Electrocardiographic predictors of clinical outcome in ST-elevation myocardial infarction

Sammanfattning: Malignant ventricular arrhythmias, particularly ventricular fibrillation (VF), remain an important contributor to mortality in ST-elevation myocardial infarction (STEMI). The size of myocardial injury is one more important factor influencing the prognosis of STEMI patients. The search for new non-invasive markers, which can be relatively simply calculated using conventional ECG recording and can predict the degree of myocardial injury and impending VF, is promising. This work is aimed at investigating cardiac repolarization and depolarization abnormalities and predictors and prognosis of ventricular arrhythmias during the course of STEMI. The thesis is composed of the experimental part (Studies I, II, III) and clinical register-based retrospective studies (Studies IV and V). Closed-chest porcine model of myocardial infarction (MI) was used in the experimental part. Occlusion of left descending artery (LAD) lasted 40 minutes and was followed by reperfusion, and ECG was continuously recorded. QRSduration and morphology, dynamics of ST-segment and T-wave alternans (TWA) were calculated, and myocardial area at risk (MaR) and infarct size (IS) were assessed. Predictors and prognostic impact of early VF in STEMI was assessed in a register-based study of 1,718 consecutive patients admitted for primary PCI during 2007-2009 who were followed up for one year. In experimental MI, the maximal level of TWA during occlusion period was associated with both MaR and IS (Study II). Rapid and marked transient increase in QRS duration associated with appearance of J-wave pattern predicted impending VF in acute ischemia (Study III). Restoration of blood flow in infarct-related artery was accompanied by reperfusion peak in all animals, and the magnitude of ST elevation at reperfusion peak was associated with infarct size (Study I). In clinical studies IV and V, the risk of VF in acute period of STEMI was higher in patients with MI history, cardiovascular risk factors such as smoking and left main stenosis, resulting in a large infarct area. Besides MI history and left main stenosis, the risk of VF at reperfusion was associated with inferior localization of STEMI, hypokalemia, high ST-elevation and shorter symptom-toballoon time. The magnitude of ST-elevation before PCI for STEMI independently predicted reperfusion VF. Patients successfully resuscitated after VF and alive at 48 hours had higher in-hospital mortality (12% vs. 2%, p<0.001). However, in VF patients who were discharged alive, 1-year mortality did not differ compared with patients without VF