Abstracts

RATIONALE: Transient relative bradycardia following generalized tonic-clonic convulsions (GTCs) has not been well investigated, despite the fact that peri-ictal cardiac perturbations likely pose a risk for sudden unexplained death in epilepsy patients (SUDEP). We undertook to quantify transient relative bradycardia after GTCs and to determine if it correlates with GTC length (and hence hypoxic duration), patient age, or baseline heart rate (HR). METHODS: All GTCs recorded in an epilepsy monitoring unit over an 18-month period were reviewed. Tracings with a clear single-lead ECG signal were analyzed for preictal and postictal HR, calculated over a >10 second period before GTC onset and after GTC resolution, respectively. The presence of transient postconvulsive relative bradycardia was defined as a ?30 beat per minute (bpm) decline in HR lasting at least 10 seconds, with subsequent rise to sinus tachycardia of >100 bpm following the GTC. RESULTS: Twenty-four GTC tracings from 13 patients were reviewed (4 female, 9 male). All patients had sinus tachycardia following GTCs (132 ? 12 bpm [mean ? SD]). Transient relative bradycardia was present following 7 of 23 (30%) GTCs. Relative bradycardia duration was 17.5 ? 4.1 seconds (range: 10-22). The mean drop in HR compared to postictal tachycardic HR was 50 ? 11 bpm (range: 30-66), corresponding to a 25-52% drop in HR during the bradycardic period. Relative bradycardia onset was approximately coincident with GTC termination (range -7 to +6 seconds from GTC end). Age (38.8 vs 35.6 years), baseline HR (71.1 vs. 77.2 bpm), and GTC duration (79.3 vs. 89.8 seconds) did not differ between those with transient relative bradycardia and those with only sinus tachycardia after GTCs, respectively (p>0.1 for all measures). In the follow-up period of this study, one patient with transient relative bradycardia died due to SUDEP. CONCLUSIONS: Postconvulsive transient relative bradycardia appears to be a common finding after GTCs. This relative bradycardia does not simply reflect GTC duration, patient age, or baseline heart rate. This suggests that dramatic short-term autonomic fluctuations occur following GTCs, and may be a contributing factor in SUDEP.