To characterize and estimate the incidence rate of new-onset atrial fibrillation (NOAF) in patients with acute myocardial infarction (MI). To explore the prognostic influences of NOAF on MI patients' clinical outcomes. To further investigate the impact of NOAF associated characteristics on patients' clinical outcomes eithier during hospitalization or follow-up period.

In the present study, investigators retrospectively reviewed the medical records of all acute MI patients who were admitted to the coronary artery unit (CCU) of Shanghai Tenth People's Hospital between February 2014 and March 2018.

All eligible patients' demographics, cardiovascular risk factors, comorbidities, laboratory tests, echocardiography data, angiography data, acute and dischage medications, and clinical outcomes will be collected. All patients admitt to our CCU department will receive CEM immediately after admission and continue until discharge. Heart thythm status and those characteristics assoicated with NOAF will be reviewed by several independent physicians and recorded in a centralized electronic database.

Several post-MI NOAF assoicated characteristics and definitions are displayed as follows:

1. Total CEM duration is defined as the period during which the monitor was started after admission and turned off before discharge.
2. AF maintained duration is defined as the period during which an AF episode presented and terminated.
3. Total AF duration is calculated by summing all AF episodes' maintained durations descripted above.
4. AF burden was calculated by dividing the total AF duration by the total CEM duration.
5. NOAF pattern included paroxysmal NOAF, persistent NOAF, transient NOAF, and persisting NOAF, definitions are demonstrated as follows:

1) Paroxysmal NOAF is defined as more than 1 episodes of AF occur during hospitalization irrespective of the discharge rhythm status or only 1 episode of AF is observed during hospitalization and maintain sinus rhythm at discharge.

2) Persistent NOAF is defined as only 1 episode of AF is observed during hospitalization and maintain AF at discharge.

3) Transient NOAF is recorded if AF episodes only occur during hospitalization with emergency department ECG, on-admission ECG and discharge ECG maintaining sinus rhythm, irrespective of the frequencies of AF.

4) Persisting NOAF is recorded if AF episodes occur during hospitalization with a discharge ECG still maintaining AF rhythm, irrespective of the frequencies of AF.

6. Frequencies of NOAF

7. Symptomatic and silent NOAF

1. Symptomatic AF is defined as AFresulting in clinical symptoms or the need for urgent cardioversion.
2. Silent AF is defined as any asymptomatic episodes of AF lasting for over 30 seconds at CEM.

Inclusion Criteria:

• Patients hospitalized for acute MI between February 2014 and March 2018 in the CCU department of Shanghai Tenth People's Hospital;
• Adult patients (>18 years old).

Exclusion Criteria:

• Patients with a medical history of pre-existing AF;
• Patietns with a medical histroy of Rheumatic valvular disease;
• Patietns with a medical histroy of sick sinus syndrome;
• Patients undergoing emergent coronary artery bypass surgery;
• Patients' medical records with serious deficiencies and critical information (e.g. demographic data, laboratory testings, etc.) cannot be retrieved;
• Patients who refused to receive electronic monitoring during hospitalization and the data of cardiac rhythm cannot be obtained;
• Premature discharge due to nonmedical reasons such as nonpayment, failure to comply with program rules, conflicting with treatment staff, etc.

Patients with acute MI without a medical history of AF.