Do PVCs Count in Heart Rate Calculation?
Premature ventricular contractions (PVCs) should be included in the total heart rate calculation, particularly when assessing PVC burden as a percentage of total heartbeats.
Understanding PVCs and Heart Rate
PVCs are early depolarizations of the myocardium originating in the ventricle that are common in the general population. When calculating heart rate:
- PVCs are counted as part of the total number of heartbeats
- PVC burden is typically expressed as a percentage of total heartbeats
- The clinical significance of PVCs is often determined by their frequency relative to normal beats
Clinical Significance of PVC Burden
The American College of Cardiology/American Heart Association guidelines emphasize the importance of quantifying PVC burden:
- Low burden: <2,000 PVCs per 24 hours or <15% of total heartbeats is generally considered low risk 1
- Moderate burden: 2,000 PVCs to 15% of total heartbeats may warrant monitoring 1
- High burden: >15% of total heartbeats is considered high risk and may lead to PVC-induced cardiomyopathy 2, 1
The guidelines specifically note that "frequent PVCs (usually >15% of the total number of beats) may produce a reversible form of LV dysfunction" 2. This definition clearly indicates that PVCs are counted as part of the total heartbeats when determining their percentage.
Monitoring and Quantification Methods
When monitoring for PVCs:
- 24-hour Holter monitoring quantifies PVC burden as a percentage of total heartbeats 1
- PVC burden is calculated by dividing the number of PVCs by the total number of heartbeats (including the PVCs themselves) 2
- This calculation is essential for risk stratification and treatment decisions
Clinical Implications
The inclusion of PVCs in heart rate calculations has important clinical implications:
- Risk assessment: A PVC burden >10-15% is associated with risk of developing PVC-induced cardiomyopathy 1
- Treatment decisions: Catheter ablation is recommended for patients with PVC burden >15% with predominantly one morphology 2, 1
- Monitoring response: Treatment efficacy is measured by reduction in PVC burden as a percentage of total beats 2
Common Pitfalls
When interpreting PVC frequency:
- Failing to account for PVCs in total heart rate may underestimate their clinical significance
- PVC frequency can vary with underlying heart rate, with most patients showing increased PVC frequency at higher heart rates 3, 4
- The relationship between PVC frequency and heart rate is reproducible in most patients and may explain phenomena such as sleep suppression of PVCs 3
In summary, PVCs are included in heart rate calculations, particularly when determining their burden as a percentage of total heartbeats, which is critical for clinical decision-making regarding treatment and risk stratification.