I44.0

First-degree AV block (I44.0): PR over 200 ms, causes, assessment and when treatment is needed.

First-degree atrioventricular block (ICD-10 I44.0) is a delay of conduction from the atria to the ventricles: the PR interval on the ECG is longer than 200 ms, but every atrial impulse still reaches the ventricles. The delay is usually in the AV node. It is a common finding: about 0.65–1.1% of healthy young adults have it, and it becomes more frequent with age. In most people it causes no symptoms and needs no treatment, but it can be a sign of conduction system disease or of medicines that slow the heart.

ICD-10 I44.0Conduction disorderAV block

ECG criterionPR > 200 ms, every P conducted

Prevalence (young adults)≈ 0.65–1.1%

Usuallyno symptoms

Treatmentusually none; remove causes

Figure 1. Left: normal PR interval. Right: first-degree AV block — PR longer than 200 ms, but every P wave is followed by a QRS complex.

Causes

High vagal tone: athletes, sleep
Medicines: beta-blockers, verapamil, diltiazem, digoxin, amiodarone and other antiarrhythmics
Degenerative disease of the conduction system with ageing
Heart disease: inferior myocardial infarction, myocarditis, Lyme carditis, rheumatic fever, infiltrative diseases (sarcoidosis, amyloidosis), after heart surgery or valve procedures
Electrolytes: high potassium, high magnesium

Assessment and treatment

An isolated mild PR prolongation in a person without symptoms usually needs no treatment, but medicines that slow AV conduction should be reviewed. Further assessment (echocardiography, Holter monitoring) is advisable when there are symptoms, other conduction abnormalities (for example bundle branch block) or heart disease. A very long PR (for example over 300 ms) can make atrial contraction occur too close to the previous ventricular contraction and cause symptoms similar to "pacemaker syndrome"; in such cases pacing may be considered. Progression to higher-degree block is uncommon but possible, especially when the delay lies below the AV node.

When to see a doctor

Dizziness, fainting, reduced exercise tolerance or a very slow pulse in a person with first-degree AV block need cardiological assessment.

References

Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay. Circulation. 2019;140(8):e382–e482. doi:10.1161/CIR.0000000000000628
Glikson M, Nielsen JC, Kronborg MB, et al. 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy. Eur Heart J. 2021;42(35):3427–3520. doi:10.1093/eurheartj/ehab364

This article is for general information and does not replace a consultation with a doctor. Diagnosis and treatment must be decided by a physician on the basis of symptoms, examination and tests.

Published on 24 March 2019