Previous studies on autonomic regulatory system function have provided data that suggest altered autonomic function in patients with epilepsy. Ictal changes in HR and BP and other autonomic functions have been described in detail, but considerably less is known about the interictal alterations of cardiovascular regulation (Brown et al. 1953, Mosier et al. 1957, McKenna et al. 1970, Marshall et al. 1983, Gilchrist 1985, Wannamaker 1985, Blumhardt et al. 1986, Schraeder & Lathers 1989, Frysinger et al. 1993, Devinsky et al. 1994, Faustmann & Ganz 1994, Vaughn et al. 1996, Massetani et al. 1997, Messenheimer et al. 1997, Tomson et al. 1998, Druschky et al. 2001, Zijlmans et al. 2002). These previous studies have used either cardiovascular reflex tests or traditional analysis of HRV in assessing autonomic function in patients with epilepsy. However, it is known that cardiovascular reflex tests provide only a limited view of the cardiovascular autonomic control, since the responses are recorded under experimental conditions and for only a short period. Therefore, especially dynamic measures of HRV using ambulatory ECG recordings may reveal new aspects of cardiovascular control mechanisms and the pathophysiology which lead to autonomic dysfunction in various diseases (Mäkikallio et al. 1996).
The present study was designed to assess quantitatively the reflectory cardiac control with standard cardiovascular reflex tests, and the tonic autonomic cardiac regulation with HR fluctuation analysis from 24-hour ECG recording in epilepsy patients. Patients with previously untreated epilepsy, partial and idiopathic generalized epilepsies as well as refractory and well controlled TLE and TLE patients with or without hippocampal sclerosis were included in the substudies. The parameters of the cardiovascular reflex test were adjusted to the baseline RR interval, and the effect of age was taken into account in the statistical analysis. For the first time, the analysis of dynamic measures of HRV was used to study autonomic regulation in epilepsy. In addition, there was an attempt to resolve whether the cardiovascular reflex test and analysis of HRV from ambulatory ECG recordings can reveal similar alterations of autonomic function in epilepsy patients.
The effects of epilepsy and AEDs on cardiovascular autonomic regulatory functions are important because of the increased risk of SUDEP that accounts for approximately 10% of the deaths in epileptic population (Devinsky et al. 1994, Johnston et al. 1997, Ficker et al. 1998, Nashef et al. 1998, Nilsson et al. 1999, Sperling et al. 1999). Most likely this usually peri-ictal phenomenon is due to the autonomic regulatory system dysfunction presenting itself either as central apnea or cardiac arrhythmia (Devinsky et al. 1994, Johnston et al. 1997, Nashef et al. 1998, Nilsson et al.1999, Sperling et al. 1999). Postmortal examination does not reveal the cause of death, but signs of neurogenic injury of various organs, especially heart and lungs are often present. (Devinsky et al. 1994, Johnston et al. 1997, Nashef et al. 1998, Sperling et al. 1999, Thom et al. 1999). However, the primary cause of SUDEP and its association with focal anatomic cerebral changes still remain unknown.
MRI is considered as the best modern technique to reveal epilepsy specific anatomic changes of the brain. MRI also makes volumetric measures of the structures of the inner temporal lobe, e.g. the hippocampus and the amygdala, possible. With this delicate method, neuronal loss associated with TLE leading to atrophy of the structures can be measured (Jackson 1994, Cascino 1997). It is not known whether these TLE specific anatomic changes contribute to the alterations of autonomic function in patients with TLE, and the subject has not been previously studied.