First-degree heart block

In cardiology, 1st degree heart block is defined as a minimal disruption in the conduction of electrical impulses that cause the muscles of the heart to contract and relax non-stop from the atria to the ventricles.

Epidemiology

Grade 1 heart block is more common in adults over 60 years of age, affecting approximately 6% of the population in this age group. The prevalence of such heart block in people under 60 is estimated at 1-1.5%. [1], [2]

According to statistics, men have 1 degree of heart block twice as often as women.

There is also AV blockade of the 1st degree in almost 10% of young athletes, which experts attribute to increased parasympathetic autonomic tone. [3]

Causes 1st degree heart block

Thus, heart block is a pathology of the conduction system of the heart, which makes it work automatically. For more information, see. - Heart rhythm and conduction disorders

Doctors call heart block a disorder of atrial-ventricular or atrioventricular conduction - the conduction of impulse from its atria (atrium) to the ventricles (ventriculus) through the atrioventricular node (nodus atrioventricularis) located on the interatrial septum of the right atrium, that is a 1 degree atrioventricular block (AV block).

Depending on how severe the disruption of the heart's conduction between its upper and lower chambers is, blockade is categorized into three degrees, and 1st degree heart block is the mildest. [4]

The causes of this disorder are quite numerous. Heart block of the 1st degree in an adult can occur at:

• coronary heart disease;
• myocarditis;
• Electrolyte imbalance with hyperkalemia;
• hypertonicity of the vagus nerve;
• sclerotic and fibrotic changes in the conduction system of the heart (Lenegr's disease);
• idiopathic Laun-Ganong-Levin clinical syndrome.

Although this condition usually develops as a person ages, 1st degree heart block in a child can be the result of: [5], [6]

• Congenital heart defects;
• diphtheria;
• cardiac type of autonomic dystonia;
• WPW (Wolff-Parkinson-White) syndrome;
• Brugada syndrome in children.

Risk factors

Are considered risk factors for 1st degree heart block:

• advanced age;
• weakening the heart muscle cardiomyopathy restrictive or hypertrophic type;
• progressive systemic myocardial sclerosis;
• rheumatoid arthritis;
• hypothyroidism;
• Lyme disease (lyme borreliosis);
• hereditary neuromuscular disorders;
• Continuous or long-term use of certain medications, such as cardiac glycosides, beta-adrenoblockers, calcium channel blockers, antipsychotics, and others;
• Scleroderma, sarcoidosis, systemic lupus erythematosus, amyloidosis and other infiltrative diseases.

Pathogenesis

In minimal heart block, the pathogenesis is due to a slowing of the conduction of electrical signals (action potentials) generated by the sinoatrial (sinus atrial) node as they travel from the atria to the ventricles.

In cases of 1st degree AV blockade, the slowing of the impulse passing through the atrioventricular node is more than 0.2 seconds beyond its programmed delay required for coordinated rhythmic contraction and relaxation of the functional syncytium (network of electrically connected cells) of the heart muscle - with complete atrial contraction and ventricular filling with blood. [7]

Then the signal, as it should, passes down the conductive pathways of the Guis-Purkinje system (the bundle of Guis, its legs and Purkinje fibers) located along the ventricular walls of the heart and makes the ventricles contract and pump blood.

Symptoms 1st degree heart block

Usually with 1st degree heart block, people don't notice any symptoms and don't know they have it until they have a normal ECG (electrocardiogram).

The ECG shows lengthening of the PQ interval (i.e., delayed conduction of the impulse through the AV node), as well as an increase of more than 0.2 seconds in the interval between the onset of atrial depolarization and the onset of ventricular depolarization - prolongation of the PR interval. [8]

Complications and consequences

What are the dangers of 1st degree heart block? This blockage is usually not serious, and people can lead normal lives if the condition does not progress - until a higher degree of heart block with slowing of the heart rate or skipping heartbeats, which increases the risk of atrial fibrillation. [9]

Diagnostics 1st degree heart block

For more information on how instrumental diagnostics is performed in cardiology, see. - Instrumental methods of cardiac examination. First of all, electrocardiography is performed.

In addition, blood tests such as: general clinical biochemical, for cholesterol and triglyceride levels, electrolytes, cardiac troponins cTn I and cTn II, aminotransferases AST and ALT, lactate dehydrogenase (LDH), creatine kinase (S-CK), and IgM antibodies (rheumatoid factor) are required.

And differential diagnosis helps to establish the exact cause of cardiac conduction disturbance and distinguish it from sinoatrial node block and bradycardia/tachycardia syndrome.

Treatment 1st degree heart block

For the vast majority of patients, no treatment is required other than routine monitoring in the form of periodic electrocardiography. [10], [11] The American Heart Association (AHA) and American College of Cardiology (ACC) guidelines do not recommend permanent pacemaker placement in patients with first-degree AV blockade, except in patients with a PR interval greater than 0.30 seconds who have symptoms suspected to be due to AV blockade. [12]

Dietary adjustments can be made for 1st degree heart block - based on heart disease diet.

Prevention

Heart block prevention focuses on managing risk factors and cardiologists, advise a healthy lifestyle that promotes not only overall health but also heart health.

Forecast

Patients with this condition have no direct symptomatology. The Framingham study showed that patients with prolonged PR intervals or first-degree heart block have twice the risk of developing atrial fibrillation and are three times more likely to require a pacemaker. [13] First-degree heart block usually does not impair quality of life and in most cases has a favorable prognosis.