Effect of autonomic blockade on ventricular repolarization shortening: Response to behavioral stimulus in paced dogs

Influence of serotonin transporter gene polymorphism (5-HTTLPR polymorphism) on the relation between brain 5-HT transporter binding and heart rate corrected cardiac repolarization interval

Objective

Serotonin transporter gene polymorphism (5-HTTLPR polymorphism) predicts the degree of structural and functional connectivity in the brain, and less consistently the degree of vulnerability for anxiety and depressive disorders. It is less known how 5-HTTLPR polymorphism influences on the coupling between brain and neuronal cardiovascular control. The present study demonstrates the impact of 5-HTTLPR polymorphism on the relations between heart rate (HR) corrected cardiac repolarization interval (QTc interval) and the brain 5-HTT binding.

Material and Methods

Thirty healthy young adults (fifteen monozygotic twin pairs) (mean age 26±1.3 years, 16 females) were imagined with single-photon emission computed tomography (SPECT) using iodine-123 labeled 2β-carbomethoxy-3β-(4-iodophenyl) nortropane (nor-β-CIT). Continuous ECG recording was obtained from each participant at supine rest. Signal averaged QTc interval on continuous ECG was calculated and compared with the brain imaging results.

Results

In the two groups [l homozygotes (n = 16, 10 females), s carriers (n = 14, 8 female)] HR and the length of QTc interval were not influenced by 5-HTTLPR polymorphism. There were no significant relations between HR and 5-HTT binding in the brain. There were significant associations between QTc interval and nor-β-CIT binding in the brain in l homozygotes, but not in s carriers (correlations for QTc interval and nor-β-CIT binding of striatum, thalamus and right temporal region were −0.8–−0.9, (p<0.0005), respectively).

Conclusion

The finding of longer QTc interval with less 5-HTT binding availability in major serotonergic binding sites in l homozygotes, but not in s carriers, implicate to differentiated control of QTc interval by 5-HTTLPR polymorphism.

Interferences of the autonomic nervous system with drug induced QT prolongation: a point to consider in non-clinical safety studies

INTRODUCTION

QT interval assessment by telemetry has become one of the most useful models in testing strategies adopted for detection of drug induced QT prolongation in non-clinical safety pharmacology studies. This study reports experimental data showing that the autonomic nervous system might influence drug induced QT prolongation.

METHODS

Animals were instrumented with telemetric transmitters and epicardial ECG leads. Effects on QT interval of reference drugs such as thioridazine and terfenadine were analysed with different approaches, the Holzgrefe's probabilistic method, the QT shift method and an individual analysis of beat-to-beat QT/RR pair distribution visualised as points-cloud.

RESULTS

Two cases of unexpected absence of QT interval prolongation are reported with thioridazine and terfenadine in conscious beagle dogs under conditions of concomitant tachycardia. The pro-arrhythmic properties of these two molecules were unmasked by co-treatment with sympatholytic agents, atenolol and clonidine respectively suggesting that sympathetic activation and/or parasympathetic withdrawal might impair a drug induced QT prolongation.

DISCUSSION

The apparent absence of changes in the QT interval due to novel drug candidates should be interpreted cautiously under conditions of concomitant tachycardia or elevated heart rate levels in non-clinical safety studies.