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Q Waves Predict Mortality in Myocardial Infarction
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Am Fam Physician. 2006 Nov 1;74(9):1609-1610.
The presence of Q waves on an electrocardiogram (ECG) during acute myocardial infarction indicates necrosis of the myocardium, and ST resolution following fibrinolytic therapy indicates successful tissue reperfusion. Wong and colleagues used data fromastudycomparingunfractionatedheparin with bivalirudin (Angiomax) as adjunctive treatments to streptokinase (Streptase) for patients with acute myocardial infarction with ST elevation. The authors studied whether early Q waves predict ST resolution with therapy and 30-day mortality.
The HERO-2 (Hirulog Early Reperfusion Occlusion) study included more than 17,000 patients who presented within six hours of onset of ischemic chest pain lasting at least 30 minutes, had ST changes or a new left bundle branch block, and were suitable for reperfusion therapy. All patients had 12-lead ECGs at randomization and 60 minutes after starting reperfusion therapy. The ECGs of the 15,222 patients with normal intra-ventricular conduction on both scans were used to identify those with Q waves on initial ECGs. Outcomes in the 10,244 patients with Q waves were compared with the 4,978 patients without.
The average age in each group was 61 years, with about 12 percent older than 75 years. About 30 percent of each group was women. Rates of current smoking (43 to 45 percent), hypertension (50 to 52 percent), and diabetes (13 to 15 percent) were almost identical between each group, as was average body mass index (26 kg per m2). Patients with Q waves were significantly more likely to report previous myocardial infarction and had a slightly greater median time from onset of symptoms to randomization.
Data were available for ST-resolution analysis 60 minutes after reperfusion therapy in 12,456 patients. More than 30 percent ST resolution was documented in 52 percent of those with initial Q waves compared with 57 percent of those without. Similarly, greater than 70 percent ST resolution was documented in 13 percent of patients with initial Q waves and 19 percent of those without. These results followed the same pattern after adjustment for history of myocardial infarction and time to presentation.
The 30-day mortality rate was significantly higher in patients with Q waves (10 versus 7 percent). This persisted after adjustment for time to randomization. Within the group with Q waves, mortality was almost the same for patients randomized within two hours of symptom onset and those randomized after four hours. The difference in mortality also was present when only patients with new myocardial infarction were analyzed. In multivariate analysis, the presence of initial Q waves was the only variable that predicted 30-day mortality. Initial Q waves increased the risk of 30-day mortality by more than 50 percent.
The authors conclude that the presence of Q waves is a more important predictor of outcome than clinical indices and time to beginning reperfusion therapy. The presence of Q waves may be especially useful in the large subset of patients who cannot accurately identify the time of symptom onset or who have little or no chest pain.
Wong CK, et al. Initial Q waves accompanying ST-segment elevation at presentation of acute myocardial infarction and 30-day mortality in patients given streptokinase therapy: an analysis from HERO-2. Lancet. June 24, 2006;367:2061–7.
Copyright © 2006 by the American Academy of Family Physicians.
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