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Experimental evaluation of atrial function in right atrium-pulmonary artery conduit operation for tricuspid atresia
J THoRAc CARDIOVASC SURG 81:762-767, 1981
Experimental evaluation of atrial function in right atrium-pulmonary artery conduit operation for tricuspid atresia Right ventricular bypass operations were performed in dogs by right atrium-pulmonary artery (RA-PA) conduits with closure of the tricuspid valve. Atrial fibrillation (AF) was induced in prebypass (control) and postbypass (postconduit) studies. Six dogs tolerated the procedure and had postoperative sinus rhythm (SR). In the postconduit studies, AF resulted in significant declines in both mean arterial pressure (73 ± 2 to 65 ± 2 mm Hg [mean ± SEM], p < 0.05) and pulmonary blood flow (/,050 ± 160 to 880 ± 110 ml/min, p < 0.05). However, there were no significant differences between the magnitude of these changes and those during control studies. Mean right atrial pressure was markedly elevated (17.3 ± 1.3 mm Hg) during SR after the conduit operations, but it did not increase significantly with AF. In volume load studies, pulmonary blood flow increased in proportion to rises between 15 and 30 mm Hg in mean right atrial pressure. The results suggest that right atrial contraction is not critical to the maintenance of pulmonary blood flow following RA-PA conduit operations.
Hikaru Matsuda, M.D., Yasunaru Kawashima, M.D., Hisateru Takano, M.D.,* Katsuhiko Miyamoto, M.D., and Tohru Mori, M.D.,** Osaka, Japan
Since Fontan and Baudet 's 1 initial report in 1971, the right atrium-pulmonary artery (RA-PA) conduit operation has been widely performed, with some modifications, as a functionally corrective procedure for both tricuspid atresia and single ventricle."? In this operation, the right atrium has been regarded as an important pump for the maintenance of pulmonary circulation, I, 8 and sinus rhythm (SR) is considered to be one of the basic criteria for selection of patients for this operation." However, it has not yet been clearly established whether right atrial contraction is essential to the success of this operation. Recently, Shemin and his associates'? reported an experimental study that suggested a less significant role for the right atrium as a
From The First Department of Surgery, Osaka University Medical School, Fukushima-ku, Osaka, Japan. Received for publication April 18, 1980. Accepted for publication Aug. 27, 1980. Address for reprints: Hikaru Matsuda, M.D., The First Department of Surgery, Osaka University Medical School, Fukushima-ku, Osaka 553, Japan. *Present address: National Cardiovascular Center, Suita, Osaka, Japan. **Present address: The Second Department of Surgery, Tottori University Medical School, Yonago, Japan.
762
pump in the RA-PA conduit model. Following a preliminary study!' which suggested that SR was not necessarily critical to the RA-PA conduit operation, we designed the present investigation to establish further the role of atrial contraction in the RA-PA conduit operation. In this experiment, hemodynamic data were compared during SR and electrically induced atrial fibrillation (AF) in dogs.
Method The operations were performed on 10 mongrel dogs weighing 13 to 17 kg. After initial injection of ketamine hydrochloride, sodium pentobarbital was used to maintain anesthesia, and respiration was controlled with a volume-type ventilator. The chest was opened bilaterally by a transstemal incision. Before cardiopulmonary bypass was established, control studies were carried out by converting cardiac rhythm from SR to AF through an electrical stimulus of 3 V applied directly to the right atrium. Electrocardiograms, arterial pressures, cardiac output, and right and left atrial pressures were monitored continuously and recorded simultaneously. Blood flow of the ascending aorta was measured with an electromagnetic flowmeter (Statham SP-2201) and used as cardiac output. Cardiopulmonary bypass using a bubble oxygenator
0022-5223/81/050762+06$00.60/0 © 1981 The C. V. Mosby Co.
