What Is Sinus Rhythm: Best 101 Guide for Laymen

When it comes to medicine, the terms usually used are difficult to understand for a non-specialist.

People often find it difficult even to pronounce them and thus neglect these terms rather than understanding them.

One such term is sinus rhythm which is commonly used but is usually misunderstood.

If you are curious to understand what is sinus rhythm¹, this is the perfect article. Read it till the end to understand this term and other related terms.

What Is Sinus Rhythm?

What is sinus rhythm, it is a straightforward term to understand if the basic concepts related to it are clearly understood. 

One of the most interesting facts about the heart muscles or cardiac muscles that makes them different from all the other types of muscles present in the body is the ability to generate electrical impulses.

No other muscles present in the body possess such a quality, thus making the cardiac muscles superior to all the other muscles. They also can conduct this impulse and propagate it throughout the heart.

Thus, there is a set pathway through which an impulse is produced and propagated throughout the organ. Knowing this is very important to understand what is sinus rhythm.

A sinus rhythm, also known as the heart rhythm, is the rate at which the impulses from the sinus node are generated.

Depending on the frequency of the impulses generated, the heartbeats are determined.

Normal sinus rhythm ranges between 60 beats per minute to 100 beats per minute.

But the most critical question that arises is how an impulse generated from the sinus node causes a heart contraction and thus generates a heart rhythm.

To know this, one must be familiar with the conducting system of the heart.

Conducting System Of The Heart

After knowing what is sinus rhythm, let us know in detail about the conducting system of the heart.

The electrical impulses that propagate through the organ are produced by the SA node or the sinus node, which is present in the upper right atrium of the heart.

The impulse then passes to the AV node or the atrioventricular node,² which is present at the bottom of the right atrium.

After this, the impulse is conducted further by a group of fibers called the Bundle Of His.

This bundle of his is then divided into left and right bundle branches, which supply the respective parts of the heart.

The end fibers of this bundle of his are called Purkinje Fibers and are the last to get stimulated by the nerve impulse.

Now that an impulse is being generated and transferred from one chamber of the heart to another, there are certain instances in which the heart’s normal sinus rhythm is not maintained.

Any variation in the normal sinus rhythm is termed sinus arrhythmia.

Now the sinus rhythm is determined by various factors, and any change in them can lead to varying rates of heart rhythm.³

Factors Determining Sinus Rhythm

To understand what is sinus rhythm, one must be aware of the factors affecting it.

Sinus rhythm depends on various factors, which can lead to a change in the average heart rate.

These factors are as below:

1. Stress

With increased stress levels, the normal sinus rhythm increases and vice versa. This is commonly encountered on daily basis and needs no medical attention

2. Age

Sinus rhythm is increased in children and decreased in old individuals.

3. Gender

A female’s heartbeat is slightly faster as compared to a male’s due to a variation in the heart size.

4. Physical activity

With the increase in physical activity, the heartbeats also increase to meet the body’s demands for oxygen.

5. Emotional status

The emotional status of human beings dramatically impacts the sinus rhythm of the heart. For example, there is an increase in the heart rate when a person experiences joy or happiness.

6. Medications

Some medications tend to alter the heart rate to decrease the elevated heart rate and thus maintain a normal sinus rhythm.

7. Health Conditions or Comorbidities

Any health condition has a multi-system involvement. One such example is blood pressure. Individuals with chronic hypertension have an elevated heart rate.

Sinus Arrhythmias

After knowing what is sinus rhythm, one must know what sinus arrhythmia is, as these terms are closely related.

Any deviation in the normal sinus rhythm leads to sinus arrhythmia. Now sinus arrhythmia is a vague term and involves many varieties depending upon the causative factor and whether the heartbeats are increased or decreased.

Sinus arrhythmi⁴a is usually clinically diagnosed using an ECG machine.

What Is An ECG?

ECG stands for Electrocardiogram. Also known as EKG, it is a method used to measure the electrical activity of the heart.

The heart’s electrical activity is recorded on graph paper and is thus known as an electrocardiograph.

How to Record an ECG?

The electrical activity of the heart is measured using ECG leads.

These leads are extremely sensitive to the impulse and catch any change in them.

The limbs are present in three types, namely:

1. Limb Leads

Limb leads are placed on the right arm, left arm, and left foot. The right foot has a neutral lead.

2. Augmented Leads

The augmented limb leads have three subtypes: lead aVr, aVf, and aVl.

3. Chest Leads

The chest leads, also known as the precordial leads, are placed across the chest and are an excellent way to detect the electrical activity of the heart.

They are a total of 6 in number, namely V1, V2, V3, V4, V5, and V6.

How To Read A Normal ECG

A normal ECG has positive and negative deflections.

It has a P wave, QRS complex, T wave, and PR interval, PP interval, and ST interval.

The P wave is the first positive deflection in the ECG and indicates atrial depolarization.

The QRS complex is the second positive deflection and represents ventricular depolarization.

The T wave is the third positive deflection in the ECG and represents ventricular repolarization.

The PR interval measures the time between the P wave and the R wave. It is the time taken between atrial depolarization and ventricular depolarization.

The pp interval measures the time between two successive atrial depolarizations and indicates the normal sinus rhythm.

