www.thefetus.net/

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Department of Obstetrics and Gynecology of Santa Casa Charity Hospital, Belo Horizonte, Minas Gerais, Brazil. Av. Francisco Sales 1800, Belo Horizonte, MG –Brazil.

Synonyms: TRAP sequence, acardia anomaly, hemiacardius (imperfectly formed heart), holoacardius (absence of heart), acardiac acephalus, acardius amorphous, acadius acormus, acardius anceps, acardius myelacephalus.

Definition: Rare anomaly in which one twin has an absent, rudimentary, or nonfunctioning heart. Twin pregnancy with acardiac results from an artery-to-artery placental anastomosis in which the pump twin, morphologically normal, perfuses the abnormal acardiac in a reversed circulation.

Case report: A-20-year-old G2,P0,A1 was referred at 24 weeks gestation with a history of twin gestation associated with polyhydramnios. The ultrasound revealed twins, monochorionic monoamniotic, with one twin appeared normal and a second twin with significant subcutaneous edema, with no evidence of cephalic pole and superior limbs; primitive thorax without pulmonary tissue clearly demonstrable and absence of cardiac chambers. The inferior limbs were observed entirely and the spinal column was present only in the sacral segment and the last four lumbar vertebrae. The bladder and kidneys were present. The umbilical cord presented a single umbilical artery. Doppler velocimetry showed increased resistance to blood flow in the umbilical artery of both fetuses. Prophylactic digitalization to try to prevent cardiac failure in the normal twin was tried.
With 31 weeks of gestation the ultrasound exam showed hepatomegaly and enlarged cardiomegaly in twin 1 with discrete pulmonary stenosis. Due to aggravation of twin 1, the parents were advised about the risks and benefits of an invasive procedure and intrauterine embolization procedure was performed by insertion of absolute alcohol in the perivascular region of the umbilical artery. An ultrasound carried out 24 hours after the interruption procedure verified a reduction in the congestion of the umbilical cord of twin 1. The arterial flow in the acardiac fetus remained occluded. Membrane rupture occurred two days after embolization and cesarean section procedure was done and a newborn male, Apgar 9/9, weighing 1515 grams was born. There was cardiomegaly regression and the infant was discharged in his 33rd day of life.
The anatomopathologic study of twin 1 revealed acardiac-acephalo fetus formed by a hemorrhagic tissue mass weighing 400 grams. The superior portion ended in a friable mass without subjacent osseous structure. The superior limbs were absent and the inferior ones were curved with four fingers in each foot. The internal organs exam revealed absence of heart, major vessels, lungs, liver, pancreas and superior gastrointestinal tract. The kidneys, suprarenal and bladder were observed in their usual positions. Radiography showed abnormal characteristics of the skeleton superior pole. Placental study revealed velamentous insertion of the umbilical cord of the acardiac fetus which presented two vessels. Vascular anastomosis was identified over corial disk.

Frontal view of acardiac fetus. One observes the good development of genitalia and inferior limbs:

Dorsum view of acardiac fetus:

Acardiac fetus and placenta:

View of the placenta showing fistula between the cord of twin 1 and of the acardiac fetus:

Radiographic aspect of acardiac fetus:

Prevalence: 1:35.000 deliveries. The incidence of acardia is higher in monoamniotic than in diamniotic monochorionic twin pairs and is more common in monozygotic triplets than in monozygotic twins. Acardia is more common in multiparous women.

Pathogenesis: The vascular theory is the most acceptable and proposes the early forthcoming of vascular anastomosis in placenta with primary defect. These anastomoses imply a counter-current perfusion of poor arterial blood in oxygen for the fetus with lower arterial pressure resulting in tissue hypoxia in the genesis phase of fetal organs and limbs. The hypoxia effects are more evident in the superior half of the body, probably due to hypoperfusion pertaining to inferior extremity, which requires lower vascular pressure to receive blood supply. This sequence results in normal morphogenesis disruption leading to skull, superior limbs and thoracic organs agenesis. The organs irrigated by aorta and iliac arteries are the ones which presents enhanced development.

Sonographic findings: Ultrasonoghaphic features useful in the diagnosis of acardia include absence of normal cardiac structure and variable structural abnormalities, include anencephaly, omphalocele and absence of upper limbs. The placentation is most commonly monochorionic diamniotic, with a thin membrane dividing the two fetuses. The umbilical cord will demonstrate a single umbilical artery in approximately two thirds of cases. Polyhydramnnios is a common feature. Color flow Doppler velocimetry may demonstrate a velamentous insertion of the cord in the acardiac fetus.

Differential diagnosis: Acardia has been mistaken for intrauterine fetal death. In a severely macerated fetus, the skeletal and visceral forms are more differentiated than in a case of acardia. The acardiac fetus may also be mistaken for an anencephalic fetus.

Prognosis: Numerous obstetric complications are associated with TRAP syndrome, such as, polyhydramnios, fetal cardiac insufficiency, premature delivery, hydrops, uterine rupture, umbilical cord accidents or fetal death. Fetal mortality occurs because of cardiac failure or extreme prematurity. The complications are related to work excess demanded by the healthy twin's heart, once it must perfuse both twins, what inevitably results in cardiac insufficiency, followed by polyhydramnios secondary to polyuria related to the increase of auricular natriuretic factor ¹.

Recurrence risk: 1:10.000. This risk is calculated from the recurrent risk for monoamniotic twinning (1%) multiplied by the frequency of the recurrence of the TRAP sequence (1%).

Management: Several therapeutic modalities have been suggested, but there is no consensus about the best therapy. The use of an interventional method presents better outcomes accounting for up 50% of fetal mortality cases. The treatment consists in either controlling the polyhydramnios and treating the healthy twin's cardiac insufficiency or interrupting the circulation between the twins. The described methods to control polyhydramnios concerns the administration of indomethacin or serial amniodrainage. These therapies, however, do not prevent the progression of cardiac insufficiency and can even precipitate it with the use of indomethacin because of the premature closure of the arterial duct. Serial amniocentesis is an alternative method, but predisposes to premature membrane rupture and delivery.
The maternal administration of digitalis for cardiac insufficiency treatment improves the fetus' cardiac function. There is recognizable effect through cardiomegaly reduction and more commonly, amniotic liquid normalization, allowing the control or even the reversion of cardiac insufficiency. Nevertheless, the heart failure settles down again after a variable period since the beginning of the control.
There are many techniques concerning circulation interruption of acardiac fetus:
1. Lasertherapy for vascular sclerosis
2. Endoscopy clamping
3. Hysterotomy with selective delivery
4. Insertion of a helical metal coil
5. The umbilical artery embolization with sclerosing substances
6. Laser coagulation