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Pulsatile cavo-pulmonary artery shunt
Pulsatile cavo-pulmonary artery shunt Surgical technique and hemodynamic characteristics Akira Furuse, M.D., Robert K. Brawley, M.D., and Vincent L. Gott, M.D., Baltimore, Md.
Ahe superior vena cava-right pulmonary artery anastomosis was first applied clinically by Glenn3 in 1958. Since then, the procedure has been used to bypass partially right heart obstructions of certain types. Superior vena caval hypertension has frequently limited the success of the operation and is usually a reflection of pulmonary vascular resistance rather than a manifestation of obstruction at the anastomosis. Following the Glenn operation, blood flow through the anastomosis is nonpulsatile, and it has been suggested that the vascular resistance of the right lung and consequently the pressure in the superior vena cava might be diminished if blood flow through the anastomosis could be made pulsatile.1 In the present investigation, the right atrium was partitioned, and the superior portion of this chamber was utilized to provide pulsatile blood flow through the superior vena cava-right pulmonary artery anastomosis. The hemodynamic characteristics of this preparation were studied and compared to those of the conventional nonpulsatile cavo-pulmonary artery anastomosis. From the Department of Surgery, The Johns Hopkins University School of Medicine, Baltimore, Md. 21205. Received for publication Nov. 15, 1971. Address for reprints: Vincent L. Gott, M.D., Department of Surgery, The Johns Hopkins Hospital, Baltimore, Md. 21205.
Materials and methods Superior vena cava-right pulmonary artery anastomoses were created in 15 unselected mongrel dogs weighing 16 to 20 kilograms. The animals were anesthetized with intravenous sodium thiopental and ventilated through endotracheal tubes with room air by means of a Harvard respirator. The chest was entered through the right fifth intercostal space, and the azygos vein was divided between ligatures. The pericardium was opened, and the interatrial groove was dissected as deeply as possible in order to enlarge the right atrial surface. The right pulmonary artery was isolated and divided at the bifurcation of the main pulmonary artery. The proximal end of the right pulmonary artery was ligated. An endto-side anastomosis was constructed between the distal end of the right pulmonary artery and the superior vena cava-right atrial junction. The right atrium was then partitioned by placement of several mattress sutures through this chamber (Fig. 1). As these sutures were placed and tied, both cavae were intermittently occluded to prevent tearing of the atrial tissue. Compartmentalization of the right atrium was accomplished during a period of approximately 30 minutes in order to prevent acute distention of the partitioned chamber. Polyethylene catheters were introduced into the superior vena cava and the left 495
The Journal of
4 9 6
Furuse,
Brawley,
Gott
Thoracic and Cardiovascular Surgery
atrium and were connected to Statham P23 Db pressure transducers. A flow probe was placed around the superior vena cava and connected to an electromagnetic flowmeter (Statham M-4001). Systemic arterial pressure was monitored through a catheter placed in the femoral artery. The animal's electrocardiogram was also monitored. All data were recorded on a Sanborn 150 recorder. Zero blood flow in the superior vena cava was obtained by temporary occlusion of the superior vena cava between the flow probe and the anastomosis. The effect of atrial contraction upon blood flow through the anastomosis was eliminated when desired by clamping the superior vena cava just caudal to the anastomosis. Left atrial pressure, superior vena caval pressure, and blood flow in the superior vena cava were measured before and after application of the right atrial clamp. The flow probe and cannulas were removed, and the thoracotomy was closed. Nine of the 15 animals were studied again 6 weeks after the initial procedure. They were anesthetized with sodium thiopental. The right chest was reopened, and left atrial pressure, superior vena caval pressure, and superior vena caval blood flow were determined. Again, the effect of pulsatile and nonpulsatile blood flow upon these measurements was evaluated by clamping the superior vena cava just caudal to the anastomosis. In 6 of the animals that were studied at 6 weeks, oxygen saturations of blood from the right and left pulmonary veins were determined with an American Optical oximeter during periods of pulsatile and nonpulsatile blood flow. The animals were then put to death, and the hearts and lungs were examined grossly. A superior vena cavagram was obtained in 1 animal that was allowed to survive 6 months following superior vena cava-right pulmonary artery anastomosis. Results Five of the 15 animals survived less than 2 weeks following cavo—pulmonary anastomosis. Atelectasis, pneumonia, and empy-
Fig. 1. Drawing of superior vena cava-right pulmonary artery anastomosis as constructed in the present study. The right atrium has been partitioned with sutures, and the contracting upper portion of this chamber was utilized to provide pulsatile blood flow through the anastomosis. Application of a vascular clamp just caudal to the anastomosis converted right pulmonary blood flow from pulsatile to nonpulsatile. SVC, Superior vena cava. RPA, Right pulmonary artery. RPV, Right pulmonary vein. JVC, Inferior vena cava. RV, Right ventricle.
