1st degree av block

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first-degree AV block ECG PR interval management guideline

First-degree AV block is an ECG finding in which conduction from atria to ventricles is delayed, but every P wave is still followed by a QRS complex.

ECG criterion: PR interval > 200 ms (more than 5 small squares), with a constant PR interval and 1:1 AV conduction.
Mechanism: usually delayed conduction through the AV node.
Common settings/causes: high vagal tone in athletes or during sleep, aging or cardiac disease, and drugs that slow AV-node conduction such as beta-blockers, verapamil/diltiazem, digoxin, and sometimes antiarrhythmics.
Symptoms: usually none. A markedly prolonged PR interval, especially >300 ms, can occasionally cause fatigue, exercise intolerance, dizziness, or palpitations because AV timing becomes inefficient.
Management: an isolated, asymptomatic first-degree AV block usually needs no treatment or pacemaker. Review medications and assess for underlying heart disease when appropriate. The ACC/AHA/HRS bradycardia guideline supports observation in asymptomatic cases.

Seek prompt clinical assessment if there is syncope, chest pain, shortness of breath, marked bradycardia, new AV block with myocardial infarction symptoms, or associated bundle-branch block/widened QRS.

Braunwald’s Heart Disease, p. 1315.

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