Journal Article

QT and RR Intervals in Conscious and Anesthetized Guinea Pigs with Highly Varying RR Intervals and Given QTc-Lengthening Test Articles

Robert L. Hamlin, Anusak Kijtawornrat, Bruce W. Keene and David M. Hamlin

in Toxicological Sciences

Volume 76, issue 2, pages 437-442
Published in print December 2003 | ISSN: 1096-6080
Published online December 2003 | e-ISSN: 1096-0929 | DOI: http://dx.doi.org/10.1093/toxsci/kfg254
QT and RR Intervals in Conscious and Anesthetized Guinea Pigs with Highly Varying RR Intervals and Given QTc-Lengthening Test Articles

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A facile system for obtaining electrocardiograms from conscious animals was used to conduct studies on 12 animals studied both conscious and anesthetized, on 4 conscious animals given vehicle (0.5% methylcellulose) and QT-lengthening test articles, and on 6 animals given test articles thought to not lengthen QTc. In 12 animals whose ECGs were monitored via a bipolar transthoracic ECG, heart rates were slowed with 1.0 mg/kg zatebradine, while they were conscious in their slings, and after being anesthetized with ketamine/xylazine. The following regression equations were obtained relating QT to RR: QT = 44.7 ln RR - 132.9, r2 = 0.7, for conscious animals; QT = 79.4 ln RR - 287.4, r2 = 0.8 for anesthetized animals, with RR intervals varying between 150 and 550 ms. The anesthetic increases QT at all RR intervals (p < 0.001), but does not change the slope of the relationship between QT and RR when compared with the conscious guinea pig. The Fridericia method was best for correcting QT for RR interval in conscious guinea pigs, but the Bazett method was best for correcting in anesthetized animals. QTc lengthened significantly in all conscious guinea pigs given, orally, cisapride, ketoconazole, and sotalol (positive test articles) and did not change with methylcellulose (the vehicle) or with propranolol, verapamil, or enalapril (negative controls). These techniques and relationships demonstrate that this methodology may be useful in exploring torsadogenic effects of novel pharmacological entities.

Keywords: guinea pig; QT; RR; QTc; anesthesia; electrophysiology

Journal Article.  3656 words.  Illustrated.

Subjects: Medical Toxicology ; Toxicology (Non-medical)

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