First-degree atrioventricular block

PR interval on the electrocardiogram (ECG) is measured from the beginning of the atrial depolarization (P wave) to the beginning of ventricular depolarization (QRS complex). In adults, the duration of the PR interval is in the range of 0.12 - 0.20 seconds in normal heart rate. First-degree atrioventricular block is defined as the increase in the PR interval more than 0.20 seconds. First-degree atrioventricular block is usually asymptomatic at rest. With a significant increase in the PR interval duration exercise tolerance can be reduced in some patients with left ventricular systolic dysfunction. Fainting may be a result or a sign of the transition to a higher degree atrioventricular block, primarily accompanied by intranodal block and a wide QRS complex.

Causes:

• Sport Training. Well-trained athletes may experience first-degree atrioventricular block (and sometimes higher degree atrioventricular block) due to increased vagal tone.
• Ischaemic heart disease.
• In presence of acute myocardial infarction, there is first-degree atrioventricular block in less than 15% of patients who received adequate therapy.
• AV block is more common in the cases of infarction of left ventricular myocardial bottom wall.
• Carrying out of thrombolytic therapy in myocardial infarction. Patients, who developed atrioventricular block after thrombolytic therapy, have a higher mortality in the hospital and in the next year, in comparing to patients without atrioventricular block. In patients with atrioventricular block focus of infarct is often located in areas supplied by the branches of the right coronary artery. It is believed that in cases of atrioventricular block there is large infarct focus.
• Stenocardia (Angina pectoris).
• Prinzmetal angina.
• Idiopathic degenerative diseases of the condaction system.
• Lev's disease. It is expressed as degenerative progressive fibrosis and calcification of cardiac structures. Lev's disease begins in the fourth decade and is considered secondary to the deterioration of these structures under the influence of ventricular muscle effort. As a result of conduction disturbances in the proximal part of the atrioventricular node, bradycardia and different severity of atrioventricular blocks appear.
• Lenegre disease, which is idiopathic, fibro-degenerative disease with a limited lesion of His-Purkinje system. Lenegre disease involves a conduction disorders in the middle and distal part of the atrioventricular node, and in contrast to the Lev's disease affects the younger generation.
• Medications. Calcium channel blockers, beta-blockers, digoxin, amiodarone may result in the occurrence of first-degree atrioventricular block. Despite the fact that the presence of first-degree atrioventricular block is not an absolute contraindication to the use of these drugs, you should have extreme caution in using these drugs in these patients, since there is a risk of occurrence of higher degree atrioventricular block.
• Calcification of rings of mitral and aortic valves. The main areas of the branching of bundle of His are located at the base of the front leaf of the mitral valve and the non-coronary leaf of the aortic valve. Calcium deposits in patients with calcification of the aortic ring and the mitral valve are associated with an increased risk of atrioventricular block.
• Infectious diseases. Infective endocarditis, diphtheria, rheumatic fever, Chagas disease, Lyme disease, tuberculosis can cause first-degree atrioventricular block.
• The spread of infection in infective endocarditis on its own or an artificial valve (e.g., valve ring abscess) and adjacent areas of myocardium may lead to atrioventricular block.
• Systemic collagenoses with vascular lesions. Rheumatoid arthritis, systemic lupus erythematosus, scleroderma can lead to atrioventricular block.
• Infiltrative diseases such as amyloidosis or sarcoidosis.
• Myotonic dystrophy.