When the heart suddenly starts racing

You expect your heartbeat to accelerate if you're exercising or feeling extremely anxious. But in a small number of people, an electrical glitch in the heart's upper chamber causes their heart rate to suddenly soar for no apparent reason—sometimes as high as 200 beats per minute.

Called paroxysmal supraventricular tachycardia (PSVT), the condition is usually not dangerous (see "What is paroxysmal supraventricular tachycardia?"). "People often describe the symptoms as palpitations or a fluttering sensation in the chest," says Dr. Paul Zei, director of the Comprehensive Atrial Fibrillation Program at Harvard-affiliated Brigham and Women's Hospital. While these episodes typically appear out of the blue, exercise, stress, or certain foods and drugs (such as caffeine or other stimulants) sometimes trigger an episode. For some people, bending over at the waist can set off PSVT, he says.

The frequency and duration of the episodes varies widely. Some people have a bout just once every few years, while others have them several times a day. The episode may last just a few seconds or minutes. Others last for hours or, in rare cases, even days. These rapid-fire beats mean the ventricles don't have time to fill before the heart contracts. As a result, blood flow to the brain and body may drop, causing symptoms such as lightheadedness, breathlessness, and fainting, says Dr. Zei.

How is PSVT diagnosed?

Fewer than about three in every 1,000 people have PSVT. It occurs in people of all ages, from babies to older adults, but half of all cases are in people ages 50 to 64. Women account for just over two-thirds of all cases.

Because a fast heartbeat and breathlessness are also common symptoms of anxiety, primary care doctors (who often aren't familiar with PSVT) may misdiagnose the problem as anxiety, especially in women, Dr. Zei says. An accurate diagnosis requires an electrocardiogram (ECG), a recording of the heart's electrical signature, at the time symptoms occur. Because the episodes don't last long, the heartbeat has usually returned to its normal rate by the time a person seeks medical attention. As a result, people with suspected PSVT usually need to wear a small ECG monitor on their chest for several days or weeks to confirm the diagnosis. Using a smartwatch or other device that can record an ECG is another option. "If a specialist examines the data, these readings can be quite accurate for diagnosing PSVT," says Dr. Zei.

Treatment options

People with bothersome symptoms can try a handful of simple tricks that stimulate the vagus nerve, which helps slow the conduction of electrical impulses through the heart and may resolve the tachycardia. They include

• coughing or gagging
• putting an ice-cold, wet towel on your face
• pressing gently on your closed eyes
• holding your breath while bearing down as if for a bowel movement.

The most effective technique, the modified Valsalva maneuver, involves sitting upright while blowing into a straw or small tube for 15 seconds. Next, you lie flat on your back and raise your legs to a 45° angle with another person supporting your legs for another 15 seconds. But if these methods don't work, people with persistent tachycardia usually need to go to urgent care or the emergency room to receive an injection or infusion of medication to return the heart to a normal beat. A nasal spray containing the experimental drug etripamil for treating PSVT is currently under FDA review.

Zapping away the problem

People with frequent, bothersome symptoms may want to consider catheter ablation, a short procedure done under mild sedation (meaning you're awake but relaxed and pain-free). After a doctor threads a catheter through a vein up to the heart, a zap of radiofrequency energy emitted from a device inside the catheter destroys the small area of tissue causing the errant electrical signal. For PSVT, catheter ablation has a 98% success rate and is quite safe. "It's one of the few cardiac procedures for which we can almost always tell patients they've been cured, and the problem won't ever occur again," says Dr. Zei. As with any procedure, make sure you understand all the pros and cons beforehand.