Variation of the PR interval for confirming ventricular pre-excitation on a 12-lead ECG.

We present the case of a 14-year-old female patient with recurrent episodes of paroxysmal supraventricular tachycardia (PSVT). Her ECG showed a PR interval of 160 ms in lead II, and a delta wave pattern in leads V2 and V3, with a normal QRS interval of 100 ms. We analyzed the three criteria for confirmation of minimal pre-excitation: (i) absence of a Q wave in V6; (ii) presence of an R wave in V1 and (iii) absence of an R wave in avR. The 3 criteria were not met and failed to establish a diagnosis of ventricular pre-excitation. The electrophysiological study confirmed the presence of a left accessory pathway. A new criterion was analyzed: the variation of the PR interval on the same ECG. A difference of >30 ms was successful to confirm the presence of an accessory pathway before ablation and its absence after catheter ablation.