ema accounted for the deaths of the 5 dogs, and thrombosis of the anastomosis was found in only 1 of these animals. Neither brachiocephalic venous distention nor edema was observed in any animal; however, right pleural effusions necessitating thoracocenteses were commonly observed during the first 2 postoperative weeks. A normal sinus rhythm was present in all dogs that survived the operation. Fig. 2 shows typical records of pressures and flows obtained from 1 of the dogs studied. When the superior vena caval clamp was released, atrial contraction produced prominent pressure waves in the superior vena cava and changed the pattern of blood flow from nonpulsatile to pulsatile. After release of the caval clamp, instantaneous blood flow became negative at peak superior vena caval pressure, but mean forward blood flow in the superior vena cava actually increased.
Volume 63
Pulsatile cavo-pulmonary
Number 3
artery shunt
497
March, 1972
S.V.C. Pressure {mm. Hg)
10
r> S.V.C. Phuic Flo*
(Ltaln)
,
$IXZ**i"'">***J*Mm'1 IM»U« Of cross -damp o n S . V.C.
'itf
Fig. 2. Recordings of the electrocardiogram (EKG), femoral artery pressure, superior vena cava (SVC) pressure, and SVC blood flow in 1 of the animals studied. When the SVC clamp is released, atrial contraction produces pulsatile pressures and flow in the SVC. NP, Nonpulsatile. P, Pulsatile.
Table I summarizes the hemodynamic data obtained immediately after and 6 weeks after cavo-pulmonary artery anastomoses in all dogs studied. Both immediately after anastomosis and 6 weeks later, dogs with pulsatile shunts had significantly lower (p < 0.001) mean pressures, slightly higher peak pressures, and significantly higher (p < 0.001) pulse pressures in the superior vena cava than dogs with nonpulsatile shunts. Mean blood flow in the superior vena cava was significandy (p < 0.001) higher in dogs with pulsatile shunts both immediately and 6 weeks after anastomosis. Left atrial pressure remained essentially unchanged throughout all experiments. Pulmonary vascular resistance in the right lung was calculated by dividing the pressure difference between the superior vena cava and the left atrium by the superior
vena caval blood flow. This calculation assumes that collateral flow between the two cavae is negligible. This assumption was substantiated by preliminary studies in which radioactive microspheres (strontium 85 and cerium 141) were injected into the brachial veins of dogs with pulsatile superior vena cava-right pulmonary artery anastomoses. Collateral blood flow from the superior to the inferior vena cava as determined by measured radioactivity in the left lung was found to be less than 0.4 per cent of superior vena caval blood flow immediately after cavo-pulmonary artery anastomosis and less than 1.0 per cent 6 weeks following the shunt. In addition, the azygos vein was divided in all animals, and the flow probe was positioned around the superior vena cava immediately above the anastomosis to assure that measured blood flow in
The Journal of
498
Furuse, Brawley, Gott
Thoracic and Cardiovascular Surgery
Table I. Mean values (± standard deviation) in dogs with pulsatile and nonpulsatile superior vena cava-right pulmonary artery anastomoses Parameter
Immediately after anastomosis 15 dogs)
Six weeks after anastomosis (9 dogs)
SVC mean pressure (mm. Hg) Pulsatile Nonpulsatile
13.4 15.6
± ±
SVC peak pressure (mm. H g ) Pulsatile Nonpulsatile
20.8 17.2
± 2.9 ± 2.6
17.2 ± 3.0 15.4 + 2.0
SVC pulse pressure (mm. H g ) Pulsatile Nonpulsatile
10.3 3.4
± ±
1.3 1.0*
10.0 + 1.1 3.7 ± 0.9*
± ±
123 139*
± ±
1.6 1.6
±
385
SVC blood flow (ml./min.) Pulsatile Nonpulsatile Left atrial pressure (mm. Hg) Pulsatile Nonpulsatile Right pulmonary vascular resistance (dynes/ sec/cm."5) Pulsatile Nonpulsatile
558 460 4.0 4.1
1,450 2,122
1.9 1.7*
+ 510*
10.7 13.5
663 464
± 2.0 ± 1.6*
± ±
161 148*
4.4 + 1.4 4.6 ± 1.6
834 1,700
± ±
258 458*
Legend: SVC, Superior vena cava. *p < 0.001 by paired Student's analysis.
