From the Guidelines
A short PR interval on an EKG should be evaluated for potential accessory pathways and managed based on symptoms and risk of arrhythmic events, with catheter ablation being a reasonable option for high-risk patients or those with symptomatic pre-excitation syndromes, as recommended by the 2015 ACC/AHA/HRS guideline for the management of adult patients with supraventricular tachycardia 1.
Key Considerations
- A short PR interval is defined as less than 120 milliseconds and may indicate an accessory pathway between the atria and ventricles, bypassing the normal conduction delay at the AV node.
- Asymptomatic patients with an isolated short PR interval may require no specific treatment beyond periodic monitoring, as the risk of sudden cardiac death is small, especially in adults 1.
- For symptomatic patients with pre-excitation syndromes, options include medication therapy with antiarrhythmic drugs such as flecainide (50-200 mg twice daily), propafenone (150-300 mg three times daily), or beta-blockers like metoprolol (25-100 mg twice daily) 1.
- Definitive treatment often involves catheter ablation of the accessory pathway, which has a success rate of over 95% for most accessory pathways and is recommended for high-risk patients or those with symptomatic pre-excitation syndromes 1.
Risk Stratification
- Noninvasive testing, such as exercise testing and ambulatory monitoring, can help identify patients at low risk of rapid conduction over the accessory pathway and life-threatening ventricular arrhythmias 1.
- Electrophysiological (EP) study is reasonable in asymptomatic patients with pre-excitation to risk-stratify for arrhythmic events, especially if the presence of pre-excitation precludes specific employment or if the patient engages in moderate- or high-level competitive sports 1.
- Patients with short PR intervals should avoid medications that enhance AV nodal conduction like digoxin, verapamil, and diltiazem, as these can potentially accelerate conduction through the accessory pathway and precipitate dangerous arrhythmias, particularly during atrial fibrillation 1.
From the Research
Definition and Causes of Short PR Interval
- A short PR interval on an electrocardiogram (EKG) represents a shorter than normal time for an impulse to travel through the atrium and atrioventricular (AV) conduction system to the ventricles 2.
- The PR interval is influenced by the autonomic tone, with parasympathetic and sympathetic tone balanced at rest in patients with normal AV nodal function 2.
- Certain drugs, such as slow channel blockers and beta blockers, can affect AV nodal function and alter the PR interval 2, 3.
Clinical Significance of Short PR Interval
- A short PR interval may be associated with an otherwise normal EKG or various electrocardiographic abnormalities, and the individual may be asymptomatic or experience complex arrhythmias 4.
- In patients with abnormal AV conduction, the effect of the parasympathetic system is more marked, and the PR interval can be shortened 2.
- A short PR interval can be a sign of pre-excitation syndromes, such as Wolff-Parkinson-White syndrome, which can increase the risk of arrhythmias 4.
Diagnosis and Evaluation of Short PR Interval
- The evaluation of the PR interval can be done using electrical transoesophageal atrial stimulation and atropine testing 5.
- The Wenckebach period (WP) can be used to assess AV nodal function, and a good correlation between the PR interval and WP has been found in patients with WP less than or equal to 110 ppm 5.
- A PR interval greater than 240 ms can be a sign of first-degree AV block, while a shorter PR interval can be a sign of AV depression 5.
Treatment and Management of Short PR Interval
- Beta blockers can be effective in controlling the ventricular rate during atrial fibrillation and maintaining sinus rhythm 3.
- The use of beta blockers, such as metoprolol, can be beneficial in patients with atrial fibrillation, especially after myocardial infarction and in those with chronic heart failure and arterial hypertension 3.
- The effects of beta blockers on heart rate variability and RR interval variability can be significant, with an increase in vagal tone and a reduction in sympathetic activation 6.