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PEDIATRIC PERSPECTIVE

Fainting spell shows medicine's uncertainties

The teenager fainted so suddenly she cut her head on a table as she fell. I wrote a letter saying she could return to high school, but I wasn't able to promise what the school really wanted: that she wouldn't suddenly drop dead.

Though few doctors admit this openly, medicine is a statistical gamble. By examining a patient and performing tests, a doctor can determine whether a diagnosis is likely or unlikely, but almost never can he or she be sure. This is true for everything from ear infections to attention deficit disorder, but it is especially problematic for possible sudden death.

The previously healthy teen had come to the pediatric cardiology clinic because she'd begun fainting, which can be caused by lots of things, including potentially fatal heart problems.

Similar to a computer's ''power save" mode, the brain, when starved for oxygen, can shut down all nonessential functions -- a reflex that prevents the buildup of dangerous acids that cause permanent damage. Since oxygen is carried by blood cells, which in turn are pumped by the heart, the fainting spells could indicate heart trouble.

A heartbeat is caused by cardiac nerves forcefully pumping out charged atoms of calcium; about once a second, the atoms suddenly crash back into the nerve -- and the resulting electrical current makes the heart muscle beat. In a normal lifetime, this particle shuffle occurs uneventfully almost 3 billion times, and the heart pumps enough blood to fill several supertankers. Yet, somewhat terrifyingly, the system is delicate.

A Globe article from Christmas 2003 provides one example: Twin brothers from Melrose were horsing around, and one nudged the other in the chest. This glancing blow thumped the sibling's heart at precisely the wrong moment in the ion shuffle, just after the current discharged.

Suddenly, instead of beating in orderly waves, the teenager's heart experienced a mutiny. Sections began contracting and relaxing randomly. Thankfully, paramedics and a next-door neighbor -- an off-duty firefighter -- helped resuscitate the boy, and he survived. (Preventing this problem, called ''commotio cordis," is the reason advocates have lobbied for chest protectors and softer balls in some sports.)

My patient's fainting spell might have been caused by the same sort of rhythm problem, which can also be triggered by an underlying genetic heart disorder.

These rhythm problems are bizarre; in one form of a condition called long QT syndrome, patients can unexpectedly get cardiac arrest in response to hearing an alarm clock. In another variant, some patients die suddenly when immersed in water, as when swimming. Some Italian researchers recently speculated that this hard-to-detect syndrome, which is a genetic defect in the atom pumps in heart cells, is an important cause of sudden infant death syndrome in apparently healthy babies. On the other hand, my patient (whose mother gave me permission to tell her story but asked me not to name her) could merely have ''neurocardiogenic syncope," an annoying but harmless condition in which stress or changes in body position confuse the heart for very brief periods of time, causing light-headedness and occasional fainting. The cause is unknown.

Because the teenager's fainting spells were so worrisome and because she had a relative with a genetic heart rhythm disturbance, she was hospitalized for further testing. Among other tests, we recorded her heartbeat for a full day, assessed her cardiac rhythm when she ran on a treadmill, and took ultrasound pictures of her heart. The tests showed no troubles at all.

Deciding whether a child's heartbeat is normal is like the airport screening problem. To prevent hijacking, an airport screening must examine every piece of luggage for any dangerous item, since even a single miss could be catastrophic. This is extraordinarily tough, since the ''signal" (that is, number of weapons smuggled) is so low compared to ''noise" (that is, all the items that resemble weapons but aren't). Similarly, screening millions of heartbeats for suspicious activity is complicated, and we could have missed something.

In the end, therefore, all of the negative tests still don't exclude a serious cardiac rhythm; they only make it unlikely. From time to time, just as a suspicious package makes it past an airport screener, a severe heart problem eludes detection.

One way to guarantee the safety of every heartbeat is to implant a cardiac defibrillator, a box that senses abnormal heart rhythms and shocks the heart automatically if fibrillation occurs. The Melrose boy got one after his brush with death, according to the news story.

But it doesn't make either medical or financial sense to implant one in every child who faints -- especially in those who might not even have a heart problem. According to a 2003 New England Journal of Medicine review of several studies of the device, roughly 9 in 10 patients with proven episodes of life-threatening heart rhythms don't live longer after getting a defibrillator. And implanting one can cause complications like infections and bleeding.

In the end, I explained to the teen's family that the testing made a serious rhythm problem highly unlikely, though not impossible, but that implanting a defibrillator was probably not worthwhile.

Despite prolonged testing to the limits of medical science, some things remain unknowable. We're forced to choose an arbitrary level of doubt and simply hope for the best. It's reminiscent of the Greek myth of Damocles, a courtier who became a king only to find a sword suspended over his throne by a fragile strand of horse-hair. Much like the teenager whose heart may or may not fibrillate, Damocles needed to accept the chance that the sword could fall.

In last month's New England Journal of Medicine, Dr. Sandeep Jauhar of Long Island Jewish Medical Center argued that modern medicine is increasingly defined by the need to eliminate any uncertainty. That's why, for example, doctors rely less on talking to and examining patients and more on doing complicated tests that may give more precise information.

Precision is an admirable goal. Yet, as my patient's case demonstrates, even the fanciest testing can't eliminate uncertainty, which is why a great challenge in medicine -- for both doctor and patient -- is learning to communicate and accept uncertainty.

Dr. Darshak Sanghavi can be reached at www.darshaksanghavi.com.  

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