Ventricular action potential

Ventricular action potential is a term used in cardiac electrophysiology to describe the changes in membrane potential that occur during the cardiac cycle in the ventricular myocytes. This process is crucial for the proper functioning of the heart, as it allows for the coordinated contraction of the heart muscle, which in turn enables the efficient pumping of blood throughout the body.

Overview

The ventricular action potential is initiated by an electrical impulse from the sinoatrial node, the heart's natural pacemaker. This impulse travels through the atrioventricular node and the bundle of His before reaching the ventricular myocytes.

The ventricular action potential consists of five phases (0-4), each representing a different stage in the electrical activity of the ventricular myocytes.

Phases

Phase 0

Phase 0, or the upstroke, is characterized by a rapid depolarization of the ventricular myocytes. This is caused by the opening of voltage-gated sodium channels, which allows for a rapid influx of sodium ions into the cell.

Phase 1

Phase 1, or the initial repolarization, is marked by the closure of the sodium channels and the opening of potassium channels. This allows for a brief efflux of potassium ions out of the cell, causing a slight decrease in the membrane potential.

Phase 2

Phase 2, or the plateau phase, is characterized by a balance between the influx of calcium ions through calcium channels and the efflux of potassium ions. This results in a prolonged period of depolarization.

Phase 3

Phase 3, or the rapid repolarization, is marked by the closure of the calcium channels and the continued efflux of potassium ions. This causes the membrane potential to return to its resting state.

Phase 4

Phase 4, or the resting phase, is the period between action potentials. During this phase, the membrane potential is maintained by the sodium-potassium pump, which actively transports sodium ions out of the cell and potassium ions into the cell.

Clinical significance

Abnormalities in the ventricular action potential can lead to various cardiac arrhythmias, including ventricular tachycardia and ventricular fibrillation. These conditions can be life-threatening and require immediate medical attention.