What is the role of electrocardiography in the workup of first-degree atrioventricular (AV) block?

Updated: Jan 06, 2020
  • Author: Jamshid Alaeddini, MD, FACC, FHRS; Chief Editor: Jose M Dizon, MD  more...
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Answer

On a surface ECG, the PR interval exceeds 200 msec, and all P waves conduct to the ventricle with constant but prolonged PR interval (see the images below).

First-degree atrioventricular block. The PR interv First-degree atrioventricular block. The PR interval is 0.24 seconds (240 ms) in a patient with asymptomatic first-degree atrioventricular block.
First-degree atrioventricular block. 12-Lead elect First-degree atrioventricular block. 12-Lead electrocardiogram from a patient with first-degree heart block.
First-degree atrioventricular block. 12-Lead elect First-degree atrioventricular block. 12-Lead electrocardiogram from a patient with first-degree heart block.

His bundle ECG is necessary only in patients with symptomatic (ie, presyncope and syncope) first-degree AV block and a wide QRS complex, indicative of bundle-branch block. The study is used to locate the site of the block in these patients. As many as 50% of patients show an infranodal conduction delay.

Follow-up ECGs may be indicated in patients who are treated with AV nodal agents while in the emergency department (ED), as well as for patients with a concomitant myocardial infarction (MI).


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