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J Thorac Cardiovasc Surg 1994;108:134-139
© 1994 Mosby, Inc.
CARDIOPULMONARY BYPASS, |
Petach Tikva and Tel-Aviv, Israel
Received for publication Feb. 18, 1993. Accepted for publication Nov. 2, 1993. Address for reprints: Prof. B. A. Vidne, Head, Cardiothoracic Surgery Department, Beilinson Medical Center, Petach Tikva, Israel.
Abstract
Patients who undergo surgical repair of congenital heart defects that are characterized by hypoplastic right ventricle or pulmonary hypertension are at high risk for the development of postoperative right heart failure. To minimize this risk, a new one-way, valved, atrial septal patch was developed that serves as an artificial one-way foramen ovale. The feasibility of this device was tested in five dogs in which reversible right heart failure had been induced. Use of the one-way valved patch significantly improved right ventricular performance and reduced right ventricular hydrostatic pressures. The interatrial pressure gradient was reduced from 10 ± 3.5 mm Hg during right heart failure to 4.4 ± 1.4 mm Hg. When the device was opened, cardiac output increased significantly. This hemodynamic improvement was achieved at the expense of systemic arterial desaturation, which was, however, well tolerated. When the state of right heart failure was reversed, the one-way valved patch spontaneously closed, allowing no interarterial shunting. The results of this experimental trial suggest that this device can play a useful role in selected patients in whom postoperative right heart failure can be anticipated after surgical repair of certain congenital heart defects. (J THORACCARDIOVASCSURG1994;108:134-9)
Patients who undergo an operation for the correction of congenital heart defects that are characterized by hypoplastic right ventricle (RV) or pulmonary hypertension are at a high risk for the development of right heart failure (RHF) because of decreased compliance of the RV. 
1-3 The conventional treatment for RHF usually improves the patient's hemodynamic status, but there are some cases in which this is not sufficient. 4-7
Patients with patent foramen ovale may be less prone to the development of RHF than those without a patent foramen ovale. 8 In such patients, right-to-left atrial shunting may serve to unload the RV. 9 It has been reported that the artificial creation of an atrial septal defect in patients with RHF dramatically improved their hemodynamic state, but at the expense of desaturation of the systemic arterial blood. 9-12 The major disadvantage of this procedure, however, is that the iatrogenic damage to the interatrial septum must be corrected by a subsequent invasive procedure.
The need for this further procedure can be obviated by the use of a one-way, valved, atrial septal patch. The one-way valved patch serves as a patent foramen ovale and provides a right-to-left shunt at the atrial level, but prevents any left-to-right shunt. The feasibility and effectiveness of this new technique was studied in animals. This paper describes the new technique.
MATERIALS AND METHODS
Five mongrel dogs weighing 20 to 25 kg were anesthetized, intubated, and the lungs ventilated. All animals received humane care in compliance with the "Principles of Laboratory Animal Care" (NIH Publication No. 86-23, revised 1985).
The new device (Fig. 1) is fashioned from two layers of woven Dacron fabric. A central circular opening, 0.5 cm in diameter, 13,14 is created in one of the layers. This opening is then covered by a second, smaller Dacron fabric layer, which is sutured to the first along one side only, creating the simple mechanism of a one-way valve. Two side stitches (Fig. 1, second panel) are inserted and are important for maintaining the "curtain" in the correct position for closure. The patch used in the animal experiment contained a U suture locking mechanism (Fig. 1, third panel). It was implanted in the locked position and subsequently unlocked when required by withdrawing the U suture (Fig. 1, third panel). The "curtain" of the device was opened toward the roof of the atrium (Fig. 2).
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Through the right atrium a round opening, 2 cm in diameter, was made in the interatrial septum. The one-way, valved, atrial septal patch device was implanted in its locked position. Catheters were placed in the right atrium, left atrium, RV, and ascending aorta.
An isolated RHF model was induced by a combination of a severe reversible increase in RV afterload and mild tricuspid insufficiency. Reversible increase in RV afterload was achieved by inflating a balloon catheter placed in the distal main pulmonary artery. Tricuspid insufficiency was caused by mechanically dilating the tricuspid anulus with Tubbs dilators. The pericardium was left open during the entire experiment. 15
The following parameters were recorded and calculated: hydrostatic pressure and oxygen saturation in the right atrium, left atrium, aorta, and RV. Systemic and pulmonary blood flows were calculated by the Fick method. 16 The changes in heart geometry were followed and documented by intraoperative echocardiography. The presence and direction of the interatrial shunt was further demonstrated by contrast echocardiography with the use of aerated saline containing microbubbles.
Measurements were taken during four different experimental phases (Fig. 3):
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Phase 2: Reversible RHF was induced by gradual inflation of the balloon in the distal main pulmonary artery.
