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sTable 1 International Classification of Diseases, Ninth Edition, Clinical Modification (ICD-9-CM) Codes and Elixhauser Comorbidity Index (ECI) Used

to Identify the covariates

Covariates Code(s)

Patient Characteristics Female

The patient characteristics are obtained from the variables of NRD directly. Elective STEMI Payer Household income Severity of illness Comorbidities Smoking V15.82, 30.51 (ICD-9-CM) Dyslipidemia 272.0–4 (ICD-9-CM) Hypertension CM_HTN_C (ECI) Diabetes CM_DM、CM_DMCX (ECI)

Obesity CM_OBESE (ECI)

Heart failure CM_CHF (ECI)

Known CAD 414.00–07 (ICD-9-CM)

Prior MI 412 (ICD-9-CM)

Prior PCI V45.82 (ICD-9-CM)

Prior CABG V45.81 (ICD-9-CM)

Carotid artery disease 433.10 (ICD-9-CM) Prior TIA/stroke V12.54, 438.x (ICD-9-CM) Atrial fibrillation 427.31 (ICD-9-CM)

Prior PPM V45.01 (ICD-9-CM)

Prior ICD V45.02 (ICD-9-CM)

Peripheral vascular

disease CM_PERIVASC (ECI)

Anemia CM_ANEMDEF、CM_BLDLOSS (ECI)

Chronic lung disease CM_CHRNLUNG (ECI) Liver disease CM_LIVER (ECI)

Coagulopathy CM_COAG (ECI)

Dementia 290.xx, 294.1x, 294.2x, 294.8, 331.0–2, 331.82, 797 (ICD-9-CM)

Depression CM_DEPRESS (ECI)

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Fluid and electrolyte disorders CM_LYTES (ECI) Other neurological disorders CM_NEURO (ECI) Pulmonary circulation disorders CM_PULMCIRC (ECI)

Cancer CM_METS、CM_TUMOR、CM_LYMPH (ECI)

Alcohol misuse CM_ALCOHOL (ECI)

Peptic ulcer disease CM_ULCER (ECI) Valvular heart disease CM_VALVE (ECI) Renal failure CM_RENLFAIL (ECI) Hospital Characteristics

Bed size

The hospital characteristics are obtained from the variables of NRD directly.

Teaching Metropolitan

In-hospital Procedures

Bifurcation 00.44 (ICD-9-CM)

Circulatory support 37.61, 37.68, 39.65 (ICD-9-CM) Vasopressor use 00.17 (ICD-9-CM)

Intra-aortic balloon pump 97.44 (ICD-9-CM) Fractional flow reserve 00.59 (ICD-9-CM) Intravascular ultrasound 00.2x (ICD-9-CM) Drug-eluting stent 36.07 (ICD-9-CM) In-hospital outcomes

Complete heart block 426.0 (ICD-9-CM)

TIA/stroke 431, 433.x1, 434.x1, 435.x, 344.6x, 997.01 (ICD-9-CM) Cardiogenic shock 785.51 (ICD-9-CM)

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Major bleeding 430, 431, 432.x, 336, 362.43, 362.81, 363.61,363.62, 363.72, 364.41, 3736.32, 377.42, 379.23; 423.0 + 37.0; 923.x + 729.71, 924.x + 729.72, 922.2–9 + 729.73; 456.0, 456.20, 530.7, 530.82, 531.00, 531.01, 531.20, 531.21, 531.40, 531.41, 531.60, 531.61,532.00, 532.01, 532.20, 532.21, 532.40, 532.41,532.60, 532.61, 533.00, 533.01, 533.20, 533.21,533.40, 533.41, 533.60, 533.61, 534.00, 534.01,534.20, 534.21, 534.40, 534.41, 534.60, 534.61,569.3, 578.0, 578.1, 578.9, 568.81, 599.70, 599.71,719.1x, 784.7, 784.8, 459, 998.11, 998.12, 285.1 + 998.00, 998.09, 785.50, 785.59, 276.52 + 00.17 + 99.0x (ICD-9-CM)

