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EXPERIMENTAL INDUCTION OF CHRONIC COMPLETE HEART BLOCK
EXPERIMENTAL I N D U C T I O N OF CHRONIC COMPLETE HEART BLOCK Coleman J. Connolly, M.D., Donald IV. Hannon, M.D., and Jesse E. Edwards, M.D., St. Paul and Minneapolis,
Minn.
T
wo factors have interfered with the experimental study of chronic complete heart block. These are the tendency for animals to die (1) shortly after in duction of the conduction disturbance or (2) during anesthesia when a subse quent procedure is attempted. As our experience has tended to surmount these two obstacles, we are reporting the method employed to induce complete heart block in the dog. Starzl, Gaertner, and Baker 1 performed functional studies of short-term nature in dogs with complete heart block. They stated that the conduction dis turbance was induced by section of the bundle of His through a right auricular myocardotomy during temporary occlusion of the cavae. They did not, however, supply further detail as to the procedure used for induction of the heart block. METHOD
Ten healthy mongrel dogs, each with electrocardiographically demonstrated sinus rhythm, were employed (Fig. 1). Under Nembutal anesthesia, a rightsided thoracotomy was done through the fifth intercostal space. The pericardium was opened anterior to the phrenic nerve and then retracted with silk sutures. Umbilical tapes were placed about the superior and inferior venae cavae and then the ends of the tapes were pulled through short pieces of rubber tubing. The azygos vein was ligated. A purse-string suture of 2-0 silk was placed in the anterolateral wall of the right atrium about half way between the inferior vena caval orifice and the base of the right atrial appendage. The atrial wall was then engaged between two curved hemostats in the area outlined by the pursestring suture. The tapes about the cavae were pulled up so as to occlude the flow of blood into the heart. An opening was then made in the atrium and the opening retracted with a suction tip and one small retractor. After the blood in the right atrium was removed by suction, the septal wall of this chamber From the Departments of Surgery, St. Joseph's Hospital and The Charles T. Miller Hospi tal, St. Paul, Minn., the Research Laboratory of the St. Paul Outpatient Center, the Depart ments of Pathology, The Charles T. Miller Hospital, St. Paul, and the University of Minnesota, Minneapolis, Minn. This study was supported by Research Grant No. HE-5694 of the National Heart Institute, U. S. Public Health Service. Received for publication June 17, 1964. 313
314
CONNOLLY, HANNON, EDWARDS
J. Thoracic and Cardiovas. Surg.
and related structures were visualized. To divide the bundle of His, a vertical incision was made in the atrial septum just above the tricuspid valve, about 1.75 cm. anterior to the ostium of the coronary sinus. The incision was then cauterized by electrocautery. No attempt was made to identify the conduction tissue by in vivo staining.2"7 Following the procedure described, which involved from about 2 to 4 minutes of caval occlusion, the tapes about the cavae were loosened and the right atrium filled with blood. The purse-string suture in the atrial wall was tied, the vena caval retentions released, and the pericardial and thoracotomy wounds closed.
F i g . 1.—Essential s t e p s in p r o c e d u r e of i n t e r r u p t i o n of b u n d l e of H i s for i n d u c t i o n of complete h e a r t block in t h e dog.
RESULTS
Upon incising and cauterizing the atrial septum, one usually observes a change in the state of cardiac contraction characterized by the ventricular beat being slow and asynchronous with the rapid atrial beat. This feature is used as a guide during the operation to indicate that complete heart block has been induced. Eleetrocardiographic confirmation is obtained following the operation. Of the 10 dogs employed, complete heart block was observed in 5 im mediately after performance of the procedure described. In 3 other dogs the first attempt failed to induce complete heart block. In each of these the caval occlusion was repeated, the right atrium was reopened, and the incision in the septal wall was enlarged and recauterized. In each of these, complete heart
Vol. 49, No. 2 February, 1965
CHRONIC COMPLETE HEART BLOCK
315
block was identified following the second attempt. Of the 10 dogs, complete heart block was induced in 8 (Fig. 2). Two failures resulted. These were re lated to the appearance of ventricular fibrillation at the time of initial cautery of the septal incision. A third dog, 1 of the 8 with complete heart block, died suddenly on the fifth postoperative day, while 7 dogs have continued in a state of complete heart block confirmed electrocardiographically for periods varying from 5 to 19 months. Among the surviving animals, prevailing ventricular rates vary from 25 to 35 beats per minute. No syncopal attacks have been noted among the animals, although no attempt at exercising the animals has been made.
