In the latest Case Record of the Massachusetts General Hospital, a 32-year-old woman was seen in the neurology clinic because of episodes of altered consciousness — staring, aphasia, and occasional sudden loss of postural tone and collapse. EEG revealed left-temporal-lobe seizures; brain imaging revealed a left-temporal-lobe mass.
The relationship between seizures and cardiac dysrhythmia may take several demonstrated or hypothetical forms. For example, dysrhythmia can cause seizure (convulsive syncope), seizure can cause dysrhythmia (arrhythmogenic epilepsy), treatment can cause dysrhythmia, or seizure and dysrhythmia can occur as epiphenomena caused by a shared underlying mechanism.
• How common are cardiac dysrhythmias in epilepsy?
Cardiac dysrhythmias in epilepsy are not uncommon and have been hypothesized to underlie sudden unexplained death in epilepsy (sometimes referred to as SUDEP), which affects 0.5 to 1.0% of patients with epilepsy each year and is the leading cause of death associated with epilepsy. Both bradyarrythmias and tachyarrhythmias have been described. Ictal tachycardia is most common, although in one study, 7 of 20 patients had ictal bradycardia in at least one seizure, and 3 of those patients had asystolic events. Only a minority of events recorded from any given patient show bradyarrhythmia, indicating that this phenomenon can be intermittent.
• How might seizures cause dysrhythmia?
It is possible that catecholamine release, acidosis, or hyperkalemia resulting from prolonged convulsive activity could induce arrhythmia. Alternatively, seizure activity may involve cerebral structures that are important in the regulation of cardiac rhythm, including the amygdala, insula, or hypothalamus. Studies of cortical stimulation in humans indicate that direct electrical stimulation or transcranial direct-current stimulation of the left hemisphere, particularly the insula, may activate parasympathetic descending pathways, leading to bradycardia. Similarly, the infusion of amobarbital into the left carotid artery anesthetizes the left hemisphere and produces tachycardia, whereas infusion into the right carotid artery produces the opposite result. Case reports of ictal asystole suggest that the onset of seizures occurs predominantly on the left side, but clear cases of onset on the right side have been documented.
Morning Report Questions
Q: What is the relationship between long-QT syndrome and epilepsy?
A: The loci for long-QT syndrome include more than 17 genes encoding ion channels, connexins, and transcription factors. Mutations in these genes produce paroxysmal bradycardia and syncope; electrocardiographic features include long and short QT intervals, torsades de pointes, and asystole. Most of these genes show dual expression in the heart and brain, and perhaps additional expression in the autonomic nerves, defining a singular mechanism linking epilepsy, cardiac arrhythmia, and sudden death. Patients with the long-QT syndrome have a high incidence of seizures; furthermore, seizures, the long-QT syndrome, and sudden cardiac death occur in transgenic mice carrying human genes with mutations in the most common gene for the long-QT syndrome.
Q: What are the indications for surgical treatment of epilepsy?
A: Indications for surgical treatment of epilepsy include medical intractability, disabling seizures, and a reasonable likelihood that the situation can be improved at an acceptable level of risk. Additional indications are seizures that are immediately life-threatening and a diagnosis of underlying lesions, usually tumors.