Atrioventricular (AV) conduction describes the journey of electrical signals within the heart, a process essential for its ability to pump blood effectively. This electrical pathway ensures the heart’s chambers contract in a synchronized manner, allowing for efficient blood flow throughout the body. Without this coordinated electrical activity, the heart cannot circulate blood. AV conduction is important for cardiovascular health.
The Heart’s Electrical Wiring
The heart’s ability to pump blood relies on an internal electrical system. This system originates with the sinoatrial (SA) node, the heart’s natural pacemaker, which generates the initial electrical impulse. This signal then travels across the upper chambers, the atria, causing them to contract and push blood into the lower chambers.
The electrical signal next reaches the atrioventricular (AV) node, a small cluster of specialized cells located near the center of the heart. From the AV node, the impulse moves into the Bundle of His, a conduit for electrical signals. The Bundle of His then divides into left and right bundle branches, which extend down the septum separating the ventricles.
These branches further subdivide into Purkinje fibers. These fibers spread rapidly throughout the inner walls of the ventricles, ensuring the electrical signal reaches nearly all ventricular muscle cells simultaneously. This electrical “wiring” allows for a swift and coordinated contraction of the ventricles, enabling them to efficiently pump blood.
Orchestrating the Heartbeat
Atrioventricular conduction is a sequence that ensures effective blood pumping. After the electrical impulse spreads through the atria, prompting their contraction, it arrives at the atrioventricular (AV) node. Here, a brief delay in the electrical signal occurs, lasting approximately a fraction of a second.
This delay is a deliberate aspect of normal heart function. It provides time for the atria to fully contract and empty their blood into the ventricles. Without this pause, the atria and ventricles would contract almost simultaneously, leading to inefficient filling of the ventricles and reduced blood outflow.
Once the ventricles are sufficiently filled, the electrical signal is rapidly transmitted from the AV node, through the Bundle of His and Purkinje fibers, triggering a synchronized contraction of the ventricles. This coordinated timing, orchestrated by the AV node’s brief delay, maximizes the volume of blood pumped with each heartbeat. This sequence allows the heart to function as an effective pump.
When Conduction Goes Awry
Disruptions in atrioventricular conduction can lead to heart block, also known as atrioventricular (AV) block. This occurs when the electrical signal traveling from the atria to the ventricles is either slowed or completely interrupted. The severity of heart block varies, impacting how effectively the heart can maintain a steady beat and pump blood.
In milder forms, known as first-degree heart block, the electrical signal reaches the ventricles but travels slower than normal. Individuals with this type often experience no symptoms and may only discover it during routine medical examinations. As the electrical disruption becomes more pronounced, such as in second-degree heart block, some electrical signals may fail to reach the ventricles entirely, leading to skipped beats or a slower heart rate.
The most severe form, third-degree or complete heart block, involves a complete blockage of electrical signals between the atria and ventricles. In this situation, the ventricles may generate their own, much slower, and often unreliable rhythm, independent of the atria. This can impair the heart’s ability to pump enough blood.
Symptoms associated with more severe forms of heart block can include a slow heart rate (bradycardia), dizziness, fatigue, shortness of breath, and even fainting spells. These symptoms arise because the body’s organs and tissues are not receiving adequate oxygenated blood due to the inefficient pumping action of the heart. While some cases may not require intervention, more severe forms of heart block often necessitate medical treatment, such as the implantation of a pacemaker, to restore a regular and effective heart rhythm.