The Kir2.1^E299V mutation increases atrial fibrillation vulnerability while protecting the ventricles against arrhythmias in a mouse model of short QT syndrome type 3

Short QT syndrome type 3 (SQTS3) is a rare arrhythmogenic disease caused by gain-of-function mutations in KCNJ2, the gene coding the inward rectifier potassium channel Kir2.1. We used a multidisciplinary approach and investigated arrhythmogenic mechanisms in an in-vivo model of de-novo mutation Kir2.1^E299V identified in a patient presenting an extremely abbreviated QT interval and paroxysmal atrial fibrillation.

We used intravenous adeno-associated virus-mediated gene transfer to generate mouse models, and confirmed cardiac-specific expression of Kir2.1^WT or Kir2.1^E299V. On ECG, the Kir2.1^E299V mouse recapitulated the QT interval shortening and the atrial-specific arrhythmia of the patient. The PR interval was also significantly shorter in Kir2.1^E299V mice. Patch-clamping showed extremely abbreviated action potentials in both atrial and ventricular Kir2.1^E299V cardiomyocytes due to a lack of inward-going rectification and increased I_K1 at voltages positive to −80 mV. Relative to Kir2.1^WT, atrial Kir2.1^E299V cardiomyocytes had a significantly reduced slope conductance at voltages negative to −80 mV. After confirming a higher proportion of heterotetrameric Kir2.x channels containing Kir2.2 subunits in the atria, in-silico 3D simulations predicted an atrial-specific impairment of polyamine block and reduced pore diameter in the Kir2.1^E299V-Kir2.2^WT channel. In ventricular cardiomyocytes, the mutation increased excitability by shifting I_Na activation and inactivation in the hyperpolarizing direction, which protected the ventricle against arrhythmia. Moreover, Purkinje myocytes from Kir2.1^E299V mice manifested substantially higher I_Na density than Kir2.1^WT, explaining the abbreviation in the PR interval.

The first in-vivo mouse model of cardiac-specific SQTS3 recapitulates the electrophysiological phenotype of a patient with the Kir2.1^E299V mutation. Kir2.1^E299V eliminates rectification in both cardiac chambers but protects against ventricular arrhythmias by increasing excitability in both Purkinje-fiber network and ventricles. Consequently, the predominant arrhythmias are supraventricular likely due to the lack of inward rectification and atrial-specific reduced pore diameter of the Kir2.1^E299V-Kir2.2^WT heterotetramer.