Thoracotomy and Pericardiotomy for Access to the Heart in Horses: Surgical Procedure and Effects on Anesthetic Variables.

This research presents a surgical procedure giving complete access to a horse’s heart, and evaluates the impact on the horse’s pulmonary gas exchange during surgery. Two groups were studied: one undergoing the surgical procedure and another as a control group.

Research Methodology

In conducting this research, the researchers used two experimental arms:

• The first arm included 11 Standardbred horses that had atrial fibrillation, a heart condition experimentally induced by tachypacing, a method to deliberately induce rapid heart rate. These horses underwent thoracotomy, which is a surgical procedure to open up the chest.
• The second arm consisted of 6 control Standardbred horses, which were anesthetized for unrelated reasons and thus did not undergo the surgical intervention.

Anesthetic Procedure

The horses were anesthetized using zolazepam and tiletamine. Anesthesia was maintained with isoflurane in 100% oxygen. The horses’ breathing was controlled by intermittent positive pressure ventilation, and no positive end-expiratory pressure was performed.

Surgical Procedure

To obtain complete access to the heart, rib resection, which involves the surgical removal of a rib, and pericardiotomy, opening up the pericardium which is the sac-like covering around the heart, were carried out. Arterial blood samples were drawn before, as well as 5 and 30 minutes after puncturing the pleura parietalis, which is the portion of the lining of the thoracic cavity that covers the chest wall. In 10 out of 11 horses, removal of the fifth rib was enough for heart exposure. In one case, it was necessary to remove the sixth rib as well.

Results of the Study

The research found that the duration of the surgical procedure (thoracotomy, pericardiotomy) was less than 45 minutes. During the thoracotomy, the oxygen partial pressure (PaO2) significantly decreased from 291.8 ± 82.8 mmHg to 165.2 ± 73.5 mmHg but it remained within the normal range compared to the anesthetized control horses. The carbon dioxide partial pressure (PaCO2) also stayed within normal limits during the surgery.