of RLS along the time of the first microbubble occurrence was recorded. The positive rates were 21.8%, 36.9% and 47.3% for RS, CM and BM, respectively (p < 0.001). BM resulted in a significantly higher positive rate (p = 0.010), and there was a significant difference between the two different methods of VM in terms of the degree of RLS detection (p < 0.001). Further, the first microbubble occurred later during BM than CM (10.22 ± 3.77 s vs. 9.44 ± 4.36 s, p < 0.05). This modified maneuver is an alternative to the conventional one, especially for those who cannot perform the conventional maneuver adequately, but are highly suspected of having RLS.

Comparison of Vertebral Artery and Middle Cerebral Artery Monitoring for Right-to-left Shunt Detection by Contrast-enhanced Transcranial Doppler

Contrast-enhanced transcranial Doppler (c-TCD) is a reliable and reproducible method for right-to-left shunt (RLS) detection, with high sensitivity. Monitoring the middle cerebral artery (MCA) is an optimal choice, yet for patients with insufficient temporal bone windows or severe stenosis of carotid arteries, an alternative should be established. The aim of the present study was to further establish whether c-TCD with vertebral artery (VA) monitoring is as effective as MCA monitoring for RLS detection. We evaluated 194 subjects for RLS detection with VA and MCA monitoring simultaneously. There was no significant difference between the positive rates of VA and MCA monitoring for RLS detection. c-TCD with VA monitoring could be an alternative for RLS detection, with high sensitivity and specificity both at rest and during the Valsalva manoeuvre.