Management of the Heart Rate during Coronary Artery Bypass Grafting on the Beating Heart: Newly Devised Methods of Decreasing Heart Rate -A Preliminary Report-

Background: To develop new methods for achieving bradycardia, we studied the feasibility of producing transient, reversible bradycardia with atrial stimulation and cooling of the sinoatrial node. Methods: In an animal study, the atrium was stimulated electrically during the refractory period of the atrioventricular node. Alternatively, an area of the sinoatrial node was cooled regionally. The two methods were also performed in combination. In a clinical study, atrial stimulation was applied in seven consecutive patients who underwent coronary artery bypass grafting (CABG). Results: In the animal study, atrial stimulation was effective only when 2 mg/kg of diltiazem was administered. Such atrial stimulation decreased heart rate (beats/minute) from 95.8 ±16.9 to 64.2±20.0 (the average reduction from the control value 66.1 ±10.3%). Cooling the sinoatrial node decreased heart rate, and was effective with or without administration of diltiazem. Heart rate was decreased from 156.6±31.7 to 110.7±21.7 (average reduction from control value 71.3±9.2%) before using diltiazem and from 102.0±11.9 to 63.5±13.9 (average reduction from control value 62.0±10.4%) after administration of diltiazem. By combining the two methods, heart rate was decreased from 102.0±12.3 to 44.6±9.1 (average reduction from control value 43.5±6.3%). In our clinical study, the atrial stimulation method was effective. Conclusion: Atrial stimulation or regional cooling of the sinoatrial node slowed the heart rate. By combining the two methods, the heart rate was slowed to 40. Clinically, atrial stimulation was effective in CABG patients. (Ann Thorac Cardiovasc Surg 2001; 7: 358‐67)