What are premature ventricular contractions (PVCs)?
Premature ventricular contractions (PVCs) are premature heartbeats originating from the ventricles of the heart. Premature ventricular contractions are premature because they occur before the regular heartbeat.
Normal function of the heart
The heart has four chambers. The upper two chambers are the atria, and the lower two chambers are the ventricles.
- The atria deliver blood to the ventricles, and the ventricles deliver blood to the lungs and to the rest of the body.
- The right ventricle delivers blood to the lungs while the left ventricle delivers blood to the rest of the body.
- The heartbeat (pulse) that we feel is caused by the contraction of the ventricles.
The heartbeat is normally controlled by the electrical system of the heart. The electrical system of the heart consists of the sinoatrial (SA) node, the atrioventricular (AV) node and special tissues in the ventricles that conduct electricity.
The SA node is the heart's electrical pacemaker. It is a small patch of cells located in the wall of the right atrium; the frequency with which the SA node discharges electricity determines the rate at which the heart normally beats. The SA node keeps the heart beating in a regular manner. At rest, the frequency of the electrical discharges originating from the SA node is low, and the heart beats at the lower range of normal (60 to 80 beats/minute). During exercise or excitement, the frequency of discharges from the SA node increases, increasing the rate at which the heart beats. In people who exercise regularly, the resting heart rate may be below 50 to 60 and is not of concern.
The electrical discharges pass from the SA node through the special tissues of the atria into the AV node and through the AV node to the special conduction tissues of the ventricles, causing them to contract.