The Relationship of the Lock-step Phenomenon and Precipitous Changes in Mean Arterial Blood Pressure

The lock-step phenomenon (LSP) is the occurrence of postganglionic cardiac sympathetic discharge (PCSD) and cortical epileptiform activity (EA) in a time-locked fashion. The relationship between the LSP and precipitous changes in blood pressure (PCBP: greater than 23 mm Hg in 10 sec) was determined in 9 cats after EA was induced with pentylenetetrazol following pretreatment with phenobarbital (20 mg/kg, i.v.). Electrocorticogram (ECoG), PCSD, lead II EKG, and mean arterial blood pressure (MAP) were monitored. Since an interspike interval of 2.8 sec was frequently found to exist between ECoG spikes when the LSP was present, 4 categories of LSP were defined: LSP absent; stable LSP with 2.8 sec interval; stable LSP without 2.8 sec interval; and unstable LSP with increasing or decreasing rates of discharge. The duration of each LSP pattern and the proportion of time spent in PCBP were determined. A one-way repeated measures ANOVA and the Newman-Keuls post-hoc test showed that a higher mean proportion of time spent in PCBP was associated with the unstable LSP pattern (P less than 0.05). The LSP and associated patterns as related to precipitous changes in MAP are indicators of changes in autonomic function. Autonomic dysfunction with EA, causing cardiac arrhythmias, has been postulated as a cause of sudden unexplained death (SUD) in persons with epilepsy. Thus, an understanding of the autonomic changes, as indicated by PCBP associated with LSP, may contribute to the understanding and prevention of SUD in persons with epilepsy.