Fig. 2.—Representative electrocardiograms from one of the experimental animals. Preoperative tracings (Sept. 6, 1962) show sinus rhythm. Complete heart block in tracings made 1 and 10% months after division of bundle of His. SUMMARY
A method is described for induction of permanent complete heart block in the dog by incising the bundle of His while the subject is anesthetized and in a state of temporary circulatory arrest. Of 10 dogs used, complete heart block was obtained in 8 (a second incision was required in 3 of these). Two animals died of ventricular fibrillation during incision and cautery of the bundle of His, representing the 2 animals in which complete heart block was not induced. Death of 1 animal occurred on the fifth postoperative day. The remaining 7 dogs have continued to exhibit electrocardio graphically substantiated complete heart block for periods varying from 5 to 19 months.
316
CONNOLLY,
HANKOX,
EDWARDS
J. Thoracic and Cardiovas. Surg.
REFERENCES
1. Starzl, T. E., Gaertner, E. A., and Baker, R. R.: Acute Complete Heart Block in Dogs, Circulation 12: 82, 1955. 2. Allen, P., Lederman, J . J., and Pearl, G. J . : Prevention of Surgical Heart Block by the Use of Supravital Staining, J . THORACIC & CARDIOVAS. SURG. 38: 57, 1959.
3. Barton, E. M., and Greenwood, H. H . : Experimental Infarction of the Inter ventricular Septum of the Canine Heart, Arch. Path. 16: 15, 1933. 4. DeWitt, L. M.: Observations on the Sino-Ventricular Connecting System of the Mam malian Heart, Anat. Rec. 3 : 475, 1909. 3. Glomset, D. J., and Glomset, A. T. A . : A Morphologic Study of the Cardiac Conduction System in Ungulates, Dog, and Man, Am. Heart J . 20: 677, 1940. 6. Kisten, A. D . : Observations on the Anatomy of the Atrioventricular Bundle (Bundle of His) and the Question of the Other Muscular Atrioventricular Connections in Nor mal Human Hearts, Am. Heart J . 37: 849, 1949. 7. James, T. N . : Anatomy of the Coronarv Arteries, New York, 1961, Paul B. Hoeber, Inc., p. 211.
Minn.
T
wo factors have interfered with the experimental study of chronic complete heart block. These are the tendency for animals to die (1) shortly after in duction of the conduction disturbance or (2) during anesthesia when a subse quent procedure is attempted. As our experience has tended to surmount these two obstacles, we are reporting the method employed to induce complete heart block in the dog. Starzl, Gaertner, and Baker 1 performed functional studies of short-term nature in dogs with complete heart block. They stated that the conduction dis turbance was induced by section of the bundle of His through a right auricular myocardotomy during temporary occlusion of the cavae. They did not, however, supply further detail as to the procedure used for induction of the heart block. METHOD
Ten healthy mongrel dogs, each with electrocardiographically demonstrated sinus rhythm, were employed (Fig. 1). Under Nembutal anesthesia, a rightsided thoracotomy was done through the fifth intercostal space. The pericardium was opened anterior to the phrenic nerve and then retracted with silk sutures. Umbilical tapes were placed about the superior and inferior venae cavae and then the ends of the tapes were pulled through short pieces of rubber tubing. The azygos vein was ligated. A purse-string suture of 2-0 silk was placed in the anterolateral wall of the right atrium about half way between the inferior vena caval orifice and the base of the right atrial appendage. The atrial wall was then engaged between two curved hemostats in the area outlined by the pursestring suture. The tapes about the cavae were pulled up so as to occlude the flow of blood into the heart. An opening was then made in the atrium and the opening retracted with a suction tip and one small retractor. After the blood in the right atrium was removed by suction, the septal wall of this chamber From the Departments of Surgery, St. Joseph's Hospital and The Charles T. Miller Hospi tal, St. Paul, Minn., the Research Laboratory of the St. Paul Outpatient Center, the Depart ments of Pathology, The Charles T. Miller Hospital, St. Paul, and the University of Minnesota, Minneapolis, Minn. This study was supported by Research Grant No. HE-5694 of the National Heart Institute, U. S. Public Health Service. Received for publication June 17, 1964. 313
