(c) Premature ventricular contractions indicate myocardial irritability.
The frequency of PVCs suggests the degree of myocardial irritability.
(d) Premature ventricular contractions are considered unifocal if they
all originate from a single ventricular focus and have similar configurations.
(e) Premature ventricular contractions are considered multifocal if they
original from many different points and have different configurations.
(f) If a PVC occurs during a vulnerable (relative refractory) phase of
the cardiac cycle, the PVC can produce lethal, repetitive arrhythmias. A PVC that falls
on the downslope of a T wave is referred to as "R-on-T" phenomenon and is considered
(g) With increasing irritability, PVCs can occur in pairs called couplets
or in runs of three or more consecutive ectopics (ectopic heartbeat originating from a
place other than the SA node).
Premature ventricular contractions frequently occur in patterns such
as the following:
1 Bigeminy--a PVC every other heartbeat.
2 Trigeminy--a PVC every third beat.
3 Quadrigeminy--a PVC every fourth beat.
Bigeminy, trigeminy, and quadrigeminy can also describe patterns of
premature atrial contractions (PACS) and premature junctional contractions
Figure 2-26. Frequent premature ventricular contractions.