Prediction of clinical outcome after cardiac arrest is clinically important.Early prognostication after successful cardiopulmonary resuscitation is difficult, and there is a need for novel methods to estimate the extent of brain injury and predict outcome. In this study, the investigators will evaluate the plasma levels of microRNAs (miRNAs) and circRNAs after cardiac arrest and assessed their ability to prognosticate neurological outcome.

1. Diagnostic criteria for cardiac arrest Sudden loss of consciousness, carotid or femoral artery pulse disappeared, ECG showed ventricular asystole or ventricular fibrillation or ventricular tachycardia.
2. Diagnostic criteria for ROSC Recovery of complexion, autonomous aorta pulse can be detected, blood pressure> 90/60 mmHg, the condition above maintained stable for more than half an hour, defined as ROSC, otherwise as failed.
3. Clinical treatment CPR was applied according to the AHA2010 guidelines. Patients were admitted to SICU or EICU after confirmation of ROSC, and physical cooling machines were set at 33 degrees Celsius to protect brain within 24h after ROSC. Standard treatments for life support were performed for all the included patients.
4. Methods 4.1 Clinical data Data such as patient's age, gender, contact information, previous disease information, the major reason causing cardiac arrest, initial rhythm, the total time of CPR, utilization of an automatic chest compression device, time from cardiac arrest to ROSC and time from cardiac arrest to ICU admission was collected from each patient who was included in the study. Follow-up data for APARCHE II (acute physiology and chronic health evaluation scoring system) score, survival of 24 hours after cardiac arrest, survival of 48 hours after cardiac arrest, survival of 28 days after admission, CPC score 2 weeks after cardiac arrest and CPC score 6 months after cardiac arrest were collected.

4.2 Cerebral Performance Category (CPC) CPC is a 5-category scale for measuring neurological status 2 weeks after cardiac arrest and CPC score 6 months after cardiac arrest. The 5 categories are: CPC 1, conscious and alert with good cerebral performance; CPC 2, conscious and alert with moderate cerebral performance; CPC 3, conscious with severe cerebral disability; CPC 4, comatose or in persistent vegetative state; and CPC 5, brain dead, circulation preserved.

4.3 Sample collection and processing Whole blood sample was collected into Ethylene diamine tetra-acetic acid (EDTA) -anticoagulant tube from each patient immediately at the beginning of CPR, 24h, 48h and 7 days after cardiac arrest. Samples were centrifugated and the supernatant was stored in EP tube with out RNA enzyme at -80 degree Celsius.

4.4 Detection of miRNA and circRNA Patients were divided into two groups according to the Cerebral Performance Category （CPC） after half a year, "CPC 1-2 Group" and "CPC 3-5 Group". Five samples for 48h time point in each group were randomly selected and detected miRNA and circRNA with chips.The real-time quantitative PCR were used to detect the quantity of the selected miRNAs and circRNAs for each time point. The plasma concentration of NSE for each time point was tested by laboratory department.

1 Inclusion criteria:

1. Transferred to or hospitalized in the emergency department or other wards of Shanghai Tenth People's Hospital due to cardiac arrest;
2. Return of spontaneous circulation (ROSC)after cardiopulmonary resuscitation;
3. Age > 14 years and < 85 years;
4. Written informed consent was obtained from all patients'family members before entering the study.

2 Exclusion criteria:

1. No witnesses when cardiac arrest occurs;
2. Obvious neurological dysfunction prior to cardiac arrest;
3. Intracranial infection or cerebrovascular accidents as primary disease or secondary complication within six months in the follow-up period.

transferred to or hospitalized in the emergency department or other wards of Shanghai Tenth People's Hospital due to cardiac arrest