Rarely, when the atria are controlled by the ventricular pacemaker, the P waves are inverted and follow QRS complexes at a constant RP interval. QRS complexes are usually wider than 0.12 sec and bizarre. RR intervals are usually regular but may vary up to 0.03 sec.
Vagal stimulation has no effect on the rate.
An ECG prior to tachycardia showing premature beats of identical configuration favors ventricular origin of the tachycardia. B. Characteristics 1. Rhythm is essentially regular, but may vary slightly. May occur as a single isolated basf may recur paroxsysmally or may persist for a long run. C. Clinical Significance 1.