From the Guidelines
A PR interval shorter than 120 milliseconds (0.12 seconds) is indicative of a pre-excitation syndrome, most commonly Wolff-Parkinson-White syndrome. This shortened PR interval occurs because electrical impulses bypass the normal conduction pathway through an accessory pathway, allowing ventricular activation to begin earlier than normal. In pre-excitation syndromes, the electrical impulse travels directly from the atria to the ventricles through this abnormal accessory pathway, bypassing the atrioventricular (AV) node which normally creates a slight delay in conduction. This early activation of the ventricles not only causes the shortened PR interval but is typically accompanied by a delta wave (slurred upstroke of the QRS complex) and widened QRS complexes on electrocardiogram. Recognition of this shortened PR interval is crucial for diagnosis and management of pre-excitation syndromes, which can predispose patients to dangerous tachyarrhythmias including atrial fibrillation with rapid ventricular response and atrioventricular reentrant tachycardia, as noted in the 2015 ACC/AHA/HRS guideline for the management of adult patients with supraventricular tachycardia 1.
Some key points to consider in the management of pre-excitation syndromes include:
- The presence of a shortened PR interval and delta wave on electrocardiogram is diagnostic of pre-excitation syndrome 1.
- Patients with pre-excitation syndrome are at increased risk of sudden cardiac death, particularly if they have a history of symptomatic tachycardia, multiple accessory pathways, or a shortest pre-excited R-R interval less than 250 ms during atrial fibrillation 1.
- Catheter ablation of the accessory pathway is a recommended treatment for patients with pre-excitation syndrome who are at high risk of sudden cardiac death, as it can significantly reduce the risk of arrhythmic events 1.
- Noninvasive tests, such as intermittent loss of pre-excitation or loss of pre-excitation during exercise, may be useful in identifying patients at low risk of sudden cardiac death, but are considered inferior to invasive electrophysiological assessment 1.
Overall, the diagnosis and management of pre-excitation syndromes require careful consideration of the patient's individual risk factors and electrocardiographic findings, as well as the use of guideline-recommended treatments such as catheter ablation, as noted in the 2015 ACC/AHA/HRS guideline 1 and other studies 1.
From the Research
Pre-Excitation Syndrome Diagnosis
- A PR interval of less than 0.12 seconds is indicative of a pre-excitation syndrome, specifically Wolff-Parkinson-White syndrome 2, 3.
- This condition is characterized by an accessory conduction pathway that bypasses the atrioventricular (AV) node, creating a direct electrical connection between the atria and ventricles 2.
- The electrocardiographic features of Wolff-Parkinson-White syndrome include a short PR interval, a slurring of the initial segment of the QRS complex (delta wave), and a widened QRS complex 2, 3.
Clinical Implications
- Patients with pre-excitation syndromes may be asymptomatic or experience symptoms such as palpitations, tachyarrhythmias, and sudden cardiac death 2, 3, 4.
- The management of asymptomatic patients with ventricular pre-excitation is debated, with some electrophysiologists recommending invasive stratification and catheter ablation 4.
- In patients with atrial fibrillation and Wolff-Parkinson-White syndrome, procainamide is the preferred drug for acute ventricular rate control, as other agents such as beta-blockers and calcium channel blockers can worsen the condition 5.