What is the etiology of the early beats seen here? And why?
Answer & Explanation
There are two premature beats seen in this rhythm tracing (#4 and #7). Although they appear similar in morphology to supraventricular beats, both are PVCs by criteria that define the difference between PVC and PAC.
Both beats are followed by a pause – in these beats, a compensatory pause, which implies that the next P wave was undisturbed by the premature beat. Another way of saying the same thing is that the sinus P waves “march through” the premature beat, or that the sinus metronome marked by regular P and QRS complexes is undisturbed. Each of these descriptions say the same thing – these premature beats are both PVCs!