Supraventricular tachycardia, SVT
Supraventricular techycardia (SVT) is a heart rhythm disorder with episodes of fast and regular heart beat. Episodes of SVT start and stop suddenly. The fast heart beat can last from seconds up to days. It may happen several times a day or only few times a year.
Normal heart rate in adults is about 60-90 beats per minute (bpm) at rest. In supraventricular tachycardia, heart rate is usually between 140-180 bpm and sometimes reaches up 250 bpm. Unlike in atrial fibrillation, the pulse is regular in SVT.
Mechanism and symptoms
Under normal circumstances, heart muscle contracts and ejects the blood into circulation, then relaxes, is filled with blood and the whole process is repeated.
Heart muscle contraction is so fast that the heart cannot relax during SVT and therefore the heart is running half-empty. This reduces the amount of blood pumped to the body, causes palpitations (awareness of unpleasant rapid pulse), breathlessness, dizziness and sometimes blackouts.
The abnormal electrical impulses, that make the heart beat fast in SVT, start in the top heart chambers and override normal heart rhythm. These impulses originate in short circuit and spread around heart. There is no obvious cause of SVT and the episodes of palpitations may occur randomly without obvious trigger but SVT is usually associated with exertion, emotional upset, and change in posture, coffee and alcohol. SVT may occur at any age but it is more common in young adults and children.
In most cases the episodes of SVT are harmless, last only short period of time terminate spontaneously without treatment. Treatment can be medication (e.g. beta-blockers and calcium antagonists) to slow or block spreading the abnormal electrical signals through the heart. Ultimate solution is EP (electrophysiological) ablation that breaks the abnormal circuit and permanently cures the arrhythmia.