Pharmacologic evidence for a parasympathetic role in seizure-induced neurocardiac regulatory abnormalities

Heart rate variability in neonatal patients with seizures

OBJECTIVE

Seizures are frequently observed in neurological conditions affecting newborns. Since autonomic alterations are commonly associated with neonatal seizures (NS), we investigated the utility of heart rate variability (HRV) indexes of cardiac autonomic regulation for NS detection.

METHODS

HRV analysis was conducted on ECG tracings recorded during video-EEG monitoring in newborns with NS and matched-controls. The effects of gestational age on HRV were also evaluated.

RESULTS

Newborns with NS showed lower resting state HRV compared to controls. Moreover, seizure episodes were characterized by a short-lasting increase in vagal indexes of HRV. Pre-term newborns with NS had a lower HRV than full-term at rest. In pre-term newborns, no changes in HRV were observed before and during NS. On the contrary, full-term newborns showed significantly higher HRV before and during NS compared to the respective baseline values.

CONCLUSION

Our data point to resting autonomic impairment in newborns with NS. In addition, an increment in HRV has been observed during NS only in full term newborns.

SIGNIFICANCE

Although these findings do not allow validation of HRV measures for NS prediction and detection, they suggest that a putative protective vagal mechanism might be adopted when an advanced maturation of autonomic nervous system is achieved.

In a heartbeat: Autonomic changes during seizures

Abnormalities in Cardiac and Respiratory Function Observed during Seizures in Childhood

O'Regan ME, Brown JK

Dev Med Child Neurol 2005;47:4–9

The aim of this study was to observe any changes in cardiac and respiratory function that occur during seizures. Thirty-seven children (20 boys, 17 girls; median age, 7 years 6 months; range, 1 year 6 months to 15 years 6 months) were studied. We recorded electroencephalograms, respiratory rate, heart rate, electrocardiograms, blood pressure, oxygen saturation, heart rate variability (time-domain analysis), and cardiac vagal tone. A respiratory pause was defined as an interruption in respiration lasting more than 3 seconds but less than 15 seconds. Apnea was defined as absence of respiration for more than 15 seconds. Tachypnea was defined as a 10% increase in respiratory rate from the preictal baseline. Bradypnea was defined as a 10% decrease in respiratory rate from the preictal baseline. Significant hypoxia was defined as a saturation of less than 85%. A significant change in heart rate was taken as a 10% increase or decrease below the baseline rate. Data were obtained from 101 seizures: 40 focal seizures, 21 generalized seizures, and 40 absences. Focal seizures were frequently associated with significant respiratory abnormalities, tachypnea in 56%, apnea in 30%, frequent respiratory pauses in 70%, and significant hypoxemia in 40%. The changes seen in respiratory rate were statistically significant. Changes in cardiac parameters, an increase or decrease in heart rate, were observed in only 26% of focal seizures and 48% of generalized seizures. We conclude that seizure activity can disrupt normal physiologic regulation and control of respiratory and cardiac activity.

Cardiac Arrhythmias in Focal Epilepsy: A Prospective Long-term Study

Rugg-Gunn FJ, Simister RJ, Squirrell M, Holdright DR, Duncan JS

Lancet 2004;364:2212–2219

Purpose

Patients with epilepsy are at risk of sudden unexpected death. Neurogenic cardiac arrhythmias have been postulated as a cause. Electrocardiograms (ECGs) can be monitored by use of an implantable loop recorder for up to 18 months. We aimed to determine the frequency of cardiac arrhythmias in patients with refractory focal seizures over an extended period.

Methods

Twenty patients received an implantable loop recorder at one hospital in the United Kingdom. Devices were programmed to record automatically if bradycardia (<40 beats/min) or tachycardia ( >140 beats/min) was detected. Additionally, in the event of a seizure, patients and relatives could initiate ECG recording with an external activator device. Data were analyzed at regular intervals and correlated with seizure diaries.

Results

More than 220,000 patient-hours were monitored over a 24-month period, during which ECGs were captured on implantable loop recorders in 377 seizures. One patient withdrew from the study. In 16 patients, median heart rate during habitual seizures exceeded 100 beats/min. Ictal bradycardia (<40 beats/min) was rare, occurring in eight (2.1%) recorded events, in seven patients. Four patients (21%) had bradycardia or periods of asystole with subsequent permanent pacemaker insertion. Three of these four (16% of total) had potentially fatal asystole.

Conclusions

Clinical characteristics of patients with periictal cardiac abnormalities are closely similar to those at greatest risk of sudden unexpected death in epilepsy. Asystole might underlie many of these deaths, which would have important implications for the investigation of similar patients and affect present cardiac-pacing policies.