Do age-associated changes of voltage-gated sodium channel isoforms expressed in the mammalian heart predispose the elderly to atrial fibrillation?

Abstract

Atrial fibrillation (AF) is the most common cardiac arrhythmia worldwide. The prevalence of the disease increases with age, strongly implying an age-related process underlying the pathology. At a time when people are living longer than ever before, an exponential increase in disease prevalence is predicted worldwide. Hence unraveling the underlying mechanics of the disease is paramount for the development of innovative treatment and prevention strategies. The role of voltage-gated sodium channels is fundamental in cardiac electrophysiology and may provide novel insights into the arrhythmogenesis of AF. Na_v1.5 is the predominant cardiac isoform, responsible for the action potential upstroke. Recent studies have demonstrated that Na_v1.8 (an isoform predominantly expressed within the peripheral nervous system) is responsible for cellular arrhythmogenesis through the enhancement of pro-arrhythmogenic currents. Animal studies have shown a decline in Na_v1.5 leading to a diminished action potential upstroke during phase 0. Furthermore, the study of human tissue demonstrates an inverse expression of sodium channel isoforms; reduction of Na_v1.5 and increase of Na_v1.8 in both heart failure and ventricular hypertrophy. This strongly suggests that the expression of voltage-gated sodium channels play a crucial role in the development of arrhythmias in the diseased heart. Targeting aberrant sodium currents has led to novel therapeutic approaches in tackling AF and continues to be an area of emerging research. This review will explore how voltage-gated sodium channels may predispose the elderly heart to AF through the examination of laboratory and clinical based evidence.

Keywords: Voltage-gated, Sodium channels, Ageing, Atrial fibrillation, Na_v1.5, Na_v1.8, Late sodium current, Cardiac electrophysiology

Core tip: Na_v1.8 has been implicated by multiple studies in producing the late sodium current, predisposing the cardiomyocyte to arrhythmogenic activity. Animal models have demonstrated an enhancement of this aberrant current in aged hearts. Human studies have identified a reduction of Na_v1.5 and an increase in Na_v1.8 in both heart failure and left ventricular hypertrophy, strongly suggesting that voltage-gated sodium channel expression plays a central role in the development of arrhythmia. Clinically, sodium channel blockade through Ranolazine has proved promising in terminating the arrhythmia. Prevention of atrial fibrillation should focus on lifestyle management, as well as targeting cardiac risk factors. Irbesartan has been demonstrated to slow atrial remodelling, prevent atrial fibrillation in animal models, as well as avert the arrhythmia in human subjects.