Volume 81 Number 5
May, 1981
Tricuspid atresia
763
primed with fresh homologous blood was established by insertion of venous cannulas directly into both venae cavae. The tricuspid orifice was closed completely with several mattress sutures through a right ventriculotomy. A fresh aortic homograft containing a valve was placed between the right atrial appendage and the pulmonary artery, and the pulmonary artery trunk was ligated (Fig. 1). Cardiopulmonary bypass was discontinued with rise of venous pressure. A continuous drip of epinephrine was required on some occasions to maintain an adequate systemic pressure. The chest remained open during the hemodynamic measurements. In addition, flowmeters were placed around the grafts to measure the pulmonary blood flow or cardiac output. After measurement of the hemodynamic parameters and graft flow during SR, AF was induced electrically. After 10 to 15 minutes, hemodynamic data were again obtained. Volume load studies during SR were also conducted by raising venous pressure over relatively short periods and by measuring graft flow at varying right atrial pressures. All hemodynamic data were expressed as mean ± standard error of the mean (SEM). Results Hemodynamic studies were completed on six dogs that tolerated the operation. The period of observation was confined to within 5 hours of completion of bypass. Characteristic recordings of the postconduit studies are presented in Fig. 2. During SR, marked "a" waves were noted in the right atrial and pulmonary arterial pressures and corresponding pulsating blood flow patterns were observed in the grafts. Thus blood was being pumped from the right atrium to the pulmonary artery. During AF, however, "a" waves were not observed and graft flow was nonpulsatile. Both systemic arterial pressures and pulmonary blood flow were maintained during AF. Hemodynamic consequences resulting from AF in the control and postconduit studies are summarized and illustrated in Fig. 3. In the postconduit studies, the mean arterial pressure during SR (73 ± 2 mm Hg) decreased to 65 ± 2 mm Hg (p < 0.05); pulmonary blood flow during SR (1,050 ± 140 ml/min) also decreased, to 880 ± 110 ml/min (p < 0.05). These lower values during SR after conduit placement were not significant when compared to the control values. Although both mean arterial pressure and pulmonary blood flow fell significantly during AF following conduit placement, the magnitude of the decreases did not differ significantly from the control values for normal circulation. Average heart rates were 125 ± 5 beats/
Tricuspid Valve FIg. 1. The experimental model. A conduit (graft) is placed between the right atrial appendage and the pulmonary artery trunk after the tricuspid valve is completely closed through the right ventricle. The pulmonary artery trunk is ligated(arrow). SVC. Superiorvenacava./VC. Inferior vena cava. RA. Right atrium. RV. Right ventricle. PA. Pulmonary artery. AO. Aorta. EMF, Electromagnetic flowmeter.
min during SR and 110 ± 4 beats/min during AF in postconduit studies. Mean right atrial pressure was. markedly elevated after the conduit operation during SR (17.2 ± 1.2 mm Hg) and was almost identical to the mean pulmonary arterial pressure (17.1 ± 1.2 mm Hg). With AF, the mean right atrial pressure increased to 18.8 ± 1.5 mm Hg (NS). The mean left atrial pressure was low (6.3 ± 0.4 mm Hg) during SR following conduit placement but increased to 9.5 ± 1.5 mm Hg with AF (p < 0.01). There were no statistically significant differences in the magnitude of the change in mean left atrial pressure with AF between the control and the postconduit studies. The pulmonary blood flow, the pressure gradient between the right and left atria, and the calculated pulmonary vascular resistance were compared in postconduit studies and are presented in Table I. With AF, sig-
