62BrHeart J 1990;63:362-7

Balloon dilatation of critical stenosis of thepulmonary valve in neonates

E J Ladusans, S A Qureshi, JM Parsons, S Arab, E J Baker,M Tynan

AbstractPercutaneous balloon dilatation wasattempted in 15 consecutive neonates(mean age 7-3 (range 1-27) days andweight 3-2 (range 2-5-41) kg) withcritical stenosis of the pulmonary valve.Dilatation was successful in 11 (73%)patients. The mean balloon to annulusratio was 11 (range 0-6-177). The ratioof right ventricle to femoral artery sys-tolic pressure decreased from a mean(1 SD) of 1-4 (0 32) before to 0-8 (024)after dilatation and the transvalvargradient decreased from 81 (29-7}mm Hg before to 33 (27 7) mm Hg afterdilatation. All four (27%) patients iuwhom dilatation was unsuccessfulunderwent surgical valvotomy. Com-plications of balloon dilatation occurredin three (20%) patients; these includedretroperitoneal haematoma (one) andiliofemoral venous occlusion (two). Inone (7%) patient severe hypoxia andhypotension developed when the valvewas crossed with a guide wire andballoon catheter. Despite successfuldilatation he died 7 days after theprocedure. During a mean (1 SD) followup of 2 (1-7) years, seven (64%) of the 11patients remained free of important re-stenosis. One patient requlred repeatdilatation three weeks after the initialprocedure. In three (27%) patients re-stenosis developed 4-9 months afterdilatation and all three had surgicalvalvotomy. Of the four patients initiallyreferred for surgery three required asecond operation and one requiredballoon dilatation.Percutaneous balloon dilatation gave

effective relief of critical pulmonarystenosis in most neonates but complica-tions and restenosis requiring surgerywere common.

Department ofPaediatric Cardiology,Guy's Hospital,LondonE J LadusansS A QureshiJ M ParsonsS ArabE J BakerM TynanCorrespondence toDr S A Qureshi, Departmentof Paediatric Cardiology,Guy's Hospital, St ThomasStreet, London SEI 9RT.Accepted for publication20 December 1989

Since successful balloon dilatation of the sten-otic pulnonary valve was first described,'several studies have shown its safety andefficacy in infants and children.2' When largeenough balloons were used for dilatation,acceptable reductions in transvalvar gradientswere obtained. The results compared favour-ably with those of valvotomy."6 In these agegroups most centres prefer balloon dilatationfor the treatment of valvar pulmonary sten-osis.

Balloon dilatation is also possible in neo-

nates with critical stenosis of the pulmonaryvalve,2 but may be associated with morehaemodynamic disturbances and may be lesswell tolerated, especially if the ductusarteriosus has closed. So far only short termresults have been reported in small numbersof patients.78 We report our experience with15 consecutive neonates with critical stenosisof the pulmonary valve in whom this treat-ment was attempted.

Patients and methodsPATIENTSSince November 1983 we have attempted per-cutaneous balloon dilatation of the pulmonaryvalve in 15 consecutive neonates with criticalstenosis of the pulmonary valve. The averageage at cardiac catheterisation was 7-3 days(median age 4 days, range 1-27) and meanweight 3-2 (range 2-5-4- 1) kg. The diagnosiswas established antenatally by cross sectionalechocardiography in five (33%) patients. Inall the clinical diagnosis was confirmed bypostnatal cross sectional and Dopplerechocardiography. All patients were cyanosedand 13 were treated with prostaglandin E2infusion before catheterisation.

