Premature Ventricular Contractions (PVCs) are early contractions that originate in the ventricles, the bottom chambers of the heart. These contractions are typically caused by ventricular irritability. PVCs can occur suddenly and disrupt the normal electrical conduction process in the heart.
Don’t forget to watch the premature ventricular contractions (PVCs) lecture and to take the quiz after reviewing this material (found at the end of this article).
A typical PVC appears on an ECG as a wide and bizarre QRS complex, occurring usually within an underlying normal sinus rhythm.
For instance, above is an example of an underlying rhythm is a normal sinus rhythm with a premature ventricular contraction on the fourth beat and followed by this beat is a compensatory pause. This pause allows the heart to reset itself before the normal sinus rhythm resumes.
Key Characteristics of PVCs
When examining an ECG strip, several key characteristics of PVCs are evident:
- Wide and Bizarre QRS Complex: The QRS complex of a PVC is greater than 0.12 seconds and appears abnormal.
- Compensatory Pause: This pause follows the PVC, allowing the heart to prepare for the next beat.
- Irregular Rhythm: The rhythm becomes irregular due to the PVC, although the underlying rhythm outside of the PVC is typically regular.
- Absence of P-Wave: The P-wave is missing in PVCs, so the PR interval cannot be measured.
- Inaccurate QT Interval: Due to the wide QRS complex, the QT interval is difficult to measure accurately. An inverted T-wave may sometimes be seen after the PVC as well.
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Types of PVCs
PVCs can vary in their presentation:
- Bigeminy: A normal beat followed by a PVC, occurring every other beat.
- Trigeminy: A pattern where a PVC occurs every third beat (normal beat, normal beat, PVC).
- Uniform vs. Multiform: PVCs can be uniform (similar in appearance) or multiform (different in appearance).
- Couplets: Two PVCs occurring consecutively.
When PVCs Become a Problem
Although PVCs are often benign, certain characteristics may indicate a need for further investigation:
- R-on-T Phenomenon: A PVC occurring on the T-wave of the preceding beat can increase the risk of ventricular tachycardia (VT) or ventricular fibrillation (VF), especially in patients with heart disease.
- Variability in Appearance: Multiform PVCs suggest they originate from different areas within the ventricles.
- Consecutive PVCs: Three or more consecutive PVCs, known as a run of ventricular tachycardia, warrant further evaluation.
- Pattern of PVCs: Patterns like bigeminy or trigeminy should be assessed for underlying conditions.
Causes of PVCs
Several factors can trigger PVCs, including:
- Caffeine Intake, Stress, Nicotine: Lifestyle factors that can contribute to PVCs
- Electrolyte Imbalances: Low potassium and magnesium levels.
- Myocardial Irritability: Conditions such as heart trauma or disease.
- Anemia, Thyroid Problems: Conditions like hyperthyroidism.
- Underlying Heart Conditions: Myocardial infarction, coronary artery disease, heart failure, rhythm disorders like atrial fibrillation, and bundle branch blocks.
- Elevated Blood Pressure: Can also contribute to PVCs.
Treatment of PVCs
PVCs are often asymptomatic and do not require treatment. However, when PVCs become frequent or symptomatic, treatment may be necessary. Symptoms of frequent PVCs include dizziness, syncope, palpitations, and a drop in blood pressure due to reduced cardiac output. To address these issues, treatment may involve:
- Managing Underlying Heart Conditions: Addressing the root cause of PVCs.
- Medications: Anti-arrhythmics like flecainide, beta-blockers, or calcium channel blockers can help reduce PVC frequency.
- Cardiac Ablation: If medications are ineffective, a cardiac ablation may be considered to eliminate the source of the PVCs.
Test your Knowledge on this Material
Premature Ventricular Contractions (PVCs) Quiz
References
Amerman, E. C., & Irintcheva, V. (2016). Chapter 17 The Cardiovascular System I: The Heart. In Human Anatomy and Physiology (p. 636).
American Heart Association. (n.d.). Premature contractions (PACs and PVCs). Retrieved June 26, 2024, from https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/premature-contractions-pacs-and-pvcs
Farzam K, Richards JR. Premature Ventricular Contraction. [Updated 2023 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532991/