In an isolated dog atrium model, hypothermia suppresses SA nodal pacemaker activity and sensitivity to norepinephrine without significantly altering the relative duration of postdrive suppression.
Hypothermia effects on canine SA node warrant clinical caution; leaves open translational relevance to human arrhythmias.
Using an isolated, blood-perfused atrium preparation, the effects of temperature on SA nodal pacemaker activity were investigated in 9 preparations. The PP interval decreased as temperature was raised. Regular sinus rhythm and atrial contraction were maintained above approximately 26 degrees C. Below 26 degrees C, sinus depolarization still showed a regular rate, although atrial contractions had ceased. At about 24 degrees C, atrial rhythm became irregular. Below 20 degrees C, atrial depolarization disappeared. Chronotropic responses to norepinephrine were suppressed at decreased temperatures, not only with respect to maximum PP shortening but also to the threshold dose for inducing sinus acceleration. Overdrive suppression was not influenced significantly by decreasing temperature. These results indicate that a temperature decrease causes suppression of SA nodal pacemaker activity, although the SA node continues to function regularly until about 25 degrees C.
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Chiba et al. (1976) studied this question.
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