Materials and Methods
Patient Population
According to the treatment program at Kaohsiung Chang Gang Memorial Hospital, all patients with acute STEMI of onset less than 12 hours are eligible for primary PCI since May 1993. Since mid-2009, shortening DTB time is the government policy of Taiwan R.O.C. that is viewed as a very important variable for accreditation of a medical center. Therefore, since January 2010, shortened DTB time is the policy continuously adopted and monitored for the purpose of improving outcomes of patients with STEMI undergoing primary PCI at our hospital. This strategy was known as the "shortened DTB time." On the other hand, before the implementation of the Government policy, the DTB time recorded for patients undergoing primary PCI when the conventional strategy was used was known as the "conventional DTB time."
Between January 2008 and December 2009, 266 consecutive patients of all ages presenting with acute STEMI of less than 12-hour duration who underwent primary PCI were recruited as the "conventional DTB group." Additionally, between January 2010 and December 2011, 293 consecutive patients of all ages presenting with acute STEMI of less than 12-hour duration who underwent primary PCI were recruited as "shortened DTB group." Informed consent was obtained from each study subject receiving primary PCI. This was an observational study. The Institutional Review Committee on Human Research at our institution approved the study protocol (102-4515B).
Procedure and Protocol
Primary PCI was performed according to the protocol previously described. A 6F Kimny guiding catheter (Boston Scientific, Scimed, Maple Grove, MN) was used for both the diagnosis of coronary arterial occlusion and primary PCI. Intra-aortic balloon pump (IABP) support was performed via the femoral artery in patients experiencing acute pulmonary edema associated with unstable situations such as hemodynamic instability.
PercuSurge GuardWire (Medtronic AVE, Santa Rosa, CA) was used when angiographic feature of high-burden thrombus formation was noted in the infarct-related artery. The indications and procedure protocol were based on our previous report. Thrombectomy was performed for infarct-related arteries with high-burden thrombus formation.
Primary stenting was performed for our eligible patients who received a loading dose of clopidogrel (600 mg) and aspirin in the emergency department, followed by treatment with a maintenance dose of clopidogrel for at least 9 months. Aspirin (100 mg orally once daily) was given indefinitely to each patient. Other commonly prescribed medications also included angiotensin-converting enzyme inhibitors, statins, [beta]-blockers, isornitrate, and diuretics.
Criteria for Extracorporeal Membrane Oxygenation Installation
Extracorporeal membrane oxygenation (ECMO) was implemented at catheterization room for patients whose systolic blood pressure (SBP) could not be maintained above 75 mm Hg after IABP support and IV administration of dopamine more than 20 μg/kg/min. The procedure and protocol for ECMO support have been described in detail in our recent report.
Functional Assessment by Echocardiography
Left ventricular (LV) function was assessed using transthoracic echocardiography. With the patients in a supine position, LV internal dimensions (i.e., end-systolic diameter [ESD] and end-diastolic diameter [EDD]) were measured according to the American Society of Echocardiography leading-edge method using at least three consecutive cardiac cycles. The LV ejection fraction (LVEF) was calculated as: LVEF (%) = [(LVEDD – LVEDS)/LVEDD] × 100.
Definitions
Definitions of cardiogenic shock and profound shock were based on our previous report. Briefly, patients who experienced cardiogenic shock upon presentation or were observed at catheterization room met the following prospectively defined criteria for early cardiogenic shock: 1) chest radiograph showing pulmonary edema with SBP less than 90 mm Hg or 2) persistent hypotension with SBP less than 90 mm Hg associated with low cardiac output and clear lung fields, not related to dysrhythmia, showing no response to adequate fluid supply, and requiring vasopressor agent infusion. Furthermore, profound shock was defined as SBP less than 75 mm Hg despite IV inotropic agent administration and IABP support, associated with altered mental status and respiratory failure. Furthermore, advanced congestive heart failure (CHF) was defined as New York Heart Association (NYHA) functional class greater than or equal to 3.
Endpoints and Statistical Analysis
The study endpoint was the 30-day composite occurrence of major adverse clinical outcomes (MACOs), including advanced CHF or 30-day death.
Data were expressed as means ± SD or percentage of patients where appropriate. The clinical and laboratory data were analyzed and comparisons were done using independent t test for continuous variables and Fisher exact test or chi-square test for categorical variables. Multiple stepwise logistic regression analysis was used for assessing the independent predictors of 30-day occurrence of MACO. Statistical analysis was performed using SPSS statistical software for Windows version 13 (SPSS Inc., Chicago, IL). A p value of less than 0.05 was considered statistically significant.