Heart Block: Symptoms, Types, Causes and Treatment

Heart block is a potentially serious cardiac condition that disrupts the normal electrical signaling between the chambers of the heart. This interruption can reduce the heart’s ability to pump blood efficiently, sometimes causing distressing symptoms or even life-threatening complications. Understanding the symptoms, types, causes, and treatments of heart block is vital for early recognition and effective management.

Symptoms of Heart Block

Recognizing the symptoms of heart block is crucial since early intervention can often prevent serious outcomes. Symptoms may range from subtle to severe depending on the degree of block and underlying heart health. While some individuals remain asymptomatic, others may experience dramatic and sudden issues.

Symptom	Description	Severity	Source(s)
Syncope	Sudden fainting or loss of consciousness	Moderate-Severe	3 4 5 14
Fatigue	Persistent tiredness or low energy	Mild-Moderate	3 5
Dizziness	Feeling lightheaded or dizzy	Mild-Severe	3 4
Palpitations	Awareness of irregular heartbeats	Mild	5
Stokes-Adams attacks	Episodes of unconsciousness due to lack of blood flow to the brain	Severe	3 4 14
Sudden death	Fatal outcome from complete heart block	Life-threatening	3 9

Table 1: Key Symptoms

Overview of Symptoms

Heart block can be silent, especially in its early stages, or present with a range of symptoms that reflect impaired cardiac conduction.

Syncope and Stokes-Adams Attacks

A hallmark symptom in more severe or complete heart block is syncope—sudden fainting due to a temporary drop in blood flow to the brain. In some cases, this is classified as a Stokes-Adams attack, which can occur abruptly and without warning. These episodes are medical emergencies due to the risk of injury and sudden death 3 4 14.

Fatigue and Dizziness

Milder blocks may cause persistent fatigue, dizziness, or lightheadedness. These symptoms result from inadequate cardiac output as the heart struggles to maintain a normal rhythm 3 5.

Palpitations

Some individuals, especially those with partial or intermittent block, may feel palpitations—an uncomfortable awareness of their heartbeat. This can be unsettling but less dangerous than syncope 5.

Life-Threatening Presentations

In the most severe cases, particularly when heart block progresses to complete or third-degree block, sudden cardiac death can occur. This is often the result of a prolonged absence of effective heartbeats (asystole) or dangerous arrhythmias 3 9.

Types of Heart Block

Heart block is classified based on the location and severity of the electrical conduction disturbance. Accurate classification guides management and prognosis.

Type	Description	Key Features	Source(s)
First-degree AV	Delay in conduction through AV node	Prolonged PR interval	5 6
Second-degree AV	Intermittent failure of signal transmission	Dropped beats, Mobitz I/II	4 6
Third-degree (Complete) AV	No conduction between atria & ventricles	Complete dissociation	2 4 8
Fascicular Block	Block in specific bundle branches	May progress to higher degree	3 5 8
Trifascicular Block	Block in all three main conduction fascicles	Often leads to complete block	3 8
Congenital Heart Block	Present at birth, often autoimmune-related	May be detected in utero	13

Table 2: Types of Heart Block

First-Degree Heart Block

First-degree AV block features a prolonged PR interval on ECG, indicating delayed conduction. This type is usually benign and often asymptomatic 5 6.

Second-Degree Heart Block

Second-degree block is divided into two main types:

• Mobitz Type I (Wenckebach): Progressive lengthening of PR interval until a beat is dropped.
• Mobitz Type II: Sudden dropped beats without prior PR prolongation and is more likely to progress to complete block 4.

Both types can cause symptoms, especially if multiple beats are dropped.

Third-Degree (Complete) Heart Block

In complete heart block, there is total dissociation between atrial and ventricular activity. The atria and ventricles beat independently, often resulting in bradycardia (slow heart rate) and severe symptoms. This form is life-threatening if not managed promptly 2 4 8.

Fascicular and Trifascicular Blocks

Fascicular blocks involve one or more of the heart's bundle branches (right bundle branch, left anterior, or left posterior fascicle). These can be isolated or occur together, and higher degrees (e.g., trifascicular block) are associated with an increased risk of progression to complete heart block, syncope, and need for pacemaker implantation 3 5 8.

Congenital Heart Block

This rare form is present at birth and often related to maternal autoimmune antibodies (e.g., anti-Ro/SSA). It can be detected by fetal echocardiography and requires specialized management 13.

Causes of Heart Block

A variety of conditions can damage the heart’s conduction system, leading to heart block. Etiology may be acquired or genetic, and sometimes remains idiopathic.

