Mechanical Reperfusion in Patients With Acute Myocardial Infarction Presenting More Than 12 Hours From Symptom Onset: A Randomized Controlled Trial. Schomig et al. JAMA. 2005;293:2865-2872http://jama.jamanetwork.com/article.aspx?articleid=201080
Context: No specifically designed studies have addressed the role of primary percutaneous coronary intervention in patients with acute ST-segment elevation myocardial infarction (STEMI) presenting more than 12 hours after symptom onset. Current guidelines do not recommend reperfusion treatment in these patients.Objective: To assess whether an immediate invasive treatment strategy is associated with a reduction of infarct size in patients with acute STEMI, presenting between 12 and 48 hours after symptom onset, vs a conventional conservative strategy. Design, Setting, and Patients International, multicenter, open-label, randomized controlled trial conducted from May 23, 2001, to December 15, 2004, of 365 patients aged 18 to 80 years without persistent symptoms admitted with the diagnosis of acute STEMI between 12 and 48 hours after symptom onset.Interventions: Random assignment to either an invasive strategy (n=182) based predominantlyon coronary stenting with abciximab or a conventional conservative treatmentstrategy (n=183).Main Outcome Measures: The primary end point was final left ventricular infarct size according to single-photon emission computed tomography study with technetium Tc 99m sestamibi performed between 5 and 10 days after randomization in 347 patients (95.1%). Secondary end points included composite of death, recurrent MI, or stroke at 30 days.Results: The final left ventricular infarct size was significantly smaller in patients assigned to the invasive group (median, 8.0%; interquartile range [IQR], 2.0%-15.8%) vs those assigned to the conservative group (median, 13.0%; IQR, 3.0%-27.0%; P .001). The mean difference in final left ventricular infarct size between the invasive and conservative groups was −6.8% (95% confidence interval [CI], −10.2% to −3.5%). The secondary end points of death, recurrent MI, or stroke at 30 days occurred in 8 patients in the invasive group (4.4%) and 12 patients in the conservative group (6.6%) (relative risk, 0.67; 95% CI, 0.27-1.62; P=.37).Conclusion: An invasive strategy based on coronary stenting with adjunctive use ofabciximab reduces infarct size in patients with acute STEMI without persistent symptomspresenting 12 to 48 hours after symptom onset.
This is a section on "Acuteness" that I wrote in a Chapter on Reperfusion therapy that I wrote with Bill Brady in Critical Decisions in Emergency and Acute Care Electrocardiography. I have updated it here.
Here are a couple posts that demonstrate the issue of acuteness.
Acuteness—when is it too late for reperfusion?
In deciding on reperfusion, particularly on fibrinolytic therapy, it is important to assess the amount of viable injured myocardium at risk of infarction. This is traditionally done by assessing time since pain onset, and randomized trials of fibrinolytics found no significant advantage if pain duration was greater than 12 hours.[12, 32, 49] However, time since pain onset is a crude way of assessing amount of infarcted (irreversible), vs. ischemic (viable, salvageable), myocardium. Often, occlusion is incomplete, or collateral circulation maintains the viability of ischemic myocardium, or there is ischemic preconditioning, and myocardium that is fully salvageable may have pain duration of days. Fortunately, the ECG is a better indicator of salvageable myocardium than pain duration.
High ECG “acuteness” is associated with significant salvageable myocardium. An ECG has a high acuteness score if it has tall T-waves, and lower acuteness if there are Q-waves or T-wave inversion is present. In 395 patients, this score was shown to add the most value in situations of data disagreement: 1) in acute anterior MI when the history indicates symptom onset of greater than 2 hours but the acuteness score is high, or 2) in acute inferior MI, if history indicates a time since symptom onset less than 2 hours but the acuteness score is low. More recently, a high acuteness score was found on SPECT scanning and Cardiac MRI to be associated with more salvageable myocardium, and to be superior to time since pain onset for determining myocardium at risk (but not yet infarcted). This corresponds to other data showing that tall T-waves are an independent marker of benefit from fibrinolytics. and that, among those with positive T waves, mortality after thrombolytics is the same for those who have greater than 2 hours vs. less than 2 hours of symptoms. It is also important to know that QR-waves are present in 50% of anterior MI within the first hour, and represent ischemia of the conducting system, not infarction.