the superior vena cava was equal to that which passed through the anastomosis. Simultaneous measurements of right pulmonary artery and superior vena caval pressure obtained in several dogs both immediately and 6 weeks after cavo-pulmonary artery anastomosis failed to disclose a pressure gradient across the anastomosis. Both immediately and 6 weeks after cavopulmonary artery anastomosis, calculated vascular resistance in the right lung was consistently and significantly (p < 0.001) lower in animals with pulsatile shunts than in animals with nonpulsatile shunts. Of particular interest is the fact that the calculated vascular resistance of the right lung diminished strikingly during the 6 week period between the two studies. Six weeks after construction of the superior vena cava-right pulmonary artery anastomosis, oxygen saturations of right pulmonary venous blood were found to be slightly lower than oxygen saturations of left pulmonary venous blood whether the
shunt was pulsatile or nonpulsatile. The superior vena cavagram in 1 dog obtained 6 months after superior vena cava-right pulmonary artery anastomosis demonstrated good filling of the right pulmonary artery and minimal collateral blood flow from the superior to the inferior vena cava (Fig. 3 ) . Fig. 4 shows the heart of 1 of the 9 animals that was put to death 6 weeks after superior vena cava-right pulmonary artery anastomosis. In all 9 animals examined, the anastomosis was completely endothelialized and showed no evidence of thrombosis or stenosis. In every dog, the right atrium was completely partitioned by the mattress sutures and was free of any thrombus. There was little evidence of right atrial hypertrophy, and the lungs of all animals appeared grossly normal. Discussion There is now considerable evidence which shows that the vascular resistance of a
Volume 63 Number 3 March, 1972
Pulsatile cavo-pulmonary artery shunt 4 9 9
Fig. 3. Superior vena cavagram obtained in 1 dog 6 months after superior vena cava-right pulmonary anastomosis. The study shows that the upper portion of the partitioned right atrium and the right pulmonary artery were well filled with dye.
Fig. 4. Picture of the heart of 1 animal put to death 6 weeks after cavo-pulmonary artery anastomosis. The superior vena cava (SVC), right pulmonary artery (RPA), and upper portion of the partitioned right atrium have been opened. IVC, Inferior vena cava. RAA, Right atrial appendage.
