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Atrioventricular block

Updated : December 1, 2023





Background

An atrioventricular block is a type of heart block that occurs when there is a disruption in the electrical signals between the atria and the ventricles. The heart’s electrical system is responsible for coordinating the contraction of the atria and ventricles, allowing blood to be pumped efficiently through the circulatory system.

The electrical signals that regulate the heartbeat pass through a specific pathway in the heart, including the atrioventricular node (AV node). An AV block occurs when there is a delay or complete blockage of the signals as they pass through the AV node. This can lead to a slower or irregular heartbeat, affecting the heart’s ability to pump blood effectively.

Epidemiology

Large population-based studies on the prevalence of AV blocks are lacking. However, one recent study proposed that First-degree AV block is more commonly found in African-American patients across all age groups, except in the eighth decade of life, when compared to Caucasian patients.

Currently, there is a lack of well-established large-scale research examining the correlation between various types of AV blocks and factors such as age, race, or gender. AV block occurrences have been observed in athletes and individuals with congenital heart disorders.

Anatomy

Pathophysiology

First-Degree AV Block:

Pathophysiology: In this type, there is a delay in the transmission of electrical impulses from the atria to the ventricles. The delay occurs at the atrioventricular node (AV node), leading to a prolonged PR interval on an electrocardiogram (ECG).

Causes: First-degree AV block can result from medications, ischemia (inadequate blood supply), inflammation, or aging-related changes in the conduction system.

Second-Degree AV Block:

Type I (Wenckebach):

Pathophysiology: Progressive conduction delay within the AV node results in a characteristic pattern where each successive impulse encounters increasing delay until one impulse is blocked.

Causes: Similar to first-degree AV block, Type I may be associated with reversible factors such as medications or ischemia.

Type II:

Pathophysiology: Intermittent blockage of atrial impulses at or below the AV node, leading to dropped ventricular beats.

Causes: Often associated with structural heart disease, especially involving the bundle of His or bundle branches. It may also result from ischemia.

Third-Degree AV Block (Complete Heart Block):

Pathophysiology: Complete blockage of the atrial impulses reaching the ventricles. The atria and ventricles beat independently, resulting in a dissociation between atrial and ventricular rhythms.

Causes: Often associated with advanced heart block or damage to the AV node or infranodal conduction system. Structural heart diseases, infections, and certain medications can contribute.

Etiology

Elevated degrees of AV block beyond what might result from heightened vagal tone often indicate an underlying pathological condition, referred to as pathophysiologic AV block. Approximately half of such instances stem from chronic idiopathic fibrosis and sclerosis affecting the conduction system, as observed in Lenegre’s disease and Lev’s disease. Ischemic heart disease is another prevalent factor, accounting for roughly 40 percent of AV block cases.

Additionally, cardiomyopathies, such as hypertrophic obstructive cardiomyopathy, and infiltrative conditions like sarcoidosis and amyloidosis are associated with AV block. Infectious etiologies, including Lyme disease, endocarditis, rheumatic fever, viral infections, and autoimmune diseases like systemic lupus erythematosus, should be considered. Other potential triggers encompass cardiac surgery, certain medications, and hereditary conditions.

Genetics

Prognostic Factors

The prognosis is influenced by several factors, including age, and the presence of chronic medical conditions such as chronic kidney disease, diabetes mellitus, underlying heart disease, and the specific type of AV block.

Clinical History

Patient history should encompass both congenital and acquired heart diseases, providing a comprehensive overview. It is imperative to compile a complete list of medications, detailing dosages, with special attention to drugs such as beta-blockers, calcium channel blockers, antiarrhythmic medications, and digoxin.

Information about recent cardiac procedures is essential for a thorough understanding of the patient’s cardiac health. Additionally, signs and symptoms related to systemic diseases linked to heart block, such as amyloidosis or sarcoidosis, should be investigated.

Assessing baseline exercise capacity provides valuable insights into the patient’s cardiovascular health. Finally, inquire about potential exposure to tick bites, as this is relevant to certain infectious causes, such as Lyme disease, which can be associated with heart block.

Physical Examination

Signs of underlying heart disease, such as murmurs or abnormal heart sounds. Signs of systemic diseases associated with heart block, such as skin changes in amyloidosis or respiratory symptoms in sarcoidosis.

