The ECG as decision support in STEMI.

The electrocardiogram (ECG) can be used for determining the presence, location and extent of jeopardized myocardium during acute coronary occlusion. Accordingly, the ECG has become essential in the treatment of patients with acute coronary syndrome (ACS). This thesis aims at optimizing the decision support, provided by the ECG, for choosing the best treatment strategy in the individual patient with ST-segment elevation acute myocardial infarction (STEMI). ECG recorded in the prehospital setting has become the standard of care in many communities, but to achieve the full advantage of this early approach it is important that the ECG is recorded from accurately placed electrodes to produce an ECG that resembles the standard 12-lead ECG. Accurate electrode placement is difficult especially in the acute setting, and we investigated an alternative lead system with fewer electrodes in easily identified positions. We showed that the system produced waveforms similar to the standard 12-lead ECG. However, occasional diagnostic errors were seen, compromising general acceptance of the system. Once the ECG has been recorded a decision regarding triage must be made on the basis of a correct ECG diagnosis. We found that trained paramedics can diagnose STEMI correctly in patients without ECG confounding factors, while the presence of ECG confounding factors decreased their ability substantially. Consequently, since many patients do present with ECG confounding factors, transmission to an on-call cardiologist for an early correct diagnosis is needed. We showed that time to pPCI was reduced by more than 1 hour by transmitting prehospital ECG to a cardiologist's handheld device for diagnosis, triage, and activation of the catheterization laboratory when needed. The optimal treatment strategy is dependent on the duration of ischemia however patient information is often inaccurate. Accordingly, it would be advantageous if the first available ECG can help identify patients who will benefit greatly from acute reperfusion therapy versus patients with modest effect. We showed that by recognizing the acuteness of the infarction process the initial ECG can identify a group of patients with no potential for myocardial salvage despite short symptom duration. Urgent transport for pPCI may then not be necessary in this group of patients, and conservative treatment may be an option. Conversely, we also identified a group of patients with a large potential for myocardial salvage with acute reperfusion therapy despite long symptom duration. We also investigated whether ST-segment elevation on the initial ECG could provide prognostic information and thereby decision support for appropriate triage. All patients regardless of ST-segment elevation seemed to have most clinical benefit from pPCI. However, only patients with the greatest amount of ST-segment elevation had a reduced mortality rate with pPCI suggesting that patients with minor infarcts may achieve similar benefit from fibrinolysis followed by transfer to angiography and PCI. Once the triage decision is settled, STEMI patients must undergo ECG monitoring and receive antithrombotic therapy for optimal prehospital care. STEMI patients transported over even short distances are in danger of developing arrhythmic complications, but appropriate treatment is available when primary ambulances are supported by physician-manned ambulances in urban areas. Prehospital antithrombotic therapy must be effective in preparing the patient for pPCI without causing bleeding. Heparin is currently the standard therapy, but we showed that the direct thrombin inhibitor bivalirudin may be an attractive alternative by causing less bleeding events, and a higher frequency of preprocedure thrombolysis in myocardial infarction (TIMI) 3 flow. After reperfusion therapy a decision regarding the need for further treatment is desirable. By determining ST-segment resolution in the post-reperfusion ECG we showed that the degree of ST-segment resolution at 90 minutes and 4 hours is important for risk stratification after fibrinolysis, but not after pPCI. Interestingly, we found that patients with compete ST-segment resolution treated with fibrinolysis had the highest risk of reinfarction. Consequently, transfer to a PCI-facility should be considered in all patients treated with fibrinolysis as the initial reperfusion therapy. Based on the findings in the present thesis we conclude that the ECG is an important tool for decision support in every step from symptom onset to post-reperfusion therapy in STEMI patients.