The Journal of Thoracic and Cardiovascular Surgery
764 Matsuda et al.
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Fig. 2. Representative pressure and flow recordings during sinus rhythm (left) and atrial fibrillation (right) after RA-PA conduit. EKG. Electrocardiogram. AP, Arterial pressure. RAP, Right atrial pressure. PAP. Pulmonary artery pressure. nificant decreases in pulmonary blood flow (-17%) and in the pressure gradient (-12%) were noted. However, both of these parameters showed similar changes during AF, and calculated pulmonary vascular resistance increased only slightly (NS). In volume load studies during SR, pulmonary blood flow increased significantly in response to a rise in mean right atrial pressure between 15 and 30 mm Hg (Fig. 4). When mean right atrial pressure exceeded 20 mm Hg, however, the right atrium gradually lost its capacity to contract, although the electrocardiogram remained in SR. Discussion Supraventricular dysrhythmias in general and AF in particular have been a matter of concern after the Fontan operation because of disturbance of right atrial
function. I. 8. 10 Several clinical reports have described the hemodynamic consequences of postoperative atrial dysrhythmias. Stanford and his associates" reported less significant hemodynamic changes in junctional rhythms with loss of atrial contraction. Behrendt and Rosenthal? described a patient who tolerated well several episodes of AF following an RA-PA conduit operation for single ventricle. On the other hand, ROSS,4 Henry," and their associates described episodes of significant postoperative depression in cardiac output and arterial pressure during nodal rhythm or AF. Fontan also has described a patient in whom severe venous congestion developed following AF; in this instance, cardioversion restored SR and the patient's condition improved markedly. 8 Experimentally, Robicsek and his associates 13 have reported long-term success with complete right heart
Volume 81 Number 5 May, 1981
Tricuspid atresia
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Fig. 3. Comparison of the hemodynamic changesin meanarterialpressure(mAP), pulmonary blood flow (cardiac output)(Q), mean right atrial pressure(mRAP), and mean left atrial pressure(mLAP) resultingfrom inducedatrial fibrillation in prebypass control and postconduit studies. SR, Sinus rhythm. AF, Atrial fibrillation. bypass operations in dogs. These operations were performed by exclusion of both the right atrium and ventricle by construction of superior vena cava-right pulmonary artery and inferior vena cava-left atrium shunts. In this model, however, the venous blood from the inferior vena cava did not perfuse the lung, because it shunted directly into the left atrium, and no evidence was presented to suggest that total systemic venous return could be circulated through the pulmonary circuit in the absence of the pumping chamber. Shemin and his associates 10 conducted experiments with atrial and ventricular pacing in which mechanical atrial systole was eliminated. They observed that the right atrium does not appear to function as a pump in the maintenance of pulmonary blood flow following an RA-PA conduit operation. They further indicated that
right atrial pressure was the most important factor influencing cardiac output. Instead of the atrial and ventricular pacing that Shemin's group'? employed, we utilized electrically induced AF to obliterate atrial contraction. The results of our investigation indicated that both systemic arterial pressure and pulmonary blood flow were maintained during AF after placement of the RA-PA conduit and tricuspid valve closure. Moreover, the magnitude of the decreases noted in these two parameters and the increase in mean left atrial pressure with AF in the postconduit studies were similar to those measured during the control study, where left ventricular output was depressed with AF in normal circulation. Consequently, the loss of atrial contraction itself, particularly of the right atrium, did not significantly influence the
The Journal of Thoracic and Cardiovascular Surgery
766 Matsuda et al,
L/min 2.0 1.5 Q mean ± S.E.M.
1.0
0=5
0.5 10
25
20
15
30
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Fig. 4. Effect of volume load on pulmonary blood flow (Q) during sinus rhythm after RA-PA conduit. mRAP, Mean right atrial pressure.
Table I. Hemodynamic data/ollowing RA-PA conduit operation in dogs _ _ _ _ _ _ _ _...L..I
Pulmonary blood flow (ml/min) RA-LA pressure gradient (mmHg) PVR (dyne-sec-cm")
I-------.----
SR_ _
1,240 ± 130· 12.3 ± 0.7 830 ± 120
AF
1,030 ± 100 10.8 ± 1.0 880 ± 150
p Value
< 0.05 P < 0.05 NS
p
Legend: RA. Right atrium. PA, Pulmonary artery. SR, Sinus rhythm. AF, Atrial fibrillation. LA. Left atrium. PVR, Pulmonary vascular resistance. NS, Not significant. ·Mean ± SEM.; n = 4.