In some cases, a pacemaker may be palpable under the skin if the patient has undergone pacemaker implantation. Symptoms may include fatigue, dizziness, syncope, or chest pain. On physical examination, there may be a slow and regular pulse, but the atrial and ventricular rates are dissociated.

Age group

Associated comorbidity

Associated activity

Acuity of presentation

Differential Diagnoses

Coronary artery disease

Dilated cardiomyopathy

Myocarditis.

Endocarditis

Sarcoidosis

Amyloidosis

Laboratory Studies

Imaging Studies

Procedures

Histologic Findings

Staging

Treatment Paradigm

The management of atrioventricular block (AV block) depends on the severity of the condition and its impact on the patient’s symptoms. Impaired electrical impulses between the atria and ventricles characterize AV block. In cases of first-degree AV block, where there is a delay in conduction but all impulses reach the ventricles, intervention may not be necessary, and close monitoring may suffice.

Second-degree AV block, particularly Mobitz Type I (Wenckebach), may be managed conservatively, with a focus on addressing underlying causes such as medication adjustments. Mobitz Type II and third-degree (complete) AV block often require intervention, and temporary pacing may be necessary to maintain an adequate heart rate.

Permanent pacemaker implantation is frequently recommended for symptomatic third-degree AV block or cases of advanced second-degree block. The choice of intervention is individualized based on the patient’s clinical presentation, overall health, and the underlying etiology of the AV block. Regular follow-up is essential to assess the effectiveness of the chosen treatment and adjust therapeutic strategies as needed.

by Stage

by Modality

Chemotherapy

Radiation Therapy

Surgical Interventions

The reflexive application of urgent or emergent temporary transvenous pacemakers in response to the identification of second-degree, high-grade, or third-degree AV block is not advisable. Instead, it should be contemplated following a meticulous assessment of the risk-benefit balance in clinical contexts. Factors such as hemodynamic stability, evaluated through systolic blood pressure and the severity and duration of the patient’s symptoms, the level of AV block, and the type of escape rhythm should be considered.

Complications are frequent in patients subjected to temporary transvenous pacemaker placement, extending beyond the implantation itself to encompass post-implant care. These complications involve changes in lead position, alterations in capture threshold, pacer malfunction, erroneous programming, and potential depletion of the pacer box’s battery. Accidental lead extraction by the patient can also contribute to complications.

The utilization of a temporary pacemaker should be limited to the shortest possible duration to mitigate risks associated with patient immobility, infection, thromboembolism, and the peril of cardiac perforation. Decisions regarding temporary transvenous pacemaker use should be carefully weighed, taking into account the individual patient’s clinical condition and potential complications associated with the procedure. The routine use of a temporary transvenous pacemaker as an immediate response in cases of AV block should be avoided.

Instead, it is more judicious to consider it as a last resort, particularly when the response to positive chronotropic drugs like isoproterenol, epinephrine, or low-dose dopamine proves insufficient. The ideal scenarios for temporary transvenous pacing involve cases where there is a high-degree AV block without a stable escape rhythm or when life-threatening bradyarrhythmias occur, such as during interventional procedures like percutaneous coronary intervention.

In rare instances, it may be warranted in acute settings like acute myocardial infarction, drug toxicity, or systemic infections, where the implantation of a permanent pacing device is best deferred until the infection is cleared. Experts generally advise against routine temporary pacer implantation before a permanent pacer, as this approach may heighten the risk of complications.

These complications include device infection in the case of a permanent implant, potential risks associated with two invasive procedures instead of one, and an increased likelihood of cardiac perforation, particularly in situations where there is a prolonged gap between temporary and permanent pacer lead implantation.

