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Fetal cardiac arrhythmia: new diagnostic options. (Magnetocardiography, Pulsed Doppler).

NEW YORK -- M-mode echocardiography, pulsed Doppler, and fetal magnetocardiography have the potential to revolutionize diagnosis of fetal cardiac arrhythmias, but like many advances in diagnostic technology they will likely leave clinicians wondering what to do about what they discover.

Though they are based on different technology, both M-mode echocardiography and the newer magnetocardiography allow for precise monitoring of atrial, ventriculer, and septal wall activity making it possible to get a far more accurate sense of what is happening in the fetal heart, Dr. Charles Kleinman explained at an ob.gyn. symposium sponsored by Columbia University and Sloane Hospital for Women.

But the treatment of fetal arrhythmias is complex, since it involves giving a pregnant woman antiarrhythmic drugs. There is a lack of consensus on the indications for treatment.

Fetal arrhythmias are defined as any irregularity of fetal heart rhythm or any regular rhythm outside of the range of 100160 beats/minute, said Dr. Kleinman, professor of clinical pediatrics in obstetrics and gynecology at Columbia University New York.

Hemodynamically significant fetal arrhythmias are hardly commonplace, but they aren't rare. The largest study of the scope of the problem was published in 2000 and based on evaluation of 4,838 fetuses at a Yale University clinic between 1988 and 1997. Of these, 12% were referred for evaluation of arrhythmias. The investigators found 55% were in sinus rhythm and 43% had isolated extrasystoles. Ten had hemodynamically significant problems, and of these nine survived. Two of the 10 fetuses had cardiac structural abnormalities.

Dr. Kleinman stressed that a rhythm disturbance is by no means an absolute indication that there is a structural abnormality and in the majority of cases, an irregular rhythm is intermittent or resolves spontaneously.

Sustained fetal arrhythmias tend to be atrial. "We seldom see ventricular tachycardia in a fetus," he said.

Doppler evaluation has been the primary technology in diagnosing fetal arrhythmias. All Doppler-related techniques detect the mechanical consequences of electrical activity in the fetal heart.

Dr. Kleinman has found M-mode echocardiography to be particularly valuable since it traces cardiac chamber motion over time and permits detailed plotting of atrial versus ventricular activation in real time. It is possible to see the relationship--or in some cases, the lack thereof--between the atria and the ventricles.

In the case of a fetus with atrial flutter, a common fetal arrhythmia, M-mode will clearly show the accelerated atrial activity relative to the ventrides.

In some cases, fetal heart rate will not change with fetal activity; it remains in a more or less permanent, monotonous state of tachycardia. In these cases, M-mode echocardiography provides much information about the real-time relationships between the chamber walls that would be missed with external fetal heart rate monitoring.

Another novel technique, called Doppler tissue imaging, allows clinicians to actually follow the passage of the electrical impulse through the heart. But the technique that seems to be generating the most excitement these days is fetal magnetocardiography which detects minute perturbations in the magnetic field of the mother's abdomen. These perturbations are reflective of fetal cardiac activity and various arrhythmias cause very characteristic patterns of magnetic perturbation. Dr. Kleinman described a case in which the fetus turned out to have Wolff-Parkinson-White syndrome. Magnetocardiography allowed investigators to precisely track the onset of tachycardia and detect the mistimed atrial beats.

"Magnetocardiography is becoming more popular. But the problem is it can take roughly 8 hours to do a magnetocardiogram, and it requires a magnetically shielded room, similar to the type of room used in MRI. But this is a first step toward a true fetal electrocardiogram," he noted.

Dr. Kleinman said there's little agreement about which arrhythmias need treatment. In 1997, two independent research teams came to diametrically opposite conclusions regarding the impact of supraven-tricular tachycardia on birth outcomes. One group reported that intermittent tachyarrhythmias have "a deleterious effect on the fetus with a significant risk of death pre- or postnatally" and called for broader use of maternal antiarrhythmic drugs.

The second group reported that spontaneous resolution of supraventricular tachyarrhythmias is common and that close monitoring without therapy is usually sufficient.

In Dr. Kleinman's experience, it is the fetuses with incessant arrhythmias--the ones who do not fluctuate between normal sinus rhythm and a supraventricular tachycardia--that are at greater risk. But he stressed that treatment decisions need to be considered carefully.

Part of the problem is that there are very few good studies of intrauterine antiar-rhythmic therapy. He cited one study of 51 fetuses, including 33 with supraventricular tachycardia, 15 with atrial fibrillation, and 2 with ventricular tachycardia. Twenty-two of the fetuses had hydrops. Thirty-four of the fetuses, including all of those with hydrops, were treated via maternal digox-in dosing. The treatment resulted in successful in utero conversion to normal sinus rhythm in 82% of the cases, including 80% of those with fetal hydrops. There were a total of three fetal deaths in this cohort.

Digoxin is definitely his first-choice drug for managing fetal supraventricular tachycardia.

"It won't cause sudden fetal problems, so you can IV load the mother and see if the fetus remains in tachycardia. If the tachycardia breaks, that is great, and you can stick with digoxin. If not, you add propranolol," said Dr. Kleinman.

If the digoxin/propranolol combination still does not work, stop them both and consider the use of third-line medications such as flecainide or sotalol. "We don't add amiodarone unless we are really, really desperate. That drug has a half-life of several weeks," he pointed out.
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Author:Goldman, Erik L.
Publication:OB GYN News
Date:Jun 1, 2003
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