Relation of time to treatment and mortality in patients with acute myocardial infarction undergoing primary coronary angioplasty

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Abstract

The benefit of thrombolysis is dependent on time to treatment, but there is lack of evidence of this relation in patients undergoing primary percutaneous transluminal coronary angioplasty (PTCA). The hypothesis that the relation of time to treatment to mortality is dependent on patient risk was tested in a series of 1,336 patients who underwent successful primary PTCA and were stratified into “low-risk” and “not low-risk” patient groups according to the Thrombolysis In Myocardial Infarction criteria. After stratification, 942 patients (71%) were at not low risk, and 394 (29%) were at low risk. The 6-month mortality rate was 9.3% for not low-risk patients and 1.3% for low-risk patients (p <0.001). Among not low-risk patients, longer time to treatment was associated with increased age and a greater incidence of cardiogenic shock. Unadjusted mortality of the not low-risk patients increased from 4.8% to 12.9%, with increasing time to reperfusion up to 6 hours, whereas mortality of the low-risk group was constant, with an increased time to reperfusion. For the not low-risk group, the univariate analysis revealed a relation between time to treatment and mortality (odds ratio 1.35; 95% confidence interval 1.06 to 1.73, p = 0.017). Time to reperfusion was not an independent predictor of mortality at multivariate analysis. Mortality for not low-risk patients who undergo successful primary PTCA is related to the delay from symptom onset to treatment. The effects of other variables associated with a longer time to reperfusion may have a stronger impact on mortality, obscuring the incremental value of time to reperfusion at multivariate analysis.

Section snippets

Patients

Since January 1995, primary PTCA has been the standard treatment at our institution for all patients with AMI admitted within 6 hours of symptom onset, and for those admitted within 24 hours with evidence of continuing ischemia, without any restriction based on age, sex, or clinical status on presentation. The exclusion criteria for this study were: (1) previous fibrinolytic treatment, and (2) inabilty to provide informed consent. Angiographic criteria for exclusion from intervention were: (1)

Patients and procedural results

Between January 1995 and October 2000, 1,362 consecutive patients with AMI underwent primary mechanical intervention. Of these, 26 (2%) had an unsuccessful procedure and were excluded from the analysis, whereas 1,336 patients had successful procedures. Of the 1,336 patients with successful procedures, 942 (71%) were at not low risk, and 394 (29%) were at low risk. The baseline characteristics of the 2 groups are listed in Table 1. The not low-risk patients were a mean age of 67 ± 12 years; 73%

Discussion

In our study the relation of time to treatment with mortality is evident for not low-risk patients, whereas it is lacking for the low-risk patient subset. These numbers may be easily explained considering that the benefit of treatment is strongly related to patient risk, and it is very difficult or even impossible to show a benefit of a reperfusive treatment for patients with a very low risk of death. For not low-risk patients, mortality increased with longer time to treatment and univariate

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This study was supported by a grant of the A.R. Card. ONLUS Foundation, Florence, Italy.

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