Truncus arteriosus and previous pulmonary arterial banding: Clinical and hemodynamic assessment

Truncus Arteriosus and Previous Pulmonary Arterial Banding: Clinical and Hemodynamic Assessment

RICHARD C. McFAUL, MD DOUGLAS D. MAIR, MD, FACC ROBERT H. FELDT, MD, FACC DONALD G. RITTER, MD, FACC DWIGHT C. McGOON, MD

Rochester, Minnesota

Twenty-seven patients with truncus arteriosus and previous pulmonary arterial banding were evaluated 1 1/2 to 14 years (mean 7 years) after banding. Ages at the time of cardiac catheterization ranged from 3 to 18 years (mean 9 years). Current symptoms were severe in five patients and were related to truncal valve incompetence or decreased pulmonary blood flow (or both) rather than to age, duration of palliation or band location. Twenty-one of 22 patients with two pulmonary arteries were considered to be in a hemodynamically operable state at the time of study. The condition of three of five patients with a single pulmonary artery was subsequently found inoperable because of severe pulmonary vascular disease in the lung supplied by the single pulmonary artery, in patients with two pulmonary arteries, demonstration of low pressure in at least one normal-sized pulmonary artery established operability. Postoperative pressure measurements correlated well with preoperative prediction of operability, with 19 of 20 patients having a pulmonary arterial pressure less than 70 percent of systemic levels after repair. Bilateral pulmonary arterial banding may be more effective than central arterial banding (which frequently produces severe obstruction to the right pulmonary artery) in preventing pulmonary vascular obstructive disease in patients with truncus arteriosus who have two pulmonary arteries. Patients with truncus arteriosus and a single pulmonary artery with pulmonary arterial banding remain at high risk for the development of pulmonary vascular obstructive disease.

T h e t r e a t m e n t of truncus arteriosus in infants with intractable congestive heart failure remains a problem for both the cardiologist and the surgeon. Infants managed only medically often die within the 1st year of life. 1,2 Surgical palliation with p u l m o n a r y arterial banding was reported as early as 1961. 3 T h e success of this procedure varies, b u t most surgeons report a mortality rate in excess of 50 percent. 4 T h e availability of profound h y p o t h e r m i a p r o m p t e d trials of total corrective surgery in infants. 5 An initial report was encouraging, 6 b u t subsequent reports indicated greater mortality t h a n with p u l m o n a r y arterial banding. 7,s One aspect of this problem is the fate of infants who have survived p u l m o n a r y arterial banding. We present here a clinical and hemodynamic profile of 27 children with truncus arteriosus defects who survived previous surgical palliation. Materials and Methods From the Division of Pediatric Cardiology and Department of Surgery, Mayo Clinic and Mayo Foundation,Rochester, Minn. Manuscript received March 8, 1976; revised manuscript received May 17, 1976, accepted May 19, 1976. Address for reprints: Richard C. McFaul, MD, c/o Section of Publications,Mayo Clinic, 200 First St. S.W., Rochester, Minn. 55901.

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Cases: Twenty-seven patients (20 boys and 7 girls) with truncus arteriosus and previous pulmonary arterial banding were evaluated with cardiac catheterization at the Mayo Clinic from July 1969 to January 1975. Their ages at evaluation ranged from 3 to 18 years (mean 9 years). An attempt was made to classify the cardiac defects at operation as type I or II, using Collett and Edwards' description 9 of truncus arteriosus. One patient also had an interrupted aortic arch with a patent ductus arteriosus providing flow to the descending aorta. Two patients had a congenitally absent right pul-

