What is a normal Premature Atrial Contraction (PAC) or Premature Ventricular Contraction (PVC) burden on a Holter monitor?

Normal PAC and PVC Burden on Holter Monitoring

The normal premature ventricular contraction (PVC) burden is considered to be less than 2,000 PVCs per 24 hours or less than 1% of total beats, while a normal premature atrial contraction (PAC) burden is not clearly defined but follows similar principles of being infrequent and not associated with symptoms or structural abnormalities.

PVC Burden Classification

PVC burden can be stratified into risk categories based on 24-hour Holter monitoring:

PVC Burden	Risk Level	Clinical Significance
<2,000/24h (<1%)	Low	Generally benign [1]
2,000-10%	Intermediate	May require monitoring [1]
10-15%	High	Minimum threshold that can result in cardiomyopathy [1]
>15%	Very High	Strong association with adverse outcomes [1]
≥24%	Extremely High	Independently associated with cardiomyopathy [1]

Clinical Implications of PVC Burden

• Low burden (<2,000 PVCs/24h): Generally benign with 0% risk of underlying structural heart disease 2
• Intermediate burden (2,000-10,000 PVCs/24h): 3% risk of underlying structural heart disease 2
• High burden (>10,000 PVCs/24h): Up to 30% risk of underlying structural heart disease 2

Day-to-Day Variability in PVC Burden

It's important to note that PVC burden can vary significantly from day to day:

• The median range of daily PVC burden across 24-hour periods is 3.6% 3
• Individual ranges of daily PVC burden crossed thresholds of 10%, 15%, and 20% in 26.7%, 16.8%, and 6.9% of patients, respectively 3
• Median time to detecting maximum PVC burden was 6 days 3
• Extended monitoring (beyond 24 hours) nearly doubled the identification of patients reaching the 10% threshold 3

Prevalence of Frequent PVCs

• The prevalence of PVC burden 5.1%-10% is approximately 4% in patients undergoing Holter monitoring 4
• The prevalence of PVC burden >10% is approximately 5% in patients undergoing Holter monitoring 4
• PVCs >5% are more prevalent in older individuals, males, and Caucasians 4

Clinical Evaluation Based on PVC Burden

When multiple (≥2) PVCs are detected on a standard 12-lead ECG, further evaluation is recommended:

1. Ambulatory Holter monitoring to quantify PVC burden
2. Echocardiogram to assess for structural heart disease
3. Exercise stress test to evaluate if PVCs suppress with exercise 2

If the Holter shows ≥2,000 PVCs per 24 hours or episodes of non-sustained ventricular tachycardia, additional evaluation may include:

• Contrast-enhanced cardiac MRI
• Electrophysiology study 2

Risk Factors for Higher PVC Burden

• Advanced age
• Male gender
• Caucasian ethnicity
• Structural heart disease
• History of heart failure 4

Clinical Significance of PACs

While specific thresholds for PAC burden are less well-defined in guidelines, PACs follow similar principles to PVCs:

• Isolated or infrequent PACs are generally benign
• Frequent PACs may be associated with increased risk of developing atrial fibrillation
• PACs that trigger sustained atrial tachyarrhythmias warrant further evaluation 2

Key Takeaways

1. Normal PVC burden is <2,000 PVCs/24h or <1% of total beats
2. PVC burden >10% is associated with increased risk of developing cardiomyopathy
3. Extended monitoring (beyond 24 hours) may be necessary to accurately assess true PVC burden due to day-to-day variability
4. Risk stratification and management decisions should be based on accurate quantification of arrhythmia burden