Baseline characteristics and general information:
Fifty three of seventy two patients who were referred to our outpatient syncope clinic between April 2018 to April 2019 were eligible to participate in this study. Three patients withdrew their consent to take part in the study and the data on four patients were corrupted. Finally, 46 patients (31 patients in case and 15 patients in the control group) were analysed. Baseline characteristics of patients are summarised in Table 1. Because of the strict inclusion and exclusion criteria, all patients had a healthy heart. Therefore echocardiographic and electrocardiographic results of patients are not shown.
Table 1
Baseline characteristics of patients
Groups (no)
|
Male/female
|
Mean Age
Y (SD)
|
Mean Height CM (SD)
|
Mean Wight
KG (SD)
|
Body surface area m2 (SD)
|
No Syncope (15)
|
13/2
|
27.13 (6.46)
|
173.80 (9.45)
|
68.73 (15.02)
|
1.82 (0.21)
|
Syncope (31)
|
16/15
|
29.16 (8.97)
|
170.55 (9.68)
|
75.23 (13.48)
|
1.82 (0.20)
|
Cardioinhibitor Syncope (12)
|
8/4
|
28.33 (7.94)
|
172.42 (10.05)
|
8.67 (15.61)
|
1.93 (0.21)
|
Mixed Type Syncope (12)
|
4/8
|
30.67 (10.12)
|
168.00 (9.04)
|
74.00 (8.50)
|
1.80 (0.17)
|
Vasodepressor Syncope (7)
|
4/3
|
28.00 (9.59)
|
171.71 (10.59)
|
68.00 (12.39)
|
1.79 (0.19)
|
Significance (Syncope/No Syncope)
|
0.02
|
0.43
|
0.28
|
0.14
|
0.66
|
In the case group, 9 (29.1%) developped syncope in the passive phase of the test ( 6 CI, 1 VD, and 2 mixed type). Twenty two patients (70.9%) developped syncope in the active pase of the test (6 CI, 6 VD, and 10 mixed type).
Table 2
Comparison of mean (SD) HRV (ms2) and SBPV (mmHg2) indices in patients with and without syncope.
Index/Group
|
HRV
|
SBRV
|
control
15
|
CI
12
|
VD
7
|
Mixed
12
|
Case 31
|
control
15
|
CI
12
|
VD
7
|
Mixed
12
|
Case
31
|
LF
|
Rest
|
461 (69)
|
294 (71)*
|
277
(50) *
|
500 (290)
|
371 (113) ¶
|
14.28 (0.93)
|
8.16 (0.77)*
|
6.13 (0.23)*
|
4.71 (0.52)*
|
6.38 (0.45) ¶
|
Tilt 70
|
529 (1936)
|
593 (9569)
|
239 (1166)
|
246 (583)*
|
363 (3330)
|
10.39 (1.22)
**
|
7.08 (0.74)*
|
6.26 (0.48)*
|
4.39 (0.39)*
|
5.81 (0.39) ¶
**
|
TNG
|
535 (434)
|
611 (740)
|
27.44 (56.11) *
|
338 (610)
|
435 (2011)
|
7.33 (0.76)
|
3.92 (1.1)*
|
1.93 (1.1)*
|
3.84 (0.52)*
|
3.52 (0.47) ¶
|
HF
|
Rest
|
675 (52)
|
189 (23)*
|
334 (49)*
|
604 (389)
|
384 (136) ¶
|
4.17 (0.09)
|
1.96 (0.13)*
|
1.19 (0.08)*
|
1.03 (0.04)*
|
1.43 (0.06) ¶
|
Tilt 70
|
118 (80)
**
|
75 (51)
|
51
(30) *
|
91 (110)
|
75 (61) ¶
**
|
2.33 (0.29)
**
|
1.16 (0.7)*
|
1.11 (0.14)*
|
0.74 (0.7)*
|
0.99 (0.04) ¶
**
|
TNG
|
84 (26)
|
155 (218)
|
5.42 (7.03) *
|
203 (467)
|
134 (198)
|
1.29 (0.18)
|
0.97 (0.22)*
|
0.48 (0.16)*
|
0.69 (0.15)*
|
0.73 (0.13) ¶
|
LF/HF
|
Rest
|
0.68 (0.12)
|
1.58 (0.45)*
|
0.83 (0.13)*
|
1.00 (0.32)*
|
0.99 (0.13) ¶
|
3.42 (0.23)
|
4.14 (0.14)*
|
5.16 (0.36)*
|
4.57 (0.46)*
|
4.43 (0.15) ¶
|
Tilt 70
|
4.29 (1.52)
**
|
5.10 (2.03)
|
4.30 (3.17)
|
3.76 (3.41)
|
4.34 (1.67)
**
|
4.48 (0.47)
**
|
6.09 (0.80)*
|
5.62 (0.95)*
|
5.88
(0.92)*
|
5.86 (0.49) ¶
**
|
TNG
|
5.42 (2.6)
|
5.13 (2.05)
|
2.99 (3.60)
|
4.44 (2.59)
|
4.48 (2.15)
|
5.80 (0.76)
