Absent pulmonary valve syndrome

Absent Pulmonary Valve Syndrome (APVS) is a cardiac abnormality characterized by the existence of a dysplastic or absent pulmonary valve, associated in most instances with severe dilatation of the pulmonary trunk and branches. In most cases, this condition is associated with tetralogy of Fallot (TOF) and absence of the arterial duct^1-3, although extremely rare cases of APVS, occurring as an isolated anomaly^1-3 or associated with tricuspid atresia (APVS/TA)^{4, 5}, have been reported in the fetus.

Rare; it accounts for 0,2% to 0,4% of liveborn infants with congenital heart defects (CHD).

Three anatomic variants of APVS have been reported.^{1, 6} The most frequent variant is characterized by presence of TOF (APVS/TOF) with the addition of a rudimentary or absent pulmonary valve leaflets. This results in both right ventricular outflow tract stenosis and regurgitation, with right ventricular pressure and volume loading, inducing dilatation of the main and peripheral pulmonary arteries. The marked dilatation of the pulmonary arteries, pathognomonic of this condition, may result in bronchomalacia secondary to bronchial compression with respiratory compromise at birth.^{1-3, 6}

An interesting feature of APVS/TOF is that the arterial duct is usually absent. The role of the duct developmental derangement in the pathogenesis APVS/TOF and in the degree of pulmonary artery dilatation is still to be defined. Some authors^{7, 8} have suggested that the consequent unavailability of the ductal pathway for runoff into the systemic circulation would play a key role in the development of volume overload and engulfment of the pulmonary arteries. Others^{9, 10} believe that the extent of pulmonary artery dilatation is a mere by-product of the valve lesion causing stenosis and insufficiency. For some of these authors the combination of a patent ductus arteriosus, large VSD and a severe pulmonary regurgitation is incompatible with survival as it will resultin massive aortopulmonary shunting and biventricular volume overload.¹⁰

The other two anatomical variants are exceedingly rare and include isolated APVS and APVS/TA. Isolated APVS is defined by the presence of an intact ventricular septum, a lower degree of pulmonary artery dilatation and it is associated in most instances with a patent ductus arteriosus. In this case, a severe right ventricular hypertrophy is associated. APVS/TA is characterized by a dysplastic right ventricle, tricuspid stenosis/ atresia and a normal or narrowed ductus arteriosus.

All APVS subtypes carry a risk of fetal heart failure due to ventricular volume overload.

In APVS /TOF, associated cardiac findings include a right sided aortic arch. Extracardiac findings include chromosomal anomalies, primarily the 22q11 microdeletion ( 20%–25% of cases). Other severeaneuploidies may also be associated (trisomy 13 and 18) often related to the presence of extracardiac malformations. On the contrary, the other two rarer variants are less frequently associated with extracardiac anomalies.

Unlike most conotruncal malformations, APVS/TOF can be suspected on the four-chamberview: cardiomegaly and an abnormal cardiac axis are the two key features; on some occasions, the pulmonary trunk may be so dilated that it also becomes visible on this view. On the left outflow view, a malalignment VSD with an overriding aorta can be seen with difficulty, due to the severe dilation of the pulmonary outflow tract; in fact, sweeping further cephalad from this view, severe dilation of the pulmonary trunk and branches appears: the US aspect is so typical that, after being seen once, it will never be forgotten! In most cases no ductus arteriosus is found.

Color Doppler allows detection of the severe stenosis and insufficiency of the functionally absent pulmonary valve. Spectral Doppler can be used to quantify the steno-insufficiency of the rudimentary pulmonary valve. High velocities (200-250 cm/sec) are usually obtained across the main pulmonary valve on pulsed Doppler evaluation.

Four-dimensional echocardiography effectively demonstrates the degree of pulmonary artery dilation and can also be used to characterize the severely dysplastic pulmonary valve.

The differential diagnosis is nonexistent, due to the very typical US aspect of APVS.

Extremely rare are the variants without TOF: in isolated APVS the ductus arteriosus is usually present and the US findings include a severely dilated right ventricle with significant myocardial hypertrophy, due to the high intraventricular pressure; a lower degree of pulmonary artery dilation is often present. In APVS/TA, a dysplastic right ventricle is associated with a retrograde ductal flow.