region increases when the blood flow to that region is converted from pulsatile to nonpulsatile. This phenomenon has been previously demonstrated to occur in the pulmonary circulation1-6 as well as in the systemic circulation.2-5-8-9 Clarke1 showed that pulsatile pulmonary blood flow was as much as 80 per cent greater than nonpulsatile pulmonary blood flow at the same pulmonary artery and left atrial pressures. The present study confirms the association between pulsatile pulmonary blood flow and diminished pulmonary vascular resistance. The explanation for this phenomenon is not clear although interstitial edema of the pulmonary parenchyma11 has been suggested as the cause for the increased vascular resistance associated with nonpulsatile blood flow. This is an unlikely explanation for the changes of vascular resistance measured in the present study,
because these changes occurred almost immediately after the conversion of nonpulsatile to pulsatile blood flow. The rapidity with which this alteration occurred in the present study would suggest a direct mechanical effect of the pulsatile wave form; however, changes in vascular tone initiated by chemical or neural baroreceptors can not be excluded. Moscovitz and colleagues7 have previously suggested utilization of the right atrium as a pump to transfer blood to the pulmonary artery in situations in which the right ventricle is to be bypassed. Although others4-10 have demonstrated the feasibility of complete, permanent right ventricular bypass, a diminution in calculated pulmonary vascular resistance in animals with pulsatile superior vena cava-right pulmonary blood flow has not been previously demonstrated. Realistically, the number of patients who
The Journal of
5 0 0 Furuse, Brawley, Gott
would be candidates for the procedure described in this report will be small because it would be difficult to partition the atrium in those patients with a large atrial septal defect. However, in those children with small atrial septal defects, creation of a pulsatile superior vena cava-right pulmonary artery shunt would appear to be beneficial. Decreased pulmonary vascular resistance as a result of pulsatile pulmonary blood flow might obviate the troublesome syndrome associated with superior vena caval hypertension following conventional cavo-pulmonary artery anastomosis. Summary A technique for the creation of a superior vena cava-right pulmonary artery anastomosis which provides pulsatile pulmonary blood flow has been described. The hemodynamic characteristics of this preparation were studied and compared to those of a conventional nonpulsatile cavopulmonary artery anastomosis. When blood flow through the anastomosis was converted from nonpulsatile to pulsatile, mean pressure in the superior vena cava and the calculated pulmonary vascular resistance in the right lung decreased significantly. Concomitantly, mean blood flow into the right lung increased significantly. The hemodynamic characteristics of the pulsatile shunt were even more favorable when determined 6 weeks after operation. These findings suggest that decreased pulmonary vascular resistance as a result of pulsatile blood flow might obviate the superior vena caval obstruction syndrome following conventional cavo-pulmonary artery anastomosis. The authors wish to thank Dr. William R. Milnor, Professor of Physiology, The Johns Hopkins University School of Medicine, for his advice and
Thoracic and Cardiovascular
Surgery
suggestions with regard to the hemodynamic determinations in these studies. REFERENCES 1 Clarke, C. P., Kahn, D. R., Dufek, J. H., and Sloan, H.: The Effect of Nonpulsatile Blood Flow on Canine Lungs, Ann. Thorac. Surg. 6: 450, 1968. 2 Giron, F., Birtwell, W. C , Soroff, H. S., and Deterling, R. A.: Hemodynamic Effects of Pulsatile and Nonpulsatile Flow, Arch. Surg. 93: 802, 1966. 3 Glenn, W. W. L.: Circulatory Bypass of the Right Side of the Heart. IV. Shunt Between Superior Vena Cava and Distal Right Pulmonary Artery: Report of Clinical Application, N. Engl. J. Med. 259: 117, 1958. 4 Haller, J. A., Jr., Adkins, J. C , Worthington, M., and Ravenhorst, J.: Experimental Studies on Permanent Bypass of the Right Heart, Surgery 59: 1128, 1966. 5 Jacobs, L. A., Klopp, E. H., Seamone, W., Topaz, S. R., and Gott, V. L.: Improved Organ Function During Cardiac Bypass With a Roller Pump Modified to Deliver Pulsatile Flow, J. THORAC. CARDIOVASC. SURG. 58:
6 7
8
9
10
11
703,
1969. Mandelbaum, I., and Burnes, W. H.: Pulsatile and Nonpulsatile Blood Flow, J. A. M. A. 191: 657, 1965. Moscovitz, H. L., Donosos, E., Gelb, I. J., and Wilder, R. J.: An Atlas of Hemodynamics of the Cardiovascular System, New York, 1963, Grune & Stratton, Inc., pp. 122-125. Nakayama, K., Tamiya, T., Yamamoto, K., Izumi, T., Akimoto, S., Hashizume, S., Iimori, T., Okada, H., and Yazawa, C : High Amplitude Pulsatile Pump With Particular Reference to Hemodynamics, Surgery 54: 798, 1963. Trinkle, J. K., Helton, N. E„ Bryant, L. R„ and Griffin, W. D.: Pulsatile Cardiopulmonary Bypass: Clinical Evaluation, Surgery 68: 1074, 1970. Warden, H. E., DeWall, R. A., and Varco, R. A.: Use of the Right Auricle as a Pump for the Pulmonary Circuit, Surg. Forum 5: 16, 1954. Wilkens, H., Regelson, W., and Hoffmeister, F. S.: The Physiologic Importance of Pulsatile Blood Flow, N. Engl. J. Med. 267: 443, 1962.