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monary artery associated with the truncal defect, and three additional patients had acquired occlusion of one pulmonary artery. Twenty-six of the 27 patients had had the surgical palliation performed elsewhere. Patient histories and surgical summaries provided past clinical information. The ages of the 27 patients at the time of pulmonary arterial banding ranged from 6 weeks to 7 years (Table I). The interval between operation and our evaluation ranged from 1 1/2 to 14 years (mean 7 years). The bands had been placed on the central pulmonary arterial segment, on both pulmonary arteries or on only the left pulmonary artery (Fig. 1). Eight patients with type I truncus defect had the main pulmonary artery banded; 14 other children underwent bilateral banding, and the remaining 5 had a band placedaround the left pulmonary artery. A standard 12 lead electrocardiogram was obtained in all patients. The Boston Children's Medical Center Anthropometric Growth Chart was used to assess height and weight. Diagnostic studies: In all patients, cardiac catheterization was performed in our cardiovascular laboratory. Before catheterization, all patients were given a mixture of meperidine (Demerol®), promethazine (Phenergan ®) and chlorpromazine (Thorazine®). When general anesthesia was required, combinations of oxygen, nitrous oxide and halothane were used. Hemodynamic data were obtained while the patients were breathing room air or oxygen (or both), with partial pressure of oxygen (PO2) ranging from 170 to 760 mm Hg. Oxygen consumption was usually assumed on the basis of the patient's heart rate, age and sex. 1° Standard methods were used to calculate systemic and pulmonary blood flows. Pulmonary resistance was determined by the usual method in patients with a single pulmonary artery or with nearly identical mean pressures in both pulmonary arteries. In patients with a single pulmonary artery, the degree of pulmonary vascular disease was assessed by the principle previously re-

ported.1 t Pulmonary resistance could not be precisely calculated in patients who had only one artery entered at the time of catheterization or who had large differences in mean pressure between the right and left pulmonary arteries. Quantitative perfusion lung scans were not yet available to assess accurately the differential blood flows present in most of these patients. Large film biplane angiocardiography was performed in all patients. The right ventricle and truncal root were injected with contrast medium to evaluate ventricular anatomy, truncal valve integrity and the appearance and size of the pulmonary vessels. Results Clinical A s s e s s m e n t

The ages of t h e p a t i e n t s at the t i m e of surgical palliation are s u m m a r i z e d in T a b l e I. All t h r e e b a n d i n g t e c h n i q u e s h a d been used in infants less t h a n 6 m o n t h s

TABLE

I

A g e a t P a l l i a t i o n and M e t h o d o f P u l m o n a r y B a n d i n g

in 2"7 Cases Banding Method (no. of patients) Age 6 weeks to <6 months 6 months to <1 year 1 year to < 2 years 2 years and older Total

FIGURE 1. Location of pulmonary arterial bands in 27 patients with palliation for type I and II truncus arteriosus~defects. Figures indicate number of patients.

1

LPA

Total

3 2 4 5 14

4 3 1

3* 1 1

"8"

'5" "

10 6 6 5 27

I

I0 TYPE

CPA

BPA = bilateral pulmonary arterial bands; CPA = central pulmonary arterial band; LPA = left pulmonary arterial band. * Congenitally absent right pulmonary artery in t w o patients.

TYPE

i

BPA

2

TT--I

3

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of age. A single pulmonary band had been used in 70 percent (7 of 10) of these very young infants. Bilateral banding was successfully performed in three infants aged 6, 8 and 10 weeks, respectively. Eighty-two percent (9 of 11) of patients who underwent banding after age 1 year had bilateral banding. Improvement after the palliative surgery had occurred in two thirds of the entire group appearing for study. Eleven patients (41 percent) had marked increases in exercise tolerance, growth and development. Six others had an increased exercise capacity but various degrees of cyanosis and persistently poor growth. The condition of six patients was not improved: Significant heart failure persisted in four and severe cyanosis from excessively constricted bands developed in two. The four oldest patients, in relatively stable clinical condition, had undergone palliation to preverlt the development of pulmonary vascular disease; however, their condition was unchanged clinically after surgery. Growth was retarded in 70 percent of patients at the time of our assessment. Nineteen were classified below the third percentile for height and 11 below the third percentile for weight. Only three patients were classified above the 50th percentile for both height and weight. Eighty percent of patients were receiving a cardiac glycoside at the time of our evaluation. Six patients were essentially free of symptoms (class I). Seven others had only mild physical limitations (class II); nine had moderate to severe fatigability and cyanosis during physical activity (class III); and five were unable to attend school because of their disability (class

IV). The clinical and hemodynamic features of the asymptomatic group are compared with those of chil-

TABLE

II

Duration of Type of Palliation Pulmonary Truncal Valve (yr) Banding Insufficiency

Mean

6 1/2 4 4 12 1/2 10 3/4 4 7

LPA BPA CPA BPA BPA CPA

None Mild Mild Moderate None None

Mean

7 4 1 1/2 7 1/2

10 1/2 9 1/2

BPA BPA

3 1/2 3 6 6 1/2

CPA CPA BPA

Severe Moderateseve re None None Severe

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Case

RPA

LPA

Loca- Postoperative Rp tion of RV (PA)/LV Band Pressure Ratio ( U m =)

