Simultaneous heart rate and blood pressure variability analysis
Insight into mechanisms underlying neurally mediated cardiac syncope in children
Jeffrey P. Moak, MD, FACC*,*,
James J. Bailey, MD, MSc and
Fairouz T. Makhlouf, BS
* Children’s National Medical Center, Washington, DC, USA
Center for Information Technology, National Institutes of Health, Bethesda, Maryland, USA
Department of Statistics, American University, Washington, DC, USA
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Figure 1 Heart rate and blood pressure changes during the tilt sequences. Changes in heart rate are demonstrated in A and blood pressure in B. The solid line shows data from the HUT+ group and the dashed line for the HUT– group. In the HUT+ group, a statistically significant decrease in blood pressure presaged syncope, which was subsequently followed by a statistical decrease in heart rate. *p = 0.0002, faint vs. mid-tilt (A). *p = 0.0006 mid-tilt vs. early-tilt; #p < 0.0001 for faint vs. mid-tilt (B). HUT = head up tilt.
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Figure 2 (A) Changes in maximum systolic blood pressure dP/dT during tilt sequence. In the HUT+ group, max systolic blood pressure dP/dT decreased significantly at the mid-tilt interval and during syncope. *p < 0.0171, for mid-tilt vs. early-tilt; #p < 0.0001, faint vs. mid-tilt. (B) Changes in electrical-mechanical activation time during the tilt sequence. The electrical-mechanical interval gradually prolonged during the tilt sequence in the HUT+ group, reaching statistical significance at the time of the faint. *p = 0.0016, for faint vs. mid-tilt. For both A and B, the solid line shows data from the HUT+ group and the dashed line for the HUT– group. HUT = head up tilt.
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Figure 3 Serial radial artery pulse contour changes in response to a positive upright tilt test. Electrocardiographic lead II and blood pressure are displayed. (A) Supine position. (B) Early-tilt. (C) Early to mid-tilt.
(D) Mid to late-tilt. (E) Faint. See text for description. Time scale = 50 mm/s. Blood pressure scale = 0 to 200 mm Hg.
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Figure 4 Heart period and systolic blood pressure variability changes during head up tilt (HUT). (A) Changes in low frequency (LF) heart period variability (HPV) to tilting. The LF power initially increased significantly in both groups to a similar extent. After being upright, LF HPV gradually decreased in the HUT+ group. The decrease in the LF HPV did not reach statistical significance until the time of the faint. *p < 0.0001, early-tilt vs. supine (HUT+ group) and p < 0.0001, early-tilt vs. supine (HUT– group); #p = 0.0186 for faint vs. early-tilt (HUT+ group) and p = 0.0003 for faint/late tilt (HUT+ vs. HUT– group). (B) Changes in LF blood pressure variability (BPV) to tilting. LF power initially increased in both groups during early tilt. After being upright, LF BPV gradually decreased in the HUT+ group. LF BPV decreased below the baseline supine value of BPV at the mid-tilt interval and during the faint. The decrease in the LF BPV started shortly after the early-tilt period. In the HUT– group, LF BPV continued to increase and remain at an increased level for the duration of the tilt. *p < 0.0001 HUT+ vs. HUT– group (mid-tilt); #p = 0.0001 faint vs. early-tilt (HUT+ group).
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