Left Coronary Artery Ligation: A Surgical Murine Model of Myocardial Infarction

The surgical model permanent ligation of left artery in mice can be used to investigate the pathophysiology and associated inflammatory response after myocardial infarction. This method provides a reliable and producible mouse model of MI, which is easy, safe, and less invasive. To begin, preheat a bead sterilizer to 250 degrees Celsius and place autoclaved surgical instruments in it for a few minutes.

Ensure the depth of anesthesia in the mouse by checking the response to a firm toe pinch. Weigh the mouse to estimate the dosage of the pre-operative analgesic drug buprenorphine and inject the drug intraperitoneally. Trim the fur on the left side of the thorax using an electric razor.

After disinfecting the surgical site, place the mouse in the supine position on an inclined board. Secure the head and limbs of the mouse using an elastic band attached to the upper incisors and adhesive tape respectively. Apply sterile ophthalmic lubricant to the eyes to prevent dryness while under anesthesia.

Open the jaw and gently pull the tongue out of the oral cavity. Identify the opening of the larynx by illuminating the oral pharynx using a laryngoscope. Cut off about 0.5 centimeters from a 24 gauge catheter needle and insert the blunt needle into the plastic shield.

Direct the blunt needle with the plastic shield into the trachea. Take out the needle, leaving the plastic shield in the trachea. Set the ventilator to a respiratory rate of 137 beats per minute, optimized for the mice used in this study and tidal volume 0.18 closing capacity.

Connect the respirator tubes to the catheter shield and confirm correct intubation by looking for a synchronized chest movement with the ventilator. Disconnect the respirator tube from the catheter shield and place the animal in the supine position on a preheated temperature controlled surgical board. Reconnect the mouse to the ventilator.

After disinfecting the surgical site gently lift the skin using a pair of forceps and make a small cutaneous transverse incision along the line between the left pectoralis major and minor muscles using a pair of surgical scissors. Separate the underlying pectoralis muscles with forceps and dissecting scissors. After making an incision in the third intercostal space gently stretch the ribs apart using retractors to expose the left ventricle.

Move the pericardial fat aside and locate the left coronary artery, which runs from the edge of the left atrium toward the apex of the heart. Pass an 8-0 nylon suture under the left coronary artery with the help of a needle holder. Legate the left coronary artery with a double knot followed by a second knot.

Remove the retractors and insert a 22 gauge catheter needle into the chest cavity. Remove the needle, leaving the tip of the plastic shield in the thoracic cavity. Close the ribcage using a 4-0 nylon suture.

Connect a syringe to the 22 gauge plastic shield and slowly remove excess air trapped in the thoracic cavity by gently pressing the chest to establish a negative air pressure. Remove the plastic shield. Switch off the isoflurane supply and place the mouse on the ventilator supplying oxygen.

One spontaneous breathing of the mouse starts, switch off the ventilator. Keep the mouse under a heat lamp and monitor until it is awake. The animal should not be left unattended until it has recovered enough consciousness to maintain sternal recumbency.

Monitor the mouse daily for any sign of pain or discomfort. Continue intraperitoneal injection of buprenorphine every 6 to 8 hours for an additional two days following the surgery. Active ECG and respiration signals were verified before acquiring the echocardiographic data.

The echocardiographic measurement of cardiac functional parameters was noted 28 days after left coronary artery ligation. The M-mode images of the peroneal short axis view of SHAM and MI hearts were observed. The MI images showed defective heart wall movement following left coronary artery ligation.

Indicators of heart failure, such as increased left ventricular mass, decreased ejection fraction, and decreased cardiac output were observed in the MI group as compared to the SHAM group. Masson's trichrome staining of the lower, middle, and upper ventricle sections showed increased collagen staining in the infarcted heart, indicating augmented fibrosis. In most cases, the artery is not feasible.

However, ligating the myocardial tissue 2 to 4 millimeters below the edge of the left atrium results in efficient ligation of the artery.