Cause	Description	Typical Age Group	Source(s)
Ischemic Heart Disease	Reduced blood supply, often infarction	Older adults	10 11 14
Fibrosis/Degeneration	Age-related or idiopathic conduction system scarring	Elderly	7 10
Genetic Mutations	Inherited channelopathies (e.g., PFHBI)	All ages	1 3 9
Infections	Lyme carditis, viral myocarditis	All ages	6
Autoimmune Disease	Maternal antibodies causing fetal block	Neonates	13
Apoptosis	Programmed cell death of conduction cells	Young individuals	9
Medications/Toxins	Digitalis, beta-blockers, others	All ages	4

Table 3: Major Causes of Heart Block

Ischemic Heart Disease

Historically, coronary artery disease and myocardial infarction have been linked to heart block, especially in the elderly. Heart block frequently occurs during or after an acute infarction, particularly of the inferior wall, and is associated with increased short-term mortality 10 11 14.

Degenerative and Idiopathic Fibrosis

Age-related fibrosis of the conduction system is a common cause, particularly in older adults. Sometimes, fibrosis is isolated to the conduction system without overt coronary disease 7 10.

Genetic and Familial Causes

Some forms of heart block are inherited, such as Progressive Familial Heart Block Type I (PFHBI), often caused by mutations in the TRPM4 gene. These mutations alter ion channel function in the heart’s conduction system, particularly in the Purkinje fibers 1 3. Familial cases can present at any age and tend to be progressive.

Infectious Causes

Certain infections, notably Lyme disease, can temporarily disrupt cardiac conduction, causing reversible heart block. Early recognition and antibiotic therapy are essential, as most cases resolve after treatment 6.

Autoimmune and Congenital Causes

Congenital heart block, detected in utero or at birth, is often due to maternal antibodies (anti-Ro/SSA) crossing the placenta and damaging the fetal conduction system 13. This can be transient or permanent.

Apoptosis and Other Mechanisms

Emerging research suggests that programmed cell death (apoptosis) of conduction system cells can underpin some cases of progressive heart block in young individuals, independent of inflammation or fibrosis 9.

Medications and Toxins

Certain drugs, like digitalis or beta-blockers, can exacerbate or induce heart block, especially in susceptible individuals or those with underlying conduction disease 4.

Treatment of Heart Block

Management of heart block depends on its type, severity, symptoms, and underlying cause. Treatment can be life-saving and dramatically improve quality of life.

Treatment	Approach/Indication	Effectiveness	Source(s)
Pacemaker	Permanent or temporary pacing for severe or symptomatic block	Highly effective	14 15
Antibiotics	Lyme carditis or infectious causes	Usually curative	6
Drug therapy	Isoprenaline, corticosteroids in acute settings	Temporizing measure	14
Immunotherapy	Steroids, IVIg for autoimmune/congenital block	Variable benefit	13
Surveillance	Observation for asymptomatic, mild block	Appropriate at times	5 13

Table 4: Treatment Options

Pacing: The Cornerstone

The implantation of a pacemaker is the definitive treatment for symptomatic or advanced heart block. Pacemakers can be temporary (in acute or reversible cases) or permanent. Pacing effectively restores normal heart rhythm, prevents syncope, and reduces mortality—especially in those with Stokes-Adams attacks or severe bradycardia 14 15.

Advancements in pacemaker technology have improved patient outcomes, with modern devices being more reliable and easier to implant 15.

Treating Reversible Causes

When heart block is due to a reversible cause, such as Lyme carditis, targeted therapy with antibiotics can lead to complete recovery of normal rhythm. In these cases, temporary pacing may be required until the infection is controlled. Permanent pacemaker implantation is often unnecessary if the block resolves 6.

Drug Therapy

In acute situations, drugs like isoprenaline may be used to increase heart rate while awaiting definitive treatment. This is particularly useful in the setting of acute myocardial infarction complicated by heart block, but the benefit is limited compared to pacing 14.

Immunotherapy and Congenital Block

For congenital heart block due to maternal antibodies, immunotherapies (e.g., corticosteroids, IVIg) and hydroxychloroquine (HCQ) have been explored. These are usually initiated during pregnancy to minimize the severity of fetal heart block, with variable results 13.

Observation and Monitoring

In cases of mild or asymptomatic heart block (such as isolated first-degree block or stable fascicular block without symptoms), careful monitoring may be appropriate. Progression risk should be assessed regularly, and intervention considered if symptoms develop 5 13.

Conclusion

Heart block is a diverse and potentially serious cardiac conduction disorder. Its recognition, classification, and management require careful clinical evaluation and, often, prompt intervention. With modern treatments, especially pacing, outcomes have improved dramatically. Awareness of reversible and genetic causes is essential to avoid unnecessary procedures and to guide family counseling.

Main Points Covered:

• Symptoms range from subtle (fatigue, palpitations) to severe (syncope, sudden death).
• Types include first-, second-, and third-degree AV block, fascicular and trifascicular blocks, and congenital forms.
• Causes are diverse: ischemic heart disease, fibrosis, genetic mutations, infections, autoimmune factors, apoptosis, and drug effects.
• Treatment centers on pacing for severe block, addressing reversible causes (e.g., antibiotics for Lyme), immunotherapy for congenital block, and careful monitoring for mild cases.

Understanding heart block is key to reducing morbidity and mortality—timely diagnosis and appropriate treatment can transform outcomes for affected individuals.