To understand the cause of premature ventricular contractions (PVCs), it might help to learn more about how the heart typically beats.
The heart is made of four chambers — two upper chambers (atria) and two lower chambers (ventricles).
The heart's rhythm is controlled by a natural pacemaker (the sinus node) in the right upper chamber (atrium). The sinus node sends electrical signals that typically start each heartbeat. These electrical signals move across the atria, causing the heart muscles to squeeze (contract) and pump blood into the ventricles.
Next, the signals arrive at a cluster of cells called the AV node, where they slow down. This slight delay allows the ventricles to fill with blood. When the electrical signals reach the ventricles, the chambers contract and pump blood to the lungs or to the rest of the body.
In a typical heart, this heart signaling process usually goes smoothly, resulting in a resting heart rate of 60 to 100 beats a minute.
PVCs are irregular contractions that start in the ventricles instead of the atria. The contractions usually beat sooner than the next expected heartbeat.
The cause of premature ventricular contractions isn't always clear. Certain things including heart diseases or changes in the body can make cells in the lower heart chambers electrically unstable. Heart disease or scarring may cause the heart's signals to be misrouted.
Premature ventricular contractions may be caused by:
- Certain medications, including decongestants and antihistamines
- Alcohol or drug misuse
- Stimulants such as caffeine or tobacco
- Increased levels of adrenaline in the body due to exercise or anxiety
- Injury to the heart muscle due to disease