Blood transfusion 99.02,99.04 (ICD-9-CM)

Vascular complication 900–904, 998.2, 999.2, 997.7, 447.0, 868.04 + 39.31, 39.41, 39.49, 39.52, 39.56, 39.57, 39.59, 39.79

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sTable 2 Comorbidities, hospital characteristics, in-hospital procedures, and in-hospital outcomes

All

(n=492 550)

Age group (Years)

P value

18～54 (n=126 895) 55～64 (n=140 994) 65～74 (n=119 923) 75～ (n=104 738) Comorbidities Smoking 48.25 62.56 53.64 43.07 29.56 <0.0001 Dyslipidemia 69.78 66.33 70.36 72.47 70.13 <0.0001 Hypertension 71.66 62.57 70.18 75.83 79.92 <0.0001 Diabetes 33.71 28.84 33.44 38.42 34.56 <0.0001 Obesity 17.58 22.73 19.58 17.30 8.98 <0.0001 Heart failure 0.41 0.17 0.35 0.49 0.69 <0.0001 Known CAD 90.19 88.39 90.08 91.02 91.56 <0.0001 Prior MI 11.18 9.37 10.90 12.21 12.56 <0.0001 Prior PCI 16.29 12.58 15.94 18.53 18.68 <0.0001 Prior CABG 5.28 2.09 4.30 7.06 8.41 <0.0001

Carotid artery disease 1.58 0.35 1.03 2.20 3.07 <0.0001

Prior TIA/stroke 6.42 2.95 5.04 7.65 11.06 <0.0001

Atrial fibrillation 10.92 3.01 6.78 13.19 23.47 <0.0001

Prior PPM 1.67 0.25 0.55 1.64 4.94 <0.0001

Prior ICD 1.25 0.74 1.11 1.58 1.65 <0.0001

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All

(n=492 550)

P value

18～54 (n=126 895) 55～64 (n=140 994) 65～74 (n=119 923) 75～ (n=104 738) Anemia 10.74 5.61 7.66 12.16 19.46 <0.0001

Chronic lung disease 16.47 10.90 15.73 20.27 19.87 <0.0001

Liver disease 1.24 1.30 1.67 1.22 0.60 <0.0001

Coagulopathy 3.05 1.76 2.69 3.51 4.57 <0.0001

Dementia 2.09 0.04 0.29 1.43 7.77 <0.0001

Depression 7.02 6.94 7.45 7.20 6.32 <0.0001

Hypothyroidism 9.00 4.15 6.62 10.48 16.38 <0.0001

Fluid and electrolyte disorders 15.28 12.65 13.88 15.99 19.53 <0.0001

Other neurological disorders 3.84 2.53 3.00 4.01 6.36 <0.0001

Pulmonary circulation disorders 0.06 0.02 0.04 0.09 0.09 <0.0001

Cancer 1.91 0.70 1.52 2.58 3.13 <0.0001

Alcohol misuse 3.29 5.04 4.15 2.43 0.98 <0.0001

Peptic ulcer disease 0.02 0.01 0.01 0.03 0.02 0.0003

Valvular heart disease 0.11 0.03 0.09 0.12 0.21 <0.0001

Renal failure 12.82 5.07 8.60 15.23 25.15 <0.0001

Hospital Characteristics

Bed size 0.0008

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All

(n=492 550)

P value

18～54 (n=126 895) 55～64 (n=140 994) 65～74 (n=119 923) 75～ (n=104 738) Medium 24.63 25.00 24.84 24.21 24.39 Large 67.17 66.79 66.96 67.53 67.47 Teaching <0.0001 Non-teaching 40.64 39.77 39.87 41.41 41.86 Teaching 59.36 60.23 60.13 58.59 58.14 Metropolitan 0.0027 Non-metropolitan 6.23 6.03 6.26 6.37 6.29 Metropolitan 93.77 93.97 93.74 93.63 93.71 In-hospital Procedures Bifurcation 2.82 2.73 2.92 2.74 2.92 0.0886 Circulatory support 4.03 3.43 4.03 4.35 4.39 <0.0001 Vasopressor use 0.81 0.67 0.83 0.79 0.99 <0.0001

