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Baby's Heart Beats at Double the Normal Speed

Evaluating fussiness in a baby is tricky, but a heart rate of 220 is not ambiguous

By Mark Cohen
Aug 2, 2004 5:00 AMNov 12, 2019 6:16 AM


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When Molly brought her 2-month-old daughter, Kara, to see me one morning, one look told me something was wrong. I’d known Molly since the birth of her son, Kevin, about three years ago, and she is usually fairly relaxed and cheerful, even with a crying baby in tow. But this day her face was drawn, and her eyes looked worried.

The first line of the nurse’s brief note read, “Fussy, not eating well, no vomiting,” so I asked about the fussiness. Molly said Kara had been very fussy, but only for the past day. Evaluating fussiness in a baby can be tricky. It can signify a cold, an ear infection, or even meningitis. I quickly reviewed Kara’s short medical history: She had been a healthy full-term baby, and she had been doing well. But a couple of days ago, something changed. Molly said that even though Kara seemed hungry, she would only take a few swallows from her bottle and then stop, as if she were out of breath.

Kara’s temperature was normal, her color was good, and she was crying vigorously. All are signs of good health in a baby. Yet somehow she didn’t look well. The examination didn’t yield many clues. Her heart rate was fast, but crying could cause that. I did note that her liver was enlarged. The lower edge of the organ was about four centimeters below the rib cage, when it should have been even with the ribs.

The enlarged liver worried me, so I sent her to the hospital for an abdominal ultrasound. An hour later, the radiologist called: “The liver is big, but it looks OK otherwise. There’s some free fluid in the abdomen, but there’s also a pericardial effusion.” Now I was really concerned. The heart is encased in a membrane called the pericardium, and a pericardial effusion means that fluid has accumulated within the sac. Maybe Kara had a viral infection that was affecting both her heart and her liver. Such an infection can cause serious heart problems very quickly. I arranged for her to be admitted to the pediatric unit and drove over to the hospital. Because I was concerned about a possible myocarditis—a heart infection—I told the admitting nurse to start an IV and to put Kara on a heart monitor.

When I got to the unit, the nurse had just connected Kara to the monitor. She came out of Kara’s room, looking puzzled. “Dr. Cohen, the monitor says her heart rate is 220.” A heart rate of 220? Of course! All of a sudden, the clues fell into place.

When I listened to Kara’s heart, the rate was well over 200 beats per minute. She wasn’t crying now, so that couldn’t be contributing to the fast rate. Kara’s liver was OK—the problem was with her heart! Kara needed to see a pediatric cardiologist. I turned to the nurse. “Get an EKG and a portable chest X-ray and see if Dr. Wolf can come over right away. Tell him I have a 2-month-old with SVT and CHF.”

The EKG confirmed that Kara had SVT—supraventricular tachycardia. Sometime in the past few days, a “short circuit” in her heart’s electrical conduction system had suddenly caused the sinoatrial node—a cluster of cardiac cells that function as the heart’s pacemaker—to fire off impulses at 200 to 220 beats per minute, about twice the normal rate for a 2-month-old. Babies can tolerate this fast heart rate for longer than adults, but not for more than a few days. Kara appeared to be experiencing congestive heart failure, or CHF.

When the heart beats at high speeds for a long time, the heart muscle itself tires, and the heart can’t pump efficiently. Blood backs up in the capillaries and veins, and the increased pressure can cause fluid to leak out of capillaries and into many organs and tissues, including the abdomen, pericardium, liver, and lungs. We could already see fluid in Kara’s abdomen and pericardium on the ultrasound. Her liver was enlarged, and she had trouble breathing when she was feeding. Difficulty feeding due to shortness of breath is one of the most prominent symptoms of congestive heart failure in babies.

The chest X-ray confirmed that Kara had moderate CHF. She was still stable, but I knew that we had to slow her heart soon, before her condition deteriorated. When Dr. Wolf arrived, he and I reviewed the options for treatment. The first method surprised the nurses: He asked for an ice bag and placed it on Kara’s face. This maneuver can slow the heart rate by stimulating what is known as the diving reflex. This response was first noted in seals, whose heart rate is slowed when they dive in cold water. The cold acts on the vagus nerve, which is part of the autonomic, or involuntary, nervous system, and the slowed heart rate allows seals to remain underwater longer on their dives. As a medical treatment, stimulating the vagus nerve with cold is a way of overriding the abnormal activity of the pacemaker and resetting it to its normal rate. Unfortunately, the ice treatment didn’t slow Kara’s heart—and she didn’t like it one bit.

Next, Dr. Wolf used a defibrillator to apply an electric shock to the heart. Unlike the massive jolt you’ve seen in TV medical dramas, the one he administered was a low-intensity impulse, synchronized to occur at just the right point in her heartbeat to allow the heart’s pacemaker cells to reset. We all sighed with relief when her heart immediately reverted to a normal rhythm of about 100 beats per minute. Half a minute later, however, the rate jumped back up to 220. Two more shocks produced the same result. Finally, Dr. Wolf gave Kara an intravenous dose of adenosine, a medication that blocks the abnormal signal that causes the pacemaker to race. The drug is effective for only a few seconds before the body breaks it down, but one dose was enough. Kara’s heart reverted to a normal rhythm and stayed there.

We monitored Kara’s heart rate closely and transferred her by ambulance to the children’s hospital. But a careful evaluation failed to pinpoint the location of the short circuit that had led to her racing heart. To prevent a recurrence, Kara was started on oral digoxin. The medication is closely related to digitalis, the drug extracted from the purple foxglove plant, which has been used to treat cardiac conditions since the late 18th century. Within a few days, Kara went home.

So far, the digoxin has worked for Kara. Her heart rate—along with her growth and development—has remained normal for the past few months. She will continue on the medication for a year or two and then have a trial without it. If the problem does not return, as is often the case for infants, then she will no longer need the medication. But if Kara’s symptoms recur, her heart probably has an abnormal conduction pathway, and she will need to remain on digoxin until she is 5 or 6. At that time, a technique called radio-frequency ablation would be used to eliminate the problematic pathway. First, a cardiologist uses catheters to identify the malfunctioning cardiac tissue; the next step is to use a catheter tipped with a laser or a radio-frequency transmitter to destroy it. For now, though, Kara’s family is happy to take things one day at a time.

Mark Cohen is a pediatrician in Honolulu. The cases described in Vital Signs

are true stories, but the authors have changed some details

about the patients to protect their privacy.

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