Inverted P-waves with narrow-QRS rhythm and incomplete atrioventricular dissociation: Two case reports

When inverted P-waves coexist with narrow-QRS rhythm, multiple relationships may exist between P-waves and QRS complexes. Improper analytical approaches readily lead to misdiagnosis. The electrocardiograms (ECGs) of the two cases in this paper exhibit the following features: ① Baseline P-waves are inverted (Case 2 is complicated by sinus or atrial parasystole) with regular P-P intervals; ② R-R intervals are sometimes regular (baseline interval) and sometimes irregular (intervals related to capture and post-capture beats); the baseline R-R interval is shorter than the P-P interval; ③ The occurrence of capture beats depends on the RP interval. When the RP interval is shorter than 0.14 s, P-waves are dissociated from QRS complexes with no conduction relation. When the RP interval is ≥ 0.14 s and a baseline QRS complex has not yet appeared, the P-wave can capture the ventricle. The R-R interval of the captured beat is shorter than the baseline interval, and the post-capture R-R interval is ≤ the baseline interval; ④ QRS morphology of capture beats is identical to that of baseline QRS complexes, indicating that the baseline rhythm is junctional rhythm. The rhythm is interpreted as accelerated atrial rhythm and accelerated junctional rhythm with incomplete atrioventricular dissociation. If inverted P-waves originate from the atrioventricular junction, the entity is termed double junctional rhythm.