Short PR Syndromes (Short PR Interval Causes)
1. Wolff–Parkinson–White (WPW) Syndrome
Accessory pathway (Bundle of Kent) → pre-excitation.
ECG: PR < 120 ms, delta wave, wide QRS.
2. Lown–Ganong–Levine (LGL) Syndrome
Accessory pathway (James fibers) bypasses AV node without ventricular pre-excitation.
ECG: PR < 120 ms, normal QRS (no delta wave).
3. Junctional (AV Nodal) Rhythms
Impulse originates near/at AV node → retrograde/inverted P waves + short PR.
4. Ectopic Low Atrial Rhythms
Atrial focus close to AV node → P waves inverted in inferior leads + shortened PR.
5. Enhanced AV Nodal Conduction (EAVNC)
Faster conduction through AV node → physiologic or autonomic cause → short PR with no pre-excitation.
6. Glycogen Storage Cardiomyopathy (PRKAG2 Syndrome)
Genetic metabolic disease causing ventricular hypertrophy + pre-excitation.
ECG: short PR, WPW-like pattern, LVH.
Short PR Syndromes: Understanding the Causes of a Short PR Interval on ECG
A short PR interval on the ECG is defined as PR < 120 ms and represents either faster-than-normal conduction from atria to ventricles or bypass of the AV node through an accessory pathway. Identifying the cause is essential, as some are benign while others are associated with serious arrhythmias.
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What Does the PR Interval Represent?
The PR interval reflects the time taken for the electrical impulse to travel from the atria → AV node → ventricles.
A short PR means this conduction pathway is rapid or partially bypassed, causing early activation of ventricles.
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Major Causes of Short PR Interval
1. Wolff–Parkinson–White (WPW) Syndrome
WPW is the most common pathological cause of a short PR interval.
An accessory pathway—Bundle of Kent—bypasses the AV node, allowing impulses to reach ventricles earlier than normal.
ECG Features
PR < 120 ms
Often wide QRS
May show delta wave (slurred upstroke)
Clinical Importance
WPW predisposes to tachyarrhythmias, especially AVRT and atrial fibrillation with rapid conduction.
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2. Lown–Ganong–Levine (LGL) Syndrome
In LGL, conduction bypasses the AV node through James fibers, but does not pre-excite the ventricles.
ECG Features
PR < 120 ms
Normal QRS (no delta wave)
Clinical Importance
Patients may experience paroxysmal tachycardias, though its existence as a distinct syndrome is debated.
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3. Junctional (AV Nodal) Rhythms
When the pacemaker arises close to or within the AV node, the atria are activated retrogradely.
ECG Features
Short PR or absent PR
Inverted P waves (especially in inferior leads)
Clinical Importance
Often associated with AV nodal escape rhythms, digitalis toxicity, or high vagal tone.
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4. Ectopic Low Atrial Rhythms
Atrial depolarization originates low in the atria—close to the AV node.
ECG Features
Inverted P waves in inferior leads
Shortened PR interval
Clinical Importance
Usually benign but seen in children, athletes, and during increased vagal tone.
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5. Enhanced AV Nodal Conduction (EAVNC)
The AV node conducts impulses faster than usual due to intrinsic or autonomic factors.
ECG Features
Short PR
Normal QRS
No evidence of accessory pathway
Clinical Importance
Typically physiologic. Seen in young patients or during sympathetic stimulation.
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6. Glycogen Storage Cardiomyopathy (PRKAG2 Syndrome)
A rare genetic metabolic disorder that causes excessive glycogen buildup in the cardiac conduction system.
ECG Features
Short PR interval
Ventricular hypertrophy
WPW-like pre-excitation pattern
Clinical Importance
Progressive disease leading to:
Conduction block
Ventricular hypertrophy
Risk of sudden cardiac death
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Approach to a Patient With Short PR Interval
1. Look for signs of pre-excitation
Delta wave
Wide QRS
If present → consider WPW or PRKAG2.
2. Check P-wave morphology
Inverted P waves → junctional or low atrial rhythm.
3. Correlate clinically
Palpitations or tachyarrhythmias suggest accessory pathways.
4. Evaluate for structural heart disease
Especially in suspected PRKAG2 syndrome.
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Key Takeaways
A short PR interval is not always dangerous but may indicate significant arrhythmia risk when related to accessory pathways.
WPW is the most important cause clinically due to its association with sudden tachyarrhythmias.
Understanding P-wave morphology and QRS characteristics helps differentiate the underlying cause.
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