LETTER TO THE EDITOR

Size of patent foramen ovale and

amount of microembolic signals in

patients with ischaemic stroke

V. K. Sharma

Division of Neurology, National University

Hospital, Singapore

Correspondence: Dr Vijay Sharma,

Division of Neurology, Department of

Medicine, National University Hospital,

119074 Singapore (tel.: +65 67722597;

fax: +65 68723566;

e-mail: drvijay@singnet.com.sg).

Keywords: acute ischaemic stroke,

patent foramen ovale, transcranial

Doppler

Received 7 October 2008

Accepted 20 October 2008

Sir,

I read with interest the article by Telman

et al. [1] regarding the relationship be-

tween size of patent foramen ovale (PFO)

and the number of microembolic signals

(MES) in ischaemic stroke patients.

Their findings are important in under-

standing aetiopathogenic role played by

PFO.

Trans-oesophageal echocardiography

(TEE) employed to diagnose and estimate

the size of PFO, is poorly tolerated and

the sedation limits patients� ability for

performing adequate valsalva maneuver.

Authors [1] should be congratulated to

overcome these limitations by comple-

menting TEE with transcranial Doppler

(TCD). There are certain important issues

related to the TCD performance and

interpretation.

First, mere detection of PFO does not

delineate its true aetiological role and

�functional-potential�. TCD is considered

as more sensitive and specific than TEE

for PFO detection [2] as well as quantify-

ing its �functional-potential [3]�. Using

power M-mode TCD enhances the sensi-

tivity, because of its overlapping and

contiguous multiple gates [4]. Secondly,

patient�s position during PFO testing sig-

nificantly affects the results. MES being

lighter have an inherent tendency to rise

up due to buoyancy, therefore, echocar-

diography traditionally performed in the

left-lateral position provides a physiolog-

ically unreasonable travel path for MES,

from the physically �higher� right-atriuminto the �lower� left-atrium-defying the

well-established principles of physics!

TCD can be performed in any anatomic

position and we have previously demon-

strated that the �functional-grading� ofPFO varies with different body positions,

with larger number of MES detected in

the sitting position [5]. Probably, these

methodological factors have contributed

to some of the discrepancies between the

size of PFO on TEE with the number of

microemboli observed on TCD [1]. De-

spite the statistical significance, this is

clearly evidenced even in this study [1] –

six of 22 patients with multiple emboli

(>48) had small and 10/22 had moderate-

sized PFO instead of the �expected� large-sized PFO. As rightly mentioned by

authors [1], this discrepancy could be

avoided by performing TEE and TCD

simultaneously.

In conclusion, relationship between the

size of PFO and its functional-potential is

not linear. While TEE may be performed

to detect the presence, location and size of

PFO, TCD should be employed to deter-

mine its functional-grade. The latter may

assume important logical proportions, if

closure of PFO is indicated.

References

1. Telman G, Yalonetsky S, Kouperberg E,

Sprecher E, Lorber A, Yarnitsky D. Size of

PFO and amount of microembolic signals in

patients with ischaemic stroke or TIA.

European Journal of Neurology 2008; 15:

969–972.

2. Jauss M, Kaps M, Keberle M, Haberbosch

W, Dorndorf W. A comparison of trans-

esophageal echocardiography and transcra-

nial Doppler sonography with contrast

medium in the detection of patent foramen

ovale. Stroke 1994; 25: 1265–1267.

3. Belvis R, Leta RG, Marti-Fabregas J, et al.

Almost perfect concordance between simul-

taneous transcranial Doppler and trans-

esophageal echocardiography in the

quantification of right-to-left shunts. Jour-

nal of Neuroimaging 2006; 16: 133–138.

4. MoehringMA, Spencer MP. PowerM-mode

Doppler (PMD) for observing cerebral

blood flow and tracking emboli. Ultrasound

in Medicine and Biology 2002; 28: 49–57.

5. Lao AY, Sharma VK, Tsivgoulis G, Malk-

off MD, Alexandrov AV, Frey JL. Effect of

body positioning during transcranial

Doppler detection of right-to-left shunts.

European Journal of Neurology 2007; 14:

1035–1039.

e12� 2008 The Author(s)

Journal compilation � 2008 EFNS

European Journal of Neurology 2009, 16: e12 doi:10.1111/j.1468-1331.2008.02403.x