Diagnosis
In normal individuals, the AV node slows the conduction of electrical impulse through the heart. This is manifest on a surface ECG as the PR interval. The normal PR interval is from 120 ms to 200 ms in length. This is measured from the initial deflection of the P wave to the beginning of the QRS complex.
In first-degree heart block, the diseased 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.
First-degree heart block does not require any particular investigations except for electrolyte and drug screens, especially if an overdose is suspected.
Read more about this topic: First-degree Atrioventricular Block