o'"
right-sided circulation in this RA-PA conduit experiment. This observation was further confirmed by the absence of a significant increase in mean right atrial pressure with AF. If the right atrium had been serving as a pump for pulmonary circulation after the conduit operation, the hemodynamic depressions induced by AF might have been expected to have produced significantly different changes in systemic arterial pressure and pulmonary blood flow from the control study. These results, therefore, suggest that right atrial contraction is of secondary importance to the maintenance of pulmonary circulation following this RA-PA conduit experiment. Rushmer':' has stated that a pressure gradient as small as 6 mm Hg between the pulmonary artery pressure and left ventricular diastolic pressure will force the total systemic output into the pulmonary circuit. Our experimental study suggested similar changes between pulmonary blood flow and pressure gradient across the lung following establishment of a conduit. The volume load study further showed a proportional increase in pulmonary blood flow with increased venous pressure. Therefore, the pressure gradient across the lung together with venous pressure appears to be more critical to the maintenance of pulmonary circulation in the
RA-PA conduit operation. It appears to be necessary to maintain a low left atrial pressure in order to maintain a pressure gradient without significant elevation in venous pressure. For this to be achieved, sufficient left ventricular function with SR is necessary.
2
3
4 5
6
REFERENCES Fontan F, Baudet E: Surgical repair of tricuspid atresia. Thorax 26:240-248, 1971 Fontan F, Choussat A, Brom AG, Chauve A, Deville C, Castro-Cels A: Repair of tricuspid atresia. Surgical considerations and results, Paediatric Cardiology 1977, R Anderson, EA Shinebourne, eds., London, 1978, Churchill Livingstone, p 567 Kreutzer G, GaHndez E, Bono H, DePalma D, Laura JP: An operation for the correction of tricuspid atresia. J THORAC CARDIOVASC SURG 66:613-621, 1973 Ross DN, Somerville J: Surgical correction of tricuspid atresia. Lancet 1:845-849, 1973 Henry IN, Devloo RAE, Ritter 00, MairDD, Davis GD, Danielson GD: Tricuspid atresia. Successful surgical correction in two patients using porcine xenograft valves. Mayo Clin Proc 49:803-810, 1974 Yacoub MH, Radley-Smith R: Use of a valved conduit from right atrium to pulmonary artery for correction of single ventricle. Circulation 54:Suppl 3:63, 1976
Volume 81 Number5 May, 1981
7 Behrendt DM, Rosenthal A: Cardiovascular status after repair by Fontan procedure. Ann Thorac Surg 29:322330, 1980 8 Sharratt GP, Johnson AM, Monro JL: Persistence and effects of sinus rhythm after Fontan procedure for tricuspid atresia. Br Heart J 42:74-80, 1979 9 Choussat A, Fontan F, Besse P, Vallot F, Chauve A, Bricaud H: Selection criteria for Fontan's procedure, Paediatric Cardiology 1977, RH Anderson, EA Shinebourne, eds., London, 1978, Churchill Livingstone, p 559 10 Shemin RJ, Merrill WH, Pfeifer JS, Conkle DM, Morrow AG: Evaluation of right atrial-pulmonary artery conduits for tricuspid atresia. Experimental study. J THORAC CARDIOVASC SURG 77:685-690, 1979
Tricuspid atresia
7 67
II Matsuda H, Kawashima Y, Fujita T, Mori T, Kitamura S, Takano H, Yokota H, Tomokuni T, Manbe H, Kozuka T: Hemodynamic studies of complete right heart bypass surgery for correction for tricuspid atresia. Jpn J Assoc Thorac Surg 24:955-966, 1976 12 Stanford W, Armstrong RG, Cline RE, King TD: Right atrium-pulmonary artery allograft for correction of tricuspid atresia. J THORAC CARDIOVASC SURG 66:105111, 1973 13 Robicsek F, Sanger PW, Moore M, Daugherty HK, Robicsek LK, Bagby E: Observations following four years of complete circulatory exclusion of the right heart. Ann Thorac Surg 8:530-536, 1969 14 Rushmer RF: Cardiovascular Dynamics, ed 3, Philadelphia, 1970, W. B. Saunders Company, p 28
Experimental evaluation of atrial function in right atrium-pulmonary artery conduit operation for tricuspid atresia Right ventricular bypass operations were performed in dogs by right atrium-pulmonary artery (RA-PA) conduits with closure of the tricuspid valve. Atrial fibrillation (AF) was induced in prebypass (control) and postbypass (postconduit) studies. Six dogs tolerated the procedure and had postoperative sinus rhythm (SR). In the postconduit studies, AF resulted in significant declines in both mean arterial pressure (73 ± 2 to 65 ± 2 mm Hg [mean ± SEM], p < 0.05) and pulmonary blood flow (/,050 ± 160 to 880 ± 110 ml/min, p < 0.05). However, there were no significant differences between the magnitude of these changes and those during control studies. Mean right atrial pressure was markedly elevated (17.3 ± 1.3 mm Hg) during SR after the conduit operations, but it did not increase significantly with AF. In volume load studies, pulmonary blood flow increased in proportion to rises between 15 and 30 mm Hg in mean right atrial pressure. The results suggest that right atrial contraction is not critical to the maintenance of pulmonary blood flow following RA-PA conduit operations.
