First-degree heart block, or first-degree atrioventricular (AV) block, is defined as prolongation of the PR interval on the ECG to more than 200 msec.
While the conduction is slowed, there are no missed beats. ECG of a patient with first-degree heart block is shown below.
First-degree AV block is more common among African Americans compared with white populations.
The prevalence of first-degree AV block increases with advancing age.