Effects of thoracotomy on volume conductor properties of the canine torso

The effects of left thoracotomy on the volume conductor properties of the canine torso were studied in ten dogs. Body surface isopotential distributions were examined before and serially (3, 7 and 14-15 days) after limited thoracotomy and pericardiotomy. Changes in QRS potentials were considered to reflect surgically-induced alterations in volume conductor properties. Results demonstrated that thoracotomy caused a generalized reduction in body surface potentials, quantitated as root-mean-square errors that were greatest soon after surgery and reached low levels (less than 200 uV) two weeks postoperatively. Although voltages were reduced, overall isopotential distributions remained similiar in form, with statistically significant correlation coefficients (greater than 0.7) three days after surgery; these values increased to high (greater than 0.85), stable levels by one week. These findings help define the nature and time course of ECG changes that may be attributed to thoracotomy without direct cardiac intervention.