Hikaru Matsuda, M.D., Yasunaru Kawashima, M.D., Hisateru Takano, M.D.,* Katsuhiko Miyamoto, M.D., and Tohru Mori, M.D.,** Osaka, Japan
Since Fontan and Baudet 's 1 initial report in 1971, the right atrium-pulmonary artery (RA-PA) conduit operation has been widely performed, with some modifications, as a functionally corrective procedure for both tricuspid atresia and single ventricle."? In this operation, the right atrium has been regarded as an important pump for the maintenance of pulmonary circulation, I, 8 and sinus rhythm (SR) is considered to be one of the basic criteria for selection of patients for this operation." However, it has not yet been clearly established whether right atrial contraction is essential to the success of this operation. Recently, Shemin and his associates'? reported an experimental study that suggested a less significant role for the right atrium as a
From The First Department of Surgery, Osaka University Medical School, Fukushima-ku, Osaka, Japan. Received for publication April 18, 1980. Accepted for publication Aug. 27, 1980. Address for reprints: Hikaru Matsuda, M.D., The First Department of Surgery, Osaka University Medical School, Fukushima-ku, Osaka 553, Japan. *Present address: National Cardiovascular Center, Suita, Osaka, Japan. **Present address: The Second Department of Surgery, Tottori University Medical School, Yonago, Japan.
762
pump in the RA-PA conduit model. Following a preliminary study!' which suggested that SR was not necessarily critical to the RA-PA conduit operation, we designed the present investigation to establish further the role of atrial contraction in the RA-PA conduit operation. In this experiment, hemodynamic data were compared during SR and electrically induced atrial fibrillation (AF) in dogs.
Method The operations were performed on 10 mongrel dogs weighing 13 to 17 kg. After initial injection of ketamine hydrochloride, sodium pentobarbital was used to maintain anesthesia, and respiration was controlled with a volume-type ventilator. The chest was opened bilaterally by a transstemal incision. Before cardiopulmonary bypass was established, control studies were carried out by converting cardiac rhythm from SR to AF through an electrical stimulus of 3 V applied directly to the right atrium. Electrocardiograms, arterial pressures, cardiac output, and right and left atrial pressures were monitored continuously and recorded simultaneously. Blood flow of the ascending aorta was measured with an electromagnetic flowmeter (Statham SP-2201) and used as cardiac output. Cardiopulmonary bypass using a bubble oxygenator
0022-5223/81/050762+06$00.60/0 © 1981 The C. V. Mosby Co.
