Sinoatrial Node Isolation from Mouse Model: A Procedure to Harvest SA Node from Murine Heart

In the heart, the sinoatrial node or S-A node contains specialized muscle cells that continuously initiate and propagate electric impulses throughout the heart, setting the rate of the heartbeat.

To isolate the S-A node, first, prep an anticoagulant-treated euthanized mouse in the supine position. Anticoagulant treatment helps prevent blood clots for efficient tissue isolation.

Next, make a transverse skin incision followed by cutting the lateral walls of the rib cage to access the contents of the thoracic cavity and expose the underlying heart.

Hydrate the heart with anticoagulant-containing buffer. Remove the lungs along with trachea.

Sever the major blood vessels to excise the heart from the chest cavity. Transfer the excised heart to a buffer-containing silicone-elastomer lined dish for handling the delicate organ.

Secure the apex of the heart. Now, locate the position of the inferior and superior vena cava within the right atrium. Further, identify the location of the S-A node within the tissue patch between the venae cavae.

Remove the apex to drain blood from the heart. Now, separate the atria from the ventricles. Cut along the interatrial septum to remove the left atrium. Lay the right atrium flat and excise the S-A node tissue from it.

Begin by holding the skin of the euthanized mouse with a hemostat, and use surgical scissors to make a transverse incision in the skin, just beneath the bottom of the rib cage from the left costal arch to the right costal arch. Use surgical scissors to cut open the peritoneum, and carefully separate the liver from the diaphragm, without nicking the liver, to prevent excessive bleeding.

Incise the diaphragm along the thorax to expose the thoracic cavity. Use the surgical scissors to cut the lateral walls of the rib cage, from the edges of the costal arches up to the clavicles, to expose the heart. Then, use a 23-gauge syringe needle to pin the rib cage over the shoulder.

Use a transfer pipette to drop warm heparinized Complete Tyrode's solution on the heart to keep it moist. Hold the lungs with extra fine Graefe forceps, and sever the trachea with surgical scissors to remove the lungs. For removing the heart, hold the apex of the heart with extra fine Graefe forceps, and cut the aorta and inferior vena cava with surgical scissors.

Transfer the heart to a Petri dish containing a cured silicone elastomer, and use a transfer pipette for bathing the heart with 2 to 3 milliliters of warm heparinized Complete Tyrode's solution. Attach the apex of the heart to the dish with a dissection pin.

Hold the inferior vena cava with Dumont #2 laminectomy forceps. Insert a 22-gauge syringe needle through the inferior and superior vena cava to locate their position in the right atrium, which also identifies the approximate position of the sinoatrial node.

Hold the right atrial appendage with Dumont #2 laminectomy forceps, and put a dissection pin through the right atrial appendage to hold it in place. Repeat the same procedure for the left atrial appendage. Then, remove the syringe needle that spans the vena cava.

Use Castroviejo scissors to remove the apex of the heart by making a transverse incision across the ventricles, or releasing the blood from the heart. Then, wash the heart by adding warm heparinized Complete Tyrode's solution. Use Castroviejo scissors to cut along the atrioventricular septum until the atria are separated from the ventricles, and keep the incision closer to the ventricle.

Cut along the interatrial septum to remove the left atrium. Place the dissection pins in the periphery of the right atrium to make it lay flat. Remove any remaining fat, vessels, or tissue from the atrium using the Castroviejo scissors, and locate the sinoatrial node in the right atrium.