What is Sinus Rhythm in ECG

Normal sinus rhythm

Normal sinus rhythm is another name for the heart’s natural rhythm. The sinus node is the starting point for the signal and starts a heartbeat. These signals cause the heart to contract and the wave spreads from the right side to the left side of the heart and travels down to the atrium and ventricle.

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In a normal sinus rhythm, the heart rate ranges between 60 and 100 beats per minute. The electrical impulses that start from the sinus node send signals and make the heart contract. A heart rate of more than 100 beats per minute can also occur temporarily, like when we.

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• Exercise

• Feel stress or anxiety

• Have taken certain medications

• Take stimulants such as caffeine, nicotine, or recreational drugs

• During fever

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Conversely, sinus rhythm can decrease to 60 beats per minute.

• Young adults and athletes

• During deep sleep

• If taking medications

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Understanding Sinus rhythm

Sinus rhythm versus heart rate

The normal heartbeat pattern of our heart is called the sinus rhythm. Heart rate is the number of beats per minute. In a normal sinus rhythm heart rate ranges between 60-100 beats per minute.

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What is normal sinus rhythm?

The heart’s normal rhythm is also called sinus rhythm; the sinus node sends electrical signals that travel as impulses in the heart. These impulses are seen as the up and down waves on the electrocardiogram. The patterns so formed by the waves are uniform and conform with impulses.

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The pattern obtained from these electrical impulses reflects how the heart beats to allow blood in and out of the heart.

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• Atria are the upper chambers that receive blood from the body.

• Ventricles, the lower chambers, pump blood back into circulation.

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The pacemaker cells that start these impulses are a group of cells in the right atrium called the sinus node. The electrical impulses originate in the heart from here, making it contract and relax to push the blood into circulation in the following steps.

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• The right atrium pushes blood into the right ventricle.

• The right ventricle pushes blood into the lungs for oxygen.

• The oxygen-rich blood from the lungs is then pushed into the left atrium.

• From the left atrium, blood is pushed into the left ventricle and finally circulates in the body.

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Sinus arrhythmia

It is the time between heartbeats that can be slightly shorter or longer. It depends on whether you are breathing in or out. This is considered normal and a sign of a healthy heart. It is of 2 types.

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Respiratory sinus rhythm: When we take in a breath, the heart rate goes up, and when we breathe out, it slows down. The interval between each heartbeat is the P-P interval.

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It has a variation of less than 0.16 seconds, but in cases of respiratory sinus arrhythmia, the P-P interval is longer than 0.16 seconds when the person breathes out.

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Non-respiratory sinus rhythm:  It is similar to respiratory sinus arrhythmia, but people with this type usually have -

• Head or neck injury

• Have taken too much Digoxin

• Have heart disease

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Abnormal Sinus Rhythm

An irregular sinus rhythm is termed sinus arrhythmia. 

• A sinus rhythm faster than the normal range is called sinus tachycardia

• A slower rate is called sinus bradycardia.

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Sinus tachycardia

If the heartbeat increases after exercise, it is normal. If the heart rate increases, even at rest, it causes serious complications.

• Heart failure.

• Stroke.

• Sudden cardiac arrest.

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The symptoms of sinus tachycardia are

• Palpitations or a fluttering feeling in the heart.

• Lightheadedness or dizziness

• Chest pain or tightness

• Shortness of breath

• Fatigue

• Fainting 

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The causes of sinus tachycardia are.

• Heart damage by heart disease or a previous surgery.

• Congenital (at birth) heart conditions.

• Loss of water from the body.

• Anemia. 

• Hyperthyroidism.

• Low blood sugar.

• Pulmonary embolism (lung blockage).

• Severe bleeding.

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Sinus bradycardia

Sinus bradycardia is when the heart beats slowly. It causes the blood flow into the organs and tissues of the body to be reduced. When it happens, complications occur; they are

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• Confusion or disorientation.

• Loss of unconsciousness

• Worsening heart failure

• Sudden cardiac arrest

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Some crucial symptoms of sinus bradycardia are

• Being lightheaded or dizzy

• Fatigue

• Trouble exercising

• Chest pain

• Shortness of breath

• Fainting

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The causes of bradycardia are

• Heart damage due to aging, heart disease, or previous surgery.

• Congenital heart conditions

• Hypothyroidism

• Sleep apnoea

• Pericarditis (inflammation around the heart) 

• Myocarditis (inflammation around heart muscles)

• Rheumatic fever 

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Overview of Sinus Rhythm in ECG

Sinus rhythm is a regular heart rhythm where electrical stimuli are initiated in the SA node. Then, they are conducted to the AV node, the bundle of His and Purkinje fibers. Depolarization and repolarization of atria and the ventricles are visible as distinct waves on ECG, with a unique labeling system to identify each wave.

