Bradycardia ECG vs Normal ECG

A bradycardia ECG and a normal ECG are different. We must identify the differences to diagnose and restore a normal heart rate with treatments such as a pacemaker or medication adjustments as necessary. Bradycardia occurs when the resting heart rate is below 60 beats per minute.  Athletes often have resting rates less than 60 beats per minute.  A slow heart rate for them is a sign of fitness and a well-exercised heart. It occurs even when we sleep.

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Sinus bradycardia is when the electrical activity in the heart follows normal conduction pathways but at a slow rate. Bradycardia ECG shows upright P waves and a consistent rhythm, even though the rate is reduced. ECG shows irregular rhythms, missed beats, or prolonged intervals in more severe cases, such as heart block, and may require medical attention.

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In this blog, we will read about the causes of a slow heart rate and its meaning.

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Why is it Called Sinus Bradycardia?

The word “Bradycardia” is derived from the Greek words Bradys, meaning slow, and Kardia, meaning heart. Sinus Bradycardia means the heart is beating slowly but with a sinus rhythm.

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Sinus rhythm is when the heartbeat starts in the sinoatrial (SA) node, a group of electrically active cells in the right atrium. The SA node is a natural pacemaker. It generates an electric current, making the heart contract. Sinus Bradycardia means the sinus node is starting the heartbeat, which is expected. Individuals with sinus bradycardia may not show symptoms, especially if physically fit. However, symptoms include

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• Dizziness.

• Fatigue.

• Fainting.

• Shortness of breath.

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Types of Bradycardia:-

1. Sinus bradycardia is the increased vagal tone. It is physiological in athletes.

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2. Atrioventricular blocks occur when the atrial impulses are delayed or blocked.

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• First-degree AV block is caused by increased vagal tone, conduction impairment, or medications.

• Second-degree AV block is classified into Mobitz I, which has a progressive prolongation of the PR interval followed by a skipped beat, and Mobitz II, which occurs when a randomly dropped QRS complex is detected on the ECG.

• Third-degree or complete AV block is a lack of conduction of atrial impulses to the ventricle, leading to independent contractions.

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3. Sinus node dysfunction: Degeneration of the SA node is an ischemic event that involves the SA node, which may lead to impulse generation at a slower rate.

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• Sinus pause occurs when an absent or delayed impulse is generated from the SA node.

• Sinus arrest occurs when impulse generation fails. 

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Understanding Bradycardia:-

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1. Causes 

Bradycardia is caused by

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• Problems with the sinoatrial node, as it is  the heart’s natural pacemaker.

• When conduction pathways of the heart do not pass the electrical impulses properly from the atria to the ventricles.

• Hypothyroidism (low thyroid hormone).

• When there is damage to the heart muscles due to a heart attack or heart disease.

• Due to medications used to slow down the heart rate.

• Congenital heart defects.

• Myocarditis or infection of the heart tissue.

• Complications of heart surgery.

• Electrolyte imbalances, such as calcium and potassium.

• Sleep apnea, which is caused by repeated obstruction in breathing during sleep.

• Inflammatory diseases like rheumatic fever or lupus.

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2. Symptoms 

The symptoms include:-

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• Shortness of breath.

• Fainting.

• Feeling of tiredness during exercise.

• Chest pain.

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3. Complications

They include:-

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• Heart failure.

• Syncope (fainting).

• Cardiac arrest.

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3. Diagnosis

The diagnosis of sinus bradycardia requires:-

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1. ECG: The heart rate, rhythm, and waveform patterns can be seen on an ECG. The heart rate is below 60 beats per minute,

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• Normal P waves before each QRS complex.

• Regular rhythm showing RR intervals of similar duration is visible.

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2. Holter monitor: A wearable ECG device that continuously records heart activity for 24 to 48 hours as a patient performs daily tasks. It picks up bradycardia, which cannot be recorded during a routine ECG test.

Clinical Significance

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When is sinus bradycardia normal?

• Sleep: During sleep, the heart rate naturally decreases because the body is less demanding of oxygen and nutrients.

• Athletes or trained individuals: Athletes often have bradycardia, which is caused by an increased cardiovascular efficiency. It is also called the athlete's heart. Their strong muscles pump blood effectively even at a slower rate, making this a normal physiological adaptation. 

• Vasovagal Syncope: An accidental drop in heart rate and blood pressure causes vasovagal syncope, a temporary sinus bradycardia.

