What Is a Normal Sinus Rhythm?

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.

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:

1. Blood enters the right atrium and passes into the right ventricle.
2. The right ventricle pumps blood to the lungs where it becomes oxygenated.
3. The oxygenated blood is brought back to the heart by the pulmonary veins and passes into the left atrium.
4. 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.

What Is Bradycardia?

There are a number of circumstances in which it is normal for the sinus rhythm to be at the low end of the range of beats per minute. A slow heart rate is referred to as bradycardia.

Causes

Sinus bradycardia can occur normally during sleep, when most people experience a dip in heart rate to below 60 beats per minute. Trained athletes can have resting heart rates in the 40s even while awake.

Bradycardia may also be related to health problems that directly or indirectly affect the normal sinus rhythm. These include:

• Congenital heart disease (a heart defect present at birth)
• Heart damage caused by heart disease or heart attack
• Aging-related heart deterioration
• Obstructive sleep apnea (gaps in breathing during sleep)
• Myocarditis (heart inflammation)
• Hypothyroidism (low thyroid function)
• A complication of heart surgery
• Electrolyte imbalances, such as calcium and potassium
• Certain medications, like sedatives and opioids

Symptoms

A slow heart rhythm without symptoms is usually no cause for concern. However, when the heartbeat becomes too slow to pump enough blood throughout the body, treatment may be needed. This may include the use of a pacemaker.

If your heart rate is too slow while awake, you may have a disorder called sinus node disease or sick sinus syndrome. Symptoms include:

• Chest pain
• Severe fatigue
• Lightheadedness or dizziness
• Shortness of breath
• Confusion
• Fainting
  

What Is Tachycardia?

Sinus rhythm that is abnormally fast is referred to as sinus tachycardia. It can be normal for the heart rate to speed up during exercise to ensure there is extra blood to fuel the activity.

Causes

Sinus tachycardia also can occur in people for any number of health reasons, including:

• Fever
• Hypertension (high blood pressure)
• Hypotension (low blood pressure)
• Hyperthyroidism (overactive thyroid)
• Anemia (low red blood cells or hemoglobin)
• Electrolyte imbalances, like sodium and magnesium
• Heavy caffeine use
• Heavy alcohol use
• Certain medications, including some antidepressants and antibiotics
• Smoking
• Illegal drugs, like cocaine or methamphetamine

Some people have tachycardia for no apparent cause, referred to as inappropriate sinus tachycardia (IST). A similar condition called postural orthostatic tachycardia syndrome (POTS) occurs when a person stands upright, causing tachycardia without a drop in blood pressure.

Symptoms

Tachycardia may not cause recognizable symptoms in some people. When it does, symptoms may include:

• Rapid pulse
• A pounding heartbeat
• Palpitations (heart flutters or skipped beats)
• Chest pain
• Shortness of breath
• Dizziness or lightheadedness
• Fainting

How to Treat Abnormal Sinus Rhythm

Treatments will depend on your individual response to medications, your health history, and any underlying causes of the abnormal rhythm.

Common treatments for an abnormal rhythm include one or more medications, surgery to implant devices that control the heartbeat, and other procedures to treat problems with electrical signals.

There may also be treatments to address any underlying issues or conditions that are contributing to the irregular rhythm, such as electrolyte levels, high blood pressure, heart disease, sleep apnea, or thyroid disease.

Summary

A sinus rhythm is the beating of the heart caused by electrical impulses from the sinus node. The sinus node is a group of cells in the heart that generates these impulses, causing the heart chambers to contract and relax to move blood through the body.

A normal heartbeat is referred to as normal sinus rhythm. An abnormally slow heartbeat is called bradycardia, while an abnormally fast heartbeat is called tachycardia.