Hormone Therapy

Immunotherapy

Hyperthermia

Photodynamic Therapy

Stem Cell Transplant

Targeted Therapy

Palliative Care

Medication

 

isoprenaline 

1 to 20 mcg/minute usual dose of Continuous intravenous infusion; titrate to the clinical response



 

isoprenaline 

Infants, Children & Adolescents: 0.05 to 0.5 mcg/kg/minute continuous intravenous infusion; titrate to the effect; doses as high as 2 mcg/kg/minute can be required in some patients; 2 to 10 mcg/minute is the usual adult range



Dose Adjustments

Dosing modifications
Kidney Impairment

Dose adjustment is not necessary
Hepatic Impairment
Dose adjustment is not necessary

 

Media Gallary

References

Atrioventricular block

Updated : December 1, 2023




An atrioventricular block is a type of heart block that occurs when there is a disruption in the electrical signals between the atria and the ventricles. The heart’s electrical system is responsible for coordinating the contraction of the atria and ventricles, allowing blood to be pumped efficiently through the circulatory system.

The electrical signals that regulate the heartbeat pass through a specific pathway in the heart, including the atrioventricular node (AV node). An AV block occurs when there is a delay or complete blockage of the signals as they pass through the AV node. This can lead to a slower or irregular heartbeat, affecting the heart’s ability to pump blood effectively.

Large population-based studies on the prevalence of AV blocks are lacking. However, one recent study proposed that First-degree AV block is more commonly found in African-American patients across all age groups, except in the eighth decade of life, when compared to Caucasian patients.

Currently, there is a lack of well-established large-scale research examining the correlation between various types of AV blocks and factors such as age, race, or gender. AV block occurrences have been observed in athletes and individuals with congenital heart disorders.

First-Degree AV Block:

Pathophysiology: In this type, there is a delay in the transmission of electrical impulses from the atria to the ventricles. The delay occurs at the atrioventricular node (AV node), leading to a prolonged PR interval on an electrocardiogram (ECG).

Causes: First-degree AV block can result from medications, ischemia (inadequate blood supply), inflammation, or aging-related changes in the conduction system.

Second-Degree AV Block:

Type I (Wenckebach):

Pathophysiology: Progressive conduction delay within the AV node results in a characteristic pattern where each successive impulse encounters increasing delay until one impulse is blocked.

Causes: Similar to first-degree AV block, Type I may be associated with reversible factors such as medications or ischemia.

Type II:

Pathophysiology: Intermittent blockage of atrial impulses at or below the AV node, leading to dropped ventricular beats.

Causes: Often associated with structural heart disease, especially involving the bundle of His or bundle branches. It may also result from ischemia.

Third-Degree AV Block (Complete Heart Block):

Pathophysiology: Complete blockage of the atrial impulses reaching the ventricles. The atria and ventricles beat independently, resulting in a dissociation between atrial and ventricular rhythms.

Causes: Often associated with advanced heart block or damage to the AV node or infranodal conduction system. Structural heart diseases, infections, and certain medications can contribute.

Elevated degrees of AV block beyond what might result from heightened vagal tone often indicate an underlying pathological condition, referred to as pathophysiologic AV block. Approximately half of such instances stem from chronic idiopathic fibrosis and sclerosis affecting the conduction system, as observed in Lenegre’s disease and Lev’s disease. Ischemic heart disease is another prevalent factor, accounting for roughly 40 percent of AV block cases.

Additionally, cardiomyopathies, such as hypertrophic obstructive cardiomyopathy, and infiltrative conditions like sarcoidosis and amyloidosis are associated with AV block. Infectious etiologies, including Lyme disease, endocarditis, rheumatic fever, viral infections, and autoimmune diseases like systemic lupus erythematosus, should be considered. Other potential triggers encompass cardiac surgery, certain medications, and hereditary conditions.

The prognosis is influenced by several factors, including age, and the presence of chronic medical conditions such as chronic kidney disease, diabetes mellitus, underlying heart disease, and the specific type of AV block.

Patient history should encompass both congenital and acquired heart diseases, providing a comprehensive overview. It is imperative to compile a complete list of medications, detailing dosages, with special attention to drugs such as beta-blockers, calcium channel blockers, antiarrhythmic medications, and digoxin.

Information about recent cardiac procedures is essential for a thorough understanding of the patient’s cardiac health. Additionally, signs and symptoms related to systemic diseases linked to heart block, such as amyloidosis or sarcoidosis, should be investigated.

Assessing baseline exercise capacity provides valuable insights into the patient’s cardiovascular health. Finally, inquire about potential exposure to tick bites, as this is relevant to certain infectious causes, such as Lyme disease, which can be associated with heart block.

