From the Guidelines
First degree AV block is a cardiac conduction abnormality that typically requires no specific treatment when asymptomatic and occurs in isolation without other cardiac issues, with regular cardiac monitoring recommended to track any progression 1.
Diagnosis
First degree AV block is characterized by a prolonged PR interval (>200 milliseconds) on an electrocardiogram (ECG), indicating delayed conduction through the atrioventricular node. This condition can be diagnosed using a 12-lead ECG, which can help identify the prolonged PR interval and rule out other cardiac conditions.
Treatment
The treatment for first degree AV block depends on the underlying cause and the presence of symptoms.
- If the block is medication-induced, dose adjustment or medication change might be considered 1.
- Patients should be evaluated for underlying cardiac conditions, especially if they develop symptoms like dizziness, fatigue, or syncope, which could indicate progression to higher-degree blocks.
- Regular cardiac monitoring is recommended, with follow-up ECGs every 6-12 months to track any progression.
- In some cases, permanent pacing may be considered, especially in patients with significant prolongation of atrioventricular conduction or those with a high risk of developing complete atrioventricular block 1.
Pathophysiology
The pathophysiology of first degree AV block involves delayed electrical impulse transmission from the atria to the ventricles, though complete transmission still occurs, allowing for normal ventricular contraction sequence and typically preserving cardiac output.
- First degree AV block can be physiological in athletes or occur during sleep due to increased vagal tone.
- However, it may also result from medications (beta-blockers, calcium channel blockers, digoxin), ischemic heart disease, or degenerative conduction system disease.
Recommendations
- Regular cardiac monitoring is recommended to track any progression of the condition 1.
- Patients with first degree AV block should be evaluated for underlying cardiac conditions, especially if they develop symptoms like dizziness, fatigue, or syncope.
- Permanent pacing may be considered in patients with significant prolongation of atrioventricular conduction or those with a high risk of developing complete atrioventricular block 1.
From the Research
Diagnosis of First-Degree Atrioventricular (AV) Block
- First-degree AV block is defined as a prolongation of the PR interval beyond the upper limit of what is considered normal (generally 0.20 s) 2.
- The diagnosis of first-degree AV block can be made using an electrocardiogram (ECG) to measure the PR interval 3.
- A PR interval exceeding 0.30 s can cause symptoms due to inadequate timing of atrial and ventricular contractions, similar to the so-called pacemaker syndrome 2.
Treatment of First-Degree Atrioventricular (AV) Block
- Permanent pacemaker implantation is reasonable for first-degree AV block with symptoms similar to those of pacemaker syndrome or with hemodynamic compromise 2.
- Conventional dual-chamber pacing may improve symptoms in patients with marked first-degree AV block (PR > 0.30 s) and normal left ventricular function 4.
- Biventricular DDD device may be considered in patients with marked first-degree AV block and left ventricular systolic dysfunction and heart failure 4.
- Patients with first-degree AV block may require closer monitoring for progression to higher-grade block or bradycardia, which may warrant pacemaker implantation 5.
Clinical Implications
- First-degree AV block is associated with an increased risk of heart failure and death in patients with stable coronary artery disease 6.
- First-degree AV block may be a risk marker for more severe intermittent conduction disease and is not benign in all patients 5.
- Patients with first-degree AV block have a poorer outcome with cardiac resynchronization therapy (CRT) than patients with a normal PR interval 4.