The first-degree heart block is also known as the first atrioventricular (AV) heart block. Heart block is a disease that causes the heart to beat more slowly than normal with an irregular rhythm. Electric signals control the heartbeat. The electrical signals carried from the brain to the heart are called conduction. Conduction is the procedure by which the heart muscle gets instruction for contraction and relaxation. The sinus node controls the heartbeat. The sinus node is a component of the atria's upper heart chamber. Electrical signals that ordinarily travel from the atria to the ventricles (lower chamber of the heart) interfere in patients with heart block. As a result, a patient with a heart block suffers from irregular contractions. Ventricles cannot contract and properly pump blood if the electrical signals between your atria and ventricles cannot travel between them. The first-degree heart block is asymptomatic. The prevalence of first-degree heart block is 1 to 1.5 percent until 60 years. It is more prevalent among men compared to women.
What Is First-Degree Heart Block?
A delay in the AV (atrioventricular) conduction system is known as a first-degree atrioventricular (AV) block. The electrical characteristics can differ and be caused by delays in heart components in first-degree AV block. The PR interval (PR interval is a measurement on an electrocardiogram that reflects the time it takes for an electrical impulse to travel from the atria to the ventricles of the heart)is lengthened in first-degree heart block. It is the characteristic feature of an electrocardiogram (ECG). First-degree heart block can be associated with an increase in the combined endpoint of heart failure hospitalization or death. The heart block can be classified into three types:
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First-degree Heart Block - First-degree heart block is the least serious. First-degree heart block is defined as the slow conduction of electrical signals from the atria to the ventricles. First-degree heart block might not need any form of medical intervention.
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Second-degree Heart Block - Second-degree heart block refers to intermittent failure of conduction of electric signals between atria and ventricles.
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Third-degree Heart Block - Third-degree is a serious condition in which the conduction of electric signals fails completely. It completely prevents electrical signals from traveling from your atria to your ventricles. As a result, patients have either no pulse or an extremely sluggish pulse.
What Are the Causes of First-Degree Heart Block?
The mechanism that underlies the association between first-degree heart block and adverse cardiovascular outcomes and mortality is unclear. However, the prolongation in PR interval indicates an underlying cause of heart block, such as heart disease. In addition, the fibrotic changes (weakening of heart muscles) in older people are usually the identifiable factor of first-degree heart block.
The following are the underlying cause of first-degree heart block:
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Coronary heart disease (a condition in which the heart’s blood vessels are damaged).
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Myocardial infarction (a condition in which the heart muscle is damaged due to insufficient blood supply).
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Electrolyte abnormalities include hypokalemia (low potassium in the body) and hypomagnesemia (low magnesium in the body).
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Infections include endocarditis (inflammation of the heart’s layer), rheumatic fever (an inflammatory disease affecting the heart, brain, and joints), Chagas disease (an infectious disease caused by Trypanosoma cruzi), Lyme disease (a bacterial disease that causes rashes, fever, and fatigue), and diphtheria (an infection caused by bacterium Corynebacterium diphtheriae).
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Drugs (antiarrhythmics and Digoxin)
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Infiltrative diseases include sarcoidosis (a condition in which the accumulation of inflammatory cells occurs in different body parts).
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Collagen vascular diseases include systemic lupus erythematosus (an autoimmune disease that causes inflammation and damage to the other body organs), rheumatoid arthritis (inflammation of the joints), and scleroderma (a condition in which hardening of the skin occurs).
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Idiopathic degenerative diseases include Lenegre and Lev (a condition that causes complete heart block).
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Neuromuscular disorders.
Risk factors of first-degree heart block:
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Older age (more than 65 years).
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Hypertension (high blood pressure).
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Cardiac diseases.
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High potassium levels.
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Previous heart surgery.
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Heart failure (a condition that affects the blood pumping function of the heart).
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Atrial fibrillation (weakening of the heart’s muscles due to fibrosis).
What Are the Signs and Symptoms of First-Degree Heart Block?
The patients with first-degree heart block are asymptomatic. Therefore, most people remain undiagnosed. The patients can experience the following:
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Dizziness.
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Fainting.
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Patients may feel like their heart is skipping beats.
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Chest pain.
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Shortness of breath (dyspnea) or breathing difficulties.
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Nausea.
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Fatigue.
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Malaise.
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Lightheadedness.
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Syncope (unconsciousness).
Signs
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Bradycardia (heart rate less than 60 beats per minute)
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PR interval exceeding 0.20 seconds.
How Is First-Degree Heart Block Diagnosed?
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The first-degree heart is usually asymptomatic and undiagnosed.
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Patients get diagnosed during routine checkups.
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The problem is typically unknown to the patient until a routine electrocardiogram reveals it.
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First-degree heart can be diagnosed by thorough history and electrocardiogram (ECG). ECG can identify prolongation of the PR interval prolongation.
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It can be due to underlying causes such as congenital or acquired heart disease history, risk factors for heart disease, family history of cardiac disease, neuromuscular disease, or family history of neuromuscular disease.
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In the first-degree block of a higher grade (PR interval greater than 0.30 seconds), patients may develop severe symptoms.
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The physical signs may remain normal during the physical examination. The physical examination can identify skin problems (swelling in the hands) or murmur (irregular) sounds of the heart.
How Is First-Degree Heart Block Treated?
Most people with first-degree AV block do not require any medical intervention. For patients with first-degree AV block, several studies do not advise permanent pacemaker implantation, except for patients with a high-grade first-degree heart block (PR interval greater than 0.30 seconds) who are thought to be experiencing AV block-related symptoms. Patients with high-grade first-degree AV block neuromuscular illness or a prolonged QRS interval (The QRS interval is a measurement on an electrocardiogram that reflects the time it takes for the electrical impulse to travel through the ventricles of the heart) can be candidates for pacemaker implantation.
The following are the treatments for first-degree AV block:
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Elimination of the underlying cause is the first choice of the treatment strategy. The proper diagnosis of cardiomyopathy (heart disease) is required to cure the disease.
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Pacemaker implantation may be necessary for individuals with AV block associated with myocardial infarction (MI). However, it is frequently postponed to see if the AV block is temporary as the patient recovers from the MI.
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Antiarrhythmic medication is not indicated.
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Patients who do not exhibit symptoms must be monitored to look for signs of deteriorating AV block.
Conclusion
Several studies suggest that prolonged PR interval and first degree heart block are not benign conditions. It is associated with increased mortality, heart failure, and atrial fibrillation. Physicians should not, therefore, consider first degree heart block as a benign condition. Several studies suggest that closer monitoring may be warranted for future events, although effective risk-reduction strategies still need to be developed. Regular ECGs can be used for surveillance, and if the PR interval prolongation does not get worse, additional treatment is rarely needed. Most of the patients who are accidentally diagnosed with first-degree heart block do not require any treatment. Still, eliminating the cause is the preventive step against developing any further heart disease.
