First-Degree Atrioventricular (AV) Block on ECG

Introduction

First-degree AV block is a condition where electrical conduction between the atria and ventricles is slowed but not completely blocked. It is often asymptomatic and detected incidentally on an electrocardiogram (ECG).

ECG Characteristics

• Prolonged PR interval : A PR interval greater than 200 milliseconds (0.2 seconds) is the main ECG finding.
• Regular P wave and QRS complex : Every P wave is followed by a QRS complex, ensuring that the conduction is still occurring.
• No dropped beats : Unlike second-degree AV block, there is no missing QRS complex.

Causes and Risk Factors

• Intrinsic conduction disease (age-related degeneration)
• Increased vagal tone (common in athletes)
• Electrolyte imbalances (e.g., hyperkalemia)
• Medications (beta-blockers, calcium channel blockers, digoxin)
• Myocarditis or ischemic heart disease

Clinical Significance

• Typically benign in young and healthy individuals.
• In patients with heart disease, it may indicate a predisposition to more severe conduction abnormalities.
• If due to a reversible cause (e.g., drug effects), correcting the underlying issue is necessary.

Management

• Observation : No treatment needed in asymptomatic individuals.
• Medication review : If caused by drugs, adjusting or stopping the medication can help.
• Electrophysiological study : Rarely needed unless there is progression to a higher degree of block.

When to Seek Medical Attention?

• If symptoms such as dizziness, fatigue, or syncope (fainting) occur, further evaluation is needed.
• If there is a history of heart disease, follow-up with a cardiologist may be advised.

Source recommendations

1. American College of Cardiology/American Heart Association (ACC/AHA) Guidelines on the Evaluation and Management of Cardiac Arrhythmias

1. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001193
2. https://pubmed.ncbi.nlm.nih.gov/30586772/
3. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000549
4. https://www.acc.org/latest-in-cardiology/ten-points-to-remember/2017/03/07/23/36/2017-acc-aha-hrs-guideline-for-syncope
5. https://www.jacc.org/doi/10.1016/j.jacc.2017.03.003

2. European Society of Cardiology (ESC) Guidelines on Cardiac Pacing and Resynchronization Therapy

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/