Ann Thorac Surg 1998;65:1168-1170
© 1998 The Society of Thoracic Surgeons
How to Do It
Conversion From Routine CPB to Centrifugal Mechanical Assist by Transaortic Inflow Cannulation of the Left Ventricle
Afksendiyos Kalangos, MD, PhDa,
Nicolas Murith, MDa,
Ary Baldovinos, MDa,
Bernard Faidutti, MDa
a Clinic for Cardiovascular Surgery, University Cantonal Hospital of Geneva, Geneva, Switzerland
Accepted for publication November 13, 1997.
Address reprint requests to Dr Kalangos, Clinic for Cardiovascular Surgery, University Cantonal Hospital of Geneva, 24, rue Micheli-du-Crest, 1211 Geneva 14, Switzerland
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Abstract
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We describe a technique of conversion from cardiopulmonary bypass to centrifugal mechanical assist that consists of using the existing aortic cannula for outflow and inserting a cannula into the left ventricle through a Dacron tube and across the aortic valve for inflow.
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Introduction
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Centrifugal assist devices are widely used for anticipation of myocardial recovery after postcardiotomy ventricular failure. Despite the increasing effectiveness of these devices, the selection of cannulation sites, techniques, and size of cannulas are still considered important factors influencing morbidity and mortality related to ventricular support [1]. Unlike the outflow cannulation site, which is almost always the ascending aorta, the inflow cannulation site varies according to the preference of surgeon, the standard approach usually being the left atrium. However, Duncan and associates [2] demonstrated the advantages of a new cannulation technique, over the standard approach, in which the ascending aorta is the site for insertion of both inflow and outflow cannulas. Our experience with this technique led us to modify it to increase benefits.
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Technique and results
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We used the technique described by Duncan and associates for the institution of left ventricular (LV) support using a Bio-Medicus centrifugal pump (Bio-Medicus, Minneapolis, MN) in 3 patients in whom LV failure developed after aortocoronary bypass grafting. Duncan and associates’ technique consists of anastomosing the body of a 22 x 11-mm woven Dacron bifurcation graft to the right lateral aspect of the ascending aorta, proximal to the aortic cross-clamp, under cardiopulmonary bypass (CPB) and then placing a 24F wire-reinforced cannula into the LV through the superior limb of the graft and across the aortic valve [2]. The outflow cannula is placed into the aorta through the remaining inferior limb of the graft, and both cannulas are secured to the graft with umbilical tapes. Unfortunately, in our experience, the use of a 24F inflow cannula resulted in inadequate inflow drainage, which led us to modify this technique.
In the setting of inability to wean from CPB, we used the modified technique in 5 patients for LV support with a Bio-Medicus centrifugal pump using the existing aortic cannula, which was an 8-mm Stockert (Stockert Instrumente, Munich, Germany) cannula in all cases. Concentric pursestring sutures are employed at the ascending aortic cannulation site, and tension on these ensnared sutures is maintained using surgical clamps during routine CPB. After lateral clamping of the anterior aspect of the ascending aorta, a longitudinal aortotomy is performed between the commonly used sites of proximal coronary anastomoses. A 14-mm straight collagen-coated Dacron tube (Intervascular SA, La Ciotat, France) is first beveled obliquely and then sewn to the aortotomy using a 4-0 polypropylene running suture while CPB continues (Fig 1). Human fibrin glue is then applied around the anastomosis before the clamp is removed. A 36F wire-reinforced straight venous return cannula (Stockert) is introduced through the Dacron tube into the aorta, and its distal end is then clamped after it has filled with blood. The heart is then gradually volume loaded by reducing CPB flow, which allows the opening of the aortic valve during systole. The inflow cannula is then manually guided across the aortic valve by the right hand of the surgeon, which is placed on the posterior wall of the ascending aorta through the sinus of Theile while the left hand of the surgeon pushes the cannula toward the LV at times corresponding to the ventricular contraction (Fig 2A). During this procedure, the assistant avoids back-bleeding through the Dacron tube by tightening a tourniquet around it. The inflow cannula is then pushed toward the apex, secured to the Dacron tube by two 0 silk sutures, and connected to the device (Fig 2B). After CPB is stopped, the aortic cannula is disconnected from the circuit and then connected immediately to the centrifugal pump after air is evacuated by partial removal of the clamp applied on the aortic cannula. At the time of conversion from routine CPB to the centrifugal pump, surgical clamps maintaining the aortic pursestring sutures are eliminated after sutures are tied on the snares. Excess sutures are then wrapped around the aortic cannula and tied. After standard chest tube drainage, the sternum is left open in all cases and cannulas exit through two small lateral incisions perpendicular to the superior aspect of the sternotomy incision and secured to the skin. Thereafter, the sternotomy incision is closed by a running 3-0 polypropylene suture. Heparin is reversed with protamine, and its readministration is delayed until the coagulation profile normalizes.
