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Short PR Interval Syndromes

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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