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J Thorac Cardiovasc Surg 1994;107:359-0366
© 1994 Mosby, Inc.
Surgery for Congenital Heart Disease |
London, United Kingdom
From the Hospital for Sick Children, Great Ormond Street, London, United Kingdom.
Received for publication March 10, 1993. Accepted for publication July 7, 1993. Address for reprints: Catherine Bull, FRCP, Cardiothoracic Unit, Hospital for Sick Children, Great Ormond Street, London WC1N 3JH, Great Britain.
Abstract
The outcome in 135 patients with pulmonary atresia with intact ventricular septum was reviewed in terms of actuarial survival and "suitability" for eventual definitive repair (defined as having a tricuspid valve diameter larger than 2.4 standard deviations below the mean normal beyond the neonatal period). Of patients who underwent an initial closed valvotomy, 50% were dead, 22% were alive and suitable, and the remaining 28% were alive but unsuitable for definitive repair at 5 years. None of 66 patients who underwent primary shunt alone achieved suitability and 52% were dead at 5 years. No mode of neonatal closed valvotomy was consistently satisfactory: in only 10 of 26 survivors with serial measurements did the neonatal valvotomy alone achieve decompression to subsystemic pressures. Only half of the decompressed ventricles achieved growth of the tricuspid valve disproportionate to somatic growth as a result of the neonatal procedure. Strategies for the neonatal treatment of pulmonary atresia with intact ventricular septum should not rely on closed operations on the pulmonary valve to optimize right ventricular growth. (J THORAC CARDIOVASC SURG 1994;107:359-66)
In the 1990s pulmonary atresia with intact ventricular septum remains a dismal lesion.
1, 2 However, compared with results from the preprostaglandin era when producing survivors beyond the neonatal period was an achievement, the outcome of neonatal strategies must currently be examined from a longer-term perspective.
Outcome measures relating to immediate survival are obviously important, but the nature and success of early management strategies are also critical to subsequent changes in form and function of the right ventricle and to conferring eventual suitability for definitive repair. By better awareness of the limitations of neonatal strategies, we hope to improve the outlook for midterm survivors with this condition.
METHODS
Patients
We examined the records of all 135 patients with pulmonary atresia and intact ventricular septum resident in the United Kingdom and seen at the Hospital for Sick Children in the era from 1970 to 1989 inclusive. Patients with dilated, thin-walled right ventricles and those with critical pulmonary stenosis were excluded. All but four were first seen in the neonatal period and required operation for survival. The patients were broadly categorized according to whether they had a shunt alone or a valvotomy (with or without a shunt) as the initial procedure. On retrospective study, it was often unclear why a primary valvotomy alone, valvotomy with shunt, or shunt alone had been chosen, management only being "protocol driven" for a few of the years reviewed. However, throughout the time frame considered, the initial management effectively committed the patient to a long-term biventricular or univentricular management strategy. Since 1990, a shunt procedure and an open procedure on the right ventricular outflow tract done simultaneously or sequentially have often been part of a plan to bring patients to a later biventricular repair; the success of this strategy was not part of this evaluation.
Operation
The initial operations are shown in Table I. Only three early patients underwent an operation with the use of cardiopulmonary bypass as a primary procedure, but various closed approaches on the pulmonary valve were used. The pulmonary valve was perforated from below (Brock procedure 3) with or without excision of pulmonary valve tissue and infundibular muscle in 29 patients. A transpulmonary valvotomy was done through a left thoracotomy in 24 patients and valvectomy under inflow occlusion in 13 patients. The choice of systemic-pulmonary shunt varied with era and surgical approach.
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Table II. Outcome beyond definitive operation whether by biventricular repair or Fontan procedure was not considered here.
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4-6 Tricuspid valve diameters were expressed in terms of z units (standard deviation units relating to the normal diameters for patients of the same weight 
(Table II): normal values were derived from the data of Rowlatt, Rimoldi, and Lev, 7 who measured the tricuspid valve circumference in normal hearts at autopsy). With such z units, tricuspid valve growth disproportionately better than somatic growth is represented by a larger z. Direct measurements at catheterization or Doppler gradients were used to estimate right ventricular pressures. Right ventricular decompression to normal was considered achieved if the right ventricular pressure fell below 40 mm Hg.
