Table 1.

Summary of the threshold-based SAAs

Refs., Year	Database	Signal for FE, Segment length	Method description	Feature	Limitation	Key Findings
[10], 2007	MITDB, CUDB, AHA	Stand-alone ECG, 8 s	Counting number of boxes on a grid filled by ECG and its delay signals.	Phase space reconstruction.	No validation. Low performance.	Phase space reconstruction parameter and a threshold. VF and NSH signals show irregular and regular behaviors.
[11], 2009	MITDB, CUDB	Stand-alone ECG, 8 s	Assessment of the proportion of time in which the ECG signal is above a certain threshold.	Threshold crossing sample count.	No validation. Low performance.	Threshold crossing sample count parameter and a threshold. The time in which VF signal remains outside the threshold is larger than that in which NSH signal does.
[12], 2010	MITDB, CUDB, VFDB	Stand-alone ECG and intrinsic mode functions using EMD, 8 s	Calculation of mean absolute value of the signal for SH/NSH rhythm classification. Calculation of differences between ECG and first 2 intrinsic mode functions. Normalized mean absolute value for VF/VT classification.	Mean absolute value and normalized mean absolute value	No validation. Requirement of 2 algorithms. Low performance.	SH signal hardly goes through the baseline and low absolute amplitude of the NSH signal for most of the time. Similarity between VF signal and its first 2 intrinsic mode functions.
[13], 2011	MITDB, CUDB, VFDB	Stand-alone ECG and intrinsic mode functions using EMD, 8 s	Measurement of correlation between ECG signal and its first intrinsic mode function, residual using the angles to form a complex decision parameter.	Complex decision parameter	No validation Low performance.	Complex decision parameter and a threshold. Correlation between ECG signal and its first intrinsic mode function and residual.
[15], 2012	CUDB, NSRDB	Stand-alone ECG, 4 s	Extraction of 3 features using semantic mining algorithm. Construction of thesholds based on ANOVA model.	Natural frequency. Damping coefficient. Input signal.	No validation Low performance.	Semantic mining algorithm for feature extraction. Analysis model for threshold construction.
[14], 2012	CUDB, VFDB	Stand-alone ECG and intrinsic mode functions using EMD, 10 s	Intrinsic mode function with EMD. Approximate entropy of first intrinsic mode function.	NA	Consideration of first intrinsic mode function. No validation Low performance.	Approximate entropy threshold.