Ahe superior vena cava-right pulmonary artery anastomosis was first applied clinically by Glenn3 in 1958. Since then, the procedure has been used to bypass partially right heart obstructions of certain types. Superior vena caval hypertension has frequently limited the success of the operation and is usually a reflection of pulmonary vascular resistance rather than a manifestation of obstruction at the anastomosis. Following the Glenn operation, blood flow through the anastomosis is nonpulsatile, and it has been suggested that the vascular resistance of the right lung and consequently the pressure in the superior vena cava might be diminished if blood flow through the anastomosis could be made pulsatile.1 In the present investigation, the right atrium was partitioned, and the superior portion of this chamber was utilized to provide pulsatile blood flow through the superior vena cava-right pulmonary artery anastomosis. The hemodynamic characteristics of this preparation were studied and compared to those of the conventional nonpulsatile cavo-pulmonary artery anastomosis. From the Department of Surgery, The Johns Hopkins University School of Medicine, Baltimore, Md. 21205. Received for publication Nov. 15, 1971. Address for reprints: Vincent L. Gott, M.D., Department of Surgery, The Johns Hopkins Hospital, Baltimore, Md. 21205.
Materials and methods Superior vena cava-right pulmonary artery anastomoses were created in 15 unselected mongrel dogs weighing 16 to 20 kilograms. The animals were anesthetized with intravenous sodium thiopental and ventilated through endotracheal tubes with room air by means of a Harvard respirator. The chest was entered through the right fifth intercostal space, and the azygos vein was divided between ligatures. The pericardium was opened, and the interatrial groove was dissected as deeply as possible in order to enlarge the right atrial surface. The right pulmonary artery was isolated and divided at the bifurcation of the main pulmonary artery. The proximal end of the right pulmonary artery was ligated. An endto-side anastomosis was constructed between the distal end of the right pulmonary artery and the superior vena cava-right atrial junction. The right atrium was then partitioned by placement of several mattress sutures through this chamber (Fig. 1). As these sutures were placed and tied, both cavae were intermittently occluded to prevent tearing of the atrial tissue. Compartmentalization of the right atrium was accomplished during a period of approximately 30 minutes in order to prevent acute distention of the partitioned chamber. Polyethylene catheters were introduced into the superior vena cava and the left 495
The Journal of
4 9 6
Furuse,
Brawley,
Gott
Thoracic and Cardiovascular Surgery
atrium and were connected to Statham P23 Db pressure transducers. A flow probe was placed around the superior vena cava and connected to an electromagnetic flowmeter (Statham M-4001). Systemic arterial pressure was monitored through a catheter placed in the femoral artery. The animal's electrocardiogram was also monitored. All data were recorded on a Sanborn 150 recorder. Zero blood flow in the superior vena cava was obtained by temporary occlusion of the superior vena cava between the flow probe and the anastomosis. The effect of atrial contraction upon blood flow through the anastomosis was eliminated when desired by clamping the superior vena cava just caudal to the anastomosis. Left atrial pressure, superior vena caval pressure, and blood flow in the superior vena cava were measured before and after application of the right atrial clamp. The flow probe and cannulas were removed, and the thoracotomy was closed. Nine of the 15 animals were studied again 6 weeks after the initial procedure. They were anesthetized with