Atrial activity of ventricular extrasystoles
The manifestation of atrial activity after the ventricular extrasystole depends on whether the ventricular impulse is conducted in the retrograde direction, i.e. through the AV connection to the atria. If this happens, an inverted P wave is formed, which often overlaps the ventricular ectopic complex itself and can be hidden by it.
In those cases where the AV-compound does not conduct a ventricular impulse on the atria, the atrial activity continues regardless of ventricular activity; only in these cases, after the ventricular extrasystoles, can you see a complete compensatory pause (when the interval between the pre-and post-extrasystolic sinus complexes is equal to twice the duration of the sinus cycle).
Sometimes the ventricular impulse can “penetrate” into the AV compound only partially. In this situation, the next sinus impulse can reach the AV compound, when it is still partially refractory, which will slow down the conduction and lengthen the PR interval. This phenomenon of “hidden retrograde conduction” often occurs after interpolated ventricular extrasystoles.