Table 1.
Baseline characteristics comparing between Wave-1 and Wave-2
| Wave-1 | Wave-2 | P value | |
| (n=4278) | (n=4723) | ||
| Clinical characteristics | |||
| Age (years) | 67.6±12.2 | 68.8±12.5 | <0.001 |
| Age≥75 years* | 1336 (31%) | 1694 (36%) | <0.001 |
| Men* | 3156 (74%) | 3538 (75%) | 0.23 |
| Body Mass Index (kg/m2) | 23.6±3.5 | 23.7±3.6 | 0.40 |
| Body Mass Index<25.0 kg/m2* | 3058 (72%) | 3269 (69%) | 0.02 |
| Hypertension* | 3343 (78%) | 3768 (80%) | 0.06 |
| Diabetes mellitus* | 1395 (33%) | 1664 (35%) | 0.009 |
| On insulin therapy | 205 (4.8%) | 270 (5.7%) | 0.06 |
| Current smoking* | 1730 (40%) | 1702 (36%) | <0.001 |
| Heart failure* | 1350 (32%) | 1566 (33%) | 0.11 |
| LVEF | 52.5±12.9 | 53.8±12.4 | <0.001 |
| LVEF≤40% | 596 (18%) | 595 (14%) | <0.001 |
| Prior PCI | 364 (8.5%) | 523 (11%) | <0.001 |
| Prior CABG | 53 (1.2%) | 59 (1.2%) | 1.00 |
| Prior myocardial infarction* | 381 (8.9%) | 427 (9.0%) | 0.85 |
| Prior stroke (symptomatic)* | 394 (9.2%) | 521 (11%) | 0.005 |
| Peripheral vascular disease* | 138 (3.2%) | 209 (4.4%) | 0.004 |
| eGFR<30 mL/min/1.73 m2, without haemodialysis* | 202 (4.7%) | 288 (6.1%) | 0.005 |
| Hemodialysis* | 73 (1.7%) | 131 (2.8%) | 0.001 |
| eGFR <30 mL/min/1.73 m2 or haemodialysis | 275 (6.4%) | 419 (8.9%) | <0.001 |
| Atrial fibrillation | 418 (9.8%) | 419 (8.9%) | 0.15 |
| Anaemia (haemoglobin<11.0 g/L)* | 438 (10%) | 531 (11%) | 0.13 |
| Thrombocytopenia (platelet<100×109/L) | 84 (2.0%) | 102 (2.2%) | 0.56 |
| Chronic obstructive pulmonary disease | 140 (3.3%) | 173 (3.7%) | 0.34 |
| Liver cirrhosis | 101 (2.4%) | 101 (2.1%) | 0.52 |
| Malignancy* | 337 (7.9%) | 516 (11%) | <0.001 |
| Presentation | |||
| Living alone | 509 (13%) | 780 (17%) | <0.001 |
| Direct admission | 2215 (54%) | 2603 (57%) | 0.02 |
| Interfacility transfer | 1866 (44%) | 1983 (42%) | 0.12 |
| Killip class III/IV | 725 (17%) | 915 (19%) | 0.003 |
| Cardiogenic shock | 596 (14%) | 757 (16%) | 0.005 |
| Cardiopulmonary arrest* | 142 (3.3%) | 193 (4.1%) | 0.06 |
| Maximum CK | 2133 (1002–4077) | 1836 (767–3663) | <0.001 |
| Angiographic characteristics | |||
| Infarct related artery location | |||
| Left anterior descending coronary artery* | 1979 (46%) | 2191 (46%) | 0.91 |
| Left circumflex coronary artery | 443 (10%) | 479 (10%) | 0.76 |
| Right coronary artery | 1732 (40%) | 1898 (40%) | 0.78 |
| Left main coronary artery | 107 (2.5%) | 172 (3.6%) | 0.002 |
| Coronary artery bypass graft | 19 (0.4%) | 24 (0.5%) | 0.77 |
| Multivessel disease | 2222 (52%) | 2655 (56%) | <0.001 |
| Procedural characteristics | |||
| Onset-to-balloon time (hours) | 4.2 (2.8–7.2) | 4.0 (2.7–6.6) | <0.001 |
| Door-to-balloon time (min) | 90 (60–132) | 79 (59–110) | <0.001 |
| Intra-aortic balloon pump use | 738 (17%) | 994 (21%) | <0.001 |
| Percutaneous cardiopulmonary support use | 116 (2.7%) | 149 (3.2%) | 0.24 |
| PCI* | 4180 (98%) | 4625 (98%) | 0.48 |
| Transradial approach | 498 (12%) | 733 (16%) | <0.001 |
| Transfemoral approach | 3432 (82%) | 3640 (79%) | <0.001 |
| IVUS use for the culprit lesion | 1260 (30%) | 2653 (57%) | <0.001 |
| Stent use for the culprit lesion | 3739 (89%) | 4241 (92%) | <0.001 |
| Bare metal stent | 2946 (79%) | 1735 (41%) | <0.001 |
| DES | 793 (21%) | 2506 (59%) | <0.001 |
| Staged PCI | 932 (22%) | 1018 (22%) | 0.77 |
| Stent use including staged PCI | 3802 (91%) | 4295 (93%) | 0.001 |
| Bare metal stent | 2542 (67%) | 1490 (35%) | <0.001 |
| DES | 1260 (33%) | 2805 (65%) | <0.001 |
