What Causes Premature Ventricular Contractions (PVCs)?
PVCs arise from ectopic electrical activity originating in the ventricles, triggered by mechanisms including triggered activity, automaticity, and reentry, and their clinical significance depends entirely on the presence or absence of underlying structural heart disease. 1, 2
Fundamental Mechanisms
The three primary electrophysiologic mechanisms that generate PVCs are: 2
- Triggered activity: Abnormal impulses arising from afterdepolarizations in ventricular myocytes
- Automaticity: Enhanced spontaneous depolarization of ventricular pacemaker cells
- Reentry: Circular propagation of electrical impulses through areas of heterogeneous conduction
Clinical Context and Risk Factors
Epidemiology and Prevalence
- PVCs are extremely common, found in approximately 50% of all people regardless of heart disease status on extended monitoring 1
- In healthy populations, PVCs appear in only 0.6% of those <20 years old and 2.7% of those >50 years old on standard 12-lead ECG, but this dramatically underestimates true prevalence 1
- Frequency increases with age, making PVCs nearly universal in older adults 1, 2
Predisposing Factors
Multiple factors predict higher PVC frequency: 2
- Increasing age
- Taller height
- Higher blood pressure
- History of heart disease
- Reduced physical activity levels
- Tobacco smoking
Structural Heart Disease Association
The most critical distinction is whether PVCs occur in structurally normal hearts versus those with underlying cardiac pathology. 1, 3
- Ischemic heart disease is the most common substrate for life-threatening ventricular arrhythmias, particularly in older patients 1
- Post-myocardial infarction patients have PVCs that may predict increased mortality and can trigger more malignant ventricular arrhythmias 4
- In structural heart disease, PVCs may indicate increased risk of sudden death 3
PVC-Induced Cardiomyopathy
Critical Burden Thresholds
A direct causal relationship exists between PVC burden and left ventricular dysfunction: 1, 5
- Minimum threshold: PVC burden ≥10% of total heartbeats begins to raise concern 5
- High-risk threshold: PVC burden ≥20-24% is independently associated with cardiomyopathy development 1, 5
- Very frequent PVCs (>10,000-20,000 per day) can cause depressed LV function 1
Mechanistic Evidence
- A direct link between PVCs and cardiomyopathy has been demonstrated in animal models 1
- Among 60 patients with idiopathic frequent PVCs (>10/hour), 22% developed LV dysfunction, with those affected having greater PVC burdens 1
- Radiofrequency ablation normalized ejection fraction in 82% of patients with LV dysfunction within 6 months, proving causality 1
Additional Risk Factors for PVC-Induced Cardiomyopathy
Beyond burden alone, specific PVC characteristics increase risk: 6
- Short coupling interval (<300 ms)
- Wider QRS complexes (>160 ms)
- Right ventricular outflow tract origin (most common site at 52% of cases) 1
Distinguishing Benign from Malignant PVCs
Benign PVCs
PVCs in structurally normal hearts are usually benign and may present with: 3, 7
- Asymptomatic or very mild symptoms
- Palpitations, lightheadedness, chest discomfort
- Sensation of skipped beats
Malignant PVCs
Warning signs that PVCs may be dangerous include: 7
- Syncope or presyncope (hemodynamically significant arrhythmia) 8
- Sudden cardiac death presentation
- Family history of sudden cardiac death 8
- Sharp chest pain suggesting coronary disease 8
- Exertional symptoms suggesting ischemia or catecholaminergic polymorphic VT 8
Common Pitfalls in Clinical Practice
Critical errors to avoid: 8
- Dismissing chest heaviness as "just PVCs" without quantifying burden or excluding structural disease
- Failing to obtain 24-hour monitoring to assess true PVC burden, since symptoms correlate poorly with frequency
- Assuming all PVCs are benign without echocardiography to exclude structural abnormalities and assess left ventricular function 8
Secondary Causes
While the fundamental mechanisms remain largely unknown, PVCs may also be markers of: 3
- Underlying myocarditis
- Electrolyte imbalances
- Sympathomimetic agent use (caffeine, alcohol) 6