Twin Twin Transfusion Syndrome

The receiver often has congestive heart failure. The donor often has hypertrophic heart failure. For the recipient, there is increased preload (volume) with an absolute increase in circulating volume compared to that of the donor, with significantly higher cardiac output. The recipient is also subjected to an increased afterload in the form of increased resistance. The renin-angiotensin system (RAS) is ‘downregulated’ in the recipient's kidneys, but work has shown that the levels are as high as in the donor; it is assumed that this is mainly due to transfer from the donor. All these factors explain the development of significant myocardial ventricular hypertrophy, out of proportion to simple volume overload. A consequence of this progressive cardiomyopathy is an increase in overall heart size, a reduction in myocardial compliance, atrioventricular valvar regurgitation, and abnormal venous Dopplers. RVOT anomalies in the recipient may be in the form of valvar dysplasia, stenosis, regurgitation, or functional atresia; early involvement of the RVOT may be demonstrated by observing that the pulmonary valve annulus is equal in size to or smaller than that of the aortic valve, and this can progress to produce significant valvar pathology. It is not clear whether RVOT anomalies mirror the severity of the TTTS process, or whether the anomalies are simply due to altered hemodynamics or are a consequence of the vasoactive mediators. The prevalence of RVOT anomalies varies in different series but may be seen in some form in up to 20% of MC/DA twins, but only in recipient twins; between 9 and 12.5% had persistent anomalies requiring postnatal treatment, in spite of otherwise successful treatment for the TTTS.