An electrocardiogram (EKG or ECG) provides a picture of the heart’s electrical activity. One measurement is the PR interval, which tracks the time for an electrical signal to move from the atria (upper chambers) to the ventricles (lower chambers). A typical PR interval is between 120 and 200 milliseconds. A measurement exceeding 200 milliseconds is considered a wide or prolonged PR interval.
What a Wide PR Interval Signifies
A wide PR interval on an EKG is identified as a first-degree atrioventricular (AV) block. This term signifies a delay in the electrical signal’s journey from the atria to the ventricles. This is a slowdown in conduction, not a complete blockage.
In a first-degree AV block, every electrical impulse from the atria successfully reaches the ventricles; it just takes longer than usual. This condition is often discovered incidentally during a routine EKG and does not produce noticeable symptoms. For many individuals, an isolated first-degree AV block is a benign finding.
The delay does not typically interfere with the heart’s ability to pump blood effectively, which is why it often goes unnoticed. The delay occurs within the atrioventricular node, a gatekeeper for electrical signals between the upper and lower heart chambers. While “heart block” can sound alarming, a first-degree AV block is the mildest form.
Potential Causes of a Prolonged PR Interval
The reasons for a prolonged PR interval are varied. For instance, well-conditioned athletes may develop a “physiological” first-degree AV block due to high vagal tone, a state where the vagus nerve’s calming influence on the heart is heightened. This adaptation is considered a sign of an efficient cardiovascular system and is a normal variation.
Certain medications are a frequent cause of a widened PR interval, as drugs that slow conduction through the AV node can lead to this finding. Common examples include beta-blockers, used to manage high blood pressure, and calcium channel blockers. The heart medication digoxin can also prolong the PR interval.
Underlying medical conditions can also be responsible for the delay. These include:
- High levels of potassium in the blood (hyperkalemia)
- Inflammatory processes from infections like Lyme disease or rheumatic fever
- Structural heart disease
- Fibrosis of the AV node
Monitoring and Management Strategies
The initial diagnosis of a wide PR interval is made using a standard 12-lead EKG. This non-invasive test records the heart’s electrical signals, allowing for precise measurement. Once a first-degree AV block is identified, the management approach depends on the individual’s overall health and symptoms.
For a person who is otherwise healthy and has no symptoms, the standard approach is observation. A healthcare provider may recommend periodic EKGs to monitor the PR interval over time. This ensures the delay does not worsen or progress to more significant types of heart block.
If a specific, reversible cause is identified, management will focus on addressing that underlying issue. For example, if a medication is the cause, a doctor might adjust the dosage or switch to an alternative drug. If an electrolyte imbalance is detected, correcting it can often resolve the conduction delay.