Fractional gradients along the outflow tract of the right ventricle in tetralogy of Fallot

J THoRAc

CARDIOVASC SURG

81:774-780, 1981

Fractional gradients along the outflow tract of the right ventricle in tetralogy of Fallot Anatomic and hemodynamic correlative study In 16 patients undergoing surgical correction of tetralogy of Fallot, attempts were made to determine where, in the outflow tract, the most critical preoperative obstruction was located. In the open chest, pressures were taken in the right ventricle, proximal conus, distal conus, and pulmonary artery. Pressure gradients between these levels were indicative of stenosis at the infundibular ostium (Ost.), conus (C), and pulmonary valve (PV), respectively. Total liP = liP Ost. + liP C + liP PV, where liP is the pressure gradient between the right ventricle and the pulmonary artery. In order to evaluate the contribution of each obstructive segment to the overall obstruction, we introduced a new term, the fractional gradient (FG). The FG is defined by the following formula: FG = (liP segmental! liP total). The average total pressure gradient in this series was 72 mm Hg. The average segmental gradients were 15.5, 39.0, and /7.0 mm Hg for the infundibular ostium, conus, and pulmonary valve, respectively. The FGs across segments were 0.20, 0.54, and 0.26, indicating that only 20% of the average obstruction was located in the infundibular ostium. The remaining obstruction is distal and unrelated to the infundibular ostium. Analysis of the FGs in the various types of conus indicated, from an anatomic viewpoint, that in 80% of patients with tetralogy the infundibulectomy does not have to be radical.

Aram Smolinsky, M.D., Mordechai Tamarkin, M.D., and Daniel A. Goor, M.D., Tel-Hashomer and Tel-Aviv, Israel

DesPite the initial good operative results in complete repair of tetralogy of Fallot, long-term follow-up occasionally is disappointing. The more serious late problems are sudden death, I, 2 significant ventricular arrhythmias," and dysfunction of the right ventricle. 2,4,5 It was our impression that extensive resection of muscle bundles in the right ventricular outflow tract (RVOT) may not be necessary, may even be harmful, and may contribute to ventricular arrhythmias and right ventricular dysfunction. We used two approaches to evaluate this question systematically. First, we employed a modified conservative infundibulectomy. The initial results with this approach will be presented in a concomitant report." Second, we conducted a study From the Department of Cardiac Surgery, The Chaim Sheba Medical Centre, Tel-Hashomer, and The Sackler School of Medicine, University of Tel-Aviv, Tel-Aviv, Israel. Received for publication March 31, 1980. Accepted for publication Nov. 5, 1980. Address for reprints: Daniel A. Goor, M.D., Department of Cardiac Surgery, Chaim Sheba Medical Centre, Tel-Hashomer, Israel.

774

concentrating on the fundamental functional anatomy of the pulmonary conus in tetralogy of Fallot. Information gained from this latter study is the basis for the present report. Review of the literature revealed that just a few reports ,5, 7-13 only partially related to that question, have been published and none offers a definite answer. In the present work, a method to evaluate the relative contribution to obstruction of each segment of the RVOT was developed. In more than 80% of the cases, the critical obstruction was found to be distal and unrelated to the muscle bundles that usually are extensively resected at operation. Method

The segmental anatomy of the conus is much more obvious in tetralogy of Fallot than in the normal heart, and in most cases the infundibular ostium, conus, and pulmonary valve are clearly delineated (Fig. 1). Three types of conus are usually recognized. 14-16 In this report we rely on the conventional terminology with, however, minor changes (Fig. 1).

0022-5223/81/050774+07$00.70/0 © 1981 The C. V. Mosby Co.

Volume 81

Tetralogy of Fallot

Number 5 May, 1981

775

DISTALCONUS (D~)

CONAL SEPTUM FACING PARIETAL WALL CONAL SEPTUM FACING INFUNDIBULAR OSTIUM

CONAL SEPTUM (CRISTA)

PROXIMAL CONUS (PC) SEPTAL BAND

VSD

INFUNDIBULAR OSTIUM

BY

B

A CONUS TYPE I

(OBSTRUCTIVE OSTIUM I

C

CONUS TYPE ]I (OBSTRUCTIVE CRISTA)