TECHNIQUE OF CARDIAC CATHETERISATION ANDBALLOON DILATATIONCardiac catheterisation and balloon dilatationwere performed under general anaesthesia ineight patients and under local anaesthesia withintravenous ketamine in the remainder. A fullpreliminary diagnostic catheterisation wasperformed via a percutaneous femoral veinpuncture. Arterial pressure was monitoredcontinuously by either femoral, umbilical,radial, or brachial arterial lines. A right ven-tricular angiogram was performed andrecorded in the anteroposterior or the leftlateral projections or both. The diameter ofthe pulmonary valve annulus was thenmeasured from the lateral cineangiogram atthe level of the attachment of the valve leaf-lets. We corrected this measurement for themagnification of the angiogram by referenceto the external diameter of the angiographycatheter. Then we selected a balloon catheterthat was appropriate for the corrected annulussize. During the initial period of the study weused balloons with a diameter equal to orsomewhat larger than the annulus. Sub-sequently we used balloons 20%-40% biggerthan the annulus. The ductus arteriosus wasopen in 13 patients, though it was only smallin five of them.

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The pulmonary valve was crossed bystandard 0-020 inch (two patients) or 0O018inch (four patients) guide wires (WilliamCook Europe) and 4 or 5 French multipurposeend hole catheters. In the latter half of thestudy period when it was not possible to crossthe valve with the standard guide wires weused a "super floppy" or "steerable"exchange guide wire (Schneider Shiley UK,0X018-0 020 inch diameter) in five patientsbefore abandoning the attempt. Once the endhole catheter was across the valve we used it topass an exchange wire of a diameterappropriate for the balloon catheter. In sevenpatients the guide wire was positioned in theperipheral left pulmonary artery, in onepatient in the right pulmonary artery, and inthree through the ductus arteriosus. In onepatient a guide wire (standard 0-018 inchwire) could not be passed to a stable position.In three patients with angiographically dys-plastic valves the pulmonary valve was notcrossed (in two with standard guide wires andin one patient with additional Ebstein'sanomaly a "steerable" wire was used).When the guide wire was in a satisfactory

position the end hole catheter and venoussheath were removed and the balloon dilata-tion catheter was passed over the wire(Schneider Shiley UK, Mansfield Scientific,and Meadox Surgimed USA). We used stillframes from the angiograms as a guide toplacing the balloon catheter with its mid-pointacross the valve. The balloon was theninflated with dilute contrast medium until theconstriction caused by the stenosed pulmon-ary valve disappeared. The inflation-deflationcycle lasted 15-20 s. After balloon dilatationthe balloon catheter was exchanged for aGoodale-Lubin catheter to measure thetransvalve withdrawal gradient and right ven-tricular pressure. Repeat angiography was notroutinely performed. The mean length of theprocedure was 2-4 (range 1 1-3-9) hours. Themean duration of x ray screening was 34-8minutes (range 10-57 minutes). In patients inwhom dilatation was successful, the mean(1 SD) annulus diameter was 7-4 (1 6) mm.The diameter of the balloons used rangedfrom 3 to 10 mm. The maximum balloon toannulus ratios ranged from 0-63 to 1-77 (mean1.1 (0 28)).

BALLOON DILATATION IN STEPSOnly one balloon was used in seven patients.In the last four patients, because it was impos-sible to pass a 5 French catheter through thevalve without causing hypotension and hy-poxia, preliminary dilatation was performedwith 3-5 mm low profile coronary angioplastyballoon catheters on 3-7-4-3 French shafts toreduce- haemodynamic disturbance and easethe subsequent passage of the larger ballooncatheters (fig lA, B, and C). The details ofthis technique have been reported elsewherein a different group of patients.9 In thoseundergoing dilatation in steps two balloonswere used in one patient, three balloons intwo, and four balloons in one patient. Thefinal balloon diameters used ranged from 9 to

10 mm and the balloon to annulus ratiosachieved ranged from 1-0 to 1 77.

STATISTICAL ANALYSISData are presented as mean values (1 SD).Differences between variables before and afterballoon dilatation were assessed by Student'st test for paired data.

ResultsBALLOON DILATATIONThe pulmonary valve was successfully dilatedin 11 patients. In three patients with dysplasticvalves, one of whom also had Ebstein'sanomaly, the valve could not be crossed.Though the valve was crossed in anotherpatient, the guide wire could not be passed to astable position in either the left or right pul-monary arteries and thus the valve could not bedilated. All four of these patients had surgicalvalvotomy.