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Fig 2. (A) A 36F venous cannula is pushed through the Dacron tube by the left hand of the surgeon and guided across the aortic valve by the right hand placed on the posterior wall of the ascending aorta through the sinus of Theile at times corresponding to ventricular systole. (B) The final position of the inflow cannula into the left ventricle. The existing aortic cannula is switched to the outflow line of the assist device.
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In all patients, the average pump flow was greater than 5 L/min with a pulmonary capillary wedge pressure kept between 5 and 8 mm Hg throughout the period of LV support, which ranged from 2 to 7 days. Mediastinal exploration for relief of tamponade or excessive bleeding was not necessary in any of the patients. In all patients, repeat transesophageal echocardiographic controls showed a complete decompression of the LV and no aortic insufficiency. Two patients died of irreversible cardiac failure and 1 of septicemia. At autopsy, no damage of the aortic leaflets was detected. Two patients survived after being weaned by intraaortic balloon pumping and then were discharged from the hospital. In both patients, no aortic insufficiency or stenosis due the transvalvular cannula was detected on transesophageal echocardiography during incremental weaning. The decannulation technique consists of cutting the two silk sutures securing the cannula around the tube and pulling out the cannula while allowing bleeding during removal. The ascending aorta is then laterally clamped just below the insertion of the Dacron tube, which is cut 5 mm up to the anastomosis and sewn with a 5/0 monofilament suture, very close to the anastomosis to avoid a dead-end. Up to now, no aortic insufficiency has been detected on echocardiographic controls in both surviving patients. In another patient, Bio-Medicus left ventricular assistance was successfully instituted as a "bridge to transplantation" with the same technique without requiring CPB.
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Comment
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Although ventricular support with centrifugal pumps is an efficient, low-cost, and readily available method, morbidity and mortality still remain high. Survival is dependent not only on the selection and preassist and postassist management of patients, but also on technical aspects of the method [3]. Easier insertion and removal of the device with less manipulation of the heart, no bleeding at cannulation sites, adequate inflow drainage, myocardium-sparing cannulation technique, and no compression of the coronary artery grafts or the heart by cannulas or sternal closure are the most crucial technical factors. We believe that our conversion technique from CPB to centrifugal mechanical assist meets most of the criteria previously mentioned by Duncan and associates [2]. Its institution and removal are easy and safe. It requires no manipulation of the heart that otherwise could aggravate the circulatory instability. It provides excellent and direct inflow drainage of the LV. It avoids problems related to left atrial or apical inflow cannulation such as uncontrollable bleeding in the presence of fragile tissue, insufflation of air into the circuit through holes or incisions at the left atrial or apical cannulation site especially when the filling pressure is very low, inflow cannula obstruction by pliable left atrial wall, increased right-to-left shunt through an unrecognized patent foramen ovale [4], and stenosis of the right superior pulmonary vein after decannulation of a small left atrium. It also avoids potential compression of the right coronary artery grafts in the presence of a standard left atrial cannula crossing the right atrium [3] and that of the left coronary artery grafts in the presence of a cannula inserted into the left appendage. In addition, when compared with Duncan and associates’ technique, the use of a smaller Dacron tube on the ascending aorta renders this modified technique more applicable in the presence of a short ascending aorta or multiple proximal coronary artery anastomoses. The use of a 36F inflow cannula provides better left ventricular unloading than that of a 24F cannula. Moreover, the fact that the Dacron tube is anastomosed under lateral clamping of the aorta allows the implantation of a centrifugal pump without CPB in the intensive care unit and its subsequent conversion to CPB for patients who will undergo cardiac transplantation.
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References
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- Curtis J.J., Walls J.T., Schmaltz R.A., Demmy T.L., Wagner-Mann C.C., McKenney C.A. Use of centrifugal pumps for postcardiotomy ventricular failure: technique and anticoagulation. Ann Thorac Surg 1996;61:296-300.[Abstract/Free Full Text]
- Duncan J.M., Baldwin R.T., Igo S.R., Frazier O.H. Myocardium-sparing cannulation technique for left ventricular assist device support. Ann Thorac Surg 1991;52:565-566.[Abstract]
- Jett G.K. Atrial cannulation for left ventricular assistance: superiority of the dome approach. Ann Thorac Surg 1996;61:1014-1015.[Abstract/Free Full Text]
- Pennington D.G., Merjavy J.P., Swartz M.T., Willman V.L. Clinical experience with a centrifugal pump ventricular assist device. Trans ASAIO 1982;28:93-97.
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Abstract
Introduction
