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[Negative retrograde P wave in D1, sign of left postero-lateral Kent bundle].

A negative P wave in D1 with a mean atrial vector which is horizontal or descending in the frontal plane, occurring during paroxysmal tachycardial due to reciprocal rhythm or after ventricular stimulation suggests atrial depolarisation which starts in the left auricle at some distance from the A-V node and near the pulmonary veins. In the absence of an external anterograde ventricular pre-excitation, such P waves may indicate the presence of a hidden bundle of Kent posterolaterally on the left, allowing retrograde conduction during the tachycardia by a reciprocal rhythm.