ECG
Although the ECG and an electrophysiology study are diagnostic, the characteristic features are not always seen on ECG
Short PR interval - <0.12sec
Due to loss of normal AV node conduction delay
Differentiate from premature junctional complex
Delta wave / slurred upstroke
Due to early activation of ventricular myocardium
QRS duration > 0.10 sec
Represents a fusion beat
Dominant R wave in V1, Type A<unk> 
Left sided accessory pathway
Dominant S wave in V1, Type B<unk> 
Right sided accessory pathway
Tall R waves in V1-V3 with T wave inversion
Mimic RVH
"Negative" delta waves in III and aVF
Appear as pseudo-infarct Q waves
Mimics prior inferior infarct
Due to loss of normal AV node conduction delay
Differentiate from premature junctional complex
Due to early activation of ventricular myocardium
Represents a fusion beat
Left sided accessory pathway
Right sided accessory pathway
Mimic RVH
Appear as pseudo-infarct Q waves
Mimics prior inferior infarct
Wolff–Parkinson–White syndrome
Regular
Wernicke-Korsakoff syndrome
AV Node Independent
Vaughn Jackson syndrome
Sinus tachycardia
Sydenham's chorea
Atrial tachycardia 