Simultaneous recording of three-lead ECG obtained from the original article by Drs Wolff, Parkinson, and White.¹ (Reproduced with permission from Elsevier.)

A: The ECG strips show clear-cut ventricular pre-excitation. B: The same patient is given intravenous atropine with normalization of the ECG. This finding was thought to explain the “neurogenic” bases for the Wolff–Parkinson–White syndrome. We now appreciate that facilitation of the atrioventricular nodal conduction with atropine may mask accessory pathway conduction. Alternatively, drugs that block atrioventricular nodal conduction may encourage accessory pathway conduction.