Novel insights regarding haemodynamics in focal seizures

We explored the temporal patterns of haemodynamic parameters in four seizures of three patients using the log-ratio method.

We identified three subjects who experienced a seizure during a tilt table test: one had two focal impaired awareness seizures (FIAS, seizures#1 and#2), one had one FIAS (#3), and one had a focal to bilateral tonic-clonic seizure (fbTCS, seizure#4). Recordings included video, heart rate (HR) and continuous blood pressure (BP). We used the log-ratio method to determine the relative contributions of HR, stroke volume (SV), and total peripheral resistance (TPR) to mean arterial pressure (MAP). A 'phase' was defined as a temporary departure of MAP, HR, SV or TPR from baseline.

BP showed a decrease in all four seizures. We observed one phase with synchronous events for all haemodynamic variables during seizures 1&2; seizure#3 showed one phase for MAP and TPR, three phases for HR, and only one for SV. Seizure#4 showed no autonomic involvement during the first minute of the focal seizure, after which MAP and HR showed an asynchronous triphasic course until the signal was lost when a tonic-clonic seizure occurred.

This chance sample illustrates that haemodynamic variables may change in different directions and asynchronously during focal seizures. We speculate that these complex autonomic patterns represent different ictal propagation pathways and that they may include ictal as well as corrective changes. BP decreased in all four seizures while the literature reports BP increases. As our patients were upright, not supine, we hypothesise that ictal haemodynamic changes impair normal control and are therefore likely to cause hypotension in the upright position.