Opioid maintenance patients with QTc prolongation: congenital long QT syndrome mutation may be a contributing risk factor.

Abstract

This study investigates opioid maintenance treatment (OMT) patients found to have corrected QT (QTc) interval above 500 ms, with particular focus on past medical history, genetic testing and cardiac investigations. Detailed medical and cardiac history was obtained, with particular focus upon risk factors. Cardiac investigations, including genetic testing for the five most common long QT syndrome (LQTS) mutations, exercise electrocardiography (ECG) and 24-h ECG recordings, were performed. Of 200 OMT patients assessed with ECG, seven methadone maintained patients identified with QTc interval above 500 ms participated in this study. Two were identified as heterozygous LQTS mutation carriers. Both had experienced cardiac symptoms prior to and during OMT. No other risk factors for QTc prolongation were detected among the seven patients. Six of the seven patients underwent further cardiac investigations. QTc intervals fluctuated widely over 24h and during exercise for all patients. Only one of the LQTS mutation carriers switched to buprenorphine and started on a beta-blocker. Despite strong medical advice and information, none of the other patients wanted to switch to buprenorphine or take other cardiac protective measures. Findings indicate the importance of recording a thorough past medical history, focusing specifically on previous cardiac symptoms, and on other known risk factors for QTc prolongation, prior to initiating patients on methadone.