Page 168 - Migraine, the heart and the brain

Chapter 9
Right-to-left shunts (RLS) which we found to be more prevalent in migraineurs with aura, can only (partially) explain the risk as these are only over-represented in migraineurs with aura. However we did nd a trend towards more cerebellar silent infarcts in subjects with RLS (see also part II, the heart and migraine).
ii migraine and the heart
We showed that the prevalence of RLS in migraine with aura was increased compared to controls without migraine and migraineurs without aura. (Chapter III) However, the relative risk was not as high as in clinic based studies, probably because in our study the occurrence of RLS was also relative common in the control group. In our study all investigators were blinded for migraine diagnosis, in contrast to the earlier clinic based studies, making our nding more likely to be reliable. A broad range of embolic structures is able to cause migraine attacks, although the occurrence of actual attacks in these speci c embolic rich circumstances seems quite low. (Chapter IV)
Both the nding of the association between RLS and migraine with aura in the general population, as well as the nding that persistence of migraine activity was associated with the presence of spontaneous RLS, add to the evidence of an association between RLS and migraine, especially in migraine with aura. Several hypotheses have been raised to explain the higher prevalence of RLS in this subtype of migraine. A widely accepted theory is that small emboli from the venous circulation bypassing the pulmonary lter by crossing a right-to-left shunt may induce migraine aura as these emboli reach the cerebral circulation. In this model the RLS enables emboli reaching the brain. Chapter V summarizes numerous case-reports of patients developing migraine aura after pathological induced emboli. From animal studies there is accumulating evidence that emboli can indeed induce cortical spreading depression, the underlying pathophysiological substrate of the aura phase. In patients with ischemic stroke these cortical spreading depressions have been recorded with subdural electrocorticography.15 Another theory is that RLS enables metabolites like serotonin or carbon dioxide from the venous circulation to enter the systemic circulation. Recently, it was shown that migraineurs with RLS have a reduced capacity of effective cerebral vasodilatation, which suggests that mentioned substances from the venous circulation may affect this auto-regulation.16 The evidence for a link between RLS and migraine aura is quite strong, although the actual role of RLS is probably limited.
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