Channelopathies in Dogs: From Clinical Signs to Treatment

In human medicine, sudden cardiac death has been related to genetic mutations that affect the sodium, potassium, and calcium channels responsible for ion transport across the myocardial cell membrane. In case of loss or gain of function in one of these ion channels, the action potential is altered in ways that predispose the patient to life threatening arrhythmias. The most common reported diseases in human beings are: the long QT syndrome (LQTS), Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia. Idiopathic ventricular tachycardia has also been reported as a ventricular tachycardia in the absence of obvious structural heart diseases widely distributed in the left and right ventricle. Idiopathic ventricular tachycardia usually occurs by abnormal enhanced automatism and triggered activities, except with ventricular fascicular tachycardia which has been shown to be caused by a re-entrant mechanism.In veterinary medicine different inherited arrhythmias with increased risk of sudden cardiac death have been described in the absence of structural heart disease: inherited ventricular arrhythmias in German Shepherd, inherited supraventricular and ventricular arrhythmias in Rhodesian Ridgeback, long QT syndrome in Springer Spaniel. In German Shepherd, inherited ventricular arrhythmias are thought to be either a simple autosomal dominant trait with incomplete penetrance or a polygenic trait although its exact mode of inheritance is still unknown. The incidence of sudden death in a litter of affected puppies can be 15% to 20%. Affected dogs first develop spontaneous ventricular arrhythmias around 3 to 4 months with worsening severity seen between 5 and 7 months. The incidence of tachycardia has been reported to be at 18-20 months and decreased by this age.  Because of the underling electrophysiological mechanism, inherited ventricular arrhythmias has been shown to exacerbated by bradycardia, often secondary to high vagal tone or drug administration.In Rhodesian Ridgeback, the mutation in the Q1l1 gene has been described to result in a mitochondrial cardiomyopathy characterized by cristae abnormalities and supraventricular and ventricular arrhythmias. Holter monitoring represent the gold standard to evaluate ventricular arrhythmias correlated with channelopathies and efficacy of the antiarrhythmic treatment, even if the pharmacological treatment is aimed to reduce the ventricular ectopic burden but it has been not proven to treat the risk of sudden cardiac death. Radiofrequency catheter ablation has been described for the treatment of supraventricular arrhythmias in dogs but it represents the gold standard treatment for some forms of ventricular tachycardia.