Treatment of PAT. Bradycardiac reflexes induced by dive vs. body-tilt

It has been suggested that the dive reflex (elicited by face immersion in water with breath-hold) may be employed to induce vagally-mediated bradycardia in individuals with paroxysmal atrial tachycardia. However, in several cases the use of this reflex is reported to have led to exacerbation of the cardiac dysfunction. Examination of heart-rate and EKG T-wave amplitude changes during the dive in healthy, college-aged individuals indicated that warming the water (10 degrees through 20 degrees C to 40 degrees C) decreased the bradycardia, but did not alter the attenuation (approximately 100 mu v) of the T-wave. The latter effect was taken to indicate that sympathetic activity, as indexed by T-wave amplitude, was not reduced by increases in water temperature. On the other hand, a 90 degrees head-up to head-down body tilt produced a bradycardia response of some 30 bpm as well as a T-wave amplitude increase (sympathetic withdrawal) in the order of 100 mu v. These data suggest that individuals who exhibit symptoms of ventricular sympathetic irritability may be adversely affected by the dive maneuver, regardless of water temperature. The body-tilt induced reflex in such individuals may thus be more appropriate given the large-magnitude bradycardia and absence of T-wave attenuation. At the present, however, the body-tilt preparation has been used only with healthy normal subjects, so this suggestion remains to be directly tested.