Complete atrioventricular septal defect identified during routine 19 week fetal anomaly ultrasound

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1 CASE REPORT Complete atrioventricular septal defect identified during routine Mark Hare Royal Brisbane and Women s Hospital, Herston, QLD, Australia doi: /sono Introduction Complete atrioventricular septal defect (AVSD) is a common cardiac defect found in 4 5% of fetuses with a cardiac defect,1 approximately 0.1% of live births.1,2 Complete AVSD is a combination of an atrial septum primum defect and an inlet ventricular septal defect with a common atrioventricular valve abnormally arranged with five leaflets.1 Down syndrome is a chromosomal anomaly often associated with AVSD.3 Surgical intervention before 6 months of age is a relatively low risk procedure and has recently been reported to significantly improve morbidity and mortality.4 This case report aims to emphasise the significance of ensuring positive patient outcomes through thorough high quality investigation of the fetal heart, during routine 19-week ultrasound screening for fetal anomaly. Early detection and management will provide maximum parental options. The ultrasound system used was a GE Voluson E8 (GE Medical systems, Zipf, Austria), and a curved array C4-8 MHz broadband transducer was used. Transabdominal imaging with good visibility demonstrated normal fetal growth on the 52nd percentile at a gestational age of 19 weeks 3 days, established by her last menstrual period. The four-chamber heart view was abnormal demonstrating an atrioventricular septal defect (Figure 1). No other fetal abnormality was identified. Recommendation was made for further assessment by the Centre for Advanced Prenatal Care (CAPC) located on site at the Royal Brisbane and Women s Hospital. Amniocentesis and genetic counselling were discussed with the patient at CAPC, and an uncomplicated amniocentesis was performed 7 days post-diagnosis. No chromosomal abnormality was detected. Ultrasound findings Case report A 28-year-old woman presented for a routine secondtrimester fetal morphology scan. She had previously screened low risk for Trisomy 21 during her routine first trimester nuchal translucency and maternal serum screening. Obstetric history The patient was a gravida 1, para 0, with a pre-pregnancy weight of 61 kg and a body mass index of The pregnancy was a spontaneous conception, and the patient was a non-smoker, took no known medications and there was no relevant familial history. Correspondence: Mark Hare, Royal Brisbane and Women s Hospital, Herston, QLD, Australia. rare@live.com.au Funding: none Conflict of interest: None 52 An AVSD was the reported differential diagnosis, and it was recommended that follow-up occur with a paediatric fetal cardiology specialist. A tertiary-level fetal echocardiogram was performed 3 weeks later. Levocardia and situs solitus was confirmed as were concordant atrioventricular and ventriculoarterial arrangements. The aortic arch was left sided. An AVSD was confirmed with balanced ventricular volumes and outflow tracts. Aortic and pulmonary valves were seen to be of similar diameter. The AV valves were, however, abnormally offset, with chordal attachment noted at the ventricular crest, and there was no inflow obstruction or regurgitation. The outflow was unobstructed. Systemic venous connections were confirmed to be normal with singular left and right pulmonary veins draining to the left atrium. Ductal and aortic arches were unobstructed, and the fetal heart rate was normal and recorded at 150 beats per minute. The biventricular systolic function was qualitatively assessed to be normal.