HAEMODYNAMIC RESULTSThe table summarises the haemodynamicchanges. There was a significant decrease inright ventricular pressure, in the right ven-tricular to systemic pressure ratio, and in thetransvalvar systolic gradients after balloondilatation.

COMPLICATIONSOne patient (7%) died 7 days after balloondilatation. There were no late deaths. Thispatient, aged 3 days, had severe pulmonarystenosis and duct-dependent pulmonary cir-culation. When the pulmonary valve was cros-sed with the guide wire and catheter and thecatheter was placed in the descending aortathrough the arterial duct severe hypotensionand hypoxia developed which requiredremoval of the catheter, cardiopulmonaryresuscitation, and inotropes. Successful dilata-tion was subsequently performed with a lowprofile 5 mm balloon, but when we attemptedto pass a larger balloon the iliac vein wasdissected causing a large retroperitonealhaematoma. Though initially the patient washaemodynamically stable after the dilatation,with a Doppler estimated residual pulmonarygradient < 16 mm Hg, epileptic seizuresdeveloped and ultrasound examination showedmultiple intracerebral haemorrhages. Hebecame neurologically unresponsive and died 7days after balloon dilatation.Minor immediate complications included

transient bradycardia and hypotension onballoon inflation in all the patients. Aftersuccessful dilatation of the pulmonary valve inone patient it proved difficult to withdraw theballoon catheter from the groin. On removal ofthe catheter a ring of vascular tissue was foundwrapped around the mid-portion of theballoon. Contrast injection into the femoralvein showed a patent but irregular lumen withno extravasation of contrast material. Theleg showed considerable venous congestionimmediately after the procedure whichresolved completely over 48 hours.The long flexible tip of a "super-floppy"

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Figure I (A) Rightventricular angiogram(left lateral projection)showing a tiny jet ofcontrast across stenosedpulmonary valve.(B) Stillframe(anteroposteriorprojection) showing guidewire in distal rightpulmonary artery and3 mm coronaryangioplasty ballooninflated across thepulmonary valve."Waisting" of the balloonby the stenosed valve isvisible. (C) Stillframe(left lateral projection)showing 9 mm balloonfully inflated across thepulmonary valve. Thewaist on the balloon hasdisappeared.

A B

C

0-018 inch guide wire fractured outside thegroin in one patient. We salvaged thisprocedure by passing a short 18 gauge cannulaover the broken end and replacing the guidewire. In two patients femoroiliac venousocclusion, which prevented femoral venousaccess, was found at subsequent repeat cardiaccatheterisation.

TREATMENT AFTER DILATATION AND LENGTH OFHOSPITAL STAYWe were able to stop infusion of prostaglandinE2 within 24 hours of balloon dilatation in all

Haemodynamic changes (mean (I SD); range in parentheses) after balloon dilatation

Before balloon After balloondilatation dilatation p value*

RV pressure 108-4 (22-7) 63-9 (23-9) < 0 0005(mm Hg) (70-140) (37-125)

RV/systemic ratio 1-4 (0 32) 0-84 (0-24) < 0-001(mm Hg) (1-1-2-1) (0-51-25)

Transvalvar gradient 81-4 (29-7) 32-7 (27-7) < 0-0005(mm Hg) (20-120) (10-95)

*Paired t test. RV, right ventricular.

except three patients, in whom it was continuedfor 2-12 days. Two of these patients were alsogiven epoprostenol infusions for 5-6 days afterballoon dilatation to reduce pulmonary vas-cular resistance. Four patients required ven-tilation for >24 hours (3-10 days) after theprocedure. The average length of hospital stayfor those patients undergoing successfulballoon dilatation was 13-1 (range 5-32, median7) days.