CONUS TYPE m ( HYPOPLASTICI

~~--------------------------

CONUS

VENTRICULAR JUNCTIONAL LEVEL

_...1

Fig. 1. Functional anatomy of the conus and the various types of conus in tetralogy of Fallot. Top panel, The general anatomy of the outflow tract in tetralogy and the obstructive potentials of the infundibular ostium, crista, and pulmonary valve. Note that the crista (conal septum) is facing the anterior parietal wall as well as the infundibular ostium. Whenever the distance between the crista and the parietal wall is short, conal obstruction is present. In addition, the crista is part of the infundibular ostium and may be obstructive in that direction. Also shown are the points of pressure measurements-the right ventricle (RV), the proximal and the distal conus, and the pulmonary artery. VSD. Ventricular septal defect. Bottom panel. The three illustrations (A to C) demonstrate the three basic types of conus in tetralogy. In conus type I, the pulmonary valve and the infundibulum are normal. Obstruction is at the level of the infundibular ostium. Conus type II includes all the varieties of tetralogy which are between conus type I and III. Obstruction is mostly due to the displaced crista. Conus type III includes hypoplastic pulmonary ring and diminutive infundibulum, and there are no obvious obstructive muscle bundles at the level of the infundibular ostium.

Pressure gradients were sought in the infundibular ostium, the conal zone, and the pulmonary valve. This was done by measuring the intracardiac pressure at four points (Figs. 1 and 2). The pressure gradient of the infundibular ostium was obtained from the pressure difference measured in the right ventricular body and the proximal conus. The pressure gradient of the conus was obtained from the pressures in the proximal and the distal conus, and the pressure gradient of the pulmo-

nary valve was obtained from pressures in the distal conus and pulmonary artery. The study was performed on 16 patients undergoing complete correction of tetralogy of Fallot. After the pericardium had been opened, pressures were measured in the selected points (Figs. 1 and 2). The measurements were repeated four or five times until it was beyond doubt that the hemodynamic condition was stable. Next the patient was connected to a heart-

The Journal of Thoracic and Cardiovascular Surgery

776 Smolinsky, Tamarkin, Goor

Stitch 2

COnal incision

stitch 1

C Fig. 2. Top panel, Three operative photographs of the same heart (Case 15. Table I), A, Before onset of cardiopulmonary bypass, B, During cardioplegia, C, After termination of cardiopulmonary bypass. Two black sutures demarcate points PC (proximal conus) and DC (distal conus). Pressures were taken in these two spots in addition to right ventricular (RV) and pulmonary arterial (PA) pressures before going on bypass. The incision of ventriculotomy (conotomy) is short and does not pass the level of the septal and parietal bundles. The apex of the right ventricle is pulled with a stitch to delineate the proportional length of the incision and proportional location of stitches PC and DC. VSD, Ventricular septal defect.

lung machine, the conus was opened, and the accuracy of the location of the pressure measurement was verified (Fig, 2). Also, the anatomic features of the pulmonary valve, conus, and infundibular ostium were documented, The absolute values of pressure gradients across individual segments are functions of two parametersflow and degree of obstruction (resistance), Since the purpose of this report was to study, by pressure gradients, the relative obstructions at different levels of the R VaT, a concept which bypasses the factor of flow had to be conceived, This concept is termedfractional gradient (FG). The FG refers to the contribution of each segment to the overall obstruction. In the formula Total AP = AP Ost.

+

AP C

+

AP PV

the total ap refers to the pressure gradient between the right ventricle and the pulmonary artery and ap Ost., ap C, and aP PV refer to the pressure gradients over the infundibular ostium, the conus, and the pulmonary valve, respectively. The FGs of each obstruction are calculated by the formula:

FG

I _ AP segmental segmenta AP total

and along the outflow tract: AP Os!.

AP C

AP PV

= Total AP + Total AP + Total AP I = FG Ost. + FG C + FG PV*

Results The type of conus, densities of muscle bundles, and anatomy of the pulmonary valves are presented in Table I. The pressure measurements were as follows (Tables II and III): The average pressures and FGs of the infundibular ostium, conus, and pulmonary valves were 16 mm Hg (FG 0.20), 39 mm Hg (FG 0.54), and 17 mm Hg (FG 0.26), respectively, The average gradients in the 12 patients with conus type II were as follows (Table III): 18 mm Hg (FG *This formula as well as its applicability to flow resistances in series was endorsed by Professor C. H. Gutfinger, Dean of the Faculty of Mechanical Engineering, Israel Institute of Technology, Haifa, Israel.

Volume 81 Number 5 May, 1981

Table I. Anatomic findings in RVOT Case No.

