What prolongs the PR interval?

As a medical professional with expertise in cardiology, I can explain that the PR interval, which is measured on an electrocardiogram (ECG), represents the time it takes for the electrical impulse to travel from the atria to the ventricles through the atrioventricular (AV) node. A prolonged PR interval can be due to several factors: 1. Age: Older individuals may naturally have a longer PR interval. 2. Medication: Certain drugs, such as beta-blockers, calcium channel blockers, and digitalis, can slow the conduction through the AV node. 3. Electrolyte imbalances: Abnormal levels of potassium or calcium can affect the heart's electrical activity. 4. Cardiac conditions: Structural heart diseases, such as hypertrophic cardiomyopathy, can lead to a prolonged PR interval. 5. Congenital heart block: This is a condition present at birth that can cause a delay in electrical conduction. 6. Myocarditis: Inflammation of the heart muscle can affect the conduction system. 7. Neurocardiogenic syncope: A sudden drop in heart rate or blood pressure can cause a momentary prolongation of the PR interval. It's important to note that a prolonged PR interval is not always a cause for concern and may be a normal variant in some individuals. However, it can be a sign of an underlying condition that requires further investigation.

A prolonged PR interval indicates delayed conduction of the sinoatrial, or SA, nodal impulse to the ventricles and is called first-degree AV block. A short PR interval can be seen when the AV node delay is bypassed, such as in Wolff-Parkinson-White syndrome or Lown-Ganong-Levine syndrome.