Abstract
Effects of temperature for inducing cardiac arrest by cooling and the reactivation by rewarming were investigated in the spontaneously beating canine atrium. Moreover, effects of temperature on paced atria and ventricles were also studied. By cooling, atrial rate was linealy decreased from 111 beats/min and then sinus arrest occurred at 20 +/- 0.3 degrees C (mean +/- SE). Just before the arrest, sinus rate was 29 +/- 2.7 beats/min in 6 atrial preparations. On the other hand, atrial contraction was rather increased until about 25 degrees C and then slightly decreased by cooling. In paced preparations, contraction of the atrium and ventricle initially increased and then decreased with pulsus alternans below the control level by cooling. Finally, pacing failure usually occurred. When the reactivation was induced by rewarming after atrial arrest, atrial rhythm was suddenly recovered at about 25 degrees C, but the contraction was minimum and gradually recovered to the control level. From these results, it is suggested that atrial arrest by cooling may be due to sinoatrial conduction block and that the sinoatrial junction area may have an important role on the reactivation by rewarming. Moreover, the recovery of contraction by rewarming may be affected by several factors which may depress the tension development.
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