Evaluation of Echocardiographic Parameters During Increasing Infusion Rates of Dobutamine in Isoflurane-Anesthetized Horses

Examining the arrhythmogenicity of dobutamine when used in conjunction with isoflurane in horses: A retrospective study at a single university teaching hospital

BACKGROUND

Dobutamine is used to treat hypotension in isoflurane-anaesthetised horses but may produce arrhythmias. Halothane is a volatile anaesthetic that was, historically, widely used in horses, but in one study, 56 of 200 halothane-anaesthetised horses (28%) developed arrhythmias after dobutamine administration. Although isoflurane has largely replaced halothane, it is unknown how isoflurane and dobutamine interact in the development of arrhythmias.

METHODS

The medical records of horses undergoing general anaesthesia at the University of Georgia Veterinary Teaching Hospital in 2015 were reviewed retrospectively. Cases were selected if isoflurane was used as the maintenance inhalant anaesthetic agent and dobutamine was administered for the treatment of hypotension. Any instances of arrhythmia occurring following dobutamine administration were recorded.

RESULTS

Arrhythmia occurred after dobutamine administration in six out of a total of 148 horses (4.0%).

LIMITATIONS

The retrospective nature of this study and the fact that the horses were anaesthetised at a single institution might limit the extent to which the findings can be generalised.

CONCLUSION

Compared to halothane, isoflurane has a much lower incidence of arrhythmia when used with dobutamine. However, a larger-scale study is needed to identify risk factors associated with horses developing an arrhythmia induced by isoflurane in combination with dobutamine.

Pharmacologic inhibition of small-conductance calcium-activated potassium (SK) channels by NS8593 reveals atrial antiarrhythmic potential in horses

BACKGROUND

Small-conductance calcium-activated potassium (SK) channels have been found to play an important role in atrial repolarization and atrial fibrillation (AF).

OBJECTIVE

The purpose of this study was to investigate the existence and functional role of SK channels in the equine heart.

METHODS

Cardiac biopsies were analyzed to investigate the expression level of the most prominent cardiac ion channels, with special focus on SK channels, in the equine heart. Subcellular distribution of SK isoform 2 (SK2) was assessed by immunohistochemistry and confocal microscopy. The electrophysiologic and anti-AF effects of the relative selective SK channel inhibitor NS8593 (5 mg/kg IV) were evaluated in anesthetized horses, focusing on the potential of NS8593 to terminate acute pacing-induced AF, drug-induced changes in atrial effective refractory period, AF duration and vulnerability, and ventricular depolarization and repolarization times.

RESULTS

Analysis revealed equivalent mRNA transcript levels of the 3 SK channel isoforms in atria compared to ventricles. Immunohistochemistry and confocal microscopy displayed a widespread distribution of SK2 in both atrial and ventricular cardiomyocytes. NS8593 terminated all induced AF episodes (duration ≥15 minutes), caused pronounced prolongation of atrial effective refractory period, and reduced AF duration and vulnerability. QRS duration and QTc interval were not affected by treatment.

CONCLUSION

SK channels are widely distributed in atrial and ventricular cardiomyocytes and contribute to atrial repolarization. Inhibition by NS8593 terminates pacing-induced AF of short duration and decreases AF duration and vulnerability without affecting ventricular conduction and repolarization. Thus, inhibition by NS8593 demonstrates clear atrial antiarrhythmic properties in healthy horses.