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Intrinsic heart rate in children and young adults: an index of sinus node function isolated from autonomic control
B Marcus1, P C Gillette, A Garson
1Lillie Frank Abercrombie Section of Pediatric Cardiology, Baylor College of Medicine, Texas Children's Hospital, Houston.
Insights
Intrinsic heart rate (IHR) helps differentiate autonomic tone from sinus node (SN) disease in children. Elevated IHR, even in dysfunction cases, suggests excess vagal tone, guiding treatment and prognosis.
Area of Science:
- Pediatric Cardiology
- Autonomic Nervous System Function
- Electrophysiology
Background:
- Standard evaluation of sinus node (SN) dysfunction in children often fails to distinguish between abnormal autonomic tone and intrinsic SN disease.
- This distinction is crucial for determining appropriate therapeutic strategies and predicting patient outcomes.
Purpose of the Study:
- To assess the utility of intrinsic heart rate (IHR) and its correlation with resting heart rate (RHR) in differentiating autonomic influences from intrinsic SN disease in pediatric patients.
- To investigate the role of IHR in the diagnostic workup of children presenting with SN dysfunction.
Main Methods:
- Intrinsic heart rate (IHR) was determined in an electrophysiology laboratory setting.
- Pharmacologic autonomic blockade was achieved using intravenous propranolol (0.2 mg/kg) followed by intravenous atropine (0.04 mg/kg).
- The peak heart rate recorded post-blockade was defined as the IHR.
Main Results:
- In control subjects (normal noninvasive SN testing), mean IHR was 128 ± 24 bpm, significantly higher than mean RHR (89 ± 16 bpm).
- In patients with abnormal noninvasive SN testing, mean IHR was 103 ± 6 bpm, also significantly higher than mean RHR (71 ± 9 bpm).
- In both groups, IHR was consistently greater than RHR, with values for IHR falling within the normal age-related range even in patients with abnormal testing.
Conclusions:
- Excess vagal tone can significantly contribute to the manifestation of sinus node dysfunction in children, as indicated by IHR values within the normal range but exceeding RHR.
- Intrinsic heart rate demonstrates an age-related decline in healthy individuals.
- The finding of IHR exceeding RHR in normal subjects suggests that vagal tone predominates in the resting state, counteracting intrinsic heart rate.
Abstract:
Standard evaluation of children with sinus node (SN) dysfunction cannot distinguish abnormal autonomic tone from intrinsic SN disease. 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 intrinsic SN disease among children with SN dysfunction. IHR was determined in the electrophysiology laboratory using intravenous propranolol, 0.2 mg/kg, followed by intravenous atropine, 0.04 mg/kg; the peak HR recorded was the IHR. IHR was measured in two groups. Seven control subjects, defined as patients 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 patients 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 patients 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 SN dysfunction. (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)