There are no randomized fibrinolytic trials based on EKG characteristics of acuteness. However, PCI is proven beneficial in a randomized trial of patients with persistent ST elevation at greater than 12 hours after onset, even though they were pain free.
Finally, ischemic discomfort is far less predictive of on ongoing ischemia than is persistent STE and tall T-waves. ECG acuteness should not be ignored because of resolution of symptoms.
In summary, tall T-waves indicate a large amount of viable, salvagable, myocardium. Q-waves indicate lower acuteness, but may be present early in anterior MI; thus, in anterior MI, T-waves are more important. Inverted T-waves signify either low acuteness or an open artery (see chapter 11 on reperfusion).
12. LATE Study Group, Late assessment of thrombolytic efficacy (LATE) study with alteplase 6-24 hours after onset of acute myocardial infarction. Lancet, 1993. 342: p. 759-766.
32. Fibrinolytic Therapy Trialists' (FTT) Collaborative Group, Indications for fibrinolytic therapy in suspected acute myocardial infarction: collaborative overview of early mortality and major morbidity results from all randomised trials of more than 1000 patients. Lancet, 1994. 343: p. 311-322.
49. EMERAS (Estudio Multicentro Estreptoquinsa Republicas de America del Sur), Randomised trial of late thrombolysis in patients with suspected acute myocardial infarction. Lancet, 1993. 342(8874): p. 767-772.
50. Wilkins, M.L., et al., An electrocardiographic acuteness score for quantifying the timing of a myocardial infarction to guide decisions regarding reperfusion therapy. Am J Cardiol, 1995. 75(8): p. 617-620.
51. Corey, K.E., et al., Combined historical and electrocardiographic timing of acute anterior and inferior myocardial infarcts for prediction of reperfusion achievable size limitation. Am J Cardiol, 1999. 83(6): p. 826-831.
52. Engblom, H., et al. The evaluation of an electrocardiographic myocardial ischemia acuteness score to predict the amount of myocardial salvage achieved by early percutaneous coronary intervention ☆: Clinical validation with myocardial perfusion single photon emission computed tomography and cardiac magnetic resonance. Journal of Electrocardiology 44(5):525-532; Sept-Oct 2011.
53. Hochrein, J., et al., Higher T-wave amplitude associated with better prognosis in patients receiving thrombolytic therapy for acute myocardial infarction (a GUSTO-1 substudy). Global Utilization of Streptokinase and Tissue plasminogen activator for Occluded Coronary Arteries. Am J Cardiol, 1998. 81(9): p. 1078-1084.
54. Herz, I., et al., The prognostic implications of negative T-waves in the leads with ST segment elevation on admission in acute myocardial infarction. Cardiology, 1999. 92(2): p. 121-127.
55. Raitt, M.H., et al., Appearance of abnormal Q waves early in the course of acute myocardial infarction: implications for efficacy of thrombolytic therapy. J Am Coll Cardiol, 1995. 25(5): p. 1084-1088.
56. Schomig, A., et al., Mechanical reperfusion in patients with acute myocardial infarction presenting more than 12 hours from symptom onset: a randomized controlled trial. Jama, 2005. 293(23): p. 2865-72.
57. 2007 Writing Group to Review New Evidence and Update the ACC/AHA 2004 Guidelines for the Management of Patients With ST-Elevation Myocardial Infarction, 2007 Focused Update of the ACC/AHA 2004 Guidelines for the Management of Patients with ST-Elevation Myocardial Infarction. J Am Coll Cardiol, 2008. 51(2).