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P Wave 

The P wave represents atrial depolarization. Valves between the atria and ventricles open, and blood flows in the ventricles due to gravity and mainly due to suction caused by ventricles as they expand.

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Atrial contraction is required for the final 30% a relatively small mass is required. So, a small amount of voltage is needed to contract the atria.

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QRS Complex

After the first wave, there is a short period where the line is flat. At this point, the stimulus is delayed in the bundle of His, allowing atria time to pump all the blood into the ventricles. As ventricles fill, the pressure on the valves between the atria and ventricle increases, closing it.

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The electrical stimulus then passes from the bundle of His to Purkinje fibers. The electrical activity generated is recorded as a complex of 3 waves called the QRS complex. The voltage is shown by measuring the waves vertically. Higher voltage is required to cause ventricular contraction. And hence, the wave is much more significant.

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Q wave

It is represented as a minor negative wave immediately before the large QRS complex. It represents depolarization or contraction in the septum. The electrical signal passes from the SA node through the bundle of His, a band of muscle fibers between the ventricles.

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The signals then pass to the left and right bundle branches, distributing the impulse to the respective ventricles. The signal triggers the ventricles to contract and pumps the blood out of the heart. Bundle of His transmits the electrical signals from the atrioventricular node to the ventricles, ensuring coordinated heartbeats and proper cardiac function.

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• There is little activity 

• The Q wave is less than two small squares, and the travels in the opposite direction to the direction of conduction (right to left). 

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R Wave.

R wave is the largest wave in the QRS complex. The R wave depicts the electrical stimulus as it passes through the ventricular walls. The walls of the ventricles are thick due to the work they do. Hence, more voltage is required, and the R wave is the biggest wave generated during normal conduction.

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S Wave.

It is a small negative wave following a large R wave. It represents depolarization in Purkinje fibers. S waves travel in the opposite direction to large R waves. Purkinje fibers spread throughout the ventricles. From top to bottom. End, then back. Up through the walls of the ventricles.

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The QRS complex has three distinct waves

• Q Wave representing septal depolarization.

• R waves representing ventricular depolarization?

• S wave representing depolarization of Purkinje fibers.

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T wave

Both the ventricles are re-polarized before the cycle repeats itself. The T wave represents ventricular repolarization.

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ST segment

There is a brief period between the end of the QRS complex and the beginning of the T wave when there is no conduction, and the line is flat. It is the ST segment. It indicates myocardial ischemia and necrosis if it goes up or down.

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Duration of waves

In the cardiac cycle, each stage should be completed within a specific duration to be considered normal. The measurements of these are in fractions of a second. The ECG paper allows us to count the time and small squares. Measurements taken in small squares are universally used, then tenths and hundredths of seconds.

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Regularity of waves

Mark the center of 2 consecutive P or R waves. Measure the RR interval or the PP interval if the distance between the peaks of 2 consecutive peaks is the same, then the rhythm is regular.

•  If there are four large squares present, then the heart rate is. 300 / 4 equals 75.

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Characteristics of a Sinus Rhythm ECG

They are

• A P wave is present

• P waves should be rounded

• P waves should have the same shape

•  A QRS complex should follow a P-wave

• The PR interval should be 3 to 5 small squares and constant.

• The rhythm should be regular.

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Factors affecting Normal sinus rhythm

They are

• Electrolyte imbalance: A disturbed concentration of potassium, sodium, calcium, and magnesium electrolytes in the heart disturbs the electrical signals causing irregular rhythms.

• Medications: Certain drugs like beta-blockers, calcium channel blockers, and some anti-arrhythmic medications affect heart rate and rhythm.

• Autonomic nervous system: The sympathetic nervous system, which stimulates fight or flight response, increases the heart rate, whereas the parasympathetic nervous system, which stimulates rest, slows it down.

• Heart diseases: Coronary artery disease, Valvular heart diseases, and previous heart surgeries cause changes in the sinus node and the sinus rhythm.

• Thyroid diseases: Hyperthyroidism causes rapid heart rate. Hypothyroidism causes a slow heart rate.

• Sleep apnoea: Interrupted breathing during sleep leads to irregular heart rhythms.

• Sick sinus syndrome: A malfunction in the sign the node itself causes a slow heart rate and pauses in the rhythm.

• Age: As people age, the node can become less efficient. Thereby increasing the risk of irregular rhythms.
  
  

Conclusion

The heart’s regular beat starts from the sino-atrial node ensuring the heart functions regularly and correctly. It is seen as a consistent pattern of P wave followed by QRS complex and T wave. Identifying sinus rhythm helps check heart functions and detect irregularities that indicate heart problems.