Ionic mechanisms of cardiac arrhythmias

The heart pumps >2000 gallons of blood every day through the body's intricate vascular network. Each heartbeat is initiated and carefully regulated by specialized electrical impulses known as action potentials. These impulses are driven by electrical currents, which are composed of charged particles (ions) that flow in and out of individual cardiac myocytes. Ion currents mediate the contraction of individual cardiac myocytes and synchronize the electrical and contractile behavior of the heart; thereby, allowing its pumping function to remain efficient and highly coordinated. Disruption of normal impulse propagation throughout the heart interrupts the coordinated contraction of the cardiac chambers, and produces malignant, lethal rhythm disturbances (arrhythmias), which underlie the majority of sudden cardiac death cases in patients with heart disease. Here, we review our current understanding of normal and abnormal cardiac electrical behavior with emphasis on the ionic mechanisms of cardiac arrhythmias.