FOLLOW UPSuccessful balloon dilatationDuring a mean follow up of 1 8 (range 0 2-5-2)years, the initial good result of balloon dilata-tion was maintained in seven (64%) of the 11patients. At the latest follow up the Dopplermeasured peak velocity across the pulmonaryvalve in all seven patients was < 3 0 m/s (mean2-2, range 1s4-2-9 m/s)-equivalent to agradient of <36 mm Hg (figs 2 and 3). Onecritically ill neonate underwent preliminarydilatation with a 3 mm balloon and dilatationwas electively repeated 3 weeks later with a8 mm balloon (the outcome was a balloon/annulus ratio of 1-44). There has been no signof recurrence in this patient; the Dopplerestimated pulmonary valve pressure gradientwas 16 mm Hg 1-6 years after initial dilatation.

In three (27%) patients stenosis recurred 4-9months after the initial procedure. The meanpressure gradient at recurrence was 64 (range55-73)mm Hg. In two ofthese patients furtherballoon dilatation was not possible because offemoroiliac venous thrombosis. All three hadopen pulmonary valvotomy and two of theserequired a transannular patch.

Effect of balloon size on late resultsIn those seven patients with a persisting goodresult after balloon dilatation the mean balloon/annulus ratio was 1-2 (range 0-95-1-77). Ofthese, two patients had a balloon/annulus ratioof 0 95 and 0-96. The mean balloon/annulusratio at dilatation in the four patients requiring

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Balloon dilatation of critical stenosis of the pulmonary valve in neonates

further treatment was 0-83 (range 0 6-1 1) andin only one of them was this ratio > 10.

Initial surgical valvotomiesIn four patients initial balloon dilatation wasnot possible. In three the valve was not crossedby a catheter or guide wire and in one the guidewire could not be positioned in a satisfactoryand stable way. All underwent surgicalvalvotomy, three closed and one open with atransannular patch. During a follow up of 2-3(range 08-5-3) years, two of the three patientswho had a closed pulmonary valvotomyrequired a subsequent open valvotomy withenlargement of the outflow tract by a trans-annular patch and the third patient had balloondilatation for recurrent stenosis. At the latestfollow up the peak velocity into the pulmonaryartery measured by Doppler ranged from 10 to3 2 (mean 2 2) m/s.

DiscussionCritical pulmonary stenosis is often lethal inneonates, but if it presents in infants aged > 1month the outcome is better. Urgent relief ofobstruction is generally accepted as theappropriate treatment in neonates.'0 Varioussurgical techniques including transarterial ortransventricular pulmonary valvotomy orvalvectomy, with either inflow occlusion orcardiopulmonary bypass, or a systemic-to-pul-monary artery shunt combined with a pulmon-ary valvotomy have been used. The surgicaltreatment, however, has been associated withan operative mortality of between 33% and750.l1 12

Perioperative infusion of prostaglandin E,may improve the outcome after surgicaloperation." However, in the presence of a

Figure 2 Changes intransvalvar systolicpressure gradients afterballoon dilatation.0, continued good result;0, re-stenosis requiringfurther treatment; *severepulmonary stenosis withsuprasystemic rightventricular pressure (thegradient was low becauseof large ductus arteriosusand high pulmonaryvascular resistance).

mm Hg1251

0oo0

75-

50-

25-

oJ

hypoplastic right ventricle and raised pulmon-ary vascular resistance, the postoperativecourse can be variable. Even after successfulsurgery and survival, reoperations on the rightventricular outflow tract may be required. The5 and 10 year actuarial results for freedom fromreoperation in the survivors of surgicalvalvotomy in the neonatal period were 73%and 42% respectively; the patients oftenrequired a further pulmonary valvotomy orinsertion of a transannular patch.'2 Effectivenon-surgical treatment of this conditiontherefore offers an attractive alternative.

