A pharmacological characterization of electrocardiogram PR and QRS intervals in conscious telemetered rats.

Introduction: The conscious telemetered rat is widely used as an early in vivo screening model for assessing the cardiovascular safety of novel pharmacological agents. The current study aimed to identify its utility in assessing electrocardiogram (ECG) PR and QRS interval changes.

Method: Male Han-Wistar rats (~250 g) were implanted with radio-telemetry devices for the recording of ECG and haemodynamic parameters. Animals (n = 4-8) were treated with single doses of calcium (nifedipine, diltiazem or verapamil; CCBs) or sodium channel blockers (quinidine or flecainide; SCBs) or their corresponding vehicles in an ascending dose design. Data was recorded continuously up to 24 h post-dose. Pharmacokinetic analysis of blood samples was performed to allow comparison of effects to published data in other species.

Results: Of the CCBs, only diltiazem (300 mg/kg) prolonged the PR interval (49 ± 2 versus vehicle: 43 ± 1 ms), although this was not statistically significant (p = .11). QA interval decreased with nifedipine (30 ± 1 versus 24 ± 0 ms) and diltiazem (34 ± 1 versus 27 ± 1 ms) but increased with verapamil (30 ± 0 versus 37 ± 1 ms) demonstrating pharmacological activity of each agent. Both SCBs, caused statistically significant (p < .05) increases in both intervals - quinidine (100 mg/kg; PR: 50 ± 2 versus 43 ± 1 ms; QRS: 22 ± 2 versus 18 ± 1 ms) and flecainide (9 mg/kg; PR: 56 ± 1 versus 46 ± 1 ms; QRS: 27 ± 1 versus 21 ± 1 ms). Drug plasma exposure was confirmed in all animals.

Discussion: At similar plasma concentrations to other species, the conscious telemetered rat demonstrates limited utility in assessing PR interval prolongation by CCBs, despite significant contractility effects being observed. However, results with SCBs demonstrate a potential application for evaluating drug-induced QRS prolongation.