Volume 81 Number 5
May, 1981
Tricuspid atresia
763
primed with fresh homologous blood was established by insertion of venous cannulas directly into both venae cavae. The tricuspid orifice was closed completely with several mattress sutures through a right ventriculotomy. A fresh aortic homograft containing a valve was placed between the right atrial appendage and the pulmonary artery, and the pulmonary artery trunk was ligated (Fig. 1). Cardiopulmonary bypass was discontinued with rise of venous pressure. A continuous drip of epinephrine was required on some occasions to maintain an adequate systemic pressure. The chest remained open during the hemodynamic measurements. In addition, flowmeters were placed around the grafts to measure the pulmonary blood flow or cardiac output. After measurement of the hemodynamic parameters and graft flow during SR, AF was induced electrically. After 10 to 15 minutes, hemodynamic data were again obtained. Volume load studies during SR were also conducted by raising venous pressure over relatively short periods and by measuring graft flow at varying right atrial pressures. All hemodynamic data were expressed as mean ± standard error of the mean (SEM). Results Hemodynamic studies were completed on six dogs that tolerated the operation. The period of observation was confined to within 5 hours of completion of bypass. Characteristic recordings of the postconduit studies are presented in Fig. 2. During SR, marked "a" waves were noted in the right atrial and pulmonary arterial pressures and corresponding pulsating blood flow patterns were observed in the grafts. Thus blood was being pumped from the right atrium to the pulmonary artery. During AF, however, "a" waves were not observed and graft flow was nonpulsatile. Both systemic arterial pressures and pulmonary blood flow were maintained during AF. Hemodynamic consequences resulting from AF in the control and postconduit studies are summarized and illustrated in Fig. 3. In the postconduit studies, the mean arterial pressure during SR (73 ± 2 mm Hg) decreased to 65 ± 2 mm Hg (p < 0.05); pulmonary blood flow during SR (1,050 ± 140 ml/min) also decreased, to 880 ± 110 ml/min (p < 0.05). These lower values during SR after conduit placement were not significant when compared to the control values. Although both mean arterial pressure and pulmonary blood flow fell significantly during AF following conduit placement, the magnitude of the decreases did not differ significantly from the control values for normal circulation. Average heart rates were 125 ± 5 beats/
Tricuspid Valve FIg. 1. The experimental model. A conduit (graft) is placed between the right atrial appendage and the pulmonary artery trunk after the tricuspid valve is completely closed through the right ventricle. The pulmonary artery trunk is ligated(arrow). SVC. Superiorvenacava./VC. Inferior vena cava. RA. Right atrium. RV. Right ventricle. PA. Pulmonary artery. AO. Aorta. EMF, Electromagnetic flowmeter.
min during SR and 110 ± 4 beats/min during AF in postconduit studies. Mean right atrial pressure was. markedly elevated after the conduit operation during SR (17.2 ± 1.2 mm Hg) and was almost identical to the mean pulmonary arterial pressure (17.1 ± 1.2 mm Hg). With AF, the mean right atrial pressure increased to 18.8 ± 1.5 mm Hg (NS). The mean left atrial pressure was low (6.3 ± 0.4 mm Hg) during SR following conduit placement but increased to 9.5 ± 1.5 mm Hg with AF (p < 0.01). There were no statistically significant differences in the magnitude of the change in mean left atrial pressure with AF between the control and the postconduit studies. The pulmonary blood flow, the pressure gradient between the right and left atria, and the calculated pulmonary vascular resistance were compared in postconduit studies and are presented in Table I. With AF, sig-