Group l: Two Pulmonary Arteries (low mean pressure distally in both) 1 2 3 4 5 6 7 8

26/12 (16) 24/10 (15) 15/9 (11) 54/38 (43) 36/21 (26) 52/35 (41) 14/9 (11) 10/5 (7)

42/30 (34) 27/20 (22) 15/5 (8) 46/26 (33) 33/22 (26) 20/16 (18) 13/8 (10) 28/19 (22)

BPA BPA BPA BPA BPA BPA CPA CPA

0.3 OA T 1.0 ~ 0.5 0.3 0.3§ 0.2 0.3

Group I1: Both Pulmonary Arteries Entered (one with high and one with low mean pressure distally) 9 10 11 12

50/36 71/15 26/19 38/31

13

22/12 (15)

(40) (17) (21) (33)

112/52 (72) 72/52 (58) 103/54 (70) 91/62 (72)

BPA LPA CPA CPA

60/48 (52)

BPA

... 1.0 ~ 0.3 Awaiting operation 0.7

Group II1: Two Pulmonary Arteries (only one entered distally) 14 15 16 17 18 19

35/26 (29) 35/8 (17) NE NE 48/35 (39) NE

NE NE 65/38 (47) 43/35 (38) NE 46/32 (37)

BPA BPA CPA LPA BPA BPA

0.5 0.5 0.4 0.7 0.4 0.5

NE NE

1.0 1.1 1.1 ~3.4 1.5 1.5 1.6

23 24 25 26

2.9 0.4 0.3 0.8

BPA BPA

0.3 0.3

Congenitally absent 90/58 (69) Occluded Occluded Congenitally absent

86/54 (65)

LPA

0.4

10

Occluded 102/62 (75) 83/61 (68) 75/57 (63)

LPA CPA CPA LPA

0.6 Inoperable Inoperable Inoperable

7.6 32 23 21

Group Vl: Two Pulmonary Arteries (high mean pressure in both distally) 27

0.3 0.3

NE NE

Group V: Single Pulmonary Artery 22

BPA = bilateral pulmonary artery bands; CPA = central pulmonary artery band; LPA = left pulmonary artery band; Qp/Qs - pulmonary to systemic flow ratio.

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Preoperative Pulmonary Pressure (mm Hg)

Qp/ Qs

B. Severely Symptomatic Group (Class IV) 8 17

Preoperative and Postoperative Data in 27 Patients With Previous Palliation for Truncal Defects*

20 21

A. Asymptomatic Group (Class I) 7 4 8 7 2 12 6.7

TABLE III

Group IV: Two Pulmonary Arteries (neither entered distally)

Comparison of Clinical and Laboratory Features of S i x Asymptomatic and Five Severely Symptomatic Patients Age at Palliation (mo)

dren severely limited by their cardiac symptoms in Table II. Restricted pulmonary blood flow or significant truncal valve incompetence (or both) was present in four of the five severely symptomatic patients. In contrast, all but one asymptomatic child had a relatively balanced pulmonary to systemic flow ratio with no or only mod-

55/40 (45)

74/54 (61)

CPA

Inoperable

* Patients grouped acco[ding to pulmonary arterial anatomy and cardiac catheterization data from which operability was assessed: 1" Respiratory arrest, 2 days postoperatively. + Early death. § Late death (mediastinal hemorrhage). Figures in parentheses indicate mean pressures. BPA = bilateral pulmonary artery; CPA = central pulmonary artery; LPA = left pulmonary artery; LV = left ventricular; NE = not entered; PA = pulmonary artery; Rp = pulmonary resistance; RPA = right pulmonary artery; RV = right ventricular.

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erate truncal insufficiency. The age at palliation, duration of palliation or number of pulmonary arterial band~ used did not seem to influence the extent of physical limitation. Severe truncal incompetence was present in five patients. All five had bilateral pulmonary arterial banding. Restricted pulmonary flow was evident in three of the five; the other two had a pulmonary to systemic flow ratio of more than 3:1. The age at palliation and duration of palliation in these patients did not differ from those in the group as a whole. The cardiothoracic ratio exceeded 0.55 in all patients and the vascular patterns varied greatly, reflecting the wide range of pulmonary blood flow in these patients. Two patients with an underdeveloped left pulmonary artery had an unusual cardiac silhouette. A large aneurysmal dilation of the proximal segment of the left pulmonary artery was found at operation in one patient (Fig. 2) and was attributed to an extremely stenotic band distal to this abnormality.

