Guidelines to reducing delays in administration of thrombolytic therapy in acute myocardial infarction.
The thrombotic coronary accident that triggers a myocardial infarction initiates a 'wavefront' of ischaemic cell death that can be aborted by timely restoration of blood flow. Myocardium destined for necrosis can be salvaged by quick lysis of the culprit clot to restore perfusion, reduce infarct size and save lives. While a number of useful thrombolytic regimens have been investigated, the greatest barrier to optimising efficacy is reducing the delay between the onset of symptoms and administration of thrombolytic therapy. Clinical experience has confirmed laboratory evidence that prompt restoration of coronary blood flow can salvage more than 50% of ischaemic myocardium if achieved within 2 hours. However, after 6 hours of sustained ischaemia, the opportunity to achieve meaningful salvage is largely lost. Analysis of pooled data estimates that for each hour of delay 1.6 fewer lives are saved per 1000 patients treated. Other investigators have estimated 60 to 80 lives saved per 1000 patients treated within 1 hour of symptom onset. More realistically, the time from symptom onset to treatment averages 2.5 to 5 hours in various studies. Reluctance to seek medical help results in a delay of more than 4 hours in at least 40% of patients. There may be some benefits of late, time-independent reperfusion from 12 to 24 hours after symptoms. Some hibernating myocardium may be salvaged resulting in less adverse late ventricular remodelling, reduced infarction expansion and improved electrical stability. Barriers to timely thrombolytic treatment may be classified as presentation delay or treatment delay. Strategies to optimise timely treatment have included pre-hospital administration of thrombolytics. This achieves greatest benefit when used in a more rural setting where transportation times tend to be longer. In this setting, as much as 140 minutes has been shaved off the symptom-to-needle time with a 50% reduction in 3-month mortality sustained as a 30% reduction in 5-year mortality. Most hospitals can improve their treatment (door-to-needle) time by focusing on chronic sources of delay. An emergency room culture of quick, coordinated response to chest pain must involve registration clerks, triage nurses, ECG technicians and emergency physicians. The authority to decide thrombolytic therapy must reside with the primary care physicians in any emergency room that encounters an acute infarction. The profound, life-saving benefits of thrombolytic therapy when used in a timely way should evoke a new sense of urgency in medical personnel when encountering the individual with a potential myocardial infarction.
Williams
W L
WL
University of Ottawa Heart Institute, Ontario, Canada. WWilliam@heartinst.on.ca
D000208:Acute Disease; D006801:Humans; D009203:Myocardial Infarction / Q000628:therapy*; D017410:Practice Guidelines as Topic; D016032:Randomized Controlled Trials as Topic; D015912:Thrombolytic Therapy / Q000379:methods* / Q000592:standards*; D013997:Time Factors