The Study Of Injury About Transesophageal Cardioversion

Objective To study the safety and efficiency of transesophageal cardioversion in rabbits using a self designed bipolar esophageal electrode system.Methods We attempted transesophageal cardioversions in 8 rabbits with eight different energy levels delivered through bipolar esophageal electrode system and recorded the ECG of each rabbit before and after each shock. The esophagi connected to the electrode were apart from the rabbits one hour after shocks, then gross and histopathological examinations were performed. Meanwhile, 48 rabbits were divided into 3 groups in random, and accepted transesophageal shocks in three different energy levels. The energy they received was irrelevant to cardioversion of any tachyarrhythmia. The ECG of each rabbit was recorded. Each group was then divided into two subgroups in random. In one subgroup, the esophagi connected to the electrode and the hearts near the electrode were apart from the rabbits one hour after shocks. In the other subgroup, the same operation was attempted one week after shocks. Gross and histopathological examinations were then performed.Results (1)The influence to ECG: 56 rabbits received 322 transesophageal shocks, and ECG changes happened after 3 shocks. Atrioventricular block(2:1) was recorded in one rabbit, nonpermanent ventricular tachycardia was recorded in another, ST-T segment change was recorded in the other(P=0.1244).All the changes recovered in a few minutes. (2)The injury to esophagi: the degree of acute injury demonstrated in the 10 esophagi correlated with the total energy applied (T=0.7857,P < 0.01).One hour after shocks, there were differences in the mild to moderate injury between the low energy group and the medium energy group(p=0.0336).There were significant differences in the severe injury between the low energy group and the high energy group (p=0.0003).One week after shocks, there were no significant differences in any type of esophageal injury between the low energy group and the medium energy group (p=0.5000-1.0000). There were significant differences in the severe injury between the high energy group and the low energy group or between the high energy group and the medium energy group (p=0.0003~0.0023).There were significant differences in the degree of esophageal injury only in the medium energy group between one hour after shocks and one week after shocks (p=0.0196). It indicated that the injury is recoverable. (3)The injury to myocardium: Almost all the three energy groups had pathological changes in myocardium one hour after shocks, but these changes didn't have effects on the hearts' function. Oneweek after shocks, there were no obvious injury in myocardium in the low energy group and medium energy group. Only the high energy group had pathological changes.Conclusions (1)The degree of acute injury in esophagi increased with the total energy applied. (2)Transesophageal technique was safe in a rabbit model when single shock energy was less than 100J and cumulative shock energy was less than 510J. Single shock energy of 150/200J and cumulative shock energy of 750J caused acute and chronic injury in esophagi and myocardium, even caused esophageal performation and ulcer formation This energy should be tabooed in transesophageal technique. (3) Transesophageal shocks could cause temporary ECG changes in a rabbit model when single shock energy was more than 70J and cumulative shock energy was more than 200J.