Forebrain lateralization and the cardiovascular correlates of epilepsy

Two papers in this issue of Brain remind us that autonomic dysregulation and cardiac arrhythmias are not uncommon correlates of seizures (Druschky et al ., 2001; Tinuper et al ., 2001). These phenomena are important as mechanistic pointers towards the cause of sudden unexpected death in epilepsy (SUDEP). This condition has a frequency of ~0.5% and is independent of the type and severity of the convulsion (Leestma et al ., 1984). In a reported case of a patient who died unexpectedly whilst undergoing cardiac monitoring, a non-resuscitable malignant ventricular arrhythmia occurred, indicating the likely arrhythmogenic cause of SUDEP (Dasheiff and Dickinson, 1986). To what extent medication may be involved is unclear: many SUDEP patients have infrequent seizures and subclinical anticonvulsant levels. It has been suggested, therefore, that seizures originating from or spreading to forebrain areas of cardiovascular regulation (such as the insular cortex) desynchronize sympathovagal cardiac neural firing, which affects a heart destabilized by declining levels of anticonvulsant medication with potentially lethal consequences. Druschky and colleagues, using [123I]metaiodobenzylguanidine single photon emission computed tomography (MIBG SPECT) and heart rate variability analysis, indicate a reduction in cardiac sympathetic innervation in patients with chronic temporal lobe epilepsy (Druschky et al ., 2001). Whether this represents true denervation (secondary to transynaptic degeneration of forebrain …