Malfunctioning electrical impulses between the upper and lower chambers of the heart cause supraventricular tachycardia, abbreviated as SVT, states Pediatric Heart Specialists. About three in 1,000 children have extra conducting tissue in the heart, called an accessory pathway, which can spontaneously transmit electrical impulses that cause the heart to beat faster. An episode of supraventricular tachycardia usually occurs randomly, without advance warning.
Electrical impulses that travel along a nerve path, called the AV node, create a normal, rhythmic heartbeat, explains Pediatric Heart Specialists. When supraventricular tachycardia occurs, heart rates in infants reach 250 to 300 beats per minute, while young children experience rates of 200-250 beats per minute. Attacks last from a few seconds to a few days, and symptoms include dizziness and complaints of a racing heart. It is rarely a life-threatening occurrence, notes Pediatric Heart Specialists.
Supraventricular tachycardia diagnosis requires the use of electrocardiograms and portable devices called event monitors, which record heart rhythms, states Pediatric Heart Specialists. An effective breathing technique, called a valsalva maneuver, requires squatting or blowing into a blocked straw in order to increase pressure in the chest and reduce symptoms. For frequent or extreme episodes, doctors prescribe beta-blocker medication to retard electrical conduction in the heart. These drugs typically do not cause side effects, and they are 75 to 90 percent effective. Alternatively, a surgical procedure called ablation can permanently destroy the accessory pathway.