Strategies to improve outcome in patients with ST elevation myocardial infarction treated with primary PCI

Abstract: Background: ST elevation myocardial infarction (STEMI) caused by a ruptured atherosclerotic plaque with overlying thrombosis leads to ischemia and progressively to the death of the myocardial cells supplied by the affected coronary artery. Rapid reperfusion with primary Percutaneous Coronary Intervention (PCI) in an experienced centre is the preferred therapy for these patients. The aim of the research program on which this thesis is based was to study the effect of antiplatelet therapy with abciximab on coronary patency  when administered early to an unselected cohort of patients with STEMI intended for primary PCI, to study the impact of health care delay time on infarct size measured with contrast enhanced Magnetic Resonance Imaging (ceMRI), and to evaluate if time delays could be reduced through reorganisation of logistics and personal feedback to staff involved in the care of STEMI patients. Finally measures of wall motion on cine MRI were evaluated to elucidate if functional measurements of the left ventricular wall could detect scar tissue visualised on ceMRI in a post-acute phase of primary PCI.Material and results: In paper I we report on a study of all consecutive patients who sustained a STEMI in 2005 in the county of Östergötland and who were to be treated with primary PCI. Abciximab given as pretreatment before (n=133) or at the cath-lab after a diagnostic angiography (n=109) was associated with a patent Infarct Related Artery (IRA), i.e. Thrombolysis in Myocardial Infarction (TIMI) flow 2-3, in 45.9% of patients in the early group versus 20.2% in the cath-lab group, p=0.0001. There were no statistically significant differences in bleeding or mortality rate during the initial hospital stay, nor were there any significant differences between the groups during one-year follow up regarding a Major Adverse Cardiac Event (MACE).Paper II is based on an examination of 30 patients in a stable clinical condition with ceMRI 4-8 weeks after they had been treated with primary PCI because of STEMI. Patients were selected on the presence of extensive myocardial scar in the anteroseptal segments (n=17) or no scar visible at all in this area or in any other part of the myocardium (n=13). The purpose of the study was to evaluate the ability of a new feature tracking software to measure functional parameters of the heart. The left ventricular wall was divided into 18 segments and myocardial contraction was measured with velocity, displacement and strain in the longitudinal and radial direction. The software calculated a mean value for the 18 segments for each parameter. Receiver-operatorcharacteristics curves (ROC) were constructed. The best area-under-curve (AUC) was for radial strain where a cut-off value of 38.8% had 80% sensitivity and 86% specificity to detect segments with scar>50%.The impact of health care delay was examined in paper III based on a study in which 89 STEMI patients treated with primary PCI had their infarct size measured with ceMRI in the post-acute phase. Time from First Medical Contact (FMC) to a patent artery correlated weakly with infarct size, r=0.27, p=0.01. However, multivariable analysis showed the LAD as the Infarct Related Artery (IRA), active smoking and occlusion of the IRA at the time of the diagnostic angiogram were correlated with infarct size and that time from FMC to patent artery was not so correlated.Finally, in the study leading to paper IV, extensive measurements on time delays were performed on 67 consecutive patients with STEMI treated with primary PCI. Through collaboration with different stakeholders in the treatment of STEMI in the catchment area the following types of targeted refining of logistics were done; 1. Ambulance staff prioritise ECG recording, 2. Central evaluation of ECG in all patients with suspected STEMI, and 3. PCI team is ready to accept the patient when two out of three members are on site. Moreover, personal feedback on time delays for each STEMI patient was given to all staff involved in the treatment of the patient. Thereafter, all the time delays for a similar group of consecutive STEMI patients (n=89) were analysed and compared with the delays for the former group. Improvements seen in the post-intervention group were a reduction in time from ECG to cath-lab arrival by 11 minutes, p=0.02 and a non-significant decrease of FMC to a patent artery by six minutes. The main part of this improvement could probably be ascribed to the decision to see to it that an attending cardiologist was present 24/7 and to central evaluation of ECG.Conclusion: Abciximab given as pre-treatment to patients with STEMI intended for primary PCI was associated with a patent artery in 46% of patients. Moreover, we demonstrated a relationship between health care delay time and infarct size. This delay time could be reduced by a reorganisation of logistics and personal feedback on time delays. Finally, feature tracking analysis of cine MR images could detect segments with extensive myocardial scar in anterior infarction with 80% sensitivity and 86% specificity.