Criteria for biventricular repair
Biventricular repair (relieving any residual right ventricular outflow tract obstruction and closing any intracardiac or extracardiac shunts) can only be achieved safely when the right ventricle is of adequate size: if it is not, the circulation fails with its output limited by the low stroke volume of the right ventricle. 8, 9 No studies have yet examined all the potential risk factors for postneonatal biventricular repair, but de Leval and associates 10 and others 11, 12 have attempted to establish a threshold tricuspid valve diameter above which surgical risk is acceptable. The thresholds generated can be expressed as z values. We made allowance for the fact that autopsy studies seem to involve a systematic underestimate of cardiac dimensions (by a factor of about 0.7 13) probably because of shrinkage of specimens in formalin. Recalculating the threshold above which de Leval and associates 10 thought biventricular repair could be contemplated in terms of unadjusted standard deviation units produced a guideline of z > -2.4 (e.g., a tricuspid valve diameter of about 13 mm at 5 kg).
Statistical methods
Actuarial curves for event-free survival, "suitability" for biventricular repair, and death were generated by the method of Kaplan and Meier. 14 "Suitability" was defined as a measurement of z > -2.4 and was attained at the date when this was first measured beyond 1 month of age. By definition, no patient could therefore be defined as "suitable" at birth, however large their tricuspid valve and ventricle; "suitability" was only achieved after the patient survived one or a series of operations.
The changing proportion over time of patients who were in three mutually exclusive categories (dead before ever becoming suitable for two-ventricle repair, alive but unsuitable for two-ventricle repair, and alive and candidates for two-ventricle repair) was examined. This required preparation of curves disentangling the effects of deaths on the suitability curve and suitability on the death curve: to do this, suitability and death were treated as "absorbing" states (i.e., deaths after becoming suitable were ignored; death was considered as a "permanent condition of being unable to become suitable for definitive repair" and patients were censored beyond the time frame of interest of the study). Risk factors for events on the "dead without becoming suitable" and "suitability" curves were examined by the Cox proportional hazards model. 15 Predictors of survival after an initial shunt were explored with contingency tables, with variables subsequently entered into a logistic regression model. Relative risks from the Cox and logistic regression models are quoted with 95% confidence intervals; where these exclude one, statistical significance at at least a 5% level can be inferred.
RESULTS
Whole group
Actuarial survival of the whole group (shunts and valvotomies) is shown in Fig. 1, A, and stratified by era in Fig. 1, B. Survival at 10 years for the whole group was 42% (95% confidence limits 33% to 51%) and was worse in the era before 1976. The spectrum of initial tricuspid valve diameters, expressed as z values, is illustrated in Fig. 2. The median z value for the whole group was -4.8. This is considerably smaller than that reported from a multiinstitutional study (median z = -2.2) 16 or from the Toronto study 17 (median z = 0.0).
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Table III. Greater birth weight and recent era appear significantly protective in respect to death, whereas patients with a tricuspid valve diameter between very small and approaching normal (-5 < z < -2.4) appeared to fare particularly badly. This may be because of a too-optimistic tendency to dispense with a shunt; four of five of patients in this group who had no shunt as part of the initial procedure died. No variable observable at presentation emerged as a significant predictor of eventual suitability for definitive repair. The smallest tricuspid valve to become suitable for (and the patient to survive) definitive repair was initially estimated at 7.5 mm at 3.9 kg; three patients in whom the trabecular portion of the ventricle was initially judged to be overgrown by hypertrophied muscle eventually became suitable for definitive repair.
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Table IV. The 5 mm modified Blalock-Taussig shunt appears significantly protective relative to the Waterston shunt. Twenty patients had angiographically documented coronary abnormalities but presence of these abnormalities did not emerge as an independent risk factor for early postoperative death. The curve demonstrating deaths and suitability for biventricular repair is shown in Fig. 4, B. During follow-up, 22 of the patients surviving neonatal shunts underwent a Fontan procedure.