|
4.08 (0.99)*
|
4.02 (1.58)*
|
5.57 (1.44)*
|
4.84 (0.65) ¶
|
*= Significant difference between control and each syncope groups |
**= Significant difference resting and tilt 70 values |
¶ = Significant difference between case and control group |
HRV = Heart rate variability, SBPV = Systolic blood pressure variability, CI = Cardioinhibitory, VD = Vasodepressor, Mixed = Mixed type, LF = Low frequency in HRV by ms2 and in SBPV by mmHg2, HF = High frequency in HRV by ms2 and in SBPV by mmHg2. |
Fluctuations of HRV during HUTT (table 2):
Phase 1: Patients in the syncope group showed a significantly lower LF and HF flactuations and higher LF/HF ratio with respect to the controls (P< 0.001).
Phase 2: In comparison with the resting state, LF activity did not change but HF activity decreased and the LF/HF ratio increased significantly in both groups (P< 0.001). During tilt, LF activity was not statistically different between groups (P= 0.8) but HF activity was significantly lower in cases (P= 0.04). The LF/HF ratio was not different between study groups (p= 0.9)
Phase 3: There was no statistical difference in LF (p= 0.8), HF (p= 0.3), and LF/HF (p= 0.2) ratio between groups during phase 3 of HUTT.
Fluctuations of SBPV during HUTT (table 2):
Phase 1: LH and HF powers of SBPV had lower flactuations and the LF/HF ratio was higher in cases vs. controls (p< 0.001).
Phase 2: The fluctuations of LF, HF, and LF/HF ratio was similar to phase 1.
Phase 3: LH and HF powers of SBPV had lower flactuations and the LF/HF ratio was lower in cases vs. controls (p< 0.001).
For a better understanding of results, the entire data were divided into consecutive 30 seconds blocks during each phase of HUTT, the mean values of each block were calculated, and separate graphs for LF, HF, and LF/HF ratio fluctuations in HRV and SBPV in cases and controls were drawn. (Figures 1-3). Figure 1 upper and lower panel shows the fluctuations of LF between case and control groups in HRV and SBPV, respectively. In addition to the findings mentioned above, the dominant result is the slow fluctuations of LF in HRV during phase 2. In phase 3, fluctuations increased in both groups without significant difference. Conversely, in SBPV, there was a continuous decrement in LF power, which was shown in both groups in all phases of HUTT. Figure 2 upper and lower panel shows the fluctuations of HF between case and control groups in HRV and SBPV, respectively. After tilting, the activity of HF decreased significantly in HRV and SBPV. After that, HF activity remained low in both groups; the exception was increased activity during the early minutes of phase 3 in the HRV power of syncope patients. Figure 3 upper and lower panel shows the fluctuations of the LF/ HF ratio between cases and controls in HRV and SBPV, respectively. During phase 1 and 2 of the test, the LF/HF ratio of SBPV, although lower in controls compared to cases, increased in both groups similarly during the test, but just after starting phase 3, there was a rapid reversal of this ratio in syncope patients mainly driven by oscilations in its LF power.