314
CONNOLLY, HANNON, EDWARDS
J. Thoracic and Cardiovas. Surg.
and related structures were visualized. To divide the bundle of His, a vertical incision was made in the atrial septum just above the tricuspid valve, about 1.75 cm. anterior to the ostium of the coronary sinus. The incision was then cauterized by electrocautery. No attempt was made to identify the conduction tissue by in vivo staining.2"7 Following the procedure described, which involved from about 2 to 4 minutes of caval occlusion, the tapes about the cavae were loosened and the right atrium filled with blood. The purse-string suture in the atrial wall was tied, the vena caval retentions released, and the pericardial and thoracotomy wounds closed.
F i g . 1.—Essential s t e p s in p r o c e d u r e of i n t e r r u p t i o n of b u n d l e of H i s for i n d u c t i o n of complete h e a r t block in t h e dog.
RESULTS
Upon incising and cauterizing the atrial septum, one usually observes a change in the state of cardiac contraction characterized by the ventricular beat being slow and asynchronous with the rapid atrial beat. This feature is used as a guide during the operation to indicate that complete heart block has been induced. Eleetrocardiographic confirmation is obtained following the operation. Of the 10 dogs employed, complete heart block was observed in 5 im mediately after performance of the procedure described. In 3 other dogs the first attempt failed to induce complete heart block. In each of these the caval occlusion was repeated, the right atrium was reopened, and the incision in the septal wall was enlarged and recauterized. In each of these, complete heart
Vol. 49, No. 2 February, 1965
CHRONIC COMPLETE HEART BLOCK
315
block was identified following the second attempt. Of the 10 dogs, complete heart block was induced in 8 (Fig. 2). Two failures resulted. These were re lated to the appearance of ventricular fibrillation at the time of initial cautery of the septal incision. A third dog, 1 of the 8 with complete heart block, died suddenly on the fifth postoperative day, while 7 dogs have continued in a state of complete heart block confirmed electrocardiographically for periods varying from 5 to 19 months. Among the surviving animals, prevailing ventricular rates vary from 25 to 35 beats per minute. No syncopal attacks have been noted among the animals, although no attempt at exercising the animals has been made.
Fig. 2.—Representative electrocardiograms from one of the experimental animals. Preoperative tracings (Sept. 6, 1962) show sinus rhythm. Complete heart block in tracings made 1 and 10% months after division of bundle of His. SUMMARY
A method is described for induction of permanent complete heart block in the dog by incising the bundle of His while the subject is anesthetized and in a state of temporary circulatory arrest. Of 10 dogs used, complete heart block was obtained in 8 (a second incision was required in 3 of these). Two animals died of ventricular fibrillation during incision and cautery of the bundle of His, representing the 2 animals in which complete heart block was not induced. Death of 1 animal occurred on the fifth postoperative day. The remaining 7 dogs have continued to exhibit electrocardio graphically substantiated complete heart block for periods varying from 5 to 19 months.
316
CONNOLLY,
HANKOX,
EDWARDS
J. Thoracic and Cardiovas. Surg.
REFERENCES
1. Starzl, T. E., Gaertner, E. A., and Baker, R. R.: Acute Complete Heart Block in Dogs, Circulation 12: 82, 1955. 2. Allen, P., Lederman, J . J., and Pearl, G. J . : Prevention of Surgical Heart Block by the Use of Supravital Staining, J . THORACIC & CARDIOVAS. SURG. 38: 57, 1959.
3. Barton, E. M., and Greenwood, H. H . : Experimental Infarction of the Inter ventricular Septum of the Canine Heart, Arch. Path. 16: 15, 1933. 4. DeWitt, L. M.: Observations on the Sino-Ventricular Connecting System of the Mam malian Heart, Anat. Rec. 3 : 475, 1909. 3. Glomset, D. J., and Glomset, A. T. A . : A Morphologic Study of the Cardiac Conduction System in Ungulates, Dog, and Man, Am. Heart J . 20: 677, 1940. 6. Kisten, A. D . : Observations on the Anatomy of the Atrioventricular Bundle (Bundle of His) and the Question of the Other Muscular Atrioventricular Connections in Nor mal Human Hearts, Am. Heart J . 37: 849, 1949. 7. James, T. N . : Anatomy of the Coronarv Arteries, New York, 1961, Paul B. Hoeber, Inc., p. 211.