Prolongation of electrocardiographic intervals in women on Norplant* contraceptive: what dangers?

Abstract

This study used electrocardiography to determine any inherent cardiovascular dangers with the use of Norplant®, an implant contraceptive among Nigerian females using the device. As part of a major study of metabolic, physical and cardiovascular changes consequent upon the use of Norplant® implant contraceptive, all subjects underwent serial electrocardiograms at pre-insertion, 3, 6, and 12 months of use. Given the observed prolongation of electrocardiographic intervals, the ECG of all the study subjects were secondarily analysed for QT and corrected QT (QTc) dispersions. QT intervals was mea sured from the ECG of each of the 21 subjects who were avail able at pre-insertion and 12 months post-insertion; from the onset of QRS to the end of T wave or nadir of the curve be tween T and U waves as the case may be. Corrected QT intervals was calculated by determining the RR interval and using the Bazett's formula. The difference of the lowest and highest QT intervals and QTc intervals over the 12 leads determined their respective dispersions. These were then analysed. The subjects whose ages ranged from 25-45 years weighed between 43 and 87.2 kg. The mean QT dispersion increased with time but did not reach statistical significance by the twelve month visit (ANOVA - QT dispersion 0 month vsI2 months: F=0.98, p=0.48). However the mean QTc dispersion increased and reached statistical significance by 12 months (0 month vs 12 months: F=5.49, p=0.006). QT and QTc dispersion increases are known to predict cardiovascular death in health and disease. With the use of this device, these indices rose gradually with time reaching statistical significance by 12 months only with the QTc dispersion. The use of this device may increase the tendency to cardiovascular morbidity and mortality. Whether this translates into real risk will require a long-term study to determine. For now, application of the device on patients with cardiovascular disease or tendency thereof should still attract caution.