Differential Diagnoses for Short PR Interval and Slurred R Wave
Apart from Wolff-Parkinson-White (WPW) syndrome, several other conditions can present with a short PR interval and a slurred R wave on an electrocardiogram (ECG). The differential diagnoses can be categorized as follows:
Single Most Likely Diagnosis
- Lown-Ganong-Levine (LGL) syndrome: This condition is characterized by a short PR interval and a normal QRS complex, often with a slurred upstroke (delta wave) similar to WPW. However, unlike WPW, LGL syndrome typically does not have a wide QRS complex. The mechanism involves an accessory electrical pathway between the atria and the ventricles, but the location and properties of this pathway differ from those in WPW.
Other Likely Diagnoses
- Enhanced atrioventricular (AV) nodal conduction: Conditions that enhance AV nodal conduction, such as sympathetic stimulation or certain medications, can lead to a short PR interval. While these conditions might not typically cause a slurred R wave, variations in conduction can sometimes result in a slurred appearance.
- Familial short PR interval: Some families have been identified with a short PR interval without any apparent structural heart disease or accessory pathways. The genetic basis for this condition is not fully understood, but it is thought to be related to variations in the genes controlling cardiac conduction.
Do Not Miss Diagnoses
- Hyperkalemia: Although not directly causing a slurred R wave, hyperkalemia can lead to a short PR interval and widening of the QRS complex, which might be mistaken for a slurred R wave. It's critical to recognize hyperkalemia due to its potential for severe cardiac and systemic complications.
- Cardiac glycoside effect: Digitalis (a cardiac glycoside) can shorten the PR interval and cause various ECG changes, including those that might be mistaken for a slurred R wave. Recognizing the effects of cardiac glycosides is important due to their potential for toxicity.
Rare Diagnoses
- Fibroelastoma of the AV node: This rare cardiac tumor can infiltrate the AV node and His-Purkinje system, potentially leading to a short PR interval and abnormal ventricular activation, which might appear as a slurred R wave on the ECG.
- Mahaim fibers: These are rare accessory pathways that can connect the atria to the ventricles or the AV node to the ventricles, leading to pre-excitation and potentially a short PR interval with a slurred R wave. They are less common than the accessory pathways seen in WPW syndrome.