What is short PR (Lown‑Ganong‑Levine) syndrome, its typical symptoms, and recommended treatments?

Short PR Syndrome (Lown-Ganong-Levine Syndrome)

Definition and ECG Characteristics

Short PR syndrome, also known as Lown-Ganong-Levine (LGL) syndrome, is characterized by a PR interval less than 120 ms with a normal QRS complex (no delta wave) and a propensity for paroxysmal supraventricular tachycardia. 1, 2, 3

The key ECG features that distinguish this from other pre-excitation syndromes include:

• PR interval < 120 ms without the slurred upstroke (delta wave) or QRS widening seen in Wolff-Parkinson-White syndrome 4, 1, 2
• Normal QRS duration and morphology (typically < 120 ms), which differentiates it from WPW pattern 1, 3
• Absence of delta wave, the critical distinguishing feature from WPW syndrome 5, 6

Underlying Pathophysiology

The mechanism involves either an accessory pathway (James fibers connecting the atria to the AV node, or Brechenmacher fibers connecting atria to the His bundle) or enhanced atrioventricular nodal conduction (EAVNC) 1, 7. Electrophysiologic studies typically demonstrate:

• Unusually short atrial-to-His (AH) interval with normal His-to-ventricle (HV) interval 1
• Accelerated anterograde nodal conduction with Wenckebach point beyond 200/min 7
• In the majority of cases (46 out of 48 in one series), this represents a variant of normal conduction rather than true accessory pathway 7

Clinical Symptoms

Most patients with LGL syndrome present with:

• Paroxysmal supraventricular tachycardia as the hallmark symptom 1, 2, 3
• Palpitations during tachycardia episodes 6, 3
• Chest pain or discomfort associated with arrhythmic episodes 3
• Shortness of breath during tachycardia 3
• Syncope or near-syncope in some cases 6

Important caveat: Many individuals with isolated short PR interval remain completely asymptomatic and the finding is incidental 6, 2. The syndrome is most commonly seen in young to middle-aged women 3.

Diagnostic Evaluation Algorithm

Step 1: Confirm Short PR and Exclude WPW Pattern

• Measure PR interval carefully on 12-lead ECG; must be < 120 ms 5, 6
• Verify absence of delta wave and normal QRS morphology to exclude WPW syndrome 5, 6
• Check for proper ECG calibration, especially if QRS voltage appears unusual 5

Step 2: Assess for Structural Heart Disease

• Transthoracic echocardiography is mandatory to exclude hypertrophic cardiomyopathy, Ebstein anomaly, and glycogen storage cardiomyopathy 6, 8
• Screen for Fabry disease if left ventricular hypertrophy is present, particularly with multisystem symptoms 5
• Consider Pompe disease if extremely tall QRS complexes and cardiomegaly are present 5

Step 3: Risk Stratification for Arrhythmias

• Obtain detailed symptom history focusing on palpitations, syncope, chest discomfort, and episodes lasting > 30 minutes 6
• Family history assessment for pre-excitation syndromes, cardiomyopathy, or sudden cardiac death 6
• 24-hour Holter monitoring to detect paroxysmal tachyarrhythmias and document intermittent pre-excitation 6
• Exercise stress testing to assess for intermittent loss of pre-excitation (suggests lower risk) and unmask latent pre-excitation 6

Step 4: Consider Electrophysiologic Study

• Indicated for symptomatic patients with recurrent tachyarrhythmias to define mechanism and guide ablation 1, 8
• May be considered for high-risk asymptomatic patients based on exercise testing and Holter findings 6
• Pharmacological testing with adenosine or verapamil may unmask typical features by slowing AV node conduction 6

Treatment Recommendations

For Asymptomatic Patients with Isolated Short PR

Asymptomatic individuals with normal echocardiogram and no high-risk findings on exercise testing or Holter monitoring can be managed conservatively with periodic surveillance. 5, 6

• No restriction from competitive sports for asymptomatic athletes with isolated short PR and no structural heart disease 5
• Periodic ECG and clinical review to monitor for development of symptoms 6

For Symptomatic Patients with Tachyarrhythmias

Medical management with beta-blockers or calcium channel blockers is the first-line approach for controlling supraventricular tachycardia in symptomatic LGL syndrome. 5, 2

• Beta-blockers are recommended as preventative therapy to reduce risk of tachyarrhythmias 5, 2
• Calcium channel blockers can be used for controlling supraventricular tachycardia 5
• Digoxin has been used successfully in pregnancy-related cases 3

For Refractory or High-Risk Cases

Catheter ablation of the accessory pathway or AV nodal region is definitive treatment for patients with refractory symptoms or documented high-risk features. 1

• Ablation targets the AV nodal region when James fibers are suspected, resulting in normalized AH interval and decremental conduction properties 1
• Success rates are high with restoration of normal conduction patterns 1

Critical Distinctions and Pitfalls

Differentiating LGL from WPW Syndrome

The presence or absence of a delta wave completely changes management and risk stratification. 5, 6

• WPW pattern (short PR + delta wave + wide QRS) carries sudden cardiac death risk and requires comprehensive evaluation even if asymptomatic 5, 6
• LGL syndrome (short PR + normal QRS + no delta wave) generally has lower risk but still warrants evaluation if symptomatic 6, 1

Common Diagnostic Errors

• Dismissing short PR as benign without proper evaluation for structural heart disease 5, 6
• Failing to use age-appropriate PR interval norms, particularly in pediatric populations 5
• Attributing LVH with short PR to hypertension without considering Fabry disease 5
• Confusing physiologic PR shortening during exercise or increased sympathetic tone with pathologic short PR 5

Special Populations

• Pregnancy: LGL syndrome can be successfully managed medically during pregnancy with good maternal and fetal outcomes 3
• Athletes: Isolated short PR without delta wave is often a benign variant in athletic populations, but structural disease must be excluded 5, 6
• Critical illness: Short PR may be discovered incidentally during acute illness; distinguish from acute causes and plan appropriate outpatient follow-up 2