777

Tetralogy of Fallot

I

I

Age (yr)

I

4

2

5 11/12

3 4 5 6 7 8

9

23

12

12

13 14t

3 4 6 6

15 16

Diam. PA (mm)

15 15 12 20

5 3 5 4Y2 5 9

10 II

I

Diam. aorra (mm)

14

7

12 12

I

Diam. PV ring (mm)

7 5

12 4 7 3 8 4

16

18 4

20

19

18

10

20 25 30 25 30

25 30 15 15

25 30 15

17

17

20 18

15 15

15 12 12

20

18

10

7

6

I

I

No. of cusps

Density, trabec. trans. zone

Type of conus

5 12

2 2 3

II II + R*

4

2

+1 +1 +2 +1 +1

Diam. PV orifice (mm) 3

2 3 4 4

25 30 13 6

15 3 8 7

o

2 2 NM 3 3

2 3 3 2 3

2

o

+1 +1 +2 +1 +1 +1 +1 +1 +1

I

II II III III

II+R II I

II II II II II II

Legend: RVOT, Right ventricular outflow tract. PA, Pulmonary artery. PV. Pulmonary valve. NM, Not mentioned.

• Midconal ring. t Systemic-pulmonary Waterston shunt.

0.25) in the infundibular ostium, 38 mm Hg (FG 0.50) in the conus, and 19 mm Hg (FG 0.25) in the pulmonary valve. In the two patients with conus type I, the average pressure gradients were 72 mm Hg (FG 0.81) in the infundibular ostium, 22 mm Hg (FG 0.18) in the conus, and I mm Hg (FG 0.1) in the pulmonary valve. In the two patients with conus type III, the values were o in the infundibular ostium, 63 mm Hg (FG 0.77) in the conus, and 19 mm Hg (FG 0.23) in the pulmonary valve.

Discussion The key point of the present report is the term fractional gradient (FG). This term enables one to differentiate between the individual contribution of each segment to the overall obstruction. One must remember that all of the obstructions are distal to the ventricular septal defect and that the total pulmonary flow passes via a line of obstruction arranged in a series, in the order of infundibular ostium, conus, and pulmonary valve. The relationship between flow, obstruction, and gradients can be achieved from the formula of Gorlin and Gorlin'": ~p

=

2

Flow (Orifice area)" . K

That is, the pressure gradients are in direct relationship to the square flow and are inversely related to the square area of the stenosis. Since the total and relative

pulmonary flows differ from one patient to another and the absolute value of the pressure gradient depends upon the square flow, the absolute value of the pressure gradient cannot be considered reliable. In order to bypass this obstacle, the term fractional gradient (FG) had to be introduced. As previously explained, the FG is the segmental pressure gradient divided by the total pressure gradient, and this value gives the relative contribution of each segment to the overall obstruction in a specific patient. According to the formula of Gorlin and Gorlin.!? pressure gradient depends on two factorsthe magnitude of the flow and the severity of the obstruction. In cases in which the flow through the outflow tract is relatively stable, the FG is related only to the magnitude of the obstruction: FG = Segmental gradient = Overall gradient Flow along RVOT x segmental obstruction (resistance) Flow along RVOT x overall obstrucion (resistance) FG

=

Segmental gradient Overall gradient

The anatomy of tetralogy of Fallot and the process of pressure measurements during the study render this equation applicable to tetralogy. First, the same amount of blood that passes, at a given instant, via the infundibular ostium (proximal obstruction) is passing via the pulmonary valve (distal obstruction). Thus, at a given instant, the same amount of blood is passing through all

The Journal of

778

Smolinsky, Tamarkin, Goor

Thoracic and Cardiovascular Surgery

Table II. Preoperative pressure gradients and fractional gradients in RVOT in tetralogy of Fallot Total

Case No. I

2 3 4 5 6 7 8 9 10 II

12 13 14 15 16

Type of conus

Density of trabeculations"

RVP (mmHg)

II II

I I

75 80 85 80 70 85 100 55 80 145 70 75 110 120 69

I

2

II II III III II II

I I

0 0

I

2

II II II II II II

I I I I I I

I I

Average

I

~

P (RVP minus PAP)

I

PAP (mmHg)

Total RV-PA gradient (mm Hg)

77

0 10 10 20 0-2 2 20 10 20 30 15 15 30 14 24 4

75 70 75 60 70 83 80 45 60 115 55 60 80 106 45 73

86

14

72

Legend: <1P. Pressure gradient. RVP, Right ventricular pressure. PAP, Pulmonary artery pressure. RV, Right ventricle, PA, Pulmonary artery. FG, Fractional gradient. PCP, Proximal conus pressure. DCP. Distal conus pressure. '0 = No trabeculations. I = Mild-to-moderate trabeculations. 2 = Heavy trabeculations.

