Editing First-degree atrioventricular block (section)

== Diagnosis ==

In normal individuals, the AV node slows the conduction of electrical impulses through the heart.  This is manifest on a surface [[Electrocardiography|electrocardiogram]] (ECG) as the PR interval.  The normal PR interval is from 120 [[milliseconds|ms]] to 200 ms in length.  This is measured from the initial deflection of the P wave to the beginning of the [[QRS complex]].<ref>{{cite journal |url= https://www.ncbi.nlm.nih.gov/books/NBK448164/| title= First Degree Heart Block | website= National Center for Biotechnology Information, U.S. National Library of Medicine | year= 2023 | pmid= 28846254 |access-date= 3 July 2021 | last1= Oldroyd | first1= S. H. | last2= Quintanilla Rodriguez | first2= B. S. | last3= Makaryus | first3= A. N. }}</ref>

In first-degree heart block, the AV node conducts the electrical activity more slowly.  This is seen as a PR interval greater than 200 ms in length on the surface ECG.  It is usually an incidental finding on a routine ECG.<ref>{{cite journal |url= https://www.ncbi.nlm.nih.gov/books/NBK448164/| title= First Degree Heart Block | website= National Center for Biotechnology Information, U.S. National Library of Medicine | year= 2023 | pmid= 28846254 |access-date= 3 July 2021 | last1= Oldroyd | first1= S. H. | last2= Quintanilla Rodriguez | first2= B. S. | last3= Makaryus | first3= A. N. }}</ref>

First-degree heart block does not require any particular investigations except for electrolyte and drug screens, especially if an overdose is suspected.<ref>{{cite journal |url= https://www.ncbi.nlm.nih.gov/books/NBK448164/| title= First Degree Heart Block | website= National Center for Biotechnology Information, U.S. National Library of Medicine | year= 2023 | pmid= 28846254 |access-date= 3 July 2021 | last1= Oldroyd | first1= S. H. | last2= Quintanilla Rodriguez | first2= B. S. | last3= Makaryus | first3= A. N. }}</ref>

In comparison to [[second-degree atrioventricular block]], in first-degree block there is an absence of non-conduction or "dropped beats."

In an [[electrophysiology study]], this corresponds to a prolonged A-H interval that shows the time between atrial depolarization and [[His bundle]] depolarization near the AV node.