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A successful neonatal valvotomy will produce a survivor with an adequately decompressed right ventricle that allows regression of right ventricular hypertrophy and right ventricular growth to an extent that definitive two-ventricle repair can be successfully achieved. The strategies for neonatal valvotomy that we have explored fail to bring many patients to this goal: one third of patients who underwent neonatal closed valvotomy died within 30 days of operation; only 40% of survivors (presumably much less than 40% of the whole group) had a successful neonatal valvotomy in terms of achieving right ventricular decompression and only half of these had disproportionate growth of the tricuspid valves and presumably of the right ventricles. Unfortunately, apart from a few disastrous attempts very early in the series, the option of open procedures on the pulmonary valve and right ventricular outflow tracts is not explored in this review.
Importance of the neonatal valvotomy
The neonatal management in this condition is crucial for several reasons. First, mortality related to the initial operation is the most dominant attrition for these patients who are typically subjected to a series of operations. Second, it appears from our review that, though ventricles can be made to grow by virtue of second or third procedures on the right ventricular outflow tracts, it is usually (in 12 of 15 of our cases) the initial operation that confers suitability for definitive repair.
Progression from stenosis to atresia of a thickened but mobile and well-delineated pulmonary valve has been observed in the third trimester of fetal life by echocardiography. 18 Postnatally, a pulmonary valve can be perforated surgically, but this maneveur alone may simply revert the hemodynamics to the unfavorable prenatal state in which restenosis is the natural progression; excision of pulmonary valve tissue is probably required if any radical change is to be achieved.
Causes of death after neonatal valvotomy
The perioperative mortality rate of 13% in the era since 1986 that we report is representative of most large series of neonatal valvotomy. 2, 12, 16 The causes for this mortality can be understood in terms of limitations in the valvotomies and limitations in the ventricles.
Preoperative investigations must delineate whether the right ventricular cavity is patent up to the pulmonary valve (so-called tripartite ventricles 13 or membranous atresia) or whether the infundibular "cavity" is overgrown by fibrotic hypertrophied muscle (infundibular atresia). In the latter case, it is clear that simple excision of the pulmonary valve will be completely inadequate in relieving right ventricular outflow tract obstruction. Even in patients with a patent infundibular cavity that does not appear restrictive preoperatively, the hypertrophic infundibular muscle can provide medium-term dynamic or progressive recurrent fixed obstruction postoperatively, as postulated by the Toronto group in the context of neonatal pulmonary stenosis 19 and as observed in some of our patients. Resection of muscle or placement of an outflow tract patch, or both, may be required to abolish this potential. 12
Even if the right ventricular outflow tract is rendered unobstructive, the early period after valvotomy may be critical for patients with marginal right ventricular size and no shunt. Schmidt, Cloes, and Silverman 20 have documented that the entire hypertrophied right ventricle may collapse after decompression, decreasing its stroke volume by a third compared with the preoperative and later postoperative values, the effect being most obvious about 5 days after operation. Severe diastolic dysfunction limiting ventricular filling and exacerbating a right-to-left atrial shunt is also almost inevitable after right ventriculotomy for transannular patching and most contributions recommend placing a systemic-to-pulmonary shunt or continuation of the prostaglandin infusion for at least 6 days after operation even in patients with apparently excellent ventricles. 2, 12, 21 The choice between shunt and prostaglandin infusion depends on the assessment of the morbidity associated with continuation of a prostaglandin infusion for up to 3 weeks.
Causes of the failure of right ventricular growth
Long-term improvement in right ventricular throughput depends on resolution of right ventricular hypertrophy, which is the main cause of the cavity hypoplasia and resistance to diastolic filling. Thus an inadequate valvotomy can ruin even an apparently favorable ventricle. Unfortunately, although the rate of postnatal hypotrophy of normal right ventricular muscle is known 22 and is quite rapid, with the ventricle thinning perceptibly within 4 weeks, we cannot assume that these abnormal right ventricles when relieved of their afterload will behave in the same way. Related to the gross antenatal right ventricular afterload, there may be muscular hyperplasia and hypertrophy, 23 and the organization of the right ventricular muscle is known to be very disturbed. 24 Until a large cohort of patients with varying sizes of the cavity at presentation who have survived neonatal valvotomies with low right ventricular pressures is available, we will not know the extent to which the antenatal damage to the right ventricle will limit the capacity of the decompressed ventricle to "grow."
