Figure 30-8 Unifocal premature ventricular contractions originate in the same ectopic focus and depolarize the ventricles via the same route. The coupling interval is the same.
© Jones & Bartlett Learning.
The morphologic appearance of a PVC depends on the location of the ectopic ventricular pacer that triggered the complex and the route of depolarization. If either of those two variables is different, the appearance of the PVC will be changed.
PVCs that originate in the same ectopic pacer and depolarize via the same route through the ventricular myocardium are known as unifocal PVCs (Figure 30-8). These PVCs have the same coupling interval throughout the rhythm strip. They do not have to appear with a regular timing or at a specific recurring interval during the strip, but can occur in a random pattern. Unifocal PVCs can either appear singly or in combinations.
Figure 30-8 Unifocal premature ventricular contractions originate in the same ectopic focus and depolarize the ventricles via the same route. The coupling interval is the same.
© Jones & Bartlett Learning.
Multifocal PVCs (Figure 30-9) originate from either different ectopic pacers or in the same ectopic pacemaker, but take different routes to depolarize the ventricles. These PVCs occur randomly throughout the rhythm strip and their coupling intervals will be completely different. Multifocal PVCs can either appear singly or in combinations.
Figure 30-9 Multifocal premature ventricular contractions originate in different ectopic foci or depolarize the ventricles via different routes. The coupling intervals are different.
© Jones & Bartlett Learning.
DescriptionAs mentioned earlier, the number of PVCs occurring in a minute can vary in any one patient due to many reasons. The numbers of PVCs can vary because of electrolyte abnormalities, ischemia, diurnal (hormonal) changes, medications, and so on. If the number exceeds five or more per minute during an ECG strip, or 20 to 30 per hour during ambulatory or Holter monitoring, they are considered frequent.