LONGITUDINAL-STUDY IN 18 CASES OF FETAL SUPRAVENTRICULAR TACHYCARDIA - DOPPLER ECHOCARDIOGRAPHIC FINDINGS AND PATHOPHYSIOLOGIC IMPLICATIONS

A longitudinal study was performed in nine nonhydropic and nine hydropic fetuses with supraventricular tachycardia (SVT). First, because of a lack of reference methods in utero, the validity of spatial (length and area) and temporal parameters for semiquantitative grading of atrioventricular (AV) valve regurgitation by color Doppler flow mapping and M-Q mode imaging was evaluated by a longitudinal intraindividual study before and after drug-induced cardioversion to sinus rhythm and by correlation with the severity of hydrops and the time required for complete remission of hydrops. Second, with the demonstration of AV valve incompetence and changes in venous blood flow velocity wave forms, new data were collected concerning chronic SVT in the fetus. AV valve incompetence occurred in eight fetuses: during SVT only in three severely hydropic fetuses, during sinus rhythm in one nonhydropic fetus, and in seven hydropic fetuses including those previously mentioned, where AV incompetence outlasted tachycardia. The length and area of the regurgitant jet as imaged by color Doppler flow mapping and the temporal duration of regurgitation in relation to the systolic phase as measured by M-0 mode continuously diminished intraindividually but with great interindividual differences in the time span required for complete remission, which ranged from 5 to 42 days. Pulsed-wave Doppler studies of blood flow in the inferior vena cava and left hepatic vein demonstrated normal biphasic forward flow with a systolic and a diastolic surge during sinus rhythm in all fetuses and in two instances also during SVT of 190 and 195 beats/min, respectively. In all cases a pulsatile reversal of blood flow with systolic forward flow and diastolic reverse flow was observed during tachycardia greater than 220 beats/min. Thus the presence of functional AV valve incompetence as a result of annular enlargement seems to be a sign of SVT-induced ''cardiomyopathy'' during fetal life. AV valve incompetence during SVT was always associated with extremely severe hydrops and seemed to indicate the most severe degree of ventricular dysfunction, which could influence the selection of antiarrhythmic drugs. After termination of SVT, severe AV valve insufficiencies also occurred in other cases of hydrops, probably because of the markedly increased diastolic filling distending the already enlarged annular ring. The observed great interindividual differences in time required for disappearance of AV valve incompetence and hydrops could be explained by a different state of progression of tachycardia-induced ''cardiomyopathy'' at the time of drug-induced cardioversion. These results confirmed the assumption that color Doppler-derived spatial parameters and the temporal duration of the regurgitant jet, as measured by M-Q mode imaging, are useful for semiquantification of functional regurgitation of AV valves prenatally.