Neonatal shunt alone
Use of a shunt alone seems to carry a significant risk in this lesion, though the currently used 5 mm Blalock-Taussig shunt appeared protective relative to other options. Statistically the presence of coronary abnormalities in general did not appear to account for the unexpectedly high mortality for a simple shunt in our series, though in a few patients it would be hard to dismiss the effect of large communications associated with a steal phenomenon into the right ventricle. It seems possible that the low aortic diastolic pressure associated with a large systemic-pulmonary shunt could prejudice perfusion of areas of left ventricular myocardium distal to an organic or functional obstruction. Also, the diastolic capacity of the left ventricle and its ability to increase its stroke volume normally when the pulmonary blood flow is increased by a systemic-pulmonary shunt may be limited by gross septal bulging from the hypertensive right ventricle.
However, the main limitation of the strategy is that no patient having only a shunt during the neonatal period came to biventricular repair. A successful Fontan operation is probably a second-best option for definitive operation, though it seems possible that there are risk factors for this operation particular to the scenario of pulmonary atresia with intact ventricular septum. Moreover, an important proportion of patients who undergo neonatal shunts never become candidates even for this operation.
Basis for neonatal decision-making?
Which patients should be excluded from the long-term aim of a two-ventricle repair is still unclear because the full potential for right ventricular growth after ventricular decompression has not emerged. There may be an as yet undefined tricuspid valve diameter that will predict this inability to grow to adequate dimensions. In the small series of McCaffrey, Leatherbury, and Moore 12 (which included patients with critical pulmonary stenosis) the patient with the smallest tricuspid valve diameter, for whom outflow tract patching and medium-term prostaglandin infusion were sufficient neonatal palliation, had a tricuspid valve diameter of 8.5 mm (z of about -5 at 3 kg). Unfortunately, there are problems associated with protocol guidelines generated in terms of estimates of tricuspid valve diameters, as promoted for example by the large multicenter study. 16 First, we and others have noted substantial discrepancies between dimensions estimated echocardiographically, angiographically, and at autopsy. 11, 13, 25 Second, poor interobserver reproducibility (when each observer records and measures an image) and wide normal ranges are a serious limitation in quantitative echocardiography for intracardiac structures. 26 Third, there are large percentage errors involved in measuring tiny tricuspid valves (a 2 mm difference in tricuspid valve measurements represents a unit or more difference in z in a neonate). A combination of these factors may explain systematic differences in patterns of tricuspid valve diameter distribution among the available series of neonates with pulmonary atresia and intact ventricular septum, and such difficulties make tricuspid valve diameter an unappealing basis for management protocols in the neonate.
Neonatal decision-making on the basis of coronary artery anatomy has been clarified by the recent review of Giglia and associates. 21 The issue for the neonatal management relates to preservation of left ventricular perfusion in the face of changing hemodynamics, a difficult judgement even when aortic or right ventricular angiograms are available. Strikingly "bad" angiographic appearances are compatible with survival after both valvotomies and shunts and it may be that coronary perfusion in patients who have survived even the few perinatal hours is quite robust. We agree with the recommendation of Giglia and associates 21 that only occasional patients with both a large proportion of left ventricular myocardium evidently perfused from the right ventricle in systole and stenotic proximal lesions that jeopardize perfusion of the corresponding territory from the aorta should be denied decompression. It has not been our recent practice to suggest primary heart transplantation for such neonates.
Conclusion
With the advent of multiinstitutional studies with access to large numbers of patients submitted to contemporary treatment methods, 16 historical reviews such as this will cease to be the bread and butter of longitudinal clinical research in "our field. Such studies are potentially much more powerful in delineating early and midterm "risk factors and the relative merits of a limited number of treatment strategies. For the neonatal management of pulmonary atresia with intact ventricular septum, we need the studies to explore the following topics:
Footnotes
Present address: Cardiac Centre, University Hospital, Prague, Czechoslovakia. Dr. Sorensen is supported by the Danish Heart Foundation. 
References
This article has been cited by other articles:
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  E. A Shinebourne, M. L Rigby, and J. S Carvalho Pulmonary atresia with intact ventricular septum: from fetus to adult: Congenital heart disease Heart, October 1, 2008; 94(10): 1350 - 1357. [Full Text] [PDF]
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