Intrinsic heart rate in XXXX and young adults: an index of sinus node function isolated from autonomic control.

@entity1 @entity1817 @entity3897 @entity1169
Standard evaluation of @entity1 with @entity1817 cannot distinguish abnormal autonomic tone from @entity1817 . This distinction has potentially important therapeutic and prognostic implications. Intrinsic heart rate (IHR)--the peak heart rate (HR) measured during pharmacologic combined autonomic blockade--reflects intrinsic SN function. The purpose of this study was to evaluate the use of IHR--and its relationship with resting heart rate (RHR)--in distinguishing autonomic influence from @entity1817 among @entity1 with @entity1817 . IHR was determined in the electrophysiology laboratory using intravenous @entity1169 , 0.2 mg/kg, followed by intravenous @entity3897 , 0.04 mg/kg; the peak HR recorded was the IHR. IHR was measured in two groups. Seven control subjects, defined as @entity1 with normal noninvasive SN testing, had IHR mean of 128 +/- 24 beats/min; this was greater than RHR mean of 89 +/- 16 beats/min (p less than 0.01). Eight @entity1 with abnormal noninvasive SN testing had IHR mean of 103 +/- 6 beats/min; this was greater than RHR mean of 71 +/- 9 beats/min (p less than 0.01). We therefore reached the following conclusions. (1) Among this particular group of @entity1 with abnormal noninvasive SN testing, IHR was consistently in the normal range for age and greater than RHR, suggesting that excess vagal tone can play a significant role in the expression of @entity1817 . (2) Among normal individuals, IHR is age-related, decreasing with advancing age. IHR greater than RHR suggests that vagal tone predominates in the normal resting state as the net increase in HR during combined autonomic blockade is due to blockade of vagally mediated chronotropic inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)
