Table 4.

An explanation of the changes made in the HRV parameter, the test used, the results, and conclusions. The upper arrow (↑) indicates the increase of the HRV parameter after the treatment compared to before the treatment and the down arrow (↓) shows the opposite

Study, year	Change in HRV parameter (before and after treatment)		Test used	Main results	Conclusions
Schultz et al.,[25] 1997	HF ↓		Two-tailed Wilcoxon tests and Spearman correlation coefficients	RR interval tended to decrease after ECT and ECT markedly decreased the amplitude of respiratory sinus arrhythmia. A positive correlation was observed between the reduction of HF variability and the improvement of depressive symptoms.	The parasympathetic activity was reduced in patients treated with ECT.
Nahshoni et al,.[31] 2001	LFnu ↓, HFnu ↑, and LF/HF↓		Two-tailed paired t-tests	LF norms and the LF/HF ratio decreased significantly. The HF norm also increased significantly.	Increased cardiac vagal modulation was observed in patients treated with ECT.
Nahshoni et al.,[28] 2004	LF ↓, HF↑, and LF/HF ↓		Two-tailed paired t-test or Mann –Whitney test were performed as appropriate.	Following the ECT course, no significant changes were observed in the LF and HF bands.	ECT may result in increased vagal modulation in elderly patients with MDD. Nonlinear HRV measures may shed light on the increased risk for cardiac mortality associated with depression since they are reduced by aging, similar to cholinergic deficits.
Karpyak et al.,[32]2004	SDNN ↑, pNN50 (Uncertain change)		The difference between the mean before and after ECT within the group was evaluated using a one-tailed paired t-test. Differences between groups of patients with different responses to treatment were evaluated using two-sample t-tests.	A significant increase in SDNN was observed in eight of the patients, indicating that the HRV will improve with the positive response to ECT. As a result of ECT complications and a comorbid somatic condition, SDNNs changed in the opposite direction in two patients.	Response to ECT treatment was associated with increased SDNN. According to the results of this study, physiologic differences may be able to predict the outcome of depression treatment with ECT.
Takada et al.,[26] 2005	LF ↓, HF ↓		To compare HR and HRV, between time points, was used repeated measures of one-way ANOVA.	A study of HRV demonstrated that sympathetic activity increased during shock and that both parasympathetic and sympathetic activity decreased following shock.	Electroconvulsive therapy was found to cause transitory increases in HR and blood pressure in middle-aged and elderly patients without systemic disease, but not to result in serious adverse clinical outcomes.
Ebert et al.,[9]2010	SDNN ↑(NS), LFnu ↑(NS), HFnu ↓(NS)		repeated measures MANOVA univariate ANOVAs	After six sessions of ECT, baseline autonomic modulation did not change significantly. Response to ECT treatment was associated with increased parasympathetic activity.	Higher parasympathetic modulation before treatment can be a useful criterion for deciding to use ECT in a particular patient.
Royster et al.,[29] 2012	Patients who have responded to ECT (before ECT and after 6 ECT)	RMSSD ↓, LF ↓, HF ↓ and LF/HF ↑	Two-sample t-test	Between the patients who responded to ECT and those who did not, there were no significant differences in the HRV indices of SD1/SD2, RMSDD, and LF/HF.	Short-term analyses indicate that HRV does not significantly improve among patients treated with ECT who respond to the treatment compared to those who do not.
	Patients who have not responded to ECT (before ECT and after 6 ECT)	RMSSD ↑, LF ↓, HF ↑, and LF/HF ↑
Bozkurt et al.,[27] 2013	Patients who have responded to ECT (before ECT and after 6 weeks)	RMSSD↓, LF↓, HF↓and LF/HF ↑	Friedman and Wilcoxon signed-rank tests were used to analyze the continuous variables. evaluated by Spearman correlation coefficients.	ECT was effective for seven patients. Over the course of six weeks, there was a change in the 2-h resting HF, the RMSSD, and the pNN50 scores. After the first and third weeks, this change was not significant. There was no significant difference between the HRV values of those who responded to ECT and those who did not respond to ECT except for the value of resting HF value between week 0 and week 6 for responders and the value of 24-hour	The HRV of patients with MDD did not change consistently in response to ECT. In nine male patients with MDD who are resistant to treatment, ECT does not lead to a significant change in cardiac autonomic function when HRV is accepted as a promising surrogate marker.
	Patients who have not responded to ECT (before ECT and after 6 weeks)	RMSSD↓, LF↓, HF↓and LF/HF ↑		HF for non-responders between week 1 and week 6.
Suzuki et al.,[30] 2015	HF ↑		Paired t-test y repeated-measure ANOVA	Between 30 and 80 s after stimulation, LF/HF power increased significantly, while between 80 and 130 s after stimulation, HF power increased significantly, indicating sympathetic activity in the second phase and parasympathetic activity It is in the third stage.	After the onset of ECT stimulus, in patients with depression observed a triphasic change from parasympathetic to sympathetic to parasympathetic in cardiac autonomic activity.

HRV=heart rate variability, HR=heart rate, ECT=electroconvulsive therapy, LF=peak frequency of the low-frequency band, LF_nu=LF power in normalized units, HF=Peak frequency of the high-frequency band, HF_nu=HF power in normalized units, LF/HF=ratio of LF-to-HF power, pNN50=the percentage of adjacent NN intervals that differ from each other by more than 50 ms, RMSSD=root mean square of successive differences between RR intervals, demonstrating beat-to-beat variation, SDNN=standard deviation of NN intervals, SD1=Poincaré plot standard deviation perpendicular the line of identity, SD2=Poincaré plot standard deviation along the line of identity, SD1/SD2=Ratio of SD1-to-SD2