A Premature Ventricular Contraction (PVC) is an extra, abnormal heartbeat that originates in the heart’s lower pumping chambers, known as the ventricles. These extra beats disrupt the heart’s regular rhythm, sometimes causing a sensation of a skipped beat or a flutter in the chest. An Electrocardiogram (ECG) is a non-invasive test that records the heart’s electrical activity, providing a visual representation of the heart’s rhythm and function.
Normal ECG Rhythms and Waves
Understanding a normal heart rhythm on an ECG provides a baseline for identifying abnormalities. In a typical heart rhythm, a tiny cluster of cells called the sinoatrial (SA) node in the right atrium sends out the initial electrical signal. This signal travels through the atria, causing them to contract, and then moves to the atrioventricular (AV) node and into the ventricles, prompting their contraction. The ECG records this coordinated electrical activity as distinct waves and complexes.
The P wave represents the depolarization, or electrical activation, of the atria. It appears as a small, rounded, upward deflection. Following the P wave, the QRS complex signifies the rapid depolarization of the ventricles, which leads to their contraction. This complex is a tall, narrow spike. Finally, the T wave represents the repolarization, or electrical recovery, of the ventricles. It appears as a rounded, upward deflection after the QRS complex.
Distinctive Features of a PVC
A Premature Ventricular Contraction stands out on an ECG because its electrical impulse begins in the ventricles rather than the SA node, leading to characteristic visual differences. One of the most noticeable features is its premature occurrence; a PVC appears earlier than the next expected normal heartbeat. This early beat interrupts the regular rhythm, causing it to arrive ahead of schedule.
The QRS complex of a PVC is wide and appears “bizarre” or abnormal in shape compared to normal QRS complexes. This widened appearance is due to the impulse originating outside the normal conduction system, causing a slower and less efficient spread of electrical activity through the ventricles. The duration of a PVC’s QRS complex is greater than 0.12 seconds.
Another distinguishing characteristic is the absence of a preceding P wave before the wide QRS complex of a PVC. Since the impulse originates in the ventricles, it bypasses the atria, meaning no atrial electrical activation occurs before the ventricular contraction. Additionally, the T wave associated with a PVC often points in the opposite direction to the main deflection of the QRS complex, a phenomenon known as discordant T wave changes.
A common finding after a PVC is a compensatory pause. This pause is a longer-than-normal interval before the next regular heartbeat, allowing the heart to reset its rhythm. The sinus node continues to fire, but the impulse may not be conducted as the ventricles recover from the premature beat.
Recognizing PVC Patterns
PVCs can occur in various patterns. When a PVC alternates with every normal heartbeat, this pattern is termed bigeminy. This pattern is a repeating sequence of one normal beat followed by one PVC. Trigeminy occurs when every third beat is a PVC: two normal beats followed by a PVC.
PVCs can also appear consecutively. A couplet refers to two PVCs occurring immediately after each other. Three consecutive PVCs are known as a triplet. Three or more consecutive PVCs may be referred to as a run of PVCs or non-sustained ventricular tachycardia (NSVT), indicating a brief episode of rapid ventricular beats.
Importance of Professional ECG Interpretation
Understanding the visual features of PVCs on an ECG is informative, but interpreting an ECG requires specialized medical expertise. Heart rhythms and ECG patterns require professional evaluation. Healthcare professionals accurately diagnose and assess heart conditions based on ECG findings.
An ECG provides a snapshot of the heart’s electrical activity. Identifying a PVC on an ECG does not replace the need for a medical diagnosis or evaluation by a healthcare provider. If concerns arise regarding heart rhythm or an ECG, consulting a medical professional is essential for accurate interpretation and assessment.