First-Degree Atrioventricular (AV) Block with Sinus Rhythm

Introduction

First-degree atrioventricular (AV) block is a condition where the electrical conduction between the atria and the ventricles is delayed but not interrupted. This condition is typically benign but may indicate underlying heart disease in some cases.

Understanding First-Degree AV Block

• Definition: A first-degree AV block is diagnosed when the PR interval on an electrocardiogram (ECG) exceeds 200 milliseconds (>0.2 seconds).
• Cause: It occurs when the conduction through the AV node or His-Purkinje system is slowed.
• Symptoms: Most individuals with first-degree AV block do not experience symptoms. However, in some cases, it may be associated with fatigue or dizziness.

Causes and Risk Factors

• Intrinsic causes:

  • Age-related degeneration of the conduction system
  • Myocardial infarction (especially inferior infarctions)
  • Myocarditis
  • Congenital heart disease (e.g., atrial septal defect)

• Extrinsic causes:

  • Certain medications (e.g., beta-blockers, calcium channel blockers, digoxin, amiodarone)
  • Electrolyte imbalances (e.g., hyperkalemia)
  • Vagal tone increase (common in athletes)

Diagnosis

Diagnosis is based on an ECG showing a prolonged PR interval (>200 ms) while maintaining a 1:1 relationship between P waves and QRS complexes.

Clinical Significance & Treatment

• Generally does not require treatment if the patient is asymptomatic.
• If first-degree AV block is associated with symptoms or a worsening conduction abnormality, further investigation is necessary.
• Removing or adjusting medications that cause AV blockage may help.
• Electrolyte imbalances should be corrected.
• If first-degree AV block occurs in association with other conduction disturbances, a pacemaker may be considered.

Conclusion

For most individuals, first-degree AV block with sinus rhythm is benign and doesn’t require treatment. However, it’s important to monitor for any changes, especially if symptoms arise or if the AV block progresses to a higher degree.

Source recommendations

1. American College of Cardiology/American Heart Association (ACC/AHA) Guidelines on the Management of Bradycardia

1. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000628
2. https://www.jacc.org/guidelines/bradycardia
3. https://www.acc.org/latest-in-cardiology/ten-points-to-remember/2018/11/05/15/12/2018-acc-aha-hrs-guideline-on-bradycardia
4. https://pubmed.ncbi.nlm.nih.gov/30586772/
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 on Cardiac Pacing and Resynchronization

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Cardiac-Pacing-and-Cardiac-Resynchronization-Therapy
2. https://academic.oup.com/eurheartj/article/42/35/3427/6358547
3. https://pubmed.ncbi.nlm.nih.gov/34455430/
4. https://academic.oup.com/eurheartj/article/34/29/2281/401445
5. https://pubmed.ncbi.nlm.nih.gov/23801827/