Sinoatrial Node

The sinoatrial node, also known as the sinus node, is a minute area of the human heart muscle, which plays a crucial role in the overall functioning of the heart. Abbreviated as SA node, the major actions of the heart (contraction or beats) originate from this small region of the heart. From the SA node, cardiac impulses are transmitted to the heart conduction system and the remaining portions of the cardiac muscle for coordinated cardiac contractions.

Definition

The sinoatrial node along with other factors influences the heart rate of an individual. But, actually what is the sinoatrial node? And what structure evolved into the sinoatrial node? In short, it is a primary component of the cardiac conduction system, which is solely responsible for controlling the heart rate of an individual. Located in the upper right chamber (right atrium) of the heart, sinoatrial node comprises a group of cells and is innervated with nerve fibers (vagus and sympathetic). Stimulation via vagal fiber causes slow heart rate; while stimulation at the sympathetic nerve leads to rapid heart rate.

Functions

Giving due importance to the functions of the SA node, it is commonly known as the heart's natural or primary pacemaker. The main function of the sinoatrial node is regulating the heart rate, according to the necessities of the body. It remains in association with the autonomic nervous system (ANS). A part of the main nervous system, the ANS does the function of regulating involuntary actions of the cardiac muscle, smooth muscle and glands. The sinoatrial node acts in accordance to the command or input made by the autonomic nervous system.

In order to start the cardiac cycle phases, the ANS first triggers the sinoatrial node for generation of cardiac impulses. Generally, the rate of beats per minute falls between 60-100. Electrical impulses that have their roots in SA node are then spread from one cell to adjacent cell, until they are received by the atrioventricular node (AV node). The AV node is another group of cells, present between the atria and ventricles. By this time, the atria is contracted fully, and signals are further passed to the walls of the ventricle for initiating ventricular contraction.

When a person performs exercise or rigorous physical activities, the ANS sends the message to sinoatrial node via sympathetic nerve. Accordingly, the SA node generates electrical impulses at a fast pace, which after passing the cardiac conduction system and heart muscle, stimulate contraction. The same steps undergo repeatedly, resulting in faster heartbeats, thereby increasing oxygen supply to the body parts. Thus, in order to meet the oxygen requirements of the body cells, the heart rate of the person is increased during exercise. On the contrary, the oxygen needed during rest is low, and accordingly resting heart rate is slower (60-70 beats per minute) as compared to the reading measured during exercise.

Dysfunction

Being a major element of the cardiac conduction system, normal functioning of the sinoatrial node is responsible for maintaining optimal heart health. Any abnormality of the SA node can lead to irregular heart rate or cardiac arrhythmia. The condition may be slow heartbeats (bradycardia), rapid heartbeats (tachycardia) or a combination of both. What happens in sinoatrial node dysfunction is that wrong electrical impulses are generated by SA node, leading to irregular heartbeats.

Sinoatrial node reentrant tachycardia or SA nodal reentrant tachycardia (SANRT) is a rare type of arrhythmia that usually remains asymptomatic. People who has structural heart problems are more prone to SANRT than others. The abnormalities in the sinoatrial node function can be managed by implanting an artificial pacemaker. For introducing the same inside the body, a traditional surgery or non-invasive laparoscopy is performed. However, it is best to follow the doctor's suggestions regarding diagnosis and treatment approaches for SA node dysfunction.