2 Figure 1 Four-chamber view of the fetal heat heart demonstrating complete atrioventricular septal defect. Complete atrioventricular septal defect Prognosis: Post-natally a neonate with an AVSD would be expected to develop congestive cardiac failure. Increased pulmonary blood flow through the left to right shunts, at atrial and ventricular levels is the cause of symptomatology (Figure 2). Clinical symptoms for neonates include increased work of breathing, tachypnoea, poor feeding and weight gain or failure to thrive.1 Management: Repeat imaging was arranged for weeks gestation with the view to surgical repair at 2 6 months of age. Long-term prognosis: Rated as good although dependant on the competency of the left AV valve post-surgery. An AVSD otherwise known as atrioventricular canal defect, endocardial cushion defect or AV canal malformation is subdivided into two types: partial and complete. The defect takes place at the cardiac crux or centre of the heart.5 Partial AVSD includes a primum atrial septal defect and a cleft within the left AV valve; two AV valve annuli exist.1 Ninety-seven percent of fetal AVSDs detected are of the complete type.6 Complete AVSD results from defective fusion of the endocardial cushions during embryonic development of the heart. It is slightly more prevalent in women than men and associated with chromosomal abnormality, primarily Trisomy 21 (Down syndrome) and Trisomy 18 (Edwards syndrome), with 50% of all AVSDs seen in patients with Down syndrome. Of these, 30% are described as complete AVSDs.1,7 The defining features of a complete AVSD are a common orifice seen between the atria and ventricles, the non-union of the interatrial septum and the posterior ventricular inlet septum, and a single five-leaflet AV valve. Two of the leaflets bridge both left and right heart chambers, one superiorly and one inferiorly8 (Figures 3 and 4). Differential diagnosis Differential diagnosis can include the following: Discussion Congenital malformations of the heart are the most common form of birth defect.2 isolated inlet ventricular septal defect, a dilated coronary sinus associated with a persistent left-sided superior vena cava,1 isolated linear off set of the AV valves without a septal defect as seen with Down syndrome and a large unbalanced AVSD misdiagnosed for a single ventricle heart. In other words the appearances closely mimic a single ventricle heart; however, the RSL RLL SBL IBL LLL Figure 2 Four-chamber heart view with colour Doppler imaging demonstrating atrial and ventricular left to right shunting and increasing pulmonary blood flow. Figure 3 Single five-leaflet atrioventricular valve seen with complete atrioventricular septal defect. RSL right superior leaflet; RLL right lateral leaflet; SBL superior bridging leaflet; IBL inferior bridging leaflet; LLL left lateral leaflet. 53

3 atrial septal defect (ASD) common atrioventicular orifice with left to right shunting persistent left superior vena cava with or without unroofed coronary sinus, accessory or double orifice left atrioventricular valve, single papillary muscle in the left ventricle and additional muscular ventricular septal defects. 12 US appearances of complete AVSD single AV valve ventricular septal defect (VSD) Figure 4 Complete atrioventricular septal defect (AVSD) showing common atrioventricular shunt. prognosis is significantly more dire for single ventricle (one must be careful during evaluation). 1 Symptomatology The pathophysiological response to a ventricular septal defect is primarily due to the direction and amount of interventricular shunting combined with the degree of volume loading to each cardiac chamber. Other factors include the presence of aortic valve prolapse and pulmonary or systemic outflow tract obstruction. 11 The total interventricular flow is determined by the defect s size, and the pulmonary and systemic vascular bed resistance. Small malformations may provide intrinsic flow resistance. When a defect is non-restrictive, symptoms can be variable and this is dependent, in particular, on the age of the patient. 11 Left-to-right shunting might initially be minimal in the neonate, with fairly large defects because high pulmonary vascular resistance is characteristic of the early neonatal period. With increasing age pulmonary vascular resistance falls, left-to-right interventricular shunting increases, and the patients well-being declines because of excessive pulmonary blood flow. 11 Approximately 60% of all babies with an AVSD have other cardiac anomalies present. Thirty percent have left atrial isomerism, and the majority of these will suffer complete heart block. 6 Other associated anomalies include the following: tetralogy of Fallot, patent ductus arteriosus, left ventricular outflow tract obstruction, double outlet right ventricle with ventriculoarterial concordance, 12 unbalanced ventricles (right ventricular dominance being more frequent), B mode The four-chamber heart view, acquired during diastole, will capture the AV valve in an open phase revealing an open defect in the centre of the heart, at the cardiac crux (Figures 1 and 4). This represents the AVSD. The same image timed for systole demonstrates the singular five-leaflet AV valve in the closed phase with loss of, the usual apically offset, tricuspid valve insertion. The abnormal offset is seen as a singular linear line across the left and right chambers 1 (Figure 5). Be diligent when evaluating the four-chamber heart view as up to 96% of structural defects are detectable on this single view. 6 The apex of the heart ideally should be towards the top of the screen with the intact ventricular septum slightly oblique to the beam. 6 Mild forms of AVSD may be overlooked especially when the view is obtained in the lateral position. 1 Other anomalies seen in the four-chamber view are abnormal ventricular size, unbalanced AVSD and partial AVSD (linear AV valve sign and may have a large atrial defect and a small ventricular septal defect). 1 The atrioventricular length ratio (normal = 0.5) increases with AVSD, and this finding can be used to increase detection to 83%, in suspected mild AVSD (using a cut off value of 0.6) 1 (Figure 6). Colour Doppler The four-chamber heart view obtained during diastole documents blood flowing via a channel through the septal Figure 5 Four-chamber heart view obtained during systole demonstrates an abnormal single atrioventricular valve seen as a single linear line from left to right. 54

