Double transition in ventricular preexcitation

In the Wolff-Parkinson-White syndrome, numerous electrocardiographic (ECG) algorithms have been developed for the prediction of accessory pathway (AP) location. In addition to such algorithms, recognizing simple, unique and eye-catching ECG patterns that are specific for particular AP positions can provide further visual aid in quickly predicting the likely effective ablation site. Recently, such a distinctive ECG configuration has been introduced that showed high specificity for right posteroseptal (right paraseptal) APs. The "double transition" sign was characterized by showing more positive QRS complexes in lead V2 than in either of its neighboring leads V1 and V3. In some cases, the entire QRS complex was downgoing in V1 and V3, but upgoing in V2. In the double transition study, no explanation was provided as to the cause of this curious phenomenon, and why it had high specificity but low sensitivity for right posteroseptal APs. In this report we present our experience with the double transition sign, expand on its electrocardiographic spectrum, and offer a simple and rational explanation for the probable cause of this seemingly strange and perplexing phenomenon.