Cerebral ischemia during implantation of automatic defibrillators

In order to study the influence of repetitive episodes of ventricular fibrillation (VF) during defibrillator implantation on the electrical activity of the brain, we performed an electroencephalographic (EEG) monitoring during implantation procedure in 18 patients. For defibrillation threshold testing 62 episodes of VF (1-6 episodes per patient) were induced. The mean duration of VF was 20 ± 12 s ; the mean duration of hypotension during an episode (defined as a mean arterial pressure of 50 mm Hg or less) was 33 ± 16 s. EEG monitoring was performed using the International 10-20 System. The duration of cardiac arrest-related EEG alteration was assessed by an experienced neurologist and could be determined in 41 test-episodes; in 21 episodes analysis was not possible due to poor recordings. Ischemia-related EEG changes started 7.8 ± 4.6 s after VF induction and lasted 64 ± 49 s (range, 12-240). The duration of EEG alteration was significantly (p <.001) correlated with the duration of VF episodes (r =.71) and the associated hypotension (r =.82). With regard to patients the duration of ischemia related EEG changes also correlated significantly (p =.001) with the individual cumulative duration of VF (r =.85) and the associated hypotension (r =.88). In females EEG changes lasted longer than in males (p =.03) ; this finding, however, was only based on 2 women. Other clinical parameters, such as patient age, degree of congestive heart failure, left ventricular ejection fraction, stroke volume and cardiac index, the order of episodes within the testing sequence, and the time interval between episodes did not correlate with the duration of EEG alteration after VF induction. The duration of ischemia-related EEG alteration during VF episodes depends on the duration of cardiac arrest. In females EEG changes tended to last longer than in males, however, this finding has to be confirmed. An association with other clinical parameters has not been observed. Limitation of VF duration appears to be the most important factor to avoid prolonged cerebral ischemia.