The electrocardiogram gave little insight into the hemodynamic status of these patients. All patients had either right ventricular or biventricular hypertrophy, and there was poor correlation between the pattern of hypertrophy and the amount of pulmonary blood flow. Hemodynamic Assessment The patients were grouped according to pulmonary arterial anatomy and cardiac catheterization data, and operability was determined from these findings (Table III). Group I: Eight patients had low pressures in both pulmonary arteries (mean pressure less than half systemic pressure). Mean pressure differences between the right and left pulmonary arteries ranged from 0 to 23 mm Hg. We estimated total pulmonary vascular resistance, using an average of the mean pressure from each artery. All patients were operated on. Intraoperative pressure (after surgical repair) was measured in a pul-

FIGURE 2. Upper left, chest roentgenogram, showing large dilated pulmonary arterial segment in a 3 year old child with a left pulmonary arterial band. Upper right, truncal root angiogram defining a pulmonary arterial aneurysm proximal to stenotic band site. Bottom left, lateral view of angiogram, demonstrating left pulmonary arterial band (arrows).

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monary artery, and the right and left ventricles. Ratios of pressure in the right ventricle or pulmonary artery to that in the left ventricle ranged from 0.1 to 0.5 in seven of the eight patients (Table III). One child (Case 3) with very hypoplastic pulmonary arteries and with a pulmonary artery to left ventricle pressure ratio of 1.0 died immediately after surgery. Group II: Five patients had wide differences in mean pressure between the right and left pulmonary arteries. This group differed from Group I in that near systemic pressure (52 to 72 mm Hg mean pressure) was recorded in one pulmonary artery--the pressure in the other being less than half mean systemic pressure (15 to 40 mm Hg). All patients in this group were considered candidates for corrective surgery on the assumption that the low pressure vascular bed in at least one lung would accommodate the pulmonary flow even though the opposite lung may have been compromised by obstructive vascular changes. Intraoperative pressures were obtained in three of the four patients undergoing surgical repair. A right to left ventricular pressure ratio of only 0.3 was recorded postoperatively in Case 11, a 4 1/2 year old boy who had systemic pressure (103/54 mm Hg) in his left pulmonary artery and low pressure (26/19 mm Hg) in his right pulmonary artery 4 years after palliation. Two other children had moderate pressure elevations in the right ventricle after operation. Death occurred in the fourth patient (Case 9), a 3 year

TABLE

IV

Clinical a n d L a b o r a t o r y Features o f 27 Patients W i t h Palliation by Various Banding Methods Method of Pulmonary Arterial Banding CPA Patients (no.) Age at palliation Range Mean Duration of palliation (yr) Range Mean Patients with severe symptoms (no.) Patients with severe truncal valve incompetence Hemoglobin (g/dl) Range Mean Arterial saturation (room air) (%) Range Mean Pulmonary index (liters/ rain per m 2) Range Mean Qp/Qs Range Mean Patients approved for surgery (no.)

BPA

LPA

8

14

5

4 - 1 5 mo 7 mo

6 w k - 7 yr 15 mo

1 - 1 4 mo 8,4 mo

2 8/12 to 12 8/12 6 2

3 1/2 to 12 1/2 8 3

1 8/12 to 14 6 1/2 1

None

5 (36%)

None

11.7-19.4 16.0

13.0-18.8 14,3

12.6-15.2 14.3

67-94 82

43-93 80

80-91 85

2.6-9.3 4.5

1.1-12,8 6.2

3,0-10.3 6.1

0.4-2.9 1.0 5 (62.5%)

0,2-3.4 1.2 14 (100%)

0.8-3.1 1.7 4 (80%)

BPA = bilateral pulmonary arterial bands; CPA = central pulmonary arterial band; LPA = left pulmonary arterial band; Qp/Qs = pulmonary to systemic flow ratio.