sodium thiopental. The right chest was reopened, and left atrial pressure, superior vena caval pressure, and superior vena caval blood flow were determined. Again, the effect of pulsatile and nonpulsatile blood flow upon these measurements was evaluated by clamping the superior vena cava just caudal to the anastomosis. In 6 of the animals that were studied at 6 weeks, oxygen saturations of blood from the right and left pulmonary veins were determined with an American Optical oximeter during periods of pulsatile and nonpulsatile blood flow. The animals were then put to death, and the hearts and lungs were examined grossly. A superior vena cavagram was obtained in 1 animal that was allowed to survive 6 months following superior vena cava-right pulmonary artery anastomosis. Results Five of the 15 animals survived less than 2 weeks following cavo—pulmonary anastomosis. Atelectasis, pneumonia, and empy-
Fig. 1. Drawing of superior vena cava-right pulmonary artery anastomosis as constructed in the present study. The right atrium has been partitioned with sutures, and the contracting upper portion of this chamber was utilized to provide pulsatile blood flow through the anastomosis. Application of a vascular clamp just caudal to the anastomosis converted right pulmonary blood flow from pulsatile to nonpulsatile. SVC, Superior vena cava. RPA, Right pulmonary artery. RPV, Right pulmonary vein. JVC, Inferior vena cava. RV, Right ventricle.
ema accounted for the deaths of the 5 dogs, and thrombosis of the anastomosis was found in only 1 of these animals. Neither brachiocephalic venous distention nor edema was observed in any animal; however, right pleural effusions necessitating thoracocenteses were commonly observed during the first 2 postoperative weeks. A normal sinus rhythm was present in all dogs that survived the operation. Fig. 2 shows typical records of pressures and flows obtained from 1 of the dogs studied. When the superior vena caval clamp was released, atrial contraction produced prominent pressure waves in the superior vena cava and changed the pattern of blood flow from nonpulsatile to pulsatile. After release of the caval clamp, instantaneous blood flow became negative at peak superior vena caval pressure, but mean forward blood flow in the superior vena cava actually increased.
Volume 63
Pulsatile cavo-pulmonary
Number 3
artery shunt
497
March, 1972
S.V.C. Pressure {mm. Hg)
10
r> S.V.C. Phuic Flo*
(Ltaln)
,
$IXZ**i"'">***J*Mm'1 IM»U« Of cross -damp o n S . V.C.
'itf
Fig. 2. Recordings of the electrocardiogram (EKG), femoral artery pressure, superior vena cava (SVC) pressure, and SVC blood flow in 1 of the animals studied. When the SVC clamp is released, atrial contraction produces pulsatile pressures and flow in the SVC. NP, Nonpulsatile. P, Pulsatile.
Table I summarizes the hemodynamic data obtained immediately after and 6 weeks after cavo-pulmonary artery anastomoses in all dogs studied. Both immediately after anastomosis and 6 weeks later, dogs with pulsatile shunts had significantly lower (p < 0.001) mean pressures, slightly higher peak pressures, and significantly higher (p < 0.001) pulse pressures in the superior vena cava than dogs with nonpulsatile shunts. Mean blood flow in the superior vena cava was significandy (p < 0.001) higher in dogs with pulsatile shunts both immediately and 6 weeks after anastomosis. Left atrial pressure remained essentially unchanged throughout all experiments. Pulmonary vascular resistance in the right lung was calculated by dividing the pressure difference between the superior vena cava and the left atrium by the superior
