Calculating sympathovagal balance from heart rate variability: are there alternatives in adolescents?

OBJECTIVE: Assessing sympathovagal balance by calculating LF/HF-ratio from power spectral analysis (PSA) of heart rate variability (HRV) may be difficult in adolescents as chaotic breathing leads to methodical bias and metronomic breathing is not easy to perform. Diastolic blood pressure variability (dBPV) is less influenced and may therefore offer more stable values for calculations. The present study was performed on 72 paediatric subjects to investigate possible alternative LF/HF-calculations from PSA of HRV and dBPV. METHODS AND RESULTS: Seventy-two paediatric individuals in three groups: 12 controls, 17 heart- and heart-lung-transplanted children (TX) and 43 adolescents born small for gestational age (SGA). Short-term beat-to-beat HRV and BP-recordings were made supine and during active standing. Ratios calculated: LF/HF from HRV, LF/HF from dBPV, LF-dBPV/HF-HRV and LF-HRV/HF-dBPV. LF/HF from dBPV as well as LF-HRV/HF-dBPV did not correlate with LF/HF-HRV. Correlation of LF/HF from HRV and LF-dBPV/HF-HRV was high especially in TX and in patients with resting heart rate of above 90 beats per minute. CONCLUSIONS: In adolescents, the ratio of LF-dBPV/HF-HRV may be an alternative method for calculating sympathicovagal balance being less influenced by breathing patterns. In younger patients with elevated resting heart rate, but also in patients with very low HRV such as TX-patients this method could be a supplemental diagnostic tool whenever autonomic nervous control on the cardiocirculatory system has to be assessed.

Reinnervation after heart transplantation in children: results of short-time heart rate variability testing.

AIMS: To detect impairment in short-term heart rate variability (HRV) in children after heart and heart-lung transplantation (TX) as reported in adults. To assess vagal and sympathetic influence on the donor heart rate using frequency domain analysis of HRV. METHODS AND RESULTS: Measurement of short-term HRV was performed in 17 patients (age 16.9+/-3.6, 6.1+/-3.7 yr after TX) and 12 healthy controls (age 14.8+/-3.0 yr). Testing consisted of a resting phase of 15 minutes followed by a tilt phase of 45 min. All HRV parameters were significantly impaired in transplanted patients: RR interval (RRI) 717.2+/-122.5 m/s (controls 827+/-139.7, p<0.05), standard deviation of RR interval (RRI-SD) 20.1+/-15.5 (89.9+/-38.4, p<0.001), RRI at tilt 607.9+/-79.7 (654.0+/-104.7, NS), RRI-SD at tilt 21.1+/-20.0 (60.4+/-31.4, p<0.001). Low-frequency (LF)/High-frequency (HF) ratio of HRV showed prominent sympathetic influence in TX-patients (3.38+/-5.60 vs. 1.18+/-0.86, NS) increasing during tilting (5.91+/-8.36 vs. 4.74+/-5.27, NS). In subgroup analysis, 4 yr after TX an increasing sympathetic control of heart rate was observed. CONCLUSION: Short-term HRV is severely impaired in children after TX. If changes are observed, they are time-related and show increasing sympathetic influence starting from 4 yr after TX.

Hypertension in heart and heart-lung transplanted children: does impaired baroreceptor function play a role?

BACKGROUND: Baroreceptor control of beat-to-beat blood pressure in heart and heart-lung-transplanted children is impaired. Time-related trends of baroreceptor function recovery are studied and a possible correlation of baroreflex impairment and systolic hypertension may give evidence for supplemental medical treatment of hypertension. METHODS: Seventeen patients (six female) 6.1 +/- 3.7 years (range 0.8-13.0 years) after heart (n = 14) and heart-lung (n = 3) transplantation (TX) were studied. Twelve healthy children and 10 children after liver and bone marrow TX taking cyclosporine A (CyA) served as control groups 1 and 2, respectively. Baroreceptor sensitivity (BRS) was calculated from noninvasive systolic beat-to-beat blood pressure (sBP) measurement during a resting phase and a tilt-table test. RESULTS: BRS was significantly impaired in the study group at rest and during tilting; mean sBP was slightly elevated. Significant difference between patients on CyA and healthy controls was not observed. Discrete recovery of BRS occurred after 4 years postTX with decreased sBP (n = 12 pts, BRS 6.78 +/- 7.44 msec/mmHg, sBP 116.2 +/- 12.4 mmHg) when compared to a postTX time course of less than 4 years (n = 5 pts, BRS 4.02 +/- 4.21 msec/mmHg, sBP 122.0 +/- 6.7 mmHg, P = NS). CONCLUSION: BRS is disturbed after TX in children; four years postTX, a minimal recovery of BRS and a discrete reduction of sBP seem to occur. Those patients with a persistent low BRS and elevated sBP may profit from pharmacological influence in sympathovagal imbalance.

Tilt table testing in childhood: improved sensitivity by non-invasive haemodynamic monitoring devices?

OBJECTIVE: Tilt table testing represents a valuable diagnostic method in suspected neurally mediated syncope. As sympathovagal imbalance and impaired baroreceptor sensitivity (BRS) have been observed in these patients, both methods were used in this study to investigate whether a combination of these parameters would improve sensitivity and whether specific patterns of neurally mediated syncopes would correspond to characteristic trends in heart rate variability (HRV) and BRS. METHODS AND RESULTS: Fifty-one pts. (29 female, mean age 14.5 +/- 3.9 y) with unexplained syncope and 15 control subjects (9 female, mean age 14.8 +/- 3.0 y) were tested following a standard tilt table test protocol. Power spectral analysis (PSA) of HRV and BRS calculation were used additionally to beat-to-beat blood pressure and ECG-monitoring. Twenty-three out of 51 pts. (45%) experienced a syncope after 18 +/- 10.2 min of tilting. In 2/23 patients (8.6%) a postural tachycardia syndrome (POTS), in 14/23 (60.8%) a neurally mediated syncope of mixed type, in 2/23 (8.6%) a vasodepressor syncope and in 5/23 (21.7%) a cardioinhibitory syncope with asystole were observed. PSA of HRV and BRS revealed a specificity, sensitivity, and positive and negative predictive values of the cut-off points in combination (LF/HF > or = 2.7 and BRS > or = 8) of 93.3%, 65.2%, 93% and 39%, respectively. CONCLUSION: In this study population, BRS and PSA of HRV were able to improve sensitivity of tilt testing after unexplained syncope. Specific BRS or HRV patterns in different mechanisms of neurally mediated syncope could not be identified possibly due to the small sample size.