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old child with a congenitally hypoplastic right pulmonary artery and a poorly developed left pulmonary attery distal to a left pulmonary arterial band. Group III: We evaluated six patients for operation by measuring pressure in only one pulmonary artery (the other pulmonary artery was not entered, usually because of a very tight band). Mean pressures were less than half systemic in these arteries. Except for one patient, the postoperative pressure ratio was 0.5 or less. Group IV: In two patients with bilateral pulmonary arterial banding neither pulmonary artery was entered beyond the band site at the time of cardiac catheterization. Both patients were extremely cyanotic, and angiocardiography demonstrated tightly constricting bands with normal-appearing pulmonary arteries distal to the bands. We proceeded with operation, assuming that low pressure existed beyond these stenotic areas. Group V: Five patients had only one pulmonary artery at the time of our study: Two patients had congenital absence of the right pulmonary artery and three others had one artery completely occluded by a band. Pulmonary resistance was calculated in the usual manner. The condition of three pat!ents, with pulmonary resistance greater than 20 units m 2, was considered inoperable. Interpretation of pulmonary resistance in patients with a single pulmonary artery was modified on the premise that a given value of pulmonary resistance in patients with one pulmonary arteriolar bed does not correlate histologically with a similar resistance calculated for patients with two pulmonary arteries. ~1 Because patients with a single vascular bed have approximately half the number of pulmonary arterioles of patients with two lungs, the pulmonary blood flow for the same degree of vascular reactivity with a similar driving pressure would be approximately halved. Therefore, patients with a pulmonary resistance value of less than 20 units m 2 may be candidates for corrective surgery. This concept has been substantiated in our surgical experience in patients with a single pulmonary arterytl; a patient in this group who had a preoperative pulmonary resistance of 10 units m 2 had a postoperative pressure in the right ventricle less than half systemic pressure. Only I of 22 patients (5 percent) with two pulmonary arteries had a hemodynamic status that precluded corrective operation. This patient (Case 27) was a 14 year old child who had elevated pressure in both pulmonary arteries 13 years after surgical palliation with a central pulmonary band. Effectiveness of Palliation

The clinical and hemodynamic features of the patients subjected to the three palliative methods are shown in Table IV. The central pulmonary artery had been banded in eight patients. Only two had significant symptoms, and none had severe truncal valve incompetence. Despite this relatively stable clinical profile, three of the eight children had severe pulmonary vascular disease that precluded operation. The right pulmonary artery was occluded in two patients, and in four others the mean Volume 38

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pressure in the left pdlmonary artery was 49, 39, 16 and 15 mm Hg, respectively, greater than that in the right pulrAonary artery. The distal left pulmonary arterial mean pressure in four of the eight patients was nearly identical to the truncal root pressure. These data suggest that in central pulmonary arterial banding, preferential severe narrowing or occlusion of the right pulmonary artery often Occurs while protection to the left pulmonary vascular system is inadequate. Bilateral pulmonary arterial bands had been used in 14 patients. This type of banding resulted in more complications than did banding of a single pulmonary artery. Because of severe hypoxemia, two patients required later subclavian-pulmonary artery anastomoses. In one of these patients, a debanding and arterioplasty procedure was attempted subsequently. Three patients had hypoplastic pulmonary arteries distal to the site of banding. In two patients, the pulmonary bands migrated peripherally into the hilar region of the lung. Despite their less favorable clinical status and greater incidence of complications, all patients with bilateral pulmonary arterial bands had a hemodynamic status that permitted complete surgical repair. Only a left pulmonary arterial band had been used in five patients. In two of these patients, the right pulmonary artery was congenitally absent. Only one patient was significantly symptomatic at this time and none had severe truncal valve incompetence. The condition of one patient evaluated 14 years after palliation was considered inoperable because of severe pulmonary vascular disease. Another patient had an occluded left pulmonary artery 6 years after palliative operation but had acceptable values for pulmonary resistance in the right lung and thus was a candidate for corrective operation. Discussion

Operability of patients who have had pulmonary arterial banding: The majority of our patients with previous banding had a hemodynamic status still favorable for total corrective operation. The extent to which these results can be applied to the surgical management Of the very young infant with truncus arteriosus is uncertain because our patients were selected because they were survivors of palliation referred to us for consideration of corrective operation. Thus, certain factors predisposed our patients to a more favorable course. Fewer than 20 percent had significant truncal valve incompetence, which is less than the percentage described in young infants with truncal defects studied at autopsy. 12-14 Also, 17 of 27 patients underwent palliation after 6 months of age, when there often is spontaneous improvement. 1,2 Furthermore, the total number of infants operated on and the various methods of palliation used during the period included in our study are unknown. Comparing these data with the natural history of other congenital heart defects associated with high pressure left to right shunts shows that palliation often protects" these patients adequately from pulmonary obstructive vascular disease until the risk of corrective operation becomes less. The exception to this generally