Phase 3: The one-way valved patch device was unlocked, permitting a right-to-left atrial shunt.
Phase 4: The high pulmonary artery resistance was reversed by deflating the pulmonary artery balloon. The spontaneous closure of the shunt was tested during this phase.
Data analysis
The values for each parameter are reported as the mean plus or minus the standard deviation. The changes in the oxygen saturation in the left atrium were normalized for the saturation value at the baseline state (left atrial saturation at any given phase/left atrial saturation at phase 1). The ratio between the pulmonic flow and the systemic flow was calculated. The statistical analysis was made with the paired Student's t test. Differences were considered statistically significant at p values less than 0.05.
RESULTS
Atrial and ventricular pressure
Table I shows the influence of the one-way, valved, atrial septal patch device on the right and left atrial pressures, RV systolic pressure, RV/LV (left ventricular) systolic pressure ratio, and the right-to-left shunt through the device during the different experimental phases. These results reflect that a state of RHF was induced in phase 2. The opening of the device in phase 3 led to an immediate improvement of this state. In phase 4, there was a clear tendency for all parameters to return to baseline values.
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16 it was shown that in phase 2 the pulmonic flow/systemic flow ratio was 0.84:1 and in phase 3 it was 0.51:1. The systemic flow was elevated from 3.2 L/min in phase 2 to 5.83 L/min in phase 3 (82.3% elevation).
Geometric changes
Echocardiography showed a significant dilation of the RV and a pushed-back LV during phase 2. The reversal of this state was observed during phase 3.
DISCUSSION
The animal studies demonstrated the feasibility of the one-way, valved, atrial septal patch and its benefits in the RHF state. Right-to-left shunt at the atrial level was demonstrated by echocardiography (Fig. 4) and by the steep drop in blood oxygen saturation in the left atrium (Fig. 6). Leaving an opened atrial septal defect or patent foramen ovale is a well-known surgical option when patients who are at high risk for postoperative RHF are operated on. 17,18 Using the one-way valved patch device to retain this option for interatrial shunt if required provides a safety valve for a temporarily failing RV. The question remains whether interatrial right-to-left shunt does improve the hemodynamic state.
In phase 2, there was an elevation of the RV pressure and a reduction of LV pressure, which led to a low cardiac output state. Echocardiography demonstrated a shift of the interventricular septum to the left and dilation of the RV cavity.
Opening the device reduced the RV pressure to 44 mm Hg, which was statistically significant. However, there was an improvement in the global function of the heart, as was demonstrated by echocardiography. The shunt also improved the LV preload, which in turn improved cardiac output as shown by flow measurements. RV/LV pressure ratio was reduced significantly as a result of the shunt (
Table I). Right atrial pressure fell significantly during phase 3, which resulted in a reduction of RV end-diastolic pressure. The improvement in cardiac output and the reduction in RV end-diastolic pressure improved the RV coronary blood flow, which in turn improved RV function.
The reduction in arterial oxygen saturation could be life-threatening. 19,20 However, our data showed that when oxygen desaturation of 37.5% occurred, cardiac output doubled, so it can be assumed that the oxygen transport improved. 21 Theoretically the device should be opened whenever there is a gradient between the right atrium and the left atrium. However, in phase 4, despite a gradient of more than 1 mm Hg, the device was closed, which showed that it was resisting opening. When does the device open? Fig. 7 shows the relationship between the left atrial oxygen saturation and the right atrial–left atrial gradient. The biphasic character of the graph indicates that the device was opened in a gradient between 2 and 4 mm Hg.
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This information forms the base for a prospective clinical trial, the results of which will be submitted for publication in a separate article.
Footnotes
From the Departments of Cardiothoracic Surgery, Beilinson and Tel- Aviv a Medical Centers, and the Sackler Faculty of Medicine, Tel- Aviv University, Israel. 
References
This article has been cited by other articles:
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  B. Zhang, S. Wu, J. Liang, G. Zhang, G. Jiang, M. Zhou, and X. Li Unidirectional Monovalve Homologous Aortic Patch for Repair of Ventricular Septal Defect With Pulmonary Hypertension Ann. Thorac. Surg., June 1, 2007; 83(6): 2176 - 2181. [Abstract] [Full Text] [PDF]
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N. Ad, J. Barak, E. Birk, E. Snir, and B. A. Vidne Unidirectional Valve Patch Ann. Thorac. Surg., August 1, 1996; 62(2): 626 - 628. [Full Text]
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 N. Ad, E. Birk, J. Barak, S. Diamant, E. Snir, and B. A. Vidne A ONE-WAY VALVED ATRIAL SEPTAL PATCH: A NEW SURGICAL TECHNIQUE AND ITS CLINICAL APPLICATION J. Thorac. Cardiovasc. Surg., April 1, 1996; 111(4): 841 - 848. [Abstract] [Full Text]
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