vena caval blood flow. This calculation assumes that collateral flow between the two cavae is negligible. This assumption was substantiated by preliminary studies in which radioactive microspheres (strontium 85 and cerium 141) were injected into the brachial veins of dogs with pulsatile superior vena cava-right pulmonary artery anastomoses. Collateral blood flow from the superior to the inferior vena cava as determined by measured radioactivity in the left lung was found to be less than 0.4 per cent of superior vena caval blood flow immediately after cavo-pulmonary artery anastomosis and less than 1.0 per cent 6 weeks following the shunt. In addition, the azygos vein was divided in all animals, and the flow probe was positioned around the superior vena cava immediately above the anastomosis to assure that measured blood flow in
The Journal of
498
Furuse, Brawley, Gott
Thoracic and Cardiovascular Surgery
Table I. Mean values (± standard deviation) in dogs with pulsatile and nonpulsatile superior vena cava-right pulmonary artery anastomoses Parameter
Immediately after anastomosis 15 dogs)
Six weeks after anastomosis (9 dogs)
SVC mean pressure (mm. Hg) Pulsatile Nonpulsatile
13.4 15.6
± ±
SVC peak pressure (mm. H g ) Pulsatile Nonpulsatile
20.8 17.2
± 2.9 ± 2.6
17.2 ± 3.0 15.4 + 2.0
SVC pulse pressure (mm. H g ) Pulsatile Nonpulsatile
10.3 3.4
± ±
1.3 1.0*
10.0 + 1.1 3.7 ± 0.9*
± ±
123 139*
± ±
1.6 1.6
±
385
SVC blood flow (ml./min.) Pulsatile Nonpulsatile Left atrial pressure (mm. Hg) Pulsatile Nonpulsatile Right pulmonary vascular resistance (dynes/ sec/cm."5) Pulsatile Nonpulsatile
558 460 4.0 4.1
1,450 2,122
1.9 1.7*
+ 510*
10.7 13.5
663 464
± 2.0 ± 1.6*
± ±
161 148*
4.4 + 1.4 4.6 ± 1.6
834 1,700
± ±
258 458*
Legend: SVC, Superior vena cava. *p < 0.001 by paired Student's analysis.
the superior vena cava was equal to that which passed through the anastomosis. Simultaneous measurements of right pulmonary artery and superior vena caval pressure obtained in several dogs both immediately and 6 weeks after cavo-pulmonary artery anastomosis failed to disclose a pressure gradient across the anastomosis. Both immediately and 6 weeks after cavopulmonary artery anastomosis, calculated vascular resistance in the right lung was consistently and significantly (p < 0.001) lower in animals with pulsatile shunts than in animals with nonpulsatile shunts. Of particular interest is the fact that the calculated vascular resistance of the right lung diminished strikingly during the 6 week period between the two studies. Six weeks after construction of the superior vena cava-right pulmonary artery anastomosis, oxygen saturations of right pulmonary venous blood were found to be slightly lower than oxygen saturations of left pulmonary venous blood whether the
shunt was pulsatile or nonpulsatile. The superior vena cavagram in 1 dog obtained 6 months after superior vena cava-right pulmonary artery anastomosis demonstrated good filling of the right pulmonary artery and minimal collateral blood flow from the superior to the inferior vena cava (Fig. 3 ) . Fig. 4 shows the heart of 1 of the 9 animals that was put to death 6 weeks after superior vena cava-right pulmonary artery anastomosis. In all 9 animals examined, the anastomosis was completely endothelialized and showed no evidence of thrombosis or stenosis. In every dog, the right atrium was completely partitioned by the mattress sutures and was free of any thrombus. There was little evidence of right atrial hypertrophy, and the lungs of all animals appeared grossly normal. Discussion There is now considerable evidence which shows that the vascular resistance of a
Volume 63 Number 3 March, 1972
Pulsatile cavo-pulmonary artery shunt 4 9 9
Fig. 3. Superior vena cavagram obtained in 1 dog 6 months after superior vena cava-right pulmonary anastomosis. The study shows that the upper portion of the partitioned right atrium and the right pulmonary artery were well filled with dye.