The Journal of Thoracic and Cardiovascular Surgery
764 Matsuda et al.
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Fig. 2. Representative pressure and flow recordings during sinus rhythm (left) and atrial fibrillation (right) after RA-PA conduit. EKG. Electrocardiogram. AP, Arterial pressure. RAP, Right atrial pressure. PAP. Pulmonary artery pressure. nificant decreases in pulmonary blood flow (-17%) and in the pressure gradient (-12%) were noted. However, both of these parameters showed similar changes during AF, and calculated pulmonary vascular resistance increased only slightly (NS). In volume load studies during SR, pulmonary blood flow increased significantly in response to a rise in mean right atrial pressure between 15 and 30 mm Hg (Fig. 4). When mean right atrial pressure exceeded 20 mm Hg, however, the right atrium gradually lost its capacity to contract, although the electrocardiogram remained in SR. Discussion Supraventricular dysrhythmias in general and AF in particular have been a matter of concern after the Fontan operation because of disturbance of right atrial
function. I. 8. 10 Several clinical reports have described the hemodynamic consequences of postoperative atrial dysrhythmias. Stanford and his associates" reported less significant hemodynamic changes in junctional rhythms with loss of atrial contraction. Behrendt and Rosenthal? described a patient who tolerated well several episodes of AF following an RA-PA conduit operation for single ventricle. On the other hand, ROSS,4 Henry," and their associates described episodes of significant postoperative depression in cardiac output and arterial pressure during nodal rhythm or AF. Fontan also has described a patient in whom severe venous congestion developed following AF; in this instance, cardioversion restored SR and the patient's condition improved markedly. 8 Experimentally, Robicsek and his associates 13 have reported long-term success with complete right heart
Volume 81 Number 5 May, 1981
Tricuspid atresia
mAP
90 80 c(
E
Q 1500
r
N.S.
L
Q.
500
n=6 50
20 15
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(meaniS.E.M.)
Fig. 3. Comparison of the hemodynamic changesin meanarterialpressure(mAP), pulmonary blood flow (cardiac output)(Q), mean right atrial pressure(mRAP), and mean left atrial pressure(mLAP) resultingfrom inducedatrial fibrillation in prebypass control and postconduit studies. SR, Sinus rhythm. AF, Atrial fibrillation. bypass operations in dogs. These operations were performed by exclusion of both the right atrium and ventricle by construction of superior vena cava-right pulmonary artery and inferior vena cava-left atrium shunts. In this model, however, the venous blood from the inferior vena cava did not perfuse the lung, because it shunted directly into the left atrium, and no evidence was presented to suggest that total systemic venous return could be circulated through the pulmonary circuit in the absence of the pumping chamber. Shemin and his associates 10 conducted experiments with atrial and ventricular pacing in which mechanical atrial systole was eliminated. They observed that the right atrium does not appear to function as a pump in the maintenance of pulmonary blood flow following an RA-PA conduit operation. They further indicated that
right atrial pressure was the most important factor influencing cardiac output. Instead of the atrial and ventricular pacing that Shemin's group'? employed, we utilized electrically induced AF to obliterate atrial contraction. The results of our investigation indicated that both systemic arterial pressure and pulmonary blood flow were maintained during AF after placement of the RA-PA conduit and tricuspid valve closure. Moreover, the magnitude of the decreases noted in these two parameters and the increase in mean left atrial pressure with AF in the postconduit studies were similar to those measured during the control study, where left ventricular output was depressed with AF in normal circulation. Consequently, the loss of atrial contraction itself, particularly of the right atrium, did not significantly influence the
The Journal of Thoracic and Cardiovascular Surgery
766 Matsuda et al,
L/min 2.0 1.5 Q mean ± S.E.M.
1.0
0=5
0.5 10
25
20
15
30
mRAP
35
mmHg
Fig. 4. Effect of volume load on pulmonary blood flow (Q) during sinus rhythm after RA-PA conduit. mRAP, Mean right atrial pressure.
Table I. Hemodynamic data/ollowing RA-PA conduit operation in dogs _ _ _ _ _ _ _ _...L..I
Pulmonary blood flow (ml/min) RA-LA pressure gradient (mmHg) PVR (dyne-sec-cm")
I-------.----
SR_ _
1,240 ± 130· 12.3 ± 0.7 830 ± 120
AF
1,030 ± 100 10.8 ± 1.0 880 ± 150
p Value
< 0.05 P < 0.05 NS
p
Legend: RA. Right atrium. PA, Pulmonary artery. SR, Sinus rhythm. AF, Atrial fibrillation. LA. Left atrium. PVR, Pulmonary vascular resistance. NS, Not significant. ·Mean ± SEM.; n = 4.