• Vagal manoeuvres: Vagal manoeuvres are simple actions that stimulate the vagus nerve and slow down the fast heart rate. They are often used to treat supraventricular tachycardia. Carotid sinus massage also helps to lower the heart rate.

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 When is sinus bradycardia a matter of concern?

Sinus Bradycardia is not dangerous when it is in response to physiology. When experiencing symptoms as:-

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• dizziness.

• fatigue.

• fainting.

• shortness of breath.

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It may become a matter of concern. These symptoms indicate the heart is beating ineffectively and cannot pump sufficient blood to meet the body's requirements.

Underlying conditions that can cause sinus bradycardia are

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• Hypothyroidism decreases the body’s basal metabolic rate, causing a decrease in heart rate.

• Calcium and potassium electrolyte imbalance alter the heart's electrical activity.

• Some medications, like beta blockers and calcium channel blockers, which are used to treat hypertension and heart conditions, can lower the heart rate excessively.

• Heart disease: Sinus Bradycardia may indicate the presence of sick sinus syndrome, where the natural pacemaker of the heart malfunctions, or due to myocardial infarction or heart blocks.

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What is a Normal Sinus Rhythm?

The normal heart's electrical activity is the normal sinus rhythm. It implies that the sinus rhythm begins in the sino-atrial node. The key features of a normal sinus rhythm ECG are

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• P wave: Each wave starts with a P wave, which indicates atrial depolarisation. The P wave is biphasic in V1.

• The QRS complex follows the P wave, representing ventricular depolarisation.

• The T wave follows the QRS complex, indicating ventricular repolarisation.

• Regular intervals, the interval between each beat is regular, and the frequency of each beat is 60 to 100 beats per minute.

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All the component shapes and durations of a normal sinus rhythm, the P, QRS, and T, and intervals have normal shapes and durations. In bradycardia, they are just farther apart due to a slow heart rate.

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Sinus Bradycardia vs Normal Sinus Rhythm ECG

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Managing bradycardia

How we manage bradycardia depends on its cause, severity, and symptoms. Asymptomatic bradycardia, such as in athletes, does not require treatment. However, for symptomatic bradycardia, we need to address factors that can be reversed, such as medication adjustments, correcting electrolyte imbalances, or treating conditions like hypothyroidism.

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• Conservative management: This approach to management does not require unnecessary interventions. Reversible causes are targeted, such as medication effects or dehydration.

• Pharmacologic interventions for acute symptomatic bradycardia, such as medications like atropine, are used to stimulate heart activity.

• Pacemaker implantation is done in severe bradycardia due to AV block or sick sinus syndrome. It restores the heart rhythm by sending electrical impulses. Pacemakers are a long-term solution for patients with life-threatening bradycardia.

• Lifestyle changes: A slow resting heart rate indicates good health. It is between 60 and 100 beats per minute, but some athletes record heart rates as low as 40 beats per minute at rest.

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Ways to Reduce the Resting Heart Rate:-

Exercise reduces resting heart rate. A sedentary lifestyle is a common cause of a high resting heart rate. Moderate-intensity aerobic activity for 150 minutes or 75 minutes per week of vigorous activity is good for heart health.

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Managing stress:-

Chronic stress increases the heart rate and increases the risk of cardiovascular disease.

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• Meditate on your own.

• Do breath work techniques.

• Be mindful in everyday life.

• Make positive affirmations.

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Cut down on harmful substances:-

• Reduce caffeine intake.

• Reduce smoking and alcohol consumption.

• Avoid substance abuse.

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Sleep well: Sleep deprivation increases heart rate, and insomnia is associated with risk factors for heart disease. Stop using your smartphones before going to bed.

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How Long Does the Bradycardia Last?

Bradycardia lasts as long as a well-trained athlete maintains their usual level of exercise. If it occurs as an effect of medication, it usually recedes as the drug that triggered it is utilized by the body or excreted in the urine. Bradycardia associated with hypothyroidism is treated after the treatment with thyroid hormones, and some are even treated with permanent pacemakers.

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Conclusion

 Bradycardia is usually not a cause of concern, but it needs attention when it affects overall well-being and when symptoms are severe and persistent. Identifying it becomes important due to age, medical condition, or medications.

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Bradycardia ECG and normal ECG differ in heart rhythm patterns and rate. Diagnosing the cause is essential for proper treatment, which may involve lifestyle modification, medication adjustments, or pacemaker implantation. Gauze assists you in diagnosing and developing a treatment plan to improve outcomes.