Comparison Between Invasive and Conservative Strategies in Unstable Angina and Myocardial Infarction without ST-Segment Elevation: A Meta-Analysis

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Abstract

Objectives

The alternative choice between initial