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J Thorac Cardiovasc Surg 1994;107:1168-1169
© 1994 Mosby, Inc.
LETTERS TO THE EDITOR |
Department of Surgery
Addenbrookes Hospital
Cambridge, United Kingdom
To the Editor:
Heron's technique for cervical heterotopic cardiac transplantation in rats 
1 is a useful procedure that can be performed by researchers with limited experience in microvascular surgery. The transplantation of hearts in the abdominal cavity, as described by Ono and Lindsay, 2 is more commonly used 3 but requires microvascular anastomoses, which limits its application to researchers with experience in the field of microvascular surgery. This article describes a modification of Heron's technique that has been used in more than 600 heterotopic cardiac transplants with an almost 100% success rate.
Outbred Syrian hamsters (80 to 110 gm) were provided by Wrights Brothers (Essex, United Kingdom). PVG rats (200 to 250 gm) were provided by Bantin and Kingman (Hull, United Kingdom).
Donor hamsters are anesthetized with ether, a transverse upper abdominal incision is made, and the chest cavity is entered by dividing the diaphragmatic attachment and the chest wall on both sides up to the level of the mammary artery. The animal is heparinized (300 units intravenously), the ascending aorta is dissected from the pulmonary artery, and the dissection is carried up to the aortic arch beyond the innominate artery. The superior vena cava is ligated, and 2 ml of cardioplegic solution (St. Thomas' Hospital solution) is infused through the inferior vena cava, which is subsequently ligated. The aortic arch is divided beyond the origin of the innominate artery, the pulmonary artery, is divided beyond its bifurcation, and the bridge between the two branches is slit open. A further 3 ml of cardioplegic solution is infused down the aortic root; finally, a 6-0 tie is passed around the atrioventricular ring, which isolates the two atrial compartments, and the heart is removed and put in cold saline solution.
In recipient rats, a midline incision is made starting from just below the lower jaw down to the upper part of the chest. The two salivary glands, which are joined together across the midline by fascial layers, are separated to expose the right external jugular vein, which is dissected from its origin to its junction with the subclavian vein and irrigated with papaverine (1:20 solution).
The sternocleidomastoid muscle is freed and its vascular supply is cauterized. It is then detached from its origin and excised as high as possible. The carotid sheath is exposed by dividing the overlying muscle layer. The carotid artery is dissected from its entry into the neck up to and beyond its bifurcation and irrigated with papaverine solution, a vascular clamp is applied proximally, and the artery is ligated above its bifurcation and divided. The bridge between the two branches is slit open; this transforms the free end of the artery into a cup shape wider than the diameter of the main vessel, providing more tissue for handling during the preparation of the cuff. The artery is passed through the arterial cuff (the tip of a size 18 Medicut cannula) as described by Heron and everted over it. A Portex feeding tube (6F) (Kent, United Kingdom) is used as a venous cuff in a similar fashion to Heron's technique. On completion of the procedure, the recipient rat is kept sedated for 1 to 2 hours (by intramuscular injection of fentanyl/fluanisone [Hypnorm] at a dose of 0.2 ml/kg), which allows the transplanted heart to stick in position, preventing distortion or kinking of the vascular pedicle.
This is a detailed description of the modified technique used. It is important to understand the problems encountered during the application of Heron's technique and the modifications made to eliminate these difficulties. Heron's original technique described the division of the aorta and pulmonary artery at the level of the transverse sinus. This makes the application over the recipient's cuffs more difficult because of the limited length of artery available. This problem is remedied in the modified technique by dividing the aorta beyond the origin of the innominate artery. The bridge between the aorta and the innominate artery is slit open, thus providing both ample length and ample diameter for the introduction of the arterial cuff during the recipient's operation. Similarly, the pulmonary artery is divided beyond its bifurcation and the bridges between its branches is slit open. This step provides two fringes of tissue on both sides of the main pulmonary artery, which allows easier application over the venous cuff of the recipient and allows repeated attempts if necessary. If the main pulmonary artery is used, as in Heron's description, and another application is required, there is the risk of damaging the artery. This makes the procedure technically extremely difficult, if not impossible.
Heron did not heparinize the donor or preserve the heart in cardioplegic solution; instead, he used cold saline solution to clear the donor heart of any blood. The use of heparin prevents any chance of clot formation in the donor heart and the use of cardioplegia provides better myocardial protection. Furthermore, the use of papaverine to irrigate the vessels of the recipient will counteract any spasm incurred by dissection.
The common difficulty in Heron's technique is eversion of the recipient carotid artery. Some resolve the problem by using a smaller arterial cuff. In the modification described here, this is solved by excising the sternocleidomastoid muscle to expose the entire course of the carotid artery in the neck and by dividing the carotid artery beyond its bifurcation. This division and slitting open of the bridge between its two branches transforms the end of the carotid artery into a cup shape, with a wider diameter than the main vessel itself. This step is vital because it makes eversion of the artery far easier; if it retracts, the step can be repeated many times. If the main artery is divided before its bifurcation and the eversion fails, the wall of the main artery tends to shred and the available length of the artery becomes limited.
The stabilization of the cuff during eversion is critical; this is obtained by mounting the cuff through suitably fashioned holes in mosquito forceps, which provides a snug fit but does not distort the wall of the cuff. Kamada and Calne 4 described a method for stabilizing the cuff by fashioning an extension, providing a handle for holding the cuff with forceps. 4 Such an extension works well with cuffs of large diameter, but it is not suitable for the size of cuff used for the carotid artery.
Finally, the position of the transplanted heart in the neck poses the problem of kinking of the vascular pedicle if the animal is allowed to move early after the completion of the operation. Keeping the animal sedated for 1 hour allows the heart to adhere to the surrounding structures, thus reducing the risk of kinking of the vascular pedicle. Applying this, technique we were able to perform more than 600 xenografts and achieved a success rate of almost 100%. Furthermore, both the donor and recipient operations could be performed by a single operator within a period of 40 minutes.
References
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