Exceptions to the rule for compensatory
top: Ventricular extrasystole with less than compensatory pause. Retrograde
conduction to the atria (retrograde P waves deforms first part of St
segment) discharges the sinus pacemaker early and thus shortens the
Middle: Atrial premature contraction followed by fully compensatory
pause. The third and the eighth beats are atrial extra systoles;but
presumably because they suppress the sinus pacemaker,they are folowed
by compensatory pauses.
Bottom: Ventricular extrasystoles with less than compensatory pauses.
Each postextrasystolic cycle ends in an escape beat and so is slightly
less than compensatory.