What are the treatment options for a patient with a short PR interval, potentially indicating Wolff-Parkinson-White syndrome or hyperthyroidism, with or without symptoms such as palpitations, shortness of breath, or chest pain?

Management of Short PR Interval

For symptomatic patients with short PR interval and delta waves (Wolff-Parkinson-White syndrome), catheter ablation is the first-line definitive treatment with 95-98.5% success rates and should be performed at experienced centers. 1

Initial Diagnostic Approach

The critical first step is determining whether delta waves are present on ECG 1:

• WPW syndrome is diagnosed by the classic triad: PR interval <120 ms, slurred QRS upstroke (delta wave), and widened QRS >120 ms 1, 2
• The delta wave represents early ventricular activation through an accessory pathway bypassing the AV node 3, 2
• Isolated short PR without delta waves requires different management and may represent a normal variant, particularly with exercise or increased sympathetic tone 3

Alternative Diagnoses to Consider

• Fabry disease: X-linked lysosomal storage disorder presenting with short PR, sinus bradycardia, and left ventricular hypertrophy—consider especially with multisystem symptoms 3
• Pompe disease: Rare genetic disorder with short PR, extremely tall QRS complexes, and cardiomegaly 3
• Hyperthyroidism: Treat with methimazole while monitoring for agranulocytosis, vasculitis, and bleeding complications 4

Risk Stratification for WPW Syndrome

High-risk features requiring urgent intervention 1:

• Shortest pre-excited RR interval <250 ms during atrial fibrillation
• History of syncope or near-syncope
• Documented atrial fibrillation with pre-excitation
• Multiple accessory pathways or posteroseptal location
• Accessory pathway refractory period <240 ms

Low-risk indicators 1:

• Intermittent loss of pre-excitation on ambulatory monitoring
• Abrupt loss of pre-excitation during exercise testing

Definitive Treatment Algorithm

Symptomatic WPW Syndrome

Mandatory indications for catheter ablation 1:

• Symptomatic tachyarrhythmias
• History of syncope
• Documented atrial fibrillation with WPW
• High-risk features on electrophysiology study

The major complication rate is only 0.1-0.9%, making this an extremely safe and effective intervention 1. Sudden cardiac death risk ranges from 0.15% to 0.39% over 3-10 years, and cardiac arrest is the first manifestation in approximately 50% of WPW patients who experience it 3.

Asymptomatic WPW Pattern

• Asymptomatic athletes with isolated short PR and no structural heart disease can participate in all competitive sports 3
• However, WPW pattern requires comprehensive evaluation before sports clearance due to sudden death risk during exertion 3
• The management of asymptomatic WPW remains controversial, with guidelines endorsing both watchful waiting and early electrophysiology study 5

Acute Management of Tachyarrhythmias

Hemodynamically Unstable Patients

• Immediate synchronized DC cardioversion to prevent progression to ventricular fibrillation 1

Hemodynamically Stable Patients

For regular narrow-complex tachycardia (AVRT) 1:

• Vagal maneuvers first-line
• IV adenosine if vagal maneuvers fail 6
• Propranolol is the drug of choice for ongoing management 7

For pre-excited atrial fibrillation 1:

• IV procainamide is first-line treatment
• Alternative: IV lidocaine 7
• Flecainide, propafenone, or amiodarone prolong accessory pathway refractory periods and prevent rapid conduction 8

Critical Medication Contraindications

AV nodal blocking agents are absolutely contraindicated in pre-excited atrial fibrillation 1:

• Digoxin
• Diltiazem
• Verapamil
• Beta-blockers (metoprolol, etc.) 9

These medications accelerate conduction through the accessory pathway and can precipitate ventricular fibrillation 1. This is a common and potentially fatal pitfall.

Long-Term Pharmacologic Management

When ablation is not immediately available or declined 3, 7:

• Class Ia agents (quinidine, procainamide) slow accessory pathway conduction
• Class Ic agents (flecainide, propafenone) are highly effective 8
• Propranolol for recurrent AVRT 7
• Digitalis is nearly equally effective for regular supraventricular tachycardia but contraindicated in pre-excited atrial fibrillation 7

Diagnostic Workup for Symptomatic Patients

Mandatory evaluation 1:

• 12-lead ECG during tachycardia
• 24-hour Holter monitoring
• Exercise ECG (assesses for intermittent pre-excitation) 3
• Electrophysiology study for definitive risk stratification 3
• Echocardiography to exclude structural disease (Ebstein's anomaly, hypertrophic cardiomyopathy) 3

Urgent Evaluation Triggers

Symptoms requiring immediate assessment 1:

• Syncope or near-syncope
• New onset palpitations lasting >30 minutes
• Chest pain or dyspnea during palpitations
• Episodes occurring while driving

Management of Isolated Short PR (No Delta Wave)

• Asymptomatic patients without palpitations may not require further evaluation 3
• For symptomatic arrhythmias with isolated short PR, beta-blockers and calcium channel blockers can control supraventricular tachycardia 3
• When PR interval is excessively short (<100 ms), premature termination of atrial filling reduces stroke volume, particularly problematic in patients with impaired LV relaxation or faster heart rates 3

Special Considerations

• Hyperthyroidism management: Beta-blocker dose reduction may be needed when patients become euthyroid, as hyperthyroidism increases clearance of beta-blockers with high extraction ratios 9
• Pregnancy: WPW requires close monitoring; untreated Graves' disease increases risk of maternal heart failure, spontaneous abortion, and preterm birth 4
• Surgical procedures: Monitor prothrombin time if using antithyroid medications due to bleeding risk 4