Serum enzyme disturbances after tricyclic antidepressant overdose

In order to evaluate the enzymes CPK and LDH as potential biochemical markers of tricyclic antidepressant (TCA) cardiotoxicity, we prospectively followed 29 patients with TCA overdose. Serum CPK and LDH were obtained on all patients at admission. Population characteristics included a mean age of 33 y, a mean peak serum TCA concentration of 1190 ng/ml and mean maximal QRS interval of 0.10 sec. Seven patients (23%) had admission hypotension, 7 (23%) had severe respiratory depression, 6 (20%) had seizures and 4 (13%) had cardiac arrhythmias. One patient died. Mean admission CPK was 301 IU/L (nl less than 230 IU/L) while mean LDH was 221 IU/L (nl less than 250 IU/L). In 17 patients (57%), CPK remained in the normal range. There was no correlation between blood pressure, maximal QRS interval, serum TCA concentration, arrhythmias or seizures and CPK or LDH by regression analysis. CPK isoenzymes were obtained in 6 patients (both with and without severe myocardial dysfunction). One patient had an MB fraction of 10%; the remaining 5 had no measurable enzymes of myocardial origin. We conclude that modest elevations in CPK or LDH may occur after TCA overdose. These enzymes do not appear to originate from the myocardium and are of no utility in the assessment of antidepressant cardiotoxicity or prediction of clinical course.