Balloon dilatation of the pulmonary valvemay provide effective relief ofpulmonary valvestenosis of all degrees of severity and manystudies have confirmed its safety and efficacy ininfants and children.2 1314 Good intermediateand long term results can be obtained with fewreported complications related to the techniqueitself.'5 16The results of successful balloon dilatation

in a small number of neonates with criticalstenosis of the pulmonary valve were reportedas early as 1984.3'7 Subsequently Zeevi et alreported acceptable results of this treatment insix neonates8 and Rey et al in eight neonates.7 Inthe latter series there was one death unrelatedto the procedure and two patients requiredrepeat dilatation after the initial balloondilatation.7 Our series analysed on an "inten-tion-to-treat" basis consists of 15 unselectedconsecutive neonates presenting with criticalstenosis of the pulmonary valve and intactventricular septum since November 1983. The

mm Hg

1251

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75-

50

25

0

Beforedilatation(n=1 1)

I IImmediately Follow upafter (n=11) (n=10)

Beforedilatation(n=1 1)

81 4 (29 7)

Immediately Follow upafter (n=11) (n=10)

32-7 (27-7) 39-1 (22-5)(Mean (1SD) mm Hg)

Figure 3 Changes in mean transvalvar systolic pressuregradient after balloon dilatation.

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results show that balloon dilatation is aneffective form of emergency treatment.

Balloon dilatation in neonates is often atechnically difficult procedure but is associatedwith fewer risks than surgical operation.Several modifications in the technique areneeded to reduce the occurrence of complica-tions. Before balloon dilatation, prostaglandinE2 infusion is maintained and the patient isstabilised haemodynamically (if necessaryinotropes are also used). Goodale-Lubin andother end hole 4 or 5 French catheters are usedto attempt to cross the pulmonary valve. This isoften the most difficult part of the procedure.We now routinely attempt to cross the valvewith "super-floppy" or "steerable" guidewires of 0 014, 0-018, or 0-020 inch diameter(Schneider-Shiley). These reduce the risk ofinfundibular trauma and can reduce the timeneeded to cross the valve. Since "steerable"guide wires became available we have failed tocross the valve in only one of the last ninepatients. This patient had additional Ebstein'sanomaly. Occasionally it is difficult to positionthe guide wire in either of the branch pulmon-ary arteries. Then the wire is passed throughthe ductus arteriosus and positioned in thedescending aorta. The use of the dudtusarteriosus may compromise pulmonary bloodflow and result in haemodynamic deteriora-tion; therefore speedy initial dilatation is essen-tial. If the 5 French end hole catheter cannot bepassed easily across the valve, then a coronaryangioplasty balloon catheter of 3-3*5 mmdiameter and 3-7 French shaft is used for theinitial dilatation. This is followed by stepwisedilatation with larger balloon catheters toachieve the required balloon size.9

After dilatation the patient is weaned fromthe ventilator and prostaglandin E2 while thearterial oxygen saturation is monitored. Whendesaturation persists and the right ventricularcavity is small prostaglandin E2 infusion iscontinued for several days. Occasionally wehave also used epoprostenol infusion to reducethe pulmonary vascular resistance. None ofourpatients required a systemic-to-pulmonaryartery shunt.

In previous studies a dysplastic valve wasregarded as a contraindication to balloondilatation.2 13 18 Most stenotic pulmonary valvesin the neonate, however, seem dysplastic onechocardiography and angiography. Theyrange from thin mobile leaflets with "pure"commissural fusion to valves with mixed dys-plasia and commissural fusion and to theseverely dysplastic valve with thickened valveleaflets attached to a hypoplastic "ring" show-ing little expansion in systole."9 It is the degreeof commissural fusion that probably deter-mines the response to balloon dilatation,because disruption of commissural fusion bythe balloon is thought to be the mechanism ofrelief of the obstruction.20 One study has sug-gested that the degree of commissural fusioncan be assessed from echocardiographic andangiographic appearances.2' In neonates withcritical stenosis of the pulmonary valve we donot believe that this can be determined withconfidence. In this situation, where any reduc-

tion in pulmonary valve gradient andimprovement of pulmonary flow is valuable,we have performed balloon dilatationirrespective of the angiographic appearances,recognising that surgery may eventually benecessary.

