Results

Between 1987–94 300 102 babies were live born in the northern health region. Of 1590 who were found to have heart disease before the age of 12 months (table 1), we excluded from analysis 363 (23%) for the reasons explained above (fig 1). Of the remaining 1227 babies who were eligible for neonatal examination, 155 became symptomatic and were referred, and another five died undiagnosed, before routine neonatal examination. Thus 523 of 1590 (33%) were diagnosed before routine examination, leaving 1067 in the study (fig 1).

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Figure 1

Flow chart showing how and when diagnosis of cardiovascular abnormality was achieved in all 1590 babies.

Figure 1 shows the progress of each baby through the process of postnatal assessment. Of 1067 babies now known to have had congenital heart disease diagnosed in infancy and who underwent routine neonatal examination, 876 (82%) had been discharged undiagnosed. General paediatric follow up had been arranged for 291 of the 306 recognised at the time as possibly having congenital heart disease. We found no evidence that the detection rate in the four units providing neonatal intensive care services to the region (220 of 475 cases, or 46%) was any better than that of small units (256 of 586 cases, or 44%).

By 6 weeks of age, 570 babies (54%) remained undiagnosed, of whom 193 had been recognised at neonatal examination and were under general paediatric review. By 12 weeks of age, 379 babies (36%) remained undiagnosed, 166 of whom had been recognised and were still under paediatric review.

We were unable to trace details of a neonatal examination in six of 1067 babies (0.6%). Details of the 6 week examination were sought only in the 377 babies who were neither diagnosed nor under paediatric review by that age, but details of the examination could not be traced in 125 (33%).

During the first year of life 21 babies died before diagnosis and a cardiovascular malformation was identified only at necropsy (fig 1). In 19 of 21 the malformation was sufficient to account for death.

Five died within 24 hours of birth—two with transposition of great arteries, one with hypoplastic left heart, one with coarctation of the aorta, and one baby who died from a non-cardiac cause, had a ventricular septal defect.

Four babies died between neonatal examination and discharge from hospital—two had a murmur before death (one with tetralogy of Fallot and one with hypoplastic left heart), and in two there were no data available (one with hypoplastic left heart and one with coarctation of the aorta).

Nine babies died between discharge and 6 weeks of age—three with interruption of the aortic arch, three with coarctation of the aorta, and one each with hypoplastic left heart, pulmonary stenosis, and pulmonary atresia. All died within three weeks of birth, either suddenly at home or after presenting to hospital in extremis following a short rapid deterioration.

Three babies died after 12 weeks of age—two had severe aortic stenosis and one sustained a sudden infant death and was found to have an atrial septal defect at necropsy. Figure 1 shows that one of these babies (with aortic stenosis) had been recognised as abnormal at both the neonatal and 6 week examinations.

Our data do not suggest that severe heart disease is any easier to detect on routine examination than less serious heart disease (fig 2).

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Figure 2

Relation between recognition of abnormality at routine neonatal examination and total infant mortality for each individual diagnostic group. Most deaths were due to cardiac malformation, with others accounted for by other abnormalities or a combination of factors.

Table 2 shows the mode and timing of diagnosis by individual diagnostic group. The neonatal examination was abnormal in 0% to 73% of babies, with the lowest prevalence of murmurs in atrial septal defect and total anomalous pulmonary venous connection and the highest in aortic stenosis, pulmonary stenosis, truncus arteriosus and tetralogy of Fallot. The examination was abnormal in 49% of babies with a ventricular septal defect but in only 16% of those with a complete atrioventricular septal defect. Most abnormalities detected at neonatal examination were murmurs but the higher abnormality rates for transposition of the great arteries and pulmonary atresia reflect the detection of cyanosis. Figure 3 shows the numbers and the spectrum of abnormalities diagnosed at each stage.

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Figure 3

Timing of diagnosis and numbers of cases for each diagnostic group in 1277 babies eligible for routine examination. Displayed in this way, the spectrum of heart disease recognised at each stage is clearly shown.

Babies with Down’s syndrome and heart disease were not part of the main study cohort (see methods) but are described here for completeness. Of 107 babies, nine were preterm, five had urgent surgical problems, and in five heart disease was recognised antenatally, leaving 88 with “isolated” Down’s syndrome. As babies with Down’s syndrome have a high prevalence of heart disease,9 the neonatal examination cannot be regarded as routine. Despite this, the cardiovascular abnormalities in this group were not readily detected. Only 41% had a clinical cardiovascular abnormality (almost always a murmur) on neonatal examination (table 3). Many babies were referred for early assessment and echocardiography simply because of Down’s syndrome, yet 34% remained undiagnosed by 6 weeks of age and 24% by 12 weeks (table3).

