QT interval correction assessment in the anesthetized guinea pig

Area of Science:

• Pharmacology
• Cardiovascular Physiology
• Drug Development

Background:

• The anesthetized guinea pig (ANES GP) is a valuable small animal model for assessing drug effects on cardiac electrophysiology.
• Accurate assessment of drug-induced repolarization changes requires reliable heart rate (HR) correction of the QT interval (QTc).
• Existing QT/HR correction methods debate persists due to influences of anesthesia, autonomic tone, and species-specific factors.

Purpose of the Study:

• To evaluate the performance of common QT interval correction formulas in the ketamine/xylazine anesthetized guinea pig model.
• To determine the most appropriate QT/HR correction formula across different heart rate ranges in this specific animal model.

Main Methods:

• Utilized atrial pacing, ivabradine, and ephedrine infusions to achieve a wide range of heart rates in anesthetized guinea pigs.
• Applied Bazett (QTcb), Fridericia (QTcf), and Van de Water (QTcVdW) correction formulas.
• Determined the best-fit formula by analyzing the slope of the QT-HR linear relationship.

Main Results:

• QTcb underestimated QT interval changes from 100-220 bpm, while QTcVdW showed better performance (lower QT/HR slope).
• Above 220 bpm, QTcb outperformed QTcf and QTcVdW, exhibiting a more appropriate QT/HR slope.
• All formulas detected repolarization delay from dofetilide and sotalol, but QTcb and QTcf showed reduced sensitivity compared to pacing.

Conclusions:

• The optimal QT correction formula in the ANES GP is heart rate-dependent.
• QTcVdW is recommended for HRs below 220 bpm, and QTcb for HRs above 220 bpm.
• Given typical HR ranges in this model, QTcVdW was selected for its performance in the lower HR spectrum.