ET AL.

protective effect appears to be the patient with congenital absence of a pulmonary artery, or with surgical occlusion of one pulmonary artery, who continues to be susceptible to severe pulmonary vascular disease. Hemodynamic assessment of operability: The laboratory evaluation of these children presents difficulties. With truncus aiteriosus defects, the possible inequalities of pressure and flow between the two pulmonary arteries often make precise calculation of pulmonary resistance difficult. Neverthelessl our experience indicates that operability can be assessed without precisely defining pulmonary resistance in each lung or the quantitative difference in pulmonary blood flow. The presence of at least one adequate pulmonary artery having low distal pressure or arteriolar resistance is the minimal criterion on which operability is based; it was met by 19 of our 20 patients with two pulmonary arteries a n d catheterization of at least one pulmonary artery. Pulmonary vascular disease or underdevelopment of the pulmonary artery in one lung does not preclude corrective operation so long as the other vascular bed is normal. This finding is supported by clinical and experimental data on patients with pneumonectomy or pulmonary embolism, Whose pulmonary arterial pressure remains normal if the cross-sectional area of the pulmonary vasculature is not reduced by more than 50 percent.15,16 Location of pulmonary arterial band: The location of the pulmonary arterial band may influence future operability. Often, central pulmonary arterial banding occludes or preferentially narrows a pulmonary artery. This may occur because the central arterial segment is shorter than is frequently portrayed, 4,1%1sand the origin of the right pulmonary artery may be contiguous with the truncus arteriosus, even in type I truncus. Distinguishing between type I and type II truncus (Collett and Edwards 9) is often arbitrary, an observation also reported by Bharati et al. 19 Either the space between the right pulmonary artery and truncus cannot accommodate a band or it is so short that minimal distal migration of the band impinges on the right pulmonary artery (Fig. 3).

Problems resulting from pulmonary arterial banding have been reported. 2°,21 Excessive reduction of pulmonary blood flow results not only from an excessively

FIGURE 3. Diagram showing the close relation of the origin of the right pulmonary artery to the truncal root (left) and the possibility of narrowing after central pulmonary arterial banding (right),

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tight band but also from occasional subsequent underdevelopment of the distal pulmonary artery. T h e prenatal relation between blOod flow and arterial development postulated by Heymann and Rudolph 22 appears to apply to the postnatal period as well. Results of corrective surgery after pulmonary arterial banding: A group of 25 patients with truncus arteriosus and p~'evious pulmonary arterial banding underwent complete correction at our institution; the surgical results and postoperative course have recently been reviewed. 23 The postoperative results up to a maximum of 7 years are comparable with the follow-up results in children with truncus defects without previous surgical palliation. The overall operative mortality for the patients with banding was 20 percent, but since use of the Dacron ® conduit (Hancock Laboratories) was begun in November 1972, the operative mortality has decreased to 6 percent. Indications for banding versus corrective surgery: The outlook for the critically ill infant with large pulmonary blood flow with or without associated truncal valve incompetence is extremely poor. 24 Whether the outlook will be better as a result of banding

of the pulmonary arteries or of corrective operation is not yet established. However, the significant reduction in operative mortality to 9 percent since 1972 for older children 25 and recent reports of successful correction in infants 26,27 have persuaded us to resume a trial experience with total correction. In the absence of data clearly establishing the superiority of either of these surgical approaches, the choice should remain an individual one, based on the experience and capabilities of the particular treatment center. The optimal timing for either approach must be guided by cardiac catheterization data as well as by the clinical assessment. Because severe pulmonary vascular disease may occur before the 2nd year of life, determination of pulmonary vascular resistance is essential. Children whose pulmonary vascular resistance values approach 8 units m 2 must undergo either a corrective or a palliative procedure if irreversible pulmonary vascular changes are to be prevented. Significant reductions in calculated pulmonary resistance can be seen while some of these young children are breathing 100 percent oxygen, and this test should be performed in assessing these patients for operation.

