In
electrocardiography
Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity through repeated cardiac cycles.
It is an electrogram of the heart which is a graph of voltage versus time of t ...
, the PR interval is the period, measured in milliseconds, that extends from the beginning of the
P wave
A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at any ...
(the onset of
atrial
The atrium (; : atria) is one of the two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular mitral and tricuspid heart valves.
...
depolarization
In biology, depolarization or hypopolarization is a change within a cell (biology), cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolar ...
) until the beginning of the
QRS complex (the onset of
ventricular depolarization); it is normally between 120 and 200 ms in duration.
The PR interval is sometimes termed the PQ interval.
Interpretation
Variations in the PQ interval can be associated with certain medical conditions:
* Duration
** A long PR interval (of over 200 ms) indicates a slowing of conduction between the atria and ventricles, usually due to slow conduction through the
atrioventricular node
The atrioventricular node (AV node, or Aschoff-Tawara node) electrically connects the heart's atria and ventricles to coordinate beating in the top of the heart; it is part of the electrical conduction system of the heart. The AV node lies at the ...
(AV node).
This is known as
first degree heart block.
Prolongation can be associated with
fibrosis of the AV node, high
vagal tone, medications that slow the AV node such as
beta-blockers,
hypokalemia
Hypokalemia is a low level of potassium (K+) in the blood serum. Mild low potassium does not typically cause symptoms. Symptoms may include feeling tired, leg cramps, weakness, and constipation. Low potassium also increases the risk of an a ...
,
acute rheumatic fever, or
carditis associated with
Lyme disease
Lyme disease, also known as Lyme borreliosis, is a tick-borne disease caused by species of ''Borrelia'' bacteria, Disease vector, transmitted by blood-feeding ticks in the genus ''Ixodes''. It is the most common disease spread by ticks in th ...
.
** A short PR interval (of less than 120ms) may be associated with a
Pre-excitation syndromes such as
Wolff–Parkinson–White syndrome or
Lown–Ganong–Levine syndrome, and also junctional arrhythmia like
atrioventricular reentrant tachycardia
Atrioventricular reentrant tachycardia (AVRT), or atrioventricular reciprocating tachycardia, is a type of heart arrhythmia with an abnormally fast rhythm (tachycardia); it is classified as a type of supraventricular tachycardia (SVT). AVRT is m ...
or
junctional rhythm.
** A variable PR interval may indicate other types of
heart block.
* PR segment depression may indicate atrial injury or
pericarditis
Pericarditis () is inflammation of the pericardium, the fibrous sac surrounding the heart. Symptoms typically include sudden onset of sharp chest pain, which may also be felt in the shoulders, neck, or back. The pain is typically less severe whe ...
.
See also
*
P wave
A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at any ...
References
{{DEFAULTSORT:Pr Interval
Cardiac electrophysiology
Diagnostic cardiology