4 Figure 6 Demonstration of normal (left) and abnormal (right) values of atrioventricular length. defects from left to right. It also qualitatively demonstrates the degree of ventricular hypoplasia in an unbalanced AVSD, and can detect the amount of AV valve regurgitation. 1 Treatment and surgical management In complete AVSD, symptoms of congestive heart failure and growth restriction appear shortly post-partum, usually within the first few weeks of life. 12 Pre-surgical management of the neonate (or infant) is mostly performed by outpatient cardiologists and general paediatricians, where symptoms of congestive heart failure and other associated co-existent features of chromosomal anomalies, that is, Trisomy 21, are monitored and managed in the short term. Typically, this may include the use of diuretics and oral vasodilators such as angiotensin-converting-enzyme inhibitors. 7 The other major concern is the failure to thrive. Surgical intervention does help with the majority of these cases, although a small minority continue to do poorly despite surgical intervention. This is especially if there are other congenital anomalies or post-operative complications such as significant AV valve regurgitation. 7 Surgical repair of AVSD The goal of surgical repair of an AVSD is the elimination of the left to right cardiac shunt, via closure of the atrial and ventricular septal defects using a patch or patches (usually two) of tissue taken from the pericardium. Alternatively, a prosthetic patch technique is possible. 12 Reconstruction of two AV valves is carried out using the abnormal singular AV valve, 7 and the left-sided AV valve cleft is repaired. 7 Surgical closure of AVSDs has been successfully achieved for the past 50 years. Careful patient selection criteria, early surgical intervention and advanced post-surgical care have reduced morbidity and mortality substantially. 11 Post-operatively survival rates are now approaching 91% 13 with mortality during surgery as low as 2%. 1 Conclusion Sonographers play a critical role in the early detection of AVSD. Careful evaluation of the four-chamber heart view in both systole and diastole should be a focal point of the routine second-trimester fetal anomaly scan. Lateral fetal position during heart assessment can have a negative impact on detection rates of a small AVSD. Persistence and techniques to change fetal position must be employed to ensure the highest possible image quality during this phase of the examination. Prenatal diagnosis of isolated AVSD is associated with an overall increase of survival rate in the order of 32%. When associated with other cardiac or extra cardiac abnormalities, the survival rates, however, are very low. 1 The associated risk of Trisomy 21 is significant at 50 60%. 13 Early detection of AVSD allows patient to be offered amniocentesis and appropriate genetic counselling. Parent s options will be at a maximum as will prenatal and post-natal management strategies if an early diagnosis is obtained during the second-trimester scan. This case highlights how correct detection of AVSD by diligently assessing the fetal heart with a focus on the four-chamber heart views, during routine second-trimester ultrasound, on a low risk fetus can lead to a positive outcome. Re-assessment for aneuploidy via amniocentesis, re-evaluation of the fetal heart via fetal cardiology and prenatal care specialists allows the parents to make an informed choice on their pregnancy. Active and successful prenatal assessment, careful pre-surgical patient selection, alongside early intervention, and surgical repair have led to significant reductions in post-operative mortality. 14 This all hinges on the early diagnosis, and sonography plays a critical role in the detection and management of AVSD. References 1 Abuhamad A, Chaoui R. A Practical Guide to Fetal Echocardiography, 2nd edn. Philidelphia: Lippincott Williams and Wilkins; RobinsonSW, Morris CD, Goldmuntz E, Reller MD, Jones MA, Steiner RD, et al. Missense mutations in CRELD1 are associated with 55

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