Cardiac Conduction Velocity Overview

Cardiac Conduction Velocity

• Speed of the depolarization wave through the myocardium is measured in meters per second.
• The conduction pathway includes the sinoatrial node (SA node), atria, atrioventricular node (AV node), Bundle of His, and Purkinje fibers, completing in roughly 220 milliseconds.

Cellular Processes

• Depolarization waves travel across neighboring myocardial cells via gap junctions.
• Calcium and sodium ions trigger voltage-gated sodium channels, initiating action potentials.
• Sodium influx into cells spurs further action potentials in adjacent cells, propagating the depolarization wave.

Factors Affecting Conduction Velocity

• Presence of sodium channels and gap junctions influences conduction speed; more enhances velocity, fewer slows it.

Breakdown of Conduction Velocities

• SA Node: Depolarization wave moves through atria at approximately 1 meter per second.
• AV Node: Speed reduces to about 0.01 to 0.05 meters per second, accounting for nearly half of the 220 milliseconds despite its short length.
• His and Purkinje Fibers: Conduction accelerates to 2-4 meters per second, representing the fastest phase.

Importance of the Slowdown at the AV Node

• The AV node’s slowdown is crucial for blood flow; it allows atrial contraction to fill ventricles while they are relaxed, ensuring efficient blood ejection.

Ventricular Depolarization

• Upon reaching the ventricles, conduction continues at roughly 1 meter per second through ventricular myocytes.

Summary

• Cardiac conduction velocity is vital for effective heart pumping, influenced by sodium channels, gap junctions, and tissue types, facilitating coordinated contractions and optimal blood flow.