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.