Intra-aortic balloon pump 0.79 0.67 0.82 0.80 0.87 <0.0001

Fractional flow reserve 1.65 1.45 1.67 1.81 1.68 <0.0001

Intravascular ultrasound 5.01 5.16 4.80 5.18 4.91 0.2426

Drug-eluting stent 74.84 74.86 76.35 76.95 70.36 <0.0001

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All

(n=492 550)

P value

18～54 (n=126 895) 55～64 (n=140 994) 65～74 (n=119 923) 75～ (n=104 738)

Complete heart block 1.28 0.83 1.20 1.42 1.76 <0.0001

TIA/stroke 0.93 0.57 0.72 1.06 1.50 <0.0001

Cardiogenic shock 4.45 3.44 4.40 4.92 5.18 <0.0001

Cardiac arrest 2.67 2.93 2.93 2.52 2.19 <0.0001

Acute kidney injury 8.58 4.49 6.52 9.86 14.84 <0.0001

Major bleeding 6.28 3.99 5.20 6.91 9.80 <0.0001

Blood transfusion 2.59 1.14 1.78 3.05 4.90 <0.0001

Vascular complication 0.57 0.47 0.51 0.61 0.71 <0.0001

All values are percentage (%).

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sTable 3 The sensitivity analyses of missing data for 30-day readmission according to the age group

Outcomes Age group (Years)

18～54 55-64 65-74 75～ All cause, 30-day, unplanned readmission

Adjusted OR (95% CI) 1.05(1.01-1.11) 1(ref) 0.93(0.88-0.99) 1.01(0.95-1.08)

P Value 0.0286 0.0174 0.6553

Noncardiac cause, 30-day, unplanned readmission

P Value 0.1085 0.1060 0.5276

Infection

P Value 0.1723 0.0562 0.0018

Non-specific chest pain

P Value <0.0001 0.0002 0.0003

Gastrointestinal

P Value 0.6088 0.8865 0.8065

Cardiac cause, 30-day, unplanned readmission

P Value 0.2357 0.1161 0.0803

Heart failure

P Value 0.2357 0.1161 0.0803

Coronary artery disease including angina

P Value 0.0055 0.0004 <0.0001

Acute myocardial infarction

P Value 0.0748 0.7327 0.8528

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sTable 4 The sensitivity analyses of excluding patients whose transfers or discharges were the same day for 30-day readmission according to the age group

Outcomes Age group (Years)

18～54 55-64 65-74 75～ All cause, 30-day, unplanned readmission

P Value 0.0161 0.0326 0.5408

Noncardiac cause, 30-day, unplanned readmission

P Value 0.0947 0.1721 0.6260

Infection

P Value 0.1996 0.0340 0.0009

Non-specific chest pain

P Value <0.0001 0.0002 0.0005

Gastrointestinal

P Value 0.7032 0.8864 0.9807

Cardiac cause, 30-day, unplanned readmission

P Value 0.1644 0.1412 0.0689

Heart failure

P Value 0.0073 0.3328 <0.0001

Coronary artery disease including angina

P Value 0.0027 0.0005 <0.0001

Acute myocardial infarction

P Value 0.0501 0.6767 0.9975

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sTable 5 Early 30 day readmission across 4 age groups (<15 days vs. >15 days)

All (n=48 630)

P value 18～54 (n=9 228) (n=11 247) 55～64 (n=12 650) 65～74 (n=15 506) 75～ Days of readmission (%) ≤15 days 71.52 71.64 71.21 71.71 71.53 0.8918 >15 days 28.48 28.36 28.79 28.29 28.47

sTable 6 The interaction test between interaction terms and age groups

Outcome Effect F value P value for interaction

For “SEX”

All cause, 30-day, unplanned readmission

Sex*Age group 5.49 0.0009 Age group 4.55 0.0035

Sex 48.41 <0.0001

Noncardiac cause, 30-day, unplanned readmission

Sex*Age group 8.57 <0.0001 Age group 1.56 0.1972

Sex 42.12 <0.0001

Cardiac cause, 30-day, unplanned readmission

Sex*Age group 0.20 0.8971 Age group 3.68 0.0117

Sex 11.24 0.0008

For “Type of AMI”

