Lengthening of corrected QT during epileptic seizures

Brotherstone R, Blackhall B, and McLellan A (2009) Lengthening of corrected QT during epileptic seizures. p. (Epub).

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Abstract: PURPOSE: To measure the corrected QT cardiac repolarization time before and during epileptic seizures. METHODS: Thirty-nine video-EEG/ECG/SAO(2) (electroencephalography/electrocardiography/oxygen saturation) telemetry patients were included in this prospective study. Epileptic seizures were identified both clinically and electrographically. RR intervals and associated QT intervals were measured 5 min prior to the onset of the identified seizure. Consecutive RR and associated QT intervals were then measured from the seizure onset until the seizure had ended and the EEG had resumed its preseizure trace. Averaged RR and QT intervals over nine consecutive beats were applied to Bazett's, Hodge's, Fridericia's, and Framingham's formulas to compare the corrected QT values before and during the seizures. RESULTS: A total of 156 seizures had corrected QT analysis performed. Nine generalized tonic-clonic seizures (5 patients), 34 absences (6 patients), 12 tonic seizures (6 patients), 27 temporal lobe seizures (14 patients), 58 frontal lobe seizures (4 patients), and 16 subclinical seizures (4 patients). All formulae reported a statistically significant difference in corrected QT (p < 0.001) during total seizure data compared to total preseizure values. According to Bazett's formula, 21 seizures (nine patients) transiently increased their corrected QT beyond normal limits, with a maximum corrected QT of 512 ms during a right temporal lobe seizure. CONCLUSION: Significant lengthening of corrected QT cardiac repolarization time occurred during some epileptic seizures in this study. Prolonged corrected QT may have a role in sudden unexplained death in epilepsy (SUDEP).

Keywords: Epilepsy, Cardiac repolarization, SUDEP

Context

• 39 patient study of QT interval during seizures. A number of formulae are commonly used to correct QT intervals for heart rate. Using 4 methods of correction, the authors observed ictal QT interval prolongation, but only in 21 of 156 seizures did corrected QT exceed normal limits, and this was apparently only seen with one method of QT correction. That said, the QT prolongations that did not exceed normal limits could still be of relevance for understanding the effect of seizures on heart rate. In terms of methodology, lead II was used for QT measurement. It was unclear whether readers were blinded to the ictal status of the patient, but there was substantial agreement on QT among readers. As a potential confound, shorter QT intervals at rest were found in patients with epilepsy by Teh et al., which could magnify relative changes during seizure. See Malik for additional discussion of sources of error in QT measurement. Of note the QT prolongation here was seen regardfless of whether heart rate increased or decreased during a seizure. For further discussion of QT intervals see annotation at Aurlien et al.