Discussion

Cardiovascular malformation is the most common group of congenital malformations. The prevalence at live birth diagnosed in infancy in this study was 5.3 cases per 1000 live births. This is consistent with previous large studies using similar methodology.10-12Our register of live born congenital heart disease was set up in 1990 with prospective ascertainment of all cases since then but retrospective ascertainment of cases in 1987–9. We are confident of complete ascertainment of all cases of complex or clinically significant heart disease throughout this study, but there was probably some under ascertainment of minor heart disease in 1987-1989. Recent prospective studies, with ready availability of early echocardiographic examination, have shown a higher of prevalence of live born heart disease, almost all of which is accounted for by the detection of more small ventricular septal defects.13-15

Early recognition of congenital heart disease is important because clinical presentation and deterioration may be sudden2 and some treatable defects may even cause death before diagnosis.3 16 Furthermore, in some cases early diagnosis can avoid irreversible pulmonary vascular disease. Clinical examination for signs of cardiovascular malformation is part of the recommended examination of neonates and 6 week old infants.2

We found that only 45% of babies with a cardiovascular malformation were considered to be abnormal on neonatal examination and in only 16% did the clinical findings lead to a diagnosis before discharge from hospital. Seventeen babies passed as normal on routine neonatal examination later developed symptoms and were diagnosed before discharge home. One third of these had duct dependent lesions. With the trend to increasingly early discharge after delivery, such babies will be more likely to develop symptoms at home rather than when still on a postnatal ward.

Of the babies discharged home undiagnosed, 35% were diagnosed by 6 weeks of age and 57% by 3 months. If every baby who was found to have signs or symptoms of congenital heart disease had been examined echocardiographically within four weeks of the abnormality first being noted, 58% could have been diagnosed by the time of the 6 week examination and 76% by three months. The nine babies who died undiagnosed between discharge and six weeks, would still not have been diagnosed in life as no signs of illness had been noted until immediately before death and all died before 4 weeks of age. However, one baby with aortic stenosis would have been diagnosed alive before six weeks instead of dying undiagnosed after 12 weeks.

In a previous study we showed that undiagnosed conditions most likely to lead to death soon after discharge from hospital were hypoplastic left heart, interruption of the aortic arch, and coarctation of the aorta.3 In the present study there was no relation between the likelihood of detection of abnormality and infant mortality for individual diagnoses (fig 2). The main implication of this finding is that a normal neonatal examination does not exclude serious or life threatening cardiovascular malformation. As about half of the babies noted to have murmurs in the first few days of life have structural heart disease,13 early referral of all such babies for cardiological assessment and echocardiography should be encouraged. We consider that continued local paediatric follow up in the absence of a confirmed diagnosis inappropriate.1

Many babies with life threatening cardiovascular malformation will have presented by 6 weeks of age (including all those with hypoplastic left heart or interruption of the aortic arch). However, in our study 27% of babies with coarctation were still undiagnosed by 6 weeks of age, and even by 3 months, 20% were still undiagnosed. Similarly, two thirds of babies with aortic valve stenosis were not diagnosed by six weeks and 45% by 12 weeks.

Data from the six week examination are not easily amenable to retrospective study. In many health districts there is no centralised record keeping. Despite an extensive search and good cooperation from local community paediatric departments, we could trace the results of the 6 week examination in only two thirds of the babies in whom we were interested. Even when an abnormality was suspected at the 6 week examination, this did not always lead to early diagnosis: only a third of those undiagnosed by six weeks were diagnosed by 12 weeks of age. Because about one quarter of babies noted to have a murmur at the six week examination have an underlying cardiovascular malformation,17 we recommend the need for early referral.1

Early diagnosis of heart disease in Down’s syndrome is important firstly because both the parents and the paediatrician need to know the implications of the heart defect. Secondly some major malformations with pulmonary hypertension may show no signs and may progress to irreversible pulmonary vascular disease before the heart defect has been recognised.2 Despite this we found that in a third of babies with Down’s syndrome and heart disease no diagnosis had been made by 6 weeks and a quarter remained undiagnosed as late as 3 months of age.