Complications such as iliofemoral venousocclusion may prevent repeat balloon dilata-tion. We now routinely give heparin (50 U/kg)to patients before balloon dilatation. This andthe use of balloons on smaller French sizeshafts may reduce venous occlusion.

All the procedures lasted 2-4 hours and thefluoroscopy time ranged from 25 to 57 minutes.A similar period of fluoroscopy (30-68 min-utes) was reported by Zeevi et al.8 The durationof fluoroscopy is a potential risk to these babiesbecause the dose of radiation received duringthe long screening times required for successfuldilatation is not known. Fletcher et al cal-culated the radiation doses received by neo-nates during routine radiography andestimated the risks of malignant disease fromfluoroscopy in different situations.22 The riskof malignant disease was thought to be as highas 1 in 150 for some routine catheterisationscompared with 1 in 280 000 for a single chest orabdominal radiograph. This is an overestimateof the risks of catheterisation because it wasassumed that the risks for limited bodyexposures were the same as for whole bodyexposures. Nevertheless, the actual dosereceived by the neonates should be measuredby skin dose mheters. This may be an importantfactor to consider in the risk-benefit equationwhen balloon dilatation is compared with sur-gical valvotomy.Although good initial results in infants can

be obtained with balloons that are undersizedin relation to the pulmonary annulus, theincidence of restenosis is high.2' Our seriesconfirms this in the neonate also. Restenosisrequiring further treatment developed in 60%of the patients with balloon/annulus ratios< 1 0 and in 14% in whom the balloon/annulusratio was > 1-0. As in older children balloon/annulus ratios of > 1-2 give more satisfactoryresults.52' To achieve such ratios safely, werecommend progressive balloon dilatation toreduce the incidence of haemodynamic com-plications.9While large balloon/annulus ratios are aimed

for, too large a balloon/annulus ratio may beassociated with complications. Ring et alshowed that when balloons > 150% of theannulus size were used in newborn lambs therewas an increased incidence of subendocardialhaemorrhage affecting the right ventricularfree wall and outflow tract caused by traumafrom the proximal end of the balloon straight-ening against the curvature of the outflowtract.24 In clinical studies of older childrenRadtke et al showed that balloons 300/4-600/bigger than the annulus size could be usedsafely to produce greater reductions in gradientthan those associated with smaller balloons.5Furthermore, the frequency of recurrence ofpulmonary valve stenosis requiring furthertreatment was higher for balloon/annulusratios < 1-2 than for ratios > 1 .23 No benefit

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Balloon dilatation of critical stenosis of the pulmonary valve in neonates

in terms of an immediate reduction in gradientor frequency of recurrence of stenosis was

shown for ratios > 1-5.We believe that balloon dilatation, rather

than valvotomy, is the best treatment for neo-

natal critical pulmonary stenosis. It-may beassociated with a lower morbidity and mor-

tality than surgical treatment. Restenosis mayoccur and is related to the use of undersizedballoons. Other risks-for example the radia-tion dose of fluoroscopy-and the long termresults when large balloon/annulus ratios are

used, need further evaluation.

1 Kan JS, White RI, Mitchell SE, Gardner TJ. Percutaneousballoon valvuloplasty: a new method for treating congeni-tal pulmonary valve stenosis. N Engl J Med 1982;307:540-2.

2 Tynan M, Baker EJ, Rohmer J, et al. Percutaneous balloonpulmonary valvuloplasty. Br Heart J 1985;53:520-4.

3 Sullivan ID, Robinson PJ, Macartney FJ, et al. Percutan-eous balloon valvuloplasty for pulmnonary valve stenosis ininfants and children. Br Heart J 1985;54:435-41.

4 Rey C, Marache P, Matina D, Monly A. Valvuloplastietransluminale percutanee des stenoses pulmonaires: a

propos de 24 cas. Arch Mal Coeur 1985;78:703-10.5 Radtke W, Keane JF, Fellows KE, Lang P, Lock JE.

