Differential Diagnosis for Short PR Interval

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The American College of Cardiology recommends that a short PR interval (<120 ms) be differentiated based on the presence or absence of a delta wave and QRS widening, with WPW pattern being a critical diagnosis due to sudden cardiac death risk 1, 2
WPW pattern is characterized by a short PR interval, delta wave, and wide QRS (>120 ms), resulting from an accessory pathway bypassing the AV node, causing ventricular pre-excitation 1, 2
The delta wave represents slurred initial QRS upstroke from early ventricular activation, and WPW pattern occurs in approximately 1 in 250 athletes, carrying a risk of sudden death as first presentation 1, 2
Associated structural abnormalities include Ebstein's anomaly and hypertrophic cardiomyopathy 1, 2

Fabry disease is an X-linked lysosomal storage disorder with glycosphingolipid accumulation in vascular endothelium, characterized by a short PR interval, sinus bradycardia, and left ventricular hypertrophy 3
Fabry disease must be considered in patients with short PR and LVH, especially with multisystem symptoms, and has an incidence of approximately 1 in 40,000 to 60,000 males 3, 4
Pompe disease is a rare genetic disorder that can present with a short PR interval, extremely tall QRS complexes, and cardiomegaly, particularly in infantile cases 5

The American College of Cardiology recommends a step-wise approach to evaluating a short PR interval, starting with assessment of QRS morphology to differentiate between WPW pattern and isolated short PR 1, 2, 5
For WPW pattern, a mandatory comprehensive evaluation is required, including detailed symptom history, echocardiography, exercise stress testing, and electrophysiology study if necessary 1, 2, 5
For isolated short PR, further assessment is based on clinical context, and asymptomatic athletes or patients without palpitations may not require further evaluation 1, 2, 5

The American College of Cardiology warns against dismissing WPW pattern as benign, even in asymptomatic patients, as sudden death can occur without warning 1, 2, 5
It is essential to differentiate between isolated short PR and WPW pattern, as the presence or absence of a delta wave completely changes management 1, 2, 5
Proper ECG calibration is crucial, especially in cases with extremely high QRS voltage, such as Pompe disease 5
Age-appropriate PR interval norms should be used, particularly in pediatric populations 5
Fabry disease should be considered in patients with short PR and LVH before attributing findings to hypertension or athletic heart 3, 4

Shortening of the PR interval during exercise or increased sympathetic tone is normal in young, healthy individuals, probably due to increased sympathetic tone and vagal withdrawal, with a shortening of 0.10-0.11 seconds 6, 7

The American Heart Association recommends that patients with WPW pattern undergo comprehensive evaluation, as sudden death can be the first presentation, with a risk of sudden cardiac death ranging 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 8
Exercise stress testing is used to assess for intermittent pre-excitation in patients with WPW pattern, and electrophysiology study is used for definitive risk stratification, with a strength of evidence level of IIa 8, 9

The American College of Cardiology recommends catheter ablation as the definitive treatment for WPW pattern, given the sudden death risk, and pharmacologic management with Class Ia, Ic, or III antiarrhythmic agents can be used to slow accessory pathway conduction when ablation is not immediately available 8
For patients with isolated short PR intervals and symptomatic arrhythmias, the European Society of Cardiology recommends beta-blockers and calcium channel blockers for controlling supraventricular tachycardia, with a strength of evidence level of IIb 10

When PR interval is excessively short (<100 ms), atrial filling is terminated prematurely by ventricular contraction, reducing stroke volume and cardiac output, particularly in patients with impaired LV relaxation, faster heart rates, or bundle branch block or ventricular pacing, with a moderate level of evidence 11

Asymptomatic athletes with isolated short PR and no structural heart disease can participate in all competitive sports, according to the American Heart Association, with a Class IIa recommendation 12, 13
In patients with very short PR interval and symptomatic LV outflow tract obstruction refractory to medical therapy, AV nodal ablation is not recommended by the European Society of Cardiology, but sequential AV pacing with short AV interval may be considered (Class IIb) only in highly selected patients with contraindications to septal reduction therapies 14, 15

The American College of Cardiology recommends that WPW pattern requires comprehensive evaluation before sports clearance due to sudden death risk during exertion, although no specific citation is provided in the text, athletes with WPW pattern should be evaluated according to guidelines from the European Society of Cardiology and the American Heart Association 12, 13
The European Society of Cardiology states that in patients with hypertrophic cardiomyopathy, AV nodal ablation has been advocated but is NOT recommended for very short PR interval and symptomatic LV outflow tract obstruction refractory to medical therapy 14, 15