Table III. Average pressure gradients and fractional gradients in RVOT in tetralogy of Fallot All cases (n = 16) Gradient (mm Hg) Infundibular ostium Conus Pulmonary valve RV-PA gradient

16 39 17 72

I

Conus type 1 (n = 2) FG

Gradient (mm Hg)

0.20 0.54 0.26 1.0

72

22 I

95

I.

FG

0.81 0.18 0.01 1.0

Conus type 11 (n = 12) Gradient (mm Hg) 1 FG

18 38 19 75

0.25 0.50 0.25 1.0

Conus type 111 (n = 2) Gradient (mm Hg)

o

63 19 82

I FG o 0.77

0.23 1.0

Legend: FG, Fractional gradient. RV-PA, Right ventricle-pulmonary artery.

of the obstructions in the RVOT, because in tetralogy the ventricular septal defect is located proximal to (below) the first obstruction i.e., the infundibular ostium (Fig. 1). The second critical question regarding the applicability of the FG is whether the flow during the period of measurement was stable. It takes only 45 to 60 seconds to complete a four-point measurement. The study was run in such a way that the pressure measurements were taken three or four times until the results repeated themselves. Repetition of results was indicative of a steady flow. On the basis of the FG values, obstructions were detected at three distinctive levels-the infundibular ostium, the conus, and the pulmonary valve. In patients with conus type I, the main obstruction was in the infundibular ostium. In this series there are two such

cases (12.5%), and in the literature the overall incidence of conus type I in tetralogy of Fallot is about 15%. t4. t5 In the patients with conus type II, about 50% of the obstructions were in the conus (FG 0.5) (Table III), 25% (FG 0.25) in the pulmonary valve, and 25% (FG 0.25) in the infundibular ostium. In the present series there were 12 such cases (75%), and the overall incidence of conus type II in tetralogy of Fallot is approximately 65%. t4. t5 In the patients with conus type III, 77% of the obstruction were in the conus (FG 0.77), and in the infundibular ostium the FG was O. In this series there were two such cases (12.5%), and the overall incidence of this type of conus is approximately 10%. t4, t5 Hence, among 16 studied cases, the main obstruction was distal and unrelated to the muscle bundles ofthe infundibular ostium in 13 cases (p < 0.001).

Volume 81

Tetralogy of Failot

Number 5 May, 1981

Infundibular ostium FG PCP (mmHg)

I

RVP minus PCP (mm Hg)

I

Conal FG FG, info ostium

DCP (mmHg)

I

779

Pulmonary valve FG

PCP minus DCP (mm Hg)

I

FG. conus

PAP (mmHg)

I

DCP minus PAP (mm Hg)

I

FG. pulm. valve

70 80 10 60 55 85 100 50 70 75 70 70 75 107 69 77

5 0 75 20 15 0 0 5 10 70 0 5 35 13 0 0

0.Q7 0.0 1.0 0.33 0.21 0.0 0.0 0.11 0.17 0.61 0.0 0.08 0.44 0.12 0.0 0.0

30 30 10 60 25 35 25 35 20 32 25 35 35 26 38 34

40 50 0 0 30 50 75 15 50 43 45 35 40 81 31 43

0.53 0.71 0.0 0.0 0.43 0.60 0.94 0.33 0.83 0.37 0.82 0.59 0.50 0.76 0.68 0.45

0 10 10 20 0-2 2 20 10 20 30 15 15 30 14 24 4

30 20 0 40 25 33 5 25 0 2 10 20 5 12 14 30

0.4 0.29 0.0 0.67 0.36 0.40 0.06 0.56 0.0 0.02 0.18 0.33 0.06 0.11 0.31 0.41

70

16

0.20

31

39

0.54

14

17

0.26

The question that arises in this work, namely, the location of the most critical obstruction, has been discussed in the past. 5, 7, 9-13 In the previous studies, however, either anatomic or hemodynamic evaluations were made. To the best of our knowledge, the anatomic and hemodynamic correlations that we are presenting have not been described previously. Review of pathological studies reveals that the authors assumed that the main obstruction should be in the conus. 9 - 13 According to Van Mierop and Wiglesworth;'? the obstruction is due mostly to the deviated crista (as seen in Fig. 1); this theory was accepted by most pathologists. 9, 11-13 That the conus is the most obstructive segment was shown also in the catheterization laboratory. 5. 7. 18, 19 In none of these pathological and clinical studies was the region which usually undergoes radical resection, the infundibular ostium, considered to be obstructive. The present work proves that in most cases of tetralogy of Fallot the main obstruction is indeed in the conus. However, in some cases the main obstruction is located in the infundibular ostium, and in others the obstruction is equally distributed among the infundibular ostium, conus, and pulmonary valve. REFERENCES Quattlebaum TG, Varghese PJ, Neill CA, Donahoo JS: Sudden death among postoperative patients with tetralogy of Fallot. A follow-up study of 243 patients for an aver-

