Effects of Posture 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.

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.

Body positions in the diagnosis of right-to-left shunt by contrast transcranial Doppler

Contrast transcranial Doppler (c-TCD) is sensitive in detecting right-to-left shunt (RLS). However, the methodology and ideal posture are controversial. Consecutive migraine patients were prospectively examined for RLS using c-TCD. Each patient was examined while at rest and subsequently with the Valsalva maneuver (VM) in three positions: supine, left lateral decubitus and right lateral decubitus. RLS was diagnosed with at least one microbubble detected at any position. RLS was highest in the left lateral decubitus position, both during rest and with VM. The left lateral decubitus position was associated with the highest total number of microbubbles and greater shunt grades. Patients who tested positive in the other two positions had the lowest index position failure rate during rest in the left lateral decubitus position. In some patients in whom RLS is detected at rest, it may not be detected (false negative) under VM. To ensure c-TCD's the sensitivity to RLS, testing in the left lateral decubitus position at rest and under VM is suggested; testing in other positions is necessary to avoid false negatives.

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

Contrast-enhanced transcranial Doppler (c-TCD) was performed on 117 patients to detect a right-to-left shunt (RLS). Each patient was examined during normal breathing and after performing the Valsalva maneuver (VM) in three randomly ordered positions: supine, left lateral decubitus and sitting upright. When breathing normally, RLS-positive rates were 15.4%, 23.1% and 28.2% for supine, left lateral decubitus and upright sitting positions, respectively. After VM, the positive rates were 25.6%, 28.2% and 36.8%, respectively. For each position, the RLS-positive rates were higher after VM than normal breathing and higher for the left lateral decubitus and upright sitting positions compared with the supine position, irrespective of breathing. There were no significant differences between findings for the left lateral decubitus and upright sitting positions. No significant differences in shunt grades were found across all groups. The choice of position for patients undergoing c-TCD can improve its sensitivity for the diagnosis of RLS.

Platypnea-orthodeoxia: a rare complication after repair of a contained rupture of an abdominal aortic aneurysm

After open repair of a contained rupture of a giant abdominal aortic aneurysm, the patient, a 67-year-old man, developed respiratory insufficiency, and his hemoglobin oxygen saturation dramatically decreased when his position was changed from supine to upright. Transesophageal echocardiography revealed platypnea-orthodeoxia syndrome due to a patent foramen ovale and subsequent right-to-left-shunting despite normal intracardiac pressures. After interventional patent foramen ovale closure, the patient could be separated from the respirator without difficulty.

Transcranial Doppler with bubble study as a method to detect extracardiac right-to-left shunts in patients with ischemic stroke

BACKGROUND AND PURPOSE

Paradoxical embolism through extracardiac right-to-left shunts (ECRLS) may represent an under-detected stroke mechanism. Stroke patients without evidence of cardiac right-to-left shunt (RLS) on echocardiogram may benefit from transcranial Doppler with bubble study (TCD-b) to aid in recognition of stroke etiology. This study assesses the usefulness of TCD-b in the stroke evaluation.

METHODS

Retrospective cohort study of consecutive patients undergoing TCD-b performed in our neurovascular laboratory from February 2005 to August 2009. Echocardiography results were reviewed in patients with positive TCD-b. Detailed medical record review was performed on patients with positive TCD-b and negative echocardiogram findings for RLS.

RESULTS

Of 502 patients undergoing TCD-b, 48.4% (n = 243) had a positive study suggesting the presence of RLS. Of these, 59.2% (n = 144) had an echocardiogram demonstrating a cardiac RLS, 26% (n = 63) had echocardiograms without evidence of cardiac RLS, and 14.8% (n = 36) had no echocardiogram. Data on the evaluation to determine source of potential shunting in patients with discrepant findings was available in 11(17.5%). Of these, 63.6% (7/11) had potential mechanisms for positive TCD-b: one pulmonary arteriovenous malformation (AVM), one arteriovenous fistula thrombus, one parietal AVM, and four had malignancy.

CONCLUSIONS

TCD-bubble studies may prove useful in uncovering treatable causes of stroke.