Intermittent Fetal Arrhythmia
Synopsis: Intermittent fetal tachyarrythmias may be associated with a significant risk of perinatal death. Maternal antiarrythmic therapy is often indicated.
Source: Simpson JM, et al. Outcome of intermittent tachyarrythmias in the fetus. Pediatr Cardiol 1997;18:78-82.
A total of 28 fetuses with intermittent tachyarrythmias were evaluated over a 12-year period at Guy’s Hospital in London. Twenty-four of these were supraventricular tachycardia. At the time of presentation, 14 fetuses (50%) were already hydropic, and in four of these the arrhythmia had not been noted prior to referral. The mothers of 23 fetuses were treated with cardiac drugs, chiefly digoxin and flecainide. Control of fetal arrhythmia was achieved in 10 of 11 non-hydropic fetuses (91%) and eight of 12 of hydropic fetuses (60%). The arrhythmia recurred postnatally in 11/23 (48%) of affected fetuses. Because intermittent tachyarrythmias (like persistent fetal tachycardias) may have a deleterious effect on the fetus with a significant result of perinatal death, maternal treatment may be indicated. A fetus determined to have non-immunologic hydrops fetalis by ultrasound examination should be evaluated for a cardiac cause.
COMMENT BY ALAN FRIEDMAN, MD
Fetal cardiac arrhythmias represent a common reason for referral to the fetal cardiologist. By far the most common diagnosed arrhythmia in the fetus is the isolated extrasystolethe majority of which are supraventricular. Isolated extrasystole generally are benign with stable fetal hemodynamics, but a small minority of affected fetuses (0.5%) develop supraventricular tachycardia. Fetal tachycardias are relatively uncommon. They accounted for 174 of the 1384 cases (13%) referred to the Yale Fetal Cardiovascular Center for "fetal arrhythmia." The most commonly encountered sustained fetal tachy-arrythmias are supraventricular tachycardia and atrial flutter. These sustained arrhythmias can lead to abnormal fetal hemodynamics and fetal hydrops fetalis. Hydrops fetalis is a prenatal manifestation of severe congestive heart failure and carries a poor prognosis.
Simpson and colleagues report their experience with intermittent fetal tachyarrhythmias, where the tachy-arrhythmia was interspersed with periods of normal sinus rhythm. Fetuses with intermittent tachyarrhythmias had arrhythmia types similar to those found in sustained tacharrythmiasnamely, supraventricular tachycardia with fewer cases of atrial flutter. Hydrops was common, occurring in 14 of 28 fetuses. In fact, five of 28 fetuses were referred for hydrops and were only found to have intermittent tachyarrhythmia at the time of fetal echocardiography.
Simpson et al treated all cases of intermittent tachycardia with maternal administration of antiarrhythmics. Their success rate was impressive. All but one of the non-hydropic fetuses converted to sinus rhythm. Control of the arrhythmia was achieved in eight of 12 hydropic fetuses, with four of them demonstrating resolution of hydrops. All four deaths occurred in fetuses who had hydrops at presentation.
The management of fetal tachyarrhythmias usually relies upon transplacental transfer of medications administered to the mother. As a result, there is risk for the mother. Management of fetal arrhythmia requires an understanding of the natural history of the underlying arrhythmia, its electrophysiologic mechanism, its potential to lead to hydrops, and an understanding of the pharmacokinetics of the antiarrhythmic agents both in fetus and mother. With these issues in mind, a risk and benefit analysisboth for the fetus and motherand an appropriate management plan can be instituted. When fetal tachyarrhythmias are associated with hydrops, the risk of fetal death is high, and the benefits of in utero therapy often outweigh the risks. Some physicians treat all fetal tachyarrhythmias, even in the absence of hydrops. Others use a conservative approach with monitoring of the fetus with serial echocardiography, using pharmacologic therapy only if the fetus develops hydrops. It is imperative to recognize that there is no "cookbook" answer for the management of fetal arrhythmias. (Dr. Friedman is Assistant Professor of Pediatrics and Director of the Pediatric Echocardiography Laboratory at Yale University School of Medicine.)
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