Acute open-chest complete heart block by transeptal electrocoagulation

A method of producing complete heart block (CHB) in open-chest dogs is described. Having found previous methods unreliable in our hands or excessively complex for the acute open-chest setting, we constructed an electrocautery pinch-clamp device that functions in both locating and destroying the area of the atrial septum that contains the atrioventricular node and His bundle. Fifteen male mongrel dogs were anesthetized with alpha-chloralose, intubated, and ventilated (Harvard 607). Through a left thoracotomy at the fifth intercostal space, the two arms of the clamp are introduced into the left and right atria, respectively, via the atrial appendages. The correct site for electrocautery is located by gently squeezing the atrial septum between the arms of the clamp. Systematic testing of the region of the septum that lies, roughly, between the coronary sinus ostium and the anterior portion of the septal leaflet of the tricuspid valve will result in a rhythm disturbance when the correct site is squeezed. Sustained pressure will yield overt dissociation of the atrial and ventricular contractions. The electrocautery current is then activated for 10-15 s. Lead II of the electrocardiogram is monitored, and if CHB is not sustained after 5 min, the procedure is repeated. Once CHB is established, the clamp is removed and the atrial defects are ligated. By application of this method with no prior use of the technique, 12 of 15 attempts produced stable CHB lasting at least 3-4 h. Examination of the hearts of eight of the animals revealed no septal defects or damage to the tricuspid valve. We conclude that this method offers significant advantages for the production of CHB in acute studies in the dog.