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Published on: April 5, 2011
Serum quinidine concentrations and effect on QT dispersion and interval
A Scott Mathis1, Ashesh J Gandhi
1Department of Pharmacy Practice and Administration, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ, USA. smathis@sbhcs.com
The Annals of Pharmacotherapy
|June 28, 2002
Summary
QT interval dispersion was highest at subtherapeutic serum quinidine concentrations (SQCs), despite QT interval lengthening with increasing SQCs. This suggests a potential mechanism for torsade de pointes at lower quinidine levels.
Area of Science:
- Cardiology
- Clinical Pharmacology
Background:
- Quinidine is an antiarrhythmic drug known to prolong the QT interval.
- Torsade de pointes (TdP) is a life-threatening ventricular arrhythmia associated with QT interval prolongation.
- Reports indicate TdP can occur at subtherapeutic serum quinidine concentrations (SQCs).
Purpose of the Study:
- To investigate the relationship between SQCs and QT interval dispersion.
- To compare QT interval dispersion with QT interval prolongation.
- To identify potential reasons for TdP occurrence at subtherapeutic SQCs.
Main Methods:
- Retrospective study at a university teaching hospital.
- Eleven patients with atrial arrhythmias receiving quinidine therapy were analyzed.
- QT interval dispersion was calculated from 12-lead ECGs at subtherapeutic (<2 microg/mL) and therapeutic (2-5 microg/mL) SQCs.
Main Results:
- Mean SQCs were 1.48 microg/mL (subtherapeutic) and 3.78 microg/mL (therapeutic).
- QT interval dispersion was greatest at subtherapeutic SQCs (98.2 msec) compared to therapeutic SQCs (70.9 msec) and baseline (47 msec).
- Overall analysis showed significant differences in QT dispersion across SQC levels (p=0.001).
Conclusions:
- QT interval dispersion was numerically highest at subtherapeutic SQCs, despite increasing QT intervals with higher SQCs.
- This finding may explain TdP occurrence at lower quinidine concentrations.
- Further research is needed to establish QT dispersion as a reliable marker for proarrhythmic risk with QT-prolonging drugs.
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