Nov. 27, 2019
Mechanics of supraventricular tachycardia
Supraventricular tachycardia is an abnormally fast heartbeat, sometimes as much as 300 beats a minute. It occurs when faulty electrical connections in the heart set off a series of early and abnormal impulses in the atria. It can successfully be managed by both short-term medical therapy and long-term approaches such as ablation.
Supraventricular tachycardia is an uncommon heart rhythm disturbance affecting approximately 1 in 750 young pediatric patients. Characterized by an anomalously rapid heartbeat, the condition sometimes results in the heart beating as fast as 300 beats a minute. Patients may even lose consciousness.
The condition is typically not dangerous or life-threatening. But its symptoms are distressing — often prompting a visit to the emergency room — and can severely affect a patient's quality of life and family lifestyle, according to Bryan C. Cannon, M.D., a pediatric cardiologist at Mayo Clinic's campus in Rochester, Minnesota.
Advances in technology have helped improve outcomes. Dr. Cannon explains: "We now have around a 98% chance of permanently curing this condition and typically have patients back to full activities including competitive sports within a week."
Dr. Cannon recently finished serving his first term as president of the Pediatric and Congenital Electrophysiology Society (PACES), the primary international organization for pediatric electrophysiologists, and is a co-author of the expert consensus statement on the use of catheter ablation in children and patients with congenital heart disease. These guidelines were accepted internationally in 2016 as a consensus statement from the Heart Rhythm Society, PACES, American Academy of Pediatrics, Association for European Pediatric and Congenital Cardiology, and American Heart Association; the guidelines were published in the June 2016 issue of Heart Rhythm. A 2019 Heart Rhythm article Dr. Cannon co-authored focuses on device needs. This broad expertise and experience leads him to highly value multidisciplinary collaborations to manage supraventricular tachycardia.
"When pediatric patients experience extremely rapid heartbeats — and have palpitations, and in certain cases, even pass out — it can be extremely concerning to children, parents, and health care providers," says Dr. Cannon. "A multispecialty team brings the medical depth and breadth needed for correct diagnosis and presentation of both short-term and long-term treatment options for supraventricular tachycardia to not only stabilize and improve the child's health, but also to bring peace of mind to all involved."
In the pathophysiology of supraventricular tachycardia, an extra fiber, called an accessory pathway, connects the lower and upper chambers. In a normal heart, the impulse for a beat starts in the sinus node and signals an upper chamber to contract and squeeze blood into the lower pumping chambers. A single normal connecting fiber, the atrioventricular node, transmits the signal to the bottom pumping chambers of the heart.
But in patients who have an accessory pathway, occasionally a heartbeat travels down the atrioventricular node and then up the accessory pathway, which sets up a circuit of very fast heart beats called supraventricular tachycardia. The result: extremely rapid heartbeats, palpitations, dizziness and occasional loss of consciousness.
Patients who experience very brief or infrequent bouts of supraventricular tachycardia may not require therapy and can continue to thrive and grow with regular checkups and medical vigilance. However, intervention is indicated if a child experiences regular, frequent and symptomatic bouts of rapid heartbeats, or has longer episodes. Basic intervention options available consist of medical therapy and ablation therapy.
The goal of medical therapy is to reduce the chances that a circuit of supraventricular tachycardia will initiate. Medications to control this have been used for approximately 30 years, and data show they are safe and effective for children. "But the medication route is temporary," Dr. Cannon explains. "It provides a temporary fix. The majority of patients who have supraventricular tachycardia don't resolve spontaneously, especially older children." The other option, the ablation procedure, can potentially cure the tachycardia.
Cardiac ablation can correct arrhythmias by destroying the abnormal fiber in the heart that triggers or sustains an abnormal heart rhythm. In some cases, cardiac ablation prevents abnormal electrical signals from affecting the heart and in this way prevents arrhythmia from developing. This approach consists of an electrophysiology study and an ablation procedure.
First, small, specialized catheters are inserted into the patient's legs to evaluate electrical signals of the heart, enabling physicians to detect the cause of a child's tachycardia. Once the cause is identified, it is corrected with another specialized catheter that can deliver hot or cold energy to destroy the abnormal fiber. This can be done in conjunction with the electrophysiology study and typically takes around three to four hours. "What we found from studies is that the risks of this procedure are not increased once the patient is over age 5. This means that in a child over 5, there's no advantage — as far as safety or efficacy — of waiting to do the procedure," Dr. Cannon says.
Data show that in children less than age 5, the risks may be higher. Because of this, the Mayo Clinic team reserves the ablation procedure for children who are extremely sick or potentially have a problem with the way their hearts squeeze. "In the current era, we can do this procedure with around a 95% to 98% success rate and a less than 1% incidence of complications," Dr. Cannon says.
Long-term studies show positive outcomes. There have been no data to suggest that there's an increased incidence of long-term effects after the ablation procedure. "The nice thing about this procedure is, if it's successful, then it's a permanent cure," Dr. Cannon says. "This means your child won't have to worry about his or her fast heartbeats, symptoms or other things that can occur. With today's technology we can do this very safely, and we have specific techniques to improve the safety and efficacy. In many cases, the child is back to school in two days and back to all activities within a week."
In addition to Mayo Clinic's strong record of positive outcomes with ablation, Dr. Cannon emphasizes another safety aspect of the Mayo team's approach: The combination of advanced expertise and deep experience offer the potential of doing this procedure without any radiation exposure.
Says Dr. Cannon: "There are some situations where we can do this completely without exposing the child to any radiation. We can still do this safely and effectively, and we have all the tools and equipment necessary to perform this procedure safely." Having performed about 1,500 of these procedures, Dr. Cannon is confident in the safety and efficacy and potential long-term cure. "Supraventricular tachycardia is one of the few cardiac conditions that we can completely cure, so it is very rewarding to be able to give patients a completely normal, long, healthy life."
For more information
Saul JP et al. PACES/HRS expert consensus statement on the use of catheter ablation in children and patients with congenital heart disease. Heart Rhythm. 2016;13:e251.
Dubin AM et al. Pediatric and congenital electrophysiology society initiative on device needs in pediatric electrophysiology. Heart Rhythm. 2019;16:493.