Premature Ventricular Contractions
Premature ventricular contractions (PVCs) are early or extra heartbeats that commonly occur and are usually harmless in normal hearts, but can cause problems in hearts with pre-existing disease.
Abnormally fast heart rates are classified into two types: supraventricular (meaning "above the ventricle") tachycardias, those that arise in the atria (plural of atrium) or the atrioventricular node, and ventricular tachycardias.
In both instances, an extra or early beat may trigger the rapid rhythms. Although the sinus node develops as the specialized site of impulse production, all cardiac muscle cells retain the capacity to become pacemaker cells.
Normally, the pacemaking activity of the sinus mode suppresses impulse production by other cells, but if conductance to some other part of the heart muscle is blocked, or if the heart is over stimulated, islands of cells may express their latent impulse-production ability, resulting in extra beats. In other words, impulses are fired from one or more locations in addition to the normal pacemaker, the sinus node.
Extra or early beats arising in the atria are called premature atrial contractions (PACs), atrial premature beats, atrial ectopic beats, or atrial extrasystoles. Such extra beats often occur in normal hearts and are usually harmless. They can, however, cause palpitations, as well as trigger supraventricular tachycardias. Many of these episodes are not serious and can easily be treated.
PVC's can occur in healthy, normal hearts. They are also sometimes a sign of underlying cardiac disease such as coronary artery disease, cardiomyopathy (diseased muscle tissue), or other heart problems. PVCs can also be caused by abnormalities in body chemistry, drugs or thyroid disease.
A person with PVCs may or may not sense the irregular beat, usually as a skipped beat.
Continuous electrocardiographic monitoring, especially during exercise, may reveal more frequent and complex PVCs than occur during a single routine electrocardiogram (EKG). This involves wearing a heart monitor for a period of time from several days to a few weeks while performing normal work or home activities. If episodes occur, the monitor records what has happened and can transmit electronically the information to be interpreted.
If there are frequent PVCs, the physician may order tests to rule out thyroid disease (hyperthyroidism), abnormalities in blood chemistries (potassium and magnesium), as well as rule out heart disease.
In general, if the patient is asymptomatic and has no associated cardiac disease, no therapy is indicated. If they are frequent or symptomatic, medication and other treatment will be recommended.
Drug treatment is aimed at suppressing premature ventricular contractions (PVCs) in order to prevent serious ventricular arrhythmias and to reduce the risk of sudden death.
Other developments include electrophysiology studies and treatment programs that combine drug therapy with surgery and antiarrhythmic devices, such as implantable defibrillators.
Another option for treating life-threatening ventricular arrhythmias may be the automatic cardioverter-defibrillator (AICD). Unlike other types of treatment, this does not prevent arrhythmias but instead stops them within seconds.