Signs of underlying heart disease, such as murmurs or abnormal heart sounds. Signs of systemic diseases associated with heart block, such as skin changes in amyloidosis or respiratory symptoms in sarcoidosis.

In some cases, a pacemaker may be palpable under the skin if the patient has undergone pacemaker implantation. Symptoms may include fatigue, dizziness, syncope, or chest pain. On physical examination, there may be a slow and regular pulse, but the atrial and ventricular rates are dissociated.

Coronary artery disease

Dilated cardiomyopathy

Myocarditis.

Endocarditis

Sarcoidosis

Amyloidosis

The management of atrioventricular block (AV block) depends on the severity of the condition and its impact on the patient’s symptoms. Impaired electrical impulses between the atria and ventricles characterize AV block. In cases of first-degree AV block, where there is a delay in conduction but all impulses reach the ventricles, intervention may not be necessary, and close monitoring may suffice.

Second-degree AV block, particularly Mobitz Type I (Wenckebach), may be managed conservatively, with a focus on addressing underlying causes such as medication adjustments. Mobitz Type II and third-degree (complete) AV block often require intervention, and temporary pacing may be necessary to maintain an adequate heart rate.

Permanent pacemaker implantation is frequently recommended for symptomatic third-degree AV block or cases of advanced second-degree block. The choice of intervention is individualized based on the patient’s clinical presentation, overall health, and the underlying etiology of the AV block. Regular follow-up is essential to assess the effectiveness of the chosen treatment and adjust therapeutic strategies as needed.

The reflexive application of urgent or emergent temporary transvenous pacemakers in response to the identification of second-degree, high-grade, or third-degree AV block is not advisable. Instead, it should be contemplated following a meticulous assessment of the risk-benefit balance in clinical contexts. Factors such as hemodynamic stability, evaluated through systolic blood pressure and the severity and duration of the patient’s symptoms, the level of AV block, and the type of escape rhythm should be considered.

Complications are frequent in patients subjected to temporary transvenous pacemaker placement, extending beyond the implantation itself to encompass post-implant care. These complications involve changes in lead position, alterations in capture threshold, pacer malfunction, erroneous programming, and potential depletion of the pacer box’s battery. Accidental lead extraction by the patient can also contribute to complications.

The utilization of a temporary pacemaker should be limited to the shortest possible duration to mitigate risks associated with patient immobility, infection, thromboembolism, and the peril of cardiac perforation. Decisions regarding temporary transvenous pacemaker use should be carefully weighed, taking into account the individual patient’s clinical condition and potential complications associated with the procedure. The routine use of a temporary transvenous pacemaker as an immediate response in cases of AV block should be avoided.

Instead, it is more judicious to consider it as a last resort, particularly when the response to positive chronotropic drugs like isoproterenol, epinephrine, or low-dose dopamine proves insufficient. The ideal scenarios for temporary transvenous pacing involve cases where there is a high-degree AV block without a stable escape rhythm or when life-threatening bradyarrhythmias occur, such as during interventional procedures like percutaneous coronary intervention.

In rare instances, it may be warranted in acute settings like acute myocardial infarction, drug toxicity, or systemic infections, where the implantation of a permanent pacing device is best deferred until the infection is cleared. Experts generally advise against routine temporary pacer implantation before a permanent pacer, as this approach may heighten the risk of complications.

These complications include device infection in the case of a permanent implant, potential risks associated with two invasive procedures instead of one, and an increased likelihood of cardiac perforation, particularly in situations where there is a prolonged gap between temporary and permanent pacer lead implantation.

isoprenaline 

1 to 20 mcg/minute usual dose of Continuous intravenous infusion; titrate to the clinical response



isoprenaline 

Infants, Children & Adolescents: 0.05 to 0.5 mcg/kg/minute continuous intravenous infusion; titrate to the effect; doses as high as 2 mcg/kg/minute can be required in some patients; 2 to 10 mcg/minute is the usual adult range



Dose Adjustments

Dosing modifications
Kidney Impairment

Dose adjustment is not necessary
Hepatic Impairment
Dose adjustment is not necessary

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