age of twelve years. Circulation 54:289-293, 1976 2 Gillette PC, Yeoman MA, Mullins CE, McNamara DG: Sudden death after repair of tetralogy of Fallot. Electrocardiographic and electrophysiologic abnormalities. Circulation 56:566-571, 1977 3 Rosing DR, Borer JS, Kent KM, Maron BJ, Siedes SF, Morrow AG, Epstein SE: Long-term hemodynamic and electrophysiologic assessment following operative repair of tetralogy of Fallot. Circulation 58:Suppl 1:209, 1978 4 Graham TP Jr, Cordell D, Atwood GF, Boucek RJ, Boerth RC, Bender HW, Nelson JH, Vaughn WK: Right ventricular volume characteristics before and after palliative and reparative operation in tetralogy of Fallot. Circulation 54:417-423, 1976 5 Gotsman MS: Increasing obstruction to the outflow tract in tetralogy of Fallot. Br Heart J 28:615-621, 1966 6 Goor DA, Smolinsky A, Mohr R, Caspi J, Shern-Tov A: The drop of residual right ventriclar pressure 24 hours after conservative infundibulectomy in repair of tetralogy of Fallot. J THORAC CARDIOVASC SURG (in press) 7 Kaplan S, Helmsworth JA, McKinivan CE, Benzing G III, Schwartz DC, Schreiber JT: The fate of reconstruction of the right ventricular outflow tract. J THORAC CARDIOVASC SURG 66:361-374, 1973 8 Kirklin JW, Ellis FH Jr, McGoon DC, DuShane JW, Swan HJC: Surgical treatment for the tetralogy of Fallot by open intracardiac repair. J THORAC CARDIOVASC SURG 37:22-51,1959 9 Lev M, Eckner FAO: The pathologic anatomy of tetralogy of Fallot and its variation. Chest 45:251-261, 1964 10 Van Mierop LHS, Wiglesworth FW: Pathogenesis of transposition complexes. II. Anomalies due to faulty

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transfers of the posterior great artery. Am J Cardiol 12:226-232, 1963 Goor DA, Lillehei CW, Edwards JE: Ventricular septal defects and pulmonic stenosis with and without dextroposition. Chest 60: 117-128, 1971 Rosenquist GC, Sweeney U, Stemple DR, Christianson SD, Rowe RD: Ventricular septal defect in tetralogy of Fallot. Am J Cardiol 31:749-754, 1973 Van Praagh R, Van Praagh S, Nebesar RA, Muster AT, Sinha SN, Paul MH: Tetralogy of FaIlot. Underdevelopment of the pulmonary infundibulum and its sequellae. Am J Cardiol 26:25-33, 1970. Johns TNP, Williams GR, Blalock A: The anatomy of pulmonary stenosis and atresia with comments on surgical therapy. Surgery 33:161-172, 1953 Hawe A, Rastelli GC, Ritter DG, DuShane JW, McGoon DC: Management of the right ventricular outflow tract in

Thoracic and Cardiovascular Surgery

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severe tetralogy of FaIlot. J THORAC CARDIOVASC SURG 60:131-143, 1970 Goor DA, Lillehei CW: Congenital Malformation of the Heart, ed I, New York, 1975, Grone & Stratton, Inc., p 186 Gorlin R, Gorlin SG: Hydraulic formula for calculation of the area of the stenotic mitral valve, other cardiac valves, and central circulatory shunts. 1. Am Heart J 41:1-29, 1951 Ruzyllo W, Nihill MR, Mullins CE, McNamara DG: Hemodynamic evaluation of 221 patients after intracardiac repair of tetralogy of Fallot. Am J Cardiol 34:565576, 1974 Shah P, Kidd L: Hemodynamic responses to exercise and to isoproterenol following total correction of Faller's tetralogy. J THORAC CARDIOVASC SURG 52:138-145, 1966