Third-Degree Atrioventricular (AV) Block

Introduction

Third-degree AV block, also known as complete heart block, is a serious cardiac condition where the electrical signals from the atria do not reach the ventricles. This results in the atria and ventricles beating independently, leading to a slow and often unstable heart rate.

Causes

Third-degree AV block can be caused by:

• Age-related degeneration of the conduction system (most common in elderly patients)
• Heart diseases, including myocardial infarction, myocarditis, or cardiomyopathies
• Medications, such as beta-blockers, calcium channel blockers, or digoxin
• Electrolyte imbalances, including high potassium levels (hyperkalemia)
• Congenital heart defects (in cases of congenital complete AV block)
• Surgical complications after cardiac procedures

Symptoms

Symptoms of third-degree AV block depend on the severity of bradycardia and may include:

• Dizziness or fainting (syncope) due to insufficient blood flow to the brain
• Severe fatigue and weakness
• Shortness of breath
• Chest pain (if related to myocardial ischemia)
• Palpitations or irregular heartbeats
• Congestive heart failure symptoms, such as swelling in the legs

Diagnosis

Diagnosis is based on:

• Electrocardiogram (ECG): Shows complete dissociation between P waves and QRS complexes.
• Holter monitoring: Used to assess intermittent heart block.
• Echocardiogram: Identifies structural heart diseases.
• Electrophysiological testing: Evaluates the conduction system in complex cases.

Treatment

The primary treatment for third-degree AV block is a permanent pacemaker, which helps regulate the heart rhythm. Other treatments include:

• Immediate temporary pacing for patients with severe symptoms (such as syncope or heart failure)
• Stopping or adjusting medications that may be exacerbating the condition
• Treatment of underlying heart disease (e.g., myocardial infarction or myocarditis)

Prognosis

The prognosis depends on the underlying cause. If adequately treated with a pacemaker, most patients can lead a normal life. However, untreated third-degree AV block can result in severe complications, such as sudden cardiac arrest or heart failure.

Conclusion

Third-degree AV block is a life-threatening condition requiring immediate medical attention. If you experience symptoms like dizziness, fainting, or extreme fatigue, seek emergency care. Permanent pacemaker implantation is the definitive management and significantly improves quality of life.

Source recommendations

1. American College of Cardiology/American Heart Association (ACC/AHA) Guidelines for the Management of Patients with Bradycardia and Cardiac Conduction Delay

1. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000628
2. https://pubmed.ncbi.nlm.nih.gov/30412710/
3. https://www.jacc.org/guidelines/bradycardia
4. https://www.acc.org/latest-in-cardiology/ten-points-to-remember/2018/11/05/15/12/2018-acc-aha-hrs-guideline-on-bradycardia
5. https://www.hrsonline.org/guidance/clinical-resources/2018-accahahrs-guideline-evaluation-and-management-patients-bradycardia-and-cardiac-conduction

2. European Society of Cardiology (ESC) Guidelines for the Management of Cardiac Conduction Disorders

1. https://www.escardio.org/static-file/Escardio/Guidelines/Documents/ehaa612.pdf
2. https://academic.oup.com/eurheartj/article/36/44/3075/2293384
3. https://www.escardio.org/Journals/E-Journal-of-Cardiology-Practice/Volume-19/cardiac-amyloidosis-epidemiology-diagnosis-and-therapy
4. https://academic.oup.com/eurheartj/article/39/21/1883/4939241
5. https://www.sciencedirect.com/science/article/pii/S073510970101587X