Fetal karyotyping, including array CGH and FISH analysis for the 22q11 microdeletion, is warranted in all cases of APVS–TOF. In this variant, a thorough search for associated extracardiac anomalies should also be carried out by an expert. Serial US monitoring should be provided in order to detect the possible prenatal onset of heart failure, which is due to the ventricular volume overload. In all subtypes of APVS, the delivery should take place in a tertiary referral center in order to ensure adequate neonatal management.

The outcome of the APVS cases detected prenatally is usually poor. Infact the three larger fetal case series with more than 10 cases, have reported fetal and postnatal survival rates of < 20%. The high loss rate was related to pregnancy termination, fetal heart failure, respiratory disease and chromosomal abnormalities. However, in the more recent series the outcome of APVS seems to be significant better ( survival rate of 50%) compared with those of previous series.

In APVS/TOF, respiratory distress in the newborn infant, due to bronchial compression by the dilated PAs, is the most serious syntomatology. In fact, in the most severe cases, compression may result in airway occlusion with fluid retention in the more distal lung tissues, requiring ventilator support and early surgery to alleviate the bronchial compression. There is evidence that early neonatal ventilator dependency predicts mortality, independent of the surgical result. Urgent surgical repair should, in the first place, relieve the compression of the tracheobronchial tree. Repair of the pulmonary stenosis and insufficiency required placement of a valved conduit in the right ventricular outflow tract. Repair of the APVS/TOF subtype includes also additional closure of the VSD. Newborns with isolated APVS may develop congestive heart failure after birth due to abundant left-to-right shunting over a persistently large ductus arteriosus. For this reason, urgent ductus arteriosus ligation is required. Postnatal management of APVS/TA is that of a typical tricuspid atresia.

1. Volpe P, Paladini D,Marasini M, et al. Characteristics, associations and outcome of absent pulmonary valve syndrome in the fetus. Ultrasound Obstet Gynecol 2004; 24: 623–628.
2. Razavi RS, Sharland GK, Simpson JM, et al. Prenatal diagnosis by echocardiogram and outcome of absent pulmonary valve syndrome. Am J Cardiol 2003; 91: 429–432.
3. Galindo A, Gutierrez-Larraya F, Martinez JM, et al. Prenatal diagnosis and outcome for fetuses with congenital absence of the pulmonary valve. Ultrasound Obstet Gynecol 2006; 28:32–39.
4. Litovsky S, Choy M, Park J, et al. Absent pulmonary valve with tricuspid atresia or severe tricuspid stenosis: report of three cases and review of the literature. Pediatr Dev Pathol 2000; 3: 353–366.
5. Lato K, Gembruch U, Geipel A, et al. Tricuspid atresia with absent pulmonary valve and intact ventricular septum: intrauterine course and outcome of an unusual congenital heart defect. Ultrasound Obstet Gynecol 2010; 35: 243–245.
6. Wertaschnigg D. Jaeggi M, Chitayat D Prenatal diagnosis and outcome of absent pulmonary valve syndrome: contemporary single-center experience and review of the literature. Ultrasound Obstet Gynecol 2013; 41: 162–167
7. Yeager SB, Van Der Velde ME, Waters BL, Sanders SP. Prenatal role of the ductus arteriosus in absent pulmonary valve syndrome. Echocardiography 2002; 19: 489-493.
8. Emmanoulides GC, Thanopoulos B, Siassi B, Fishbein M. ‘‘Agenesis’’ of ductus arteriosus associated with the syndrome oftetralogy of Fallot and absent pulmonary valve. Am J Cardiol 1976; 37: 403–409.
9. Razavi RS, Sharland GK, Simpson JM, et al. Prenatal diagnosis by echocardiogram and outcome of absent pulmonary valvesyndrome. Am J Cardiol 2003; 91: 429–432.
10. Ettedgui JA, Sharland GK, Chita SK, Cook A, Fagg N, Allan LD. Absent pulmonary valve syndrome with ventricular septal defect: role of the arterial duct. Am J Cardiol 1990; 66: 233–234.

Volpe P, De Robertis V, Absent Pulmonary Valve Syndrome, VISUOG, July 2014

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