Complete heart block
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Definition and Mechanism of Complete Heart Block
Complete heart block, also known as third-degree atrioventricular (AV) block, occurs when electrical signals from the atria do not reach the ventricles, causing the upper and lower chambers of the heart to beat independently and often at different rates. This results in a slow heart rhythm (bradycardia) and can lead to symptoms such as chest pain, breathlessness, palpitations, vertigo, and sweating, especially if the block is severe or develops suddenly 139.
Causes and Risk Factors of Complete Heart Block
Acquired Causes
Complete heart block can develop in association with several conditions, most notably acute myocardial infarction (heart attack), where certain conduction disturbances may precede the block. Coronary artery disease, especially in older adults, is a common underlying cause due to coronary sclerosis or infarction 146. Surgical procedures, particularly those affecting the heart or its conduction system, can also lead to complete heart block by damaging the AV node 310. Additionally, medications used during general anesthesia have been reported to cause transient, but potentially fatal, complete heart block in patients with pre-existing conduction disease .
Congenital Causes
Congenital complete heart block (CCHB) can occur in both children and adults and may go unnoticed for a long time. It is often due to developmental abnormalities in the heart’s conduction system, such as discontinuity between the atrial and ventricular tissues or defects in the AV bundle. Some cases are associated with minor congenital malformations, but these are not always severe enough to disrupt conduction 579.
Other Causes
Infections such as diphtheria, measles, and bacterial endocarditis have been linked to heart block in children, though this is rare. Trauma, neoplasms, and autoimmune conditions can also contribute to the development of complete heart block .
Clinical Presentation and Prognosis
Patients with complete heart block may present with symptoms related to low cardiac output, including syncope (fainting), which is a grave prognostic sign. In the context of acute myocardial infarction, complete heart block is a known complication and is associated with a poor prognosis and increased in-hospital mortality. Inferior wall myocardial infarctions are more likely to result in complete heart block compared to other types 1368.
Diagnosis
Diagnosis is typically made using an electrocardiogram (ECG), which shows a lack of communication between atrial and ventricular contractions. In some cases, the block may be transient and reversible, especially if caused by medications or acute illness .
Management and Treatment
Immediate treatment is crucial, especially in critical cases. Emergency temporary pacing may be indicated in acute settings, such as during a heart attack, to maintain adequate heart rate and perfusion . The use of implantable pacemakers has significantly improved outcomes, especially in patients with intractable or recurrent heart block, whether due to surgical trauma, acquired heart disease, or congenital causes. Pacemaker implantation is often recommended, but the decision can be challenging in asymptomatic patients, particularly those with congenital heart block 8910.
Thrombolytic therapy has been shown to be useful in reversing complete heart block in patients with ST-elevation myocardial infarction (STEMI) .
Conclusion
Complete heart block is a serious cardiac condition that can arise from a variety of causes, including myocardial infarction, congenital defects, surgical trauma, infections, and medications. It is associated with significant morbidity and mortality, particularly when it complicates acute cardiac events. Prompt recognition, diagnosis, and management—often involving pacemaker implantation—are essential to improve patient outcomes 13456789+1 MORE.
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