Percutaneuos balloon valvotomy of congenital pulmonarystenosis using oversized balloons. J Am Coll Cardiol1986;8:909-15.

6 Khan AMA, Yousef SA, Mullins CE. Percutaneous trans-luminal balloon pulmonary valvuloplasty for the relief ofpulmonary valve stenosis with special reference to double-balloon technique. Am Heart J 1986;112:158-66.

7 Rey C, Marache P, Francart C, Dupuis C. Percutaneoustransluminal balloon valvuloplasty of congenital pulmon-ary valve stenosis, with a special report on infants andneonates. J Am Coll Cardiol 1988;11:815-20.

8 Zeevi B, Keane JF, Fellows KE, Lock JE. Balloon dilation ofcritical pulmonary stenosis in the first week of life. J AmColl Cardiol 1988;11:821-4.

9 Qureshi SA, Ladusans EJ, Martin RP. Dilatation withprogressively larger balloons for severe stenosis of the

pulmonary valve presenting in the late neonatal period andearly infancy. Br Heart J 1989;62:311-4.

10 Nugent EW, Freedom RM, Nora JJ, Ellison RC, Rowe R,Nadas AS. Clinical course in pulmonary stenosis.Circulation 1977;56(suppl I):38-47.

11 Kirklin JW, Barratt-Boyes BG. Cardiac surgery. New York:Wiley Medical, 1986:833-4.

12 Coles JG, Freedom RM, Olley PM, Coceani F, WilliamsWG, Trusler GA. Surgical management of critical pul-monary stenosis in the neonate. Ann Thorac Surg1984;38:458-65.

13 Kveselis DA, Rocchini AP, Snider R, Rosenthal A, CrowleyDC, Dick M. Results of balloon valvuloplasty in thetreatment of congenital valvar pulrnonary stenosis inchildren. Am J Cardiol 1985;56:527-32.

14 Miller GAH. Balloon valvuloplasty and angioplasty incongenital heart disease. Br Heart J 1985;54:285-9.

15 Rao PS, Fawzy ME, Solymar L, Mardini MK. Long-termresults of balloon pulmonary valvuloplasty of valvarpulmonary stenosis. Am Heart J 1988;115:1291-6.

16 Piechaud JF, Voshtani H, Kachaner J, et al. Problemes poses

par la valvuloplastie pulmonaire percutanee chez l'enfant.Arch Mal Coeur 1987;80:413-9.

17 Tynan M, Jones 0, Joseph MC, Deverall PB, Yates AK.Relief of pulmonary valve stenosis in the first week of lifeby percutaneous balloon valvuloplasty [Letter]. Lancet1984;i:273.

18 Kan JS, White RI, Mitchell SE, Anderson JH, Gardner TJ.Percutaneous transluminal balloon valvuloplasty for pul-monary valve stenosis. Circulation 1984;69:554-60.

19 Jeffrey RF, Moller JH, Amplatz K. The dysplastic pulmon-ary valve: a new roentgenographic entity. Am J RoentgenolRad Ther Nucl Med 1972;114:322-39.

20 Robertson M, Benson LN, Smallhorn JS, et al. Themorphology of the right ventricular outflow tract afterpercutaneous pulmonary valvotomy: long term follow up.Br HeartJ 1987;58:239-44,

21 Musewe NN, Robertson MA, Benson LN, et al. Thedysplastic pulmonary valve: echocardiographic featuresand results of balloon dilatation. Br Heart J 1987;57:364-70.

22 Fletcher EWL, Baum JD, Draper G. The risk of diagnosticradiation of the newborn. Br J Radiol 1986;59:165-70.

23 Rao PS. Further observations on the effect of balloon size onthe short term and intermediate term results of balloondilatation of the pulmonary valve. Br Heart J 1988;60:507-11.

24 Ring JC, Kulik TJ, Burke BA, Lock JE. Morphologicchanges induced by dilation ofthe pulmonary valve anuluswith overlarge balloons in normal newborn lambs. Am JCardiol 1984;55:210-4.

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