Relationship of seizure morphology to the convulsive threshold.

Twenty-two patients with major depression received a course of right unilateral ECT. The convulsive threshold (CT) was determined on the first treatment. Subsequent treatments were approximately 2.25 times CT. Seizure morphology for treatments 2-6 were rated for regularity (0-6 scale; low-high) and postictal suppression (0-3; low-high). Ratings of postictal suppression were log transformed to improve the approximation to a normal distribution. A preliminary analysis of variance with CT as the independent variable compared the seizure ratings at low, mid, and high CT. Second, linear regression models for the mean values of seizure regularity and postictal suppression were determined using age, gender, and the CT as predictor variables. The degree of postictal suppression varied inversely with age, male gender, and CT in this study. Our results suggested that CT made the greatest contribution to the model. Future studies examining the predictive value of seizure morphology parameters to clinical outcome should include measurement of CT.