Table 2: Objective classification of systems.

Aim	Paper	Number
Risk or mortality prediction	[16, 18, 19, 27, 33-35]	12
Diagnosis of CVD	[13, 36-42]	8
Classification of cardiac alarm as true or false	[20, 21]	2
ECG signal and heart sound classification	[23, 43]	2
Others	[24-26]	3