Correlation of P-wave polarity with underlying electrophysiologic mechanisms of long RP′ tachycardia

In summary, our findings suggest that P-wave morphology in lead I during a long RP′ tachycardia provides a useful marker to help distinguish between atypical AVNRT and other mechanisms (PJRT or low AT) responsible for this unusual form of supraventricular tachycardia. Although a negative P wave in the inferior leads is common to all 3 mechanisms, our results suggest that a positive or isoelectric P wave in lead I strongly supports a diagnosis of atypical AVNRT, whereas a negative or biphasic P wave in lead I argues against this mechanism.