From the Guidelines
A shortened PR interval is not typically a significant finding in the context of atrial contraction, as a normal PR interval ranges from 120 to 200 milliseconds, and a shortened PR interval may not be associated with any specific cardiac condition.
Key Points
- The PR interval represents the time from the onset of atrial depolarization (P wave) to the onset of ventricular depolarization (QRS complex) 1.
- A shortened PR interval is not typically a significant finding, but a prolonged PR interval (>200 ms) is considered first-degree atrioventricular block or more accurately, atrioventricular delay, as all P waves are conducted to the ventricles, but with a delay 1.
- Atrioventricular block is classified into three degrees: first-degree (prolonged PR interval), second-degree (some P waves are not conducted), and third-degree (no P waves are conducted) 1.
- The significance of a shortened PR interval is not well-established, but it may be associated with pre-excitation syndromes, such as Wolff-Parkinson-White syndrome, where an accessory electrical pathway between the atria and ventricles causes early ventricular depolarization 1.
- In clinical practice, a shortened PR interval is not typically a concern, but it is essential to evaluate the entire electrocardiogram and clinical context to determine the significance of any abnormal findings 1.
From the Research
Significance of a Shortened PR Interval in Atrial Contraction
- A shortened PR interval is not directly addressed in the provided studies, however, the significance of PR interval prolongation is discussed in several studies 2, 3, 4, 5, 6.
- The PR interval measures the time taken by an electrical impulse generated in the sinoatrial node to propagate from atria to ventricles 2.
- A prolonged PR interval is associated with an increased risk of atrial fibrillation (AF) 3, and is a predictor for increased risk of lethal ventricular arrhythmias in patients with repaired tetralogy of Fallot 6.
- The ratio of the PR interval to the RR interval during rapid atrial pacing can be used to determine the presence of slow AV nodal pathway conduction 4.
- The PR interval can be used as a selection criterion to identify the optimal physiological pacing mode, with short PR patients benefiting from managed ventricular pacing (MVP) mode and long PR patients benefiting from standard dual-chamber pacing mode 5.
PR Interval and Atrial Contraction
- The PR interval is a composite of several distinct components, including P-wave onset to P-wave peak duration, P-wave peak to P-wave end duration, and PR-segment 3.
- These components have varying levels of association with atrial fibrillation, with P-wave onset to P-wave peak duration having the strongest association 3.
- The PR interval is correlated with right ventricular enlargement and dysfunction in patients with repaired tetralogy of Fallot, and progressive PR interval prolongation is a predictor for increased risk of lethal ventricular arrhythmias 6.