Normal range is 0.12 to 0.2 milliseconds (= 3 to 5 small squares)
A long PR = first degree heart block.
Causes of a long PR ( can be remembered as DRIP SAL, easier to remember if you have a drippy friend called Sally):
- Drugs (beta blockers, calcium channel blockers, digoxin)
- Rheumatic fever
- IHD (anterior MIs in particular can prolong the PR interval)
- Potassium - either high or low levels
- Aortic root pathology
- Lyme disease
So that was short and sweet. Onto another brief battle that should be familiar, cauda equina syndrome...