Atrioventricular block in the heart
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Types and Classification of Atrioventricular (AV) Block
Atrioventricular block is a disruption in the electrical conduction between the atria and ventricles of the heart. There are three main types: first-degree, second-degree, and third-degree AV block. First-degree AV block is characterized by a prolonged PR interval on the ECG, but every atrial impulse still reaches the ventricles. Second-degree AV block is divided into Mobitz I (Wenckebach), where the PR interval progressively lengthens until a beat is dropped, and Mobitz II, where some P waves are not followed by QRS complexes without progressive PR prolongation. Third-degree (complete) AV block is when there is no conduction from the atria to the ventricles, resulting in independent atrial and ventricular rhythms 12.
Clinical Presentation and Risks of AV Block
Patients with AV block may experience a range of symptoms, from none at all to syncope and lightheadedness, depending on the degree and type of block. Second-degree Mobitz II and third-degree AV blocks are particularly dangerous, as they can progress to complete heart block and may be fatal if not treated promptly. Third-degree AV block often requires immediate temporary pacing and usually permanent pacemaker implantation to prevent life-threatening complications 23.
First-Degree AV Block: Prognosis and Associations
First-degree AV block, once considered benign, is now recognized as being associated with increased risks of atrial fibrillation, heart failure, and mortality, especially in patients with heart failure or coronary artery disease. In heart failure patients, first-degree AV block is common and linked to worse outcomes, including higher rates of hospitalization and death. Optimizing AV delay in patients with cardiac resynchronization therapy may improve outcomes, but the best approach is still under investigation 49. Additionally, AV block can be a predictor of clinical atrial fibrillation .
Paroxysmal and Postoperative AV Block
Paroxysmal AV block is a sudden, unpredictable transition from normal conduction to complete heart block, which can cause syncope and sudden cardiac death. It is often missed due to its abrupt and intermittent nature . Postoperative AV block is a known complication after congenital heart surgery, with certain procedures carrying higher risk. While some cases resolve within days, more than half may require permanent pacemaker implantation. Risk factors include older age at surgery, preoperative endocarditis, longer aortic cross-clamp time, and high-risk surgical procedures .
Congenital and Childhood AV Block
Congenital AV block is diagnosed in utero, at birth, or within the first month of life, often due to immune-mediated injury from maternal antibodies. Childhood AV block is diagnosed between one month and 18 years of age and can be caused by genetic factors. Early diagnosis and management, including advances in permanent pacing, are crucial to prevent sudden death in these patients .
Diagnosis and Localization
AV block is diagnosed using ECG, which shows characteristic changes depending on the type and level of block. Electrophysiology studies can help determine the precise location of the block, which is important for management decisions, especially in complex or exercise-induced cases 15.
Conclusion
Atrioventricular block encompasses a spectrum of conduction disturbances with varying clinical significance. While first-degree AV block may be asymptomatic, it is associated with increased risk of arrhythmias and adverse outcomes in certain populations. Higher-degree blocks, especially Mobitz II and third-degree, can be life-threatening and often require pacemaker therapy. Early recognition, risk assessment, and appropriate management are essential to improve outcomes in patients with AV block.
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Most relevant research papers on this topic
Congenital and childhood atrioventricular blocks: pathophysiology and contemporary management
Early diagnosis and appropriate management of congenital and childhood atrioventricular blocks are crucial for preventing sudden death.
Postoperative atrioventricular block after surgery for congenital heart disease: incidence, recovery, and risks.
Postoperative atrioventricular block is common after congenital heart surgery, with more than half needing permanent pacemaker implantation, and should be delayed until after 12 postoperative days.
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