Optimal Management of ST-Segment Elevation Myocardial Infarction

Abstract

Background: ST-segment elevation myocardial infarction (STEMI) is a high-risk clinical scenario within the acute coronary syndrome spectrum. It is associated with poor clinical outcomes, particularly if acute reperfusion and appropriate care protocols are not initiated in a timely fashion. Consequently, optimal STEMI management represents a significant challenge to modern health-care provision.

Aims: This thesis intends to provide insight into contemporary, optimal STEMI management, with a specific focus on documented quality indicators.

Methods: Chapter 1 is a discussion of the modern approach to STEMI management. We explored particularly how primary percutaneous coronary intervention (PCI) and thrombolysis are integrated as acute reperfusion options into systems of care. Chapter 2 comprises a systematic review concerning the evolving use of pre-hospital electrocardiograph (ECG) technology in improving reperfusion times and clinical outcomes, with specific consideration as to how this may be used in pathways of care. In Chapter 3, a four-year study of reperfusion-eligible patients presenting to Dunedin Hospital between 2004 and 2008 was performed. Morbidity and mortality outcomes were assessed with one-year follow-up. Cases were analysed by age, gender, and hour of presentation to observe any effect these factors had on quality of care and clinical outcomes.

Results: Eighteen studies describing the use of pre-hospital ECG in improving door to balloon times or mortality outcomes were identified after a systematic literature search. While these studies were generally small and methodologically represented lower level evidence, they appeared to support the utility of this evolving technology in newer models of care to significantly reduce reperfusion times; however, there were limited reported data on mortality or changes in other outcomes. Variable approaches to pre-hospital ECG use, reporting of outcomes, and study quality precluded formal quantitative meta-analysis. A four-year review of Dunedin Hospital STEMI care identified a cohort ranging between 60 to 79 cases each year. There was a significant increase in the use of primary PCI across the years 2004–2008 (12.9% to 81.0%, p<0.001), with an accompanying reduction in the use of thrombolytic (lytic) drugs and non-use of acute reperfusion. Apart from an increase in the use of evidence-based therapies, no other significant changes were identified over the study period. In-hospital mortality ranged from 3.3% to 9.7% (p=0.511); at one year this ranged from 5.0% to 19.6% (p=0.125), and unadjusted for differing baseline characteristics did not differ between lytic or primary PCI therapy. Rates of bleeding were notably high, particularly in patients receiving thrombolysis. Older patients fared worse in many clinical outcomes assessed, as did women. Out-of-hours presentation was not observed to be associated with differences in institutional performance or clinical outcomes.

Conclusions: The systematic review of pre-hospital ECGs supports use in improving reperfusion times, and potentially as a means to facilitate regional cardiac networks. There remain some uncertainties about the specifics of technology, implementation, and cost effectiveness. It is technology that is potentially rapidly evolving and advancing, but already appears to be practicable with well-described examples of implementation reducing reperfusion times. Larger studies will be required to demonstrate ability to improve hard clinical outcomes.

Review of real-world outcomes at this institution indicates results latterly consistent with benchmarks of international trial and registry data. That there were no differences in mortality between thrombolysis and primary PCI supports the mixed-strategy approach, assuming continued allowance for the individual patient context. Identification of potential unequal provision of care due to age or gender provides potential targets for future quality improvement initiatives.