(See also Overview of Abnormal Heart Rhythms.)
Paroxysmal supraventricular tachycardia is most common among young people and is more unpleasant than dangerous. It may occur during vigorous exercise.
Paroxysmal supraventricular tachycardia may be triggered by a premature heartbeat that repeatedly activates the heart at a fast rate. This repeated, rapid activation may be caused by several abnormalities. There may be two electrical pathways in the atrioventricular node (an abnormal heart rhythm [arrhythmia] called atrioventricular nodal reentrant supraventricular tachycardia). There may be an abnormal electrical pathway between the atria and the ventricles (an arrhythmia called atrioventricular reciprocating supraventricular tachycardia). Much less commonly, the atria may generate abnormal rapid or circling impulses (an arrhythmia called true paroxysmal atrial tachycardia).
The fast heart rate tends to begin and end suddenly and may last from a few minutes to many hours. It is almost always experienced as an uncomfortable awareness of the heartbeat, such as feeling like the heart is pounding or racing (palpitations). It is often associated with other symptoms, such as weakness, light-headedness, shortness of breath, and chest pain. Usually, the heart is otherwise normal.
The doctor confirms the diagnosis by doing electrocardiography (ECG).
Episodes of paroxysmal supraventricular tachycardia often can be stopped by one of several maneuvers that stimulate the vagus nerve and thus decrease the heart rate. These maneuvers are usually conducted or supervised by a doctor, but people who repeatedly experience the arrhythmia often learn to do the maneuvers themselves. Maneuvers include
These maneuvers are most effective when they are used shortly after the arrhythmia starts.
If these maneuvers are not effective, if the arrhythmia causes severe symptoms, or if the episode lasts more than 20 minutes, people are advised to seek medical intervention to stop the episode. Doctors can usually stop an episode promptly by giving an intravenous injection of a drug, usually adenosine or verapamil. Rarely, drugs are ineffective, and cardioversion (delivery of an electrical shock to the heart) may be necessary.
Prevention is more difficult than treatment. When episodes are frequent or bothersome, doctors usually recommend catheter ablation. For this procedure, energy that has a specific frequency or cold is delivered through a catheter inserted in the heart. This energy or cold temperature destroys the tissue in which paroxysmal supraventricular tachycardia originates.
If catheter ablation is not an option, almost any antiarrhythmic drug may be effective. Drugs commonly used include beta-blockers, digoxin, diltiazem, verapamil, propafenone, and flecainide (see table Some Drugs Used to Treat Arrhythmias).