Fig. 4. Picture of the heart of 1 animal put to death 6 weeks after cavo-pulmonary artery anastomosis. The superior vena cava (SVC), right pulmonary artery (RPA), and upper portion of the partitioned right atrium have been opened. IVC, Inferior vena cava. RAA, Right atrial appendage.
region increases when the blood flow to that region is converted from pulsatile to nonpulsatile. This phenomenon has been previously demonstrated to occur in the pulmonary circulation1-6 as well as in the systemic circulation.2-5-8-9 Clarke1 showed that pulsatile pulmonary blood flow was as much as 80 per cent greater than nonpulsatile pulmonary blood flow at the same pulmonary artery and left atrial pressures. The present study confirms the association between pulsatile pulmonary blood flow and diminished pulmonary vascular resistance. The explanation for this phenomenon is not clear although interstitial edema of the pulmonary parenchyma11 has been suggested as the cause for the increased vascular resistance associated with nonpulsatile blood flow. This is an unlikely explanation for the changes of vascular resistance measured in the present study,
because these changes occurred almost immediately after the conversion of nonpulsatile to pulsatile blood flow. The rapidity with which this alteration occurred in the present study would suggest a direct mechanical effect of the pulsatile wave form; however, changes in vascular tone initiated by chemical or neural baroreceptors can not be excluded. Moscovitz and colleagues7 have previously suggested utilization of the right atrium as a pump to transfer blood to the pulmonary artery in situations in which the right ventricle is to be bypassed. Although others4-10 have demonstrated the feasibility of complete, permanent right ventricular bypass, a diminution in calculated pulmonary vascular resistance in animals with pulsatile superior vena cava-right pulmonary blood flow has not been previously demonstrated. Realistically, the number of patients who
The Journal of
5 0 0 Furuse, Brawley, Gott
would be candidates for the procedure described in this report will be small because it would be difficult to partition the atrium in those patients with a large atrial septal defect. However, in those children with small atrial septal defects, creation of a pulsatile superior vena cava-right pulmonary artery shunt would appear to be beneficial. Decreased pulmonary vascular resistance as a result of pulsatile pulmonary blood flow might obviate the troublesome syndrome associated with superior vena caval hypertension following conventional cavo-pulmonary artery anastomosis. Summary A technique for the creation of a superior vena cava-right pulmonary artery anastomosis which provides pulsatile pulmonary blood flow has been described. The hemodynamic characteristics of this preparation were studied and compared to those of a conventional nonpulsatile cavopulmonary artery anastomosis. When blood flow through the anastomosis was converted from nonpulsatile to pulsatile, mean pressure in the superior vena cava and the calculated pulmonary vascular resistance in the right lung decreased significantly. Concomitantly, mean blood flow into the right lung increased significantly. The hemodynamic characteristics of the pulsatile shunt were even more favorable when determined 6 weeks after operation. These findings suggest that decreased pulmonary vascular resistance as a result of pulsatile blood flow might obviate the superior vena caval obstruction syndrome following conventional cavo-pulmonary artery anastomosis. The authors wish to thank Dr. William R. Milnor, Professor of Physiology, The Johns Hopkins University School of Medicine, for his advice and
Thoracic and Cardiovascular
Surgery
suggestions with regard to the hemodynamic determinations in these studies. REFERENCES 1 Clarke, C. P., Kahn, D. R., Dufek, J. H., and Sloan, H.: The Effect of Nonpulsatile Blood Flow on Canine Lungs, Ann. Thorac. Surg. 6: 450, 1968. 2 Giron, F., Birtwell, W. C , Soroff, H. S., and Deterling, R. A.: Hemodynamic Effects of Pulsatile and Nonpulsatile Flow, Arch. Surg. 93: 802, 1966. 3 Glenn, W. W. L.: Circulatory Bypass of the Right Side of the Heart. IV. Shunt Between Superior Vena Cava and Distal Right Pulmonary Artery: Report of Clinical Application, N. Engl. J. Med. 259: 117, 1958. 4 Haller, J. A., Jr., Adkins, J. C , Worthington, M., and Ravenhorst, J.: Experimental Studies on Permanent Bypass of the Right Heart, Surgery 59: 1128, 1966. 5 Jacobs, L. A., Klopp, E. H., Seamone, W., Topaz, S. R., and Gott, V. L.: Improved Organ Function During Cardiac Bypass With a Roller Pump Modified to Deliver Pulsatile Flow, J. THORAC. CARDIOVASC. SURG. 58:
6 7
8
9
10
11
703,
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