Type of AMI *Age group 1.94 0.1209 Age group 2.68 0.0454 Type of AMI 4.24 0.0397 Noncardiac cause, 30-day, unplanned readmission

Type of AMI *Age group 0.49 0.6914 Age group 0.78 0.5063 Type of AMI 0.47 0.4911 Cardiac cause, 30-day, unplanned readmission

Type of AMI *Age group 2.38 0.0684 Age group 2.67 0.0461 Type of AMI 15.28 <0.0001

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sTable 7 The parameter estimates of interaction terms

Outcome Term Age group Subgroup factor

β value P value

For “SEX”

All cause, 30-day, unplanned readmission - -

reference 55～64 male

interaction term 1 18～54 female 0.0869 0.0958 interaction term 2 65～74 female -0.0527 0.2580 interaction term 3 75～ female -0.1154 0.0210 Noncardiac cause, 30-day, unplanned readmission

reference 55～64 male - - interaction term 1 18～54 female 0.1290 0.0781 interaction term 2 65～74 female -0.0942 0.1287 interaction term 3 75～ female -0.2006 0.0014 Cardiac cause, 30-day, unplanned readmission

reference 55～64 male - - interaction term 1 18～54 female 0.0359 0.6198 interaction term 2 65～74 female -0.0068 0.9194 interaction term 3 75～ female -0.0129 0.8524

For “Type of AMI”

reference 55～64 NSTEMI - - interaction term 1 18～54 STEMI -0.0759 0.1581 interaction term 2 65～74 STEMI -0.0326 0.4841 interaction term 3 75～ STEMI 0.0384 0.4385 Noncardiac cause, 30-day, unplanned readmission

reference 55～64 NSTEMI - - interaction term 1 18～54 STEMI 0.00672 0.9252 interaction term 2 65～74 STEMI -0.00611 0.9221 interaction term 3 75～ STEMI 0.0624 0.3237 Cardiac cause, 30-day, unplanned readmission

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sTable 8 The sensitivity analyses of adding each part of covariates in model for the association between age and all-cause readmission

Covariates in model Age group (Years)

18～54 55～64 65～74 75～

Patient Characteristics 0.99(0.94-1.03) ref 0.93(0.88-0.99) 1.14(1.07-1.21)

0.5369 0.0180 <0.0001

Patient Characteristics+

Hospital Characteristics 0.99(0.94-1.03) _0.5362 ref 0.93(0.88-0.99) _0.0169 1.14(1.07-1.20) _<0.0001 Patient Characteristics+ Hospital Characteristics+ Comorbidities 1.06(1.01-1.11) ref 0.94(0.89-1.00) 1.07(1.01-1.14) 0.0193 0.0436 0.0215 Patient Characteristics+ Hospital Characteristics+ Comorbidities+ In-hospital outcomes 1.07(1.02-1.12) ref 0.94(0.89-0.99) 1.02(0.96-1.09) 0.0100 0.0241 0.5260 Patient Characteristics+ Hospital Characteristics+ Comorbidities+ In-hospital outcomes+ In-hospital Procedures 1.06(1.01-1.11) ref 0.94(0.89-1.00) 1.02(0.96-1.09) 0.0129 0.0377 0.5175 Patient Characteristics+ Hospital Characteristics+ In-hospital outcomes 1.00(0.96-1.05) ref 0.92(0.87-0.98) 1.04(0.98-1.11) 0.9363 0.0052 0.2064 Patient Characteristics+ Hospital Characteristics+ In-hospital Procedures 0.98(0.94-1.03) ref 0.94(0.89-1.00) 1.13(1.06-1.20) 0.4956 0.0334 <0.0001

Remove “Severity of illness” from model

Patient Characteristics 0.93(0.89-0.98) ref 0.92(0.86-0.97) 1.24(1.17-1.32)