The increasing number of pacemaker patients correlates with the number of pacemaker meetings that attract physicians and medical engineers entering this expanding branch of medicine. The Pacemaker Colloquium organised in Brussels April 21st and 22nd 1977 was such a meeting. It was different from previous meetings as it had no surveys or summaries on patient series but instead it focused on controversial subjects that have emerged from pacing in the past and on new developments for the future. Besides controversial papers on indications for temporary and long-term pacing, new technical developments were presented in Brussels, where for the first time the important lithium battery manufacturers demonstrated their data. The surveys on electrodes, especially the fixation mechanisms and the atrial electrodes, initiated an animated discussion. This all converged in a Round Table on the choice of the electrode-pacemaker combination. Pacemaker electrocar diography and the application of cardiac stimulation in various types oftachyar rhythmias formed two clinically oriented sessions. Mter a survey ofthe various follow-up systems a series of presentations deals for the first time with the possibilities and difficulties of the application of com puters in cardiac pacing. A Round Table on the organisation of the Pacemaker clinic closed this friendly and animated meeting. It is our sincere hope that the publication of the presented papers and dis cussions in these Proceedings will help all those active in cardiac pacing to answer some of their problems and to improve the treatment of pacemaker patients."

On Friday, the 8th of October 1976, a one day Symposium on Cardiac Pacing, supported by an educational grant from Vitatron Medical, was held at the Sheraton Boston Hotel in Boston, Massachusetts. The intent of the Organizing Committee was to provide a concentrated overview of various aspects of cardiac pacemaker technology ranging from historical aspects, indications, electrode design, energy sources, engineering concepts, detection of malfunction and fol lowup of implanted systems. A look into future trends was also emphasized. The audience consisted of physicians from all parts of the United States with a special interest in pacemaker systems. Their comments, questions, and description of their own experiences, which arose during the discussion period at the end of the program, extended the breadth of the information provided. J . WARREN HARTHORNE ACKNOWLEDGEMENT The editors of this Colloquium on Cardiac Pacing (J. W. H. and H. J. Th. T. ) ac knowledge the patient understanding and support of their wives, Christa and lise through the long hours at night and weekends during which these proceedings were made ready for publication. A special note of appreciation is extended to Dr. Harthorne's secretary, Miss Stephanie Ann Murray, who transcribed the original tape-recorded presentations and typed and retyped the many corrected versions thereafter - all done without complaint and with ultimate good humor. CONTENTS Foreword . 5 J. WARREN HARTHORNE, M. D. Contributors . 9 Early History of Cardiac Pacing. II HILBERT J. TH. THALEN, M. D."