References 1. Keith JD, Rowe RD, Vlad P" Heart Disease in Infancy and Childhood, second edition. New York, Macmillan, 1967, p 773 2. Fontana RS, Edwards JE: Congenital Cardiac Disease: A Review of 357 Cases Studied Pathologically. Philadelphia, WB Saunders, 1962, p 95 3. Armer RM, DeOiiveira PF, Lurie PR: True truncus arteriosus: review of seventeen cases and report of surgery in seven patients (abstr). Circulation 24:878, 1961 4. Poirier RA, Berman MA, Stansel HC Jr: Current status of the surgical treatment of truncus arteriosus. J Thorac Cardiovasc Surg 69:169-182, 1975 5. Barratt-Boyes BG: Cardiac surgery in neonates and infants. Circulation 44:924-925, 1971 6. Barratt-Boyes BG, Neutze JM, Seelye ER, et ah Complete correction of cardiovascular malformations in the first year of life. Prog Cardiovasc Dis 15:229-253, 1972 7. Breckenridge IM, Oelert H, Graham GR, et ah Open-heart surgery in the first year of life. J Thorac Cardiovasc Surg 65:58-63, 1973 8. Appelbaum A, Bargeron LM Jr, Pacifico AD, et ah Surgical treatment of truncus arteriosus, with emphasis on infants and small children. J Thorac Cardiovasc Surg 71:436-440, 1976 9. Collett RW, Edwards JE: Persistent truncus arteriosus: a classification according to anatomic types. Surg Clin North Am 29: 1245-1270, 1949 10. LaFarge CG, MietUnen OS: The estimation of oxygen consumption. Cardiovasc Res 4:23-30, 1970 11. Mair DD, Ritter DG, Davis GD, et al- Selection of patients with truncus arteriosus for surgical correction: anatomic and hemodynamic considerations. Circulation 49:144-151, 1974 12. Deely WJ, Hagstrom JWC, Engle MA" Truncus insufficiency: common truncus arteriosus with regurgitant truncus valve: report of four cases. Am Heart J 65:542-548, 1963 13. Becker AE, Becker MJ, Edwards JG: Pathology of the semilunar valve in persistent truncus arteriosus. J Thorac Cardiovasc Surg 62:16-26, 1971 14. Tandon R, Hauck AJ, Nadas AS: Persistent truncus arteriosus: a clinical, hemodynamic, and autopsy study of nineteen cases. Circulation 28:1050-1060, 1963

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15. Fishman AP: Dynamics of the pulmonary circulation. In, Handbook of Physiology, section 2, Circulation, Vol 2 (Hamilton WF, ed). Washington DC, American Physiological SOciety, 1963, p 1713 16. Dalen JE, Haynes FW, Hoppin FG Jr, et ali Cardiovascular responses to experimental pulmonary embolism. Am J Cardiol 20: 3-9, 1967 17. Perloff JK: The Clinical Recognition of Congenital Heart Disease. Philadelphia, WB Saunders, 1970, p 550 16. Nadas AS, Fyler DC: Pediatric Cardiology, third edition. Philadelphia, WB Saunders, 1972, p 438 19. Bharati S, McAIlister HA, Rosenquist GC, et ah The surgical anatomy of truncus arteriosus communis. J Thorac Cardiovasc Surg 67:501-510, 1974 20. Friedman S, Braitman BA: Banding of the pulmonary trunk in persistent truncus arteriosus: rapid subsequent development of inadequate pulmonary blood flow. J Thorac Cardiovasc Surg 66: 799-802, 1973 21. Takahashi M, Lurie PR, Perry EL, et ah Clinical and hemodynamic effects of pulmonary artery banding. Am J Cardiol 21:174-184, 1968 22. Heymann MA, Rudolph AM: Effect of congenital heart disease on fetal and neonatal circulations. In, Neonatal Heart Disease (Friedman WF, Lesch M, Sonnenblick EH, ed). New York, Grune & Stratton, 1973, p 51 23. Parker RK, McGoon DC, Danielson GK, et ah Repair of truncus arteriosus in patients with prior banding of the pulmonary artery. Surgery 78:761-767, 1975 24. Marcelleffi C, McGoon DC, Mair DD- The natural history of truncus arteriosus, Circulation, in press 25. Marcelletti C, McGoon DC, Danielson GK, et al: Early and late results of surgical repair of truncus arteriosus (abstr). Circulation 52:Suppl 2:11-101, 1975 26. Singh A, de Leval M, Stark J: Total correction of type I truncus arteriosus in a 6-month-old infant. Br Heart J 37:1314-1316, 1975 27. Ebert PE, Robinson SJ, Stanger P, et al: Pulmonary artery conduits in infants under six months of age. Presented at the annual meeting of the American Association for Thoracic Surgery, Los Angeles, April 23-25, 1976

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