Abstract 13687: Appropriate Qt Correction Could Limit Unnecessary Avoidance of Drugs With a Risk of Tdp in Clinical Practice
Introduction: Risk monitoring of QT-prolonging drugs to avoid ventricular arrhythmias is mainly based on monitoring Bazett corrected QT-interval. However, there is a known undercorrection for high heart rates and no correction for ventricular conduction defects.
Methods: In a point prevalence study we collected 212 electrocardiograms before the first prescription of haloperidol. We compared 6 correction formulas (Bazett, Fridericia, Rautaharju, Framingham, Nomogram (range from 40-120 bpm) and Hodges). QTc-intervals <450ms for man and <470 for women were considered normal, QTc >500ms a high risk. The formulas were compared using QTc/RR linear regression slopes (QTc= BxRR+Cst), differences were compared using two-sided t-tests and chi2 analysis.
Results: Mean age of the patients was 73±15 years and 127 (60%) were male. Sinus rhythm was present in 167 (79%), 39 (18%) were in AF, 6 (3%) had pacemaker rhythm. Median HR was 81 bpm (range 47 - 153). Ventricular conduction defects were present in 31 (15%). QTcH showed overall the best rate adjustment (B=0.015±0.011), followed by QTcR (B=0.032±0.010) and QTcN (B=0.034±0.012). All correction formulas had significant shorter QTc values compared to QTcB (QTcH 429±29ms vs QTcB 449±33ms, p<0.01). Using QTcB 81 patients (38%) were considered at risk, with 16 (8%) at high risk. However, QTcH detected only 34 (16%) at risk with 2 (1%) at high risk (Chi2 test p<0.01).
Conclusions: Performing QTc prolongation risk analysis only based on Bazett’s correction formula could lead to false positive drug alert generation by automatic algorithms incorporated in electronic medical records and to unnecessary avoidance of clinically indicated drugs. The use of Hodges or Rautaharju’s (in case of ventricular conduction defects) linear correction formulas should be recommended.
Author Disclosures: B. Vandenberk: None. E. Vandael: Research Grant; Modest; EV is supported by funding of the Belgian government agency for Innovation by Science and Technology (IWT). J. Vandenberghe: None. I. Spriet: None. V. Foulon: None. R. Willems: Other; Modest; The university of Leuven receives unconditional grant support from Biotronik, Boston Scientific and Medtronic Belgium. RW is funded as a clincal researcher by the FWO.
- © 2014 by American Heart Association, Inc.