| First-generation DES use | 1257 (99%) | 47 (1.7%) | <0.001 |
| Sirolimus-eluting stent (CYPHER) | 1174 (93%) | 27 (57%) | |
| Paclitaxel-eluting stent (TAXUS) | 115 (9.1%) | 21 (45%) | |
| New-generation DES use | – | 2776 (99%) | |
| Everolimus-eluting stent (XIENCE) | – | 2054 (74%) | |
| Everolimus-eluting stent (PROMUS) | – | 1616 (58%) | |
| Biolimus-eluting stent (NOBORI) | – | 725 (26%) | |
| Zotarolimus-eluting stent (RESOLUTE) | – | 255 (9.2%) | |
| Zotarolimus-eluting stent (ENDEAVOR) | – | 49 (1.8%) | |
| CABG | 98 (2.3%) | 98 (2.1%) | 0.48 |
| Off pump | 34 (35%) | 43 (44%) | 0.19 |
| ITA use | 82 (84%) | 80 (82%) | 0.71 |
| Baseline medications | |||
| Antiplatelet therapy | |||
| Thienopyridine | 3993 (93%) | 4521 (96%) | <0.001 |
| Ticlopidine | 3652 (85%) | 124 (2.6%) | <0.001 |
| Clopidogrel | 340 (7.9%) | 4339 (92%) | <0.001 |
| Aspirin | 4209 (98%) | 4636 (98%) | 0.45 |
| Cilostazol | 1501 (35%) | 116 (2.5%) | <0.001 |
| Statins | 2281 (53%) | 3885 (82%) | <0.001 |
| High-intensity statin therapy† | 67 (1.6%) | 78 (1.7%) | 0.81 |
| Beta blockers | 1747 (41%) | 2555 (54%) | <0.001 |
| ACE inhibitors/ARB | 3040 (71%) | 3554 (75%) | <0.001 |
| Nitrates | 1269 (30%) | 832 (18%) | <0.001 |
| Calcium channel blockers | 885 (21%) | 970 (21%) | 0.88 |
| Nicorandil | 1198 (28%) | 966 (20%) | <0.001 |
| Warfarin | 495 (12%) | 591 (13%) | 0.18 |
| DOAC | – | 61 (1.3%) | – |
| Proton pump inhibitors | 1470 (34%) | 3505 (74%) | <0.001 |
| Histamine type 2 receptor blockers | 1393 (33%) | 553 (12%) | <0.001 |
Continuous variables were expressed as mean±SD or median (IQR). Categorical variables were expressed as number (percentage).
There were missing values for Body Mass Index in 341 patients (Wave-1: 232 (5.4%) and Wave-2: 109 (2.3%)), for LVEF in 1385 patients (Wave-1: 951 (22%) and Wave-2: 434 (9.2%)), for eGFR in 94 patients (Wave-1: 80 (1.9%) and Wave-2: 14 (0.3%)), for haemoglobin level in 110 patients (Wave-1: 99 (2.3%) and Wave-2: 11 (0.2%)), for platelet count in 47 patients (Wave-1: 29 (0.7%) and Wave-2: 18 (0.4%)), for max CK in 91 patients (Wave-1: 39 (0.9%) and Wave-2: 52 (1.1%)). The numbers of missing values for Body Mass Index, eGFR, haemoglobin level and platelet count were negligibly small. The missing values for these variables were imputed as ‘normal’ in the binary classification because data should have been available if abnormalities were suspected. On the other hand, the missing values for LVEF were not imputed in the categorical classification because the numbers of missing values were substantial for these variables. Onset-to-balloon time and door-to-balloon time were analysed only for patients who underwent PCI within 24 hours of the onset of symptoms excluding nosocomial onset (onset-to-balloon time: 3271 patients in Wave-1 and 3372 patients in Wave-2; door-to-balloon time: 3228 patients in Wave-1 and 3242 patients in Wave-2).
*Risk-adjusting variables for the Cox proportional hazard models.
†High-intensity statin therapy in this study was defined as the statin doses greater than or equal to atorvastatin 20 mg, pitavastatin 4 mg or rosuvastatin 10 mg.
ARB, angiotensin receptor blocker; CABG, coronary artery bypass grafting; CK, creatine kinase; DES, drug-eluting stent; DOAC, direct oral anticoagulants; eGFR, estimated glomerular filtration rate; ESRD, end-stage renal disease; ITA, internal thoracic artery; IVUS, intravascular ultrasound; LVEF, left ventricular ejection fraction; PCI, percutaneous coronary intervention.