Types of Tachycardia
When an abnormal heartbeat creates a faster-than-normal heart rate, it is called tachycardia. (A bradycardia is a slower than normal heartbeat.) Tachycardias have different names depending on where the abnormal signal is started.
Ventricular tachycardia is a fast heartbeat—anything over the normal 100 beats per minute—which starts in the lower chambers of the heart, the ventricles. It causes the ventricles to contract before they have had a chance to completely fill with blood, impairing blood flow to the body.
Ventricular tachycardia occurs in people with underlying heart abnormalities. In those who have had a heart attack, for example, the scar tissue from the heart attack causes irregular electrical pathways. The alternate pathways can create abnormal electrical conduction within the heart, and thus initiate the tachycardia.
This is a serious disorder and requires prompt treatment. It poses a serious danger in that it may evolve into the more serious, life-threatening condition, ventricular tachycardia. This condition is where the ventricles quiver, pumping very little blood out of the heart. Ventricular fibrillation is the primary cause of sudden cardiac death. Death could result if normal heart rhythm is not restored within 3–5 minutes.
Cardiac ablation is increasingly being used to interrupt the abnormal pathways that cause ventricular tachycardia. With current technology, an electrophysiologist (a cardiologist that specializes in the treatment of arrhythmias) can accurately locate the irregular pathway causing the ventricular tachycardias, thus enabling the physician to eliminate the abnormal signals causing the tachycardia.
Supraventricular Tachycardia (SVT)
Supraventricular tachycardia (SVT), also referred to as atrial tachycardia, is a general name for arrhythmias that start above the ventricles. It is sometimes called paroxysmal supraventricular tachycardia (PSVT) because it occurs intermittently, or from time to time.
SVTs usually begin and end suddenly, and at times an episode can last anywhere from seconds to hours. The SVT may cause the heart to beat 160–200 times per minute.
SVTs are generally not life-threatening, unless there is an additional existing heart problem. Symptoms can vary in severity, and the more severe forms may require treatment with medications or cardiac ablation.
AV Nodal Re-entrant Tachycardia (AVNRT)
This type of abnormal rhythm arises from malfunctioning of the atrial ventricular (AV) node. In most people, the AV node conducts impulses along a single pathway. In AVNRT, a second conducting pathway arises, confusing the electrical signals traveling from atria to ventricles. As a result, both the atria and ventricles beat at the same time instead of in sequence. This creates a fast heart rate—120–250 beats per minute. Although the heartbeat is typically regular, rather than erratic, the heart is not pumping efficiently. Most AVNRT patients do not have underlying heart disease.
More information on the different types of arrhythmias can be found on the following pages: