Response to Letter by Magrini et al
Magrini and associates argue that particular working conditions entailing frequent Valsalva maneuvers may represent a risk factor for the development of migraine in subjects with right-to-left shunt. This is a clever and intriguing observation that, besides being biologically plausible, raises the hypothesis, never considered so far, that the beneficial effect of atrial septal repair on migraine in stroke patients might result not so much from the correction of the shunt but mainly from changes in lifestyle that reduce the number or the strength of Valsalva strains. This variable will have to be taken into account in future studies.
However, the case reported by Magrini et al hardly fits with their assumption inasmuch as the degree of the detected shunt (4 bubbles after Valsalva) is by far too modest to be considered relevant not only for migraine, but also for the reported MRI abnormalities. Therefore, psychological factors may have played a major role in reducing headache severity under less demanding working conditions in the reported case. An alternative explanation, however, which would be consistent with Magrini et al theory, is that the degree of shunt in the reported patient is posture-dependent. There are examples in the literature of postural right-to-left shunt such as in the platypnea-orthodeoxya syndrome1 in which the shunt may increase in the standing position up to a point to produce a significant desaturation in blood oxygen. Increasing number of bubbles in standing as compared with the recumbent position have been reported in patients undergoing contrast-enhanced transcranial Doppler for diagnostic purposes.2,3
In a consecutive series of 26 subjects (M/F=6/20, age 44±14) with proven right-to-left shunt, we used contrast-enhanced transcranial Doppler to assess the bubble load in the right middle cerebral artery during normal breathing both in standing and in recumbent position. Half the subjects were first tested while standing, half were tested in the reversed order. Data were analyzed with a repeated measure ANOVA with POSITION (horizontal versus vertical) as within subjects and ORDER of testing (first while horizontal versus first while vertical) as between subjects factors. The POSITION factor was statistically significant (F=6587, P=0.017) with an average of 12 and 29 bubbles detected during recumbent and standing position, respec-tively. The effect was independent of the testing order (see the Figure). Fourteen subjects showed an increase in the bubble number from the horizontal to the upright position, 7 exhibited the same number, whereas in 5 the amount of shunt decreased on standing.
These findings indicate that the amount of permanent (ie, detectable on normal breathing) right-to-left shunts is posture-dependent even in normal subjects to an extent that may be variable between 1 individual and the other. Testing in upright position may thus be warranted in those cases in whom the usual assessment performed with the subject in horizontal position yields doubtful or inconclusive results.
Godart F, Rey C, Prat A, Vincentelli A, Chmait A, Francart C, Porte H. Atrial right-to-left shunting causing severe hypoxaemia despite normal right-sided pressures. Report of 11 consecutive cases corrected by percutaneous closue. Eur Heart J. 2000; 21: 483–489.
Schwarze JJ, Sander D, Kukla C, Wittich I, Babikian VL, Klingelhöfer J. Methodological parameters influence the detection of right-to-left shunts by contrast Transcranial Doppler ultrasonography. Stroke. 1999; 30: 1234–1239.