Normal sinus rhythm (NSR) is another name for a normal heart rhythm. The heartbeat is controlled by electrical signals that are transmitted to the four chambers of the heart, causing them to contract and relax in sequence to pump blood in and out of the heart.
However, the sinus rhythm can sometimes become irregular, referred to as sinus arrhythmia, and cause the heart to beat too slowly or too rapidly.
This article explains how the sinus rhythm regulates heartbeats. It also discusses how different arrhythmias occur, including their various causes and symptoms.
Sinus Rhythm vs. Heart Rate
Sinus rhythm is the pattern of your heartbeat. Heart rate is the number of times the heart beats per minute. A normal sinus rhythm is associated with a heart rate between 60 and 100 beats per minute.1
What Is a Normal Sinus Rhythm?
The heart's normal rhythm is referred to as "sinus rhythm" because the electrical signals, called impulses, are generated by the sinus node.
These impulses are what appear as up-and-down patterns of an electrocardiogram (ECG). With a normal sinus rhythm (NSR), the pattern will be uniform with high and low impulses falling within "normal" parameters.
The pattern of electrical impulses reflects the way that the chambers normally beat to allow blood in and out of the heart. There are two sets of heart chambers:
Atrium: These are the upper chambers that receive blood from the body.
Ventricles: These are the lower chambers that pump blood out of the heart and back into circulation.
The sinus node consists of a group of cells called pacemaker cells that are clustered in the right atrium of the heart. These cells produce electrical impulses that cause heart chambers to contract and relax in order so that blood can move through the heart as follows:
Blood enters the right atrium and passes into the right ventricle.
The right ventricle pumps blood to the lungs where it becomes oxygenated.
The oxygenated blood is brought back to the heart by the pulmonary veins and passes into the left atrium.
Blood passes into the left ventricle and is pumped out to the body.
When Is a Sinus Rhythm Abnormal?
An abnormal rhythm is one in which the rate of firing is irregular and either too slow, too quick, or erratic.
When heart rate becomes too slow it is known as bradycardia and when it's too fast it is known as tachycardia.
Is Sinus Arrhythmia Serious?
Sinus arrhythmia can sometimes be so brief that the overall rhythm isn't greatly affected. But some, like those that produce shortness of breath or dizziness, may point to serious conditions.