o'"
right-sided circulation in this RA-PA conduit experiment. This observation was further confirmed by the absence of a significant increase in mean right atrial pressure with AF. If the right atrium had been serving as a pump for pulmonary circulation after the conduit operation, the hemodynamic depressions induced by AF might have been expected to have produced significantly different changes in systemic arterial pressure and pulmonary blood flow from the control study. These results, therefore, suggest that right atrial contraction is of secondary importance to the maintenance of pulmonary circulation following this RA-PA conduit experiment. Rushmer':' has stated that a pressure gradient as small as 6 mm Hg between the pulmonary artery pressure and left ventricular diastolic pressure will force the total systemic output into the pulmonary circuit. Our experimental study suggested similar changes between pulmonary blood flow and pressure gradient across the lung following establishment of a conduit. The volume load study further showed a proportional increase in pulmonary blood flow with increased venous pressure. Therefore, the pressure gradient across the lung together with venous pressure appears to be more critical to the maintenance of pulmonary circulation in the
RA-PA conduit operation. It appears to be necessary to maintain a low left atrial pressure in order to maintain a pressure gradient without significant elevation in venous pressure. For this to be achieved, sufficient left ventricular function with SR is necessary.
2
3
4 5
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REFERENCES Fontan F, Baudet E: Surgical repair of tricuspid atresia. Thorax 26:240-248, 1971 Fontan F, Choussat A, Brom AG, Chauve A, Deville C, Castro-Cels A: Repair of tricuspid atresia. Surgical considerations and results, Paediatric Cardiology 1977, R Anderson, EA Shinebourne, eds., London, 1978, Churchill Livingstone, p 567 Kreutzer G, GaHndez E, Bono H, DePalma D, Laura JP: An operation for the correction of tricuspid atresia. J THORAC CARDIOVASC SURG 66:613-621, 1973 Ross DN, Somerville J: Surgical correction of tricuspid atresia. Lancet 1:845-849, 1973 Henry IN, Devloo RAE, Ritter 00, MairDD, Davis GD, Danielson GD: Tricuspid atresia. Successful surgical correction in two patients using porcine xenograft valves. Mayo Clin Proc 49:803-810, 1974 Yacoub MH, Radley-Smith R: Use of a valved conduit from right atrium to pulmonary artery for correction of single ventricle. Circulation 54:Suppl 3:63, 1976
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7 Behrendt DM, Rosenthal A: Cardiovascular status after repair by Fontan procedure. Ann Thorac Surg 29:322330, 1980 8 Sharratt GP, Johnson AM, Monro JL: Persistence and effects of sinus rhythm after Fontan procedure for tricuspid atresia. Br Heart J 42:74-80, 1979 9 Choussat A, Fontan F, Besse P, Vallot F, Chauve A, Bricaud H: Selection criteria for Fontan's procedure, Paediatric Cardiology 1977, RH Anderson, EA Shinebourne, eds., London, 1978, Churchill Livingstone, p 559 10 Shemin RJ, Merrill WH, Pfeifer JS, Conkle DM, Morrow AG: Evaluation of right atrial-pulmonary artery conduits for tricuspid atresia. Experimental study. J THORAC CARDIOVASC SURG 77:685-690, 1979
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II Matsuda H, Kawashima Y, Fujita T, Mori T, Kitamura S, Takano H, Yokota H, Tomokuni T, Manbe H, Kozuka T: Hemodynamic studies of complete right heart bypass surgery for correction for tricuspid atresia. Jpn J Assoc Thorac Surg 24:955-966, 1976 12 Stanford W, Armstrong RG, Cline RE, King TD: Right atrium-pulmonary artery allograft for correction of tricuspid atresia. J THORAC CARDIOVASC SURG 66:105111, 1973 13 Robicsek F, Sanger PW, Moore M, Daugherty HK, Robicsek LK, Bagby E: Observations following four years of complete circulatory exclusion of the right heart. Ann Thorac Surg 8:530-536, 1969 14 Rushmer RF: Cardiovascular Dynamics, ed 3, Philadelphia, 1970, W. B. Saunders Company, p 28