The ST interval is the second isoelectric line between the S wave and the T wave and represents the time taken from ventricular depolarization⁵ and ventricular repolarization⁶.

Along with knowing what is sinus rhythm, get to know some of the most common types of sinus arrhythmias They are:

• Sinus Bradycardia

• Sinus Tachycardia

• Atrial Fibrillation

• Respiratory sinus arrhythmia

• Sick sinus arrhythmia

1. Sinus Bradycardia

This is one of the most common types of sinus arrhythmia encountered.

When the activity at the sinus node is reduced and the heart rate is below 60 beats per minute, it is called sinus bradycardia.

Sinus bradycardia⁷ is normal in older individuals and during sleep.

In older individuals, the metabolic rate is reduced thus, the heart rate is reduced, leading to sinus bradycardia.

During sleep, the body is in a state of rest; thus, it does not require a high expenditure of energy to maintain the normal functions of the body leading to sinus bradycardia.

When talking about sleep and a decrease in the heart rate, one condition is sleep apnea. In medical language, apnea means complete cessation of breathing. Now apnea usually is temporary and commonly occurs during the night.

Sleep apnea is a condition in which there is a temporary cessation of breathing during the night and is relieved by sitting upright. For such a condition, medical advice, diagnosis, or treatment may be required in certain cases.

2. Sinus Tachycardia

Another form of sinus arrhythmia that is prevalent among people of all age groups is sinus tachycardia.

When the heart rate increases above 100 beats per minute, it is called sinus tachycardia.

Sinus tachycardia is very common after exercise, during stress, or in a situation of fear and anxiety.

It is also associated with many health conditions like high blood pressure, thus requiring a thorough diagnosis to find the root cause and provide adequate treatment.

It could also be the result of conduction abnormalities due to various factors.

Symptoms of sinus tachycardia include sweating, palpitations, headache, and confusion.

3. Atrial Fibrillation

Atrial fibrillation is a form of sinus tachycardia⁸ that is caused due to overactivation of the sinus node.

Atrial fibrillation should not be ignored, and one of its serious complications includes

the formation of a clot in the coronary arteries can lead to stroke.

In atrial fibrillation, there is an irregular contraction of the heart’s upper chambers with the lower chambers of the heart leading to disturbance in the normal blood flow to the respective ventricles.

Episodes of atrial fibrillation are usually accompanied by irregular heartbeats, heaviness in the chest, and chest pain.

4. Respiratory Sinus Arrhythmia

Respiratory sinus arrhythmia means a change in the rate of the heartbeats in direct synchronous with the rate of breathing.

As the cardiovascular system and the respiratory system are in direct coordination with each other, a change in one of the systems leads to a change in the other one.

This is the reason a higher rate of respiration leads to sinus arrhythmia and thus is called respiratory sinus arrhythmia.

Respiratory sinus arrhythmia is a common finding during high-strenuous activities like exercise. The lungs have to meet the oxygen supply of the body. There is an increase in the respiratory rate, and even the heart rate increases.

5. Sick Sinus Syndrome

As the name suggests, sick sinus syndrome is mainly caused due to dysfunction of the sinus node.

In sick sinus syndrome, the sinus node cannot produce an electric impulse which is necessary for the contraction of the heart and eventually pumping the blood to the entire body.

This means that the heart does not create an impulse that is appropriate for the body. This condition is usually fatal and requires medical attention.

Takeaway

Normal sinus rhythm ranges between 60 beats per minute to 100 beats per minute.

Any deviation in the normal sinus rhythm is known as sinus arrhythmia, which is a vague term and involves many subtypes.

The electrical activity of the heart rate is recorded using an Electrocardiogram. It is also known as ECG.

Sinus rhythm is widely affected by many factors and needs to be considered while studying them.

1. Valembois, Lucie, et al. “Antiarrhythmics for maintaining sinus rhythm after cardioversion of atrial fibrillation.” Cochrane Database of Systematic Reviews 9 (2019). ↩︎
2. Meijler, FRITS L., and MICHIEL J. Janse. “Morphology and electrophysiology of the mammalian atrioventricular node.” Physiological reviews 68.2 (1988): 608-647. ↩︎
3. Clarke, JoanM, et al. “The rhythm of the normal human heart.” The Lancet 308.7984 (1976): 508-512. ↩︎
4. Angelone, Alfonso, and Norman A. Coulter JR. “Respiratory sinus arrhythmia: a frequency dependent phenomenon.” Journal of Applied Physiology 19.3 (1964): 479-482. ↩︎
5. Chatterjee, K. A. N. U., et al. “Electrocardiographic changes subsequent to artificial ventricular depolarization.” British heart journal 31.6 (1969): 770. ↩︎
6. Yan, Gan-Xin, et al. “Ventricular repolarization components on the electrocardiogram: cellular basis and clinical significance.” Journal of the American College of Cardiology 42.3 (2003): 401-409. ↩︎
7. Eraut, Dennis, and David B. Shaw. “Sinus bradycardia.” British Heart Journal 33.5 (1971): 742. ↩︎
8. Olshansky, Brian, and Renee M. Sullivan. “Inappropriate sinus tachycardia.” Journal of the American College of Cardiology 61.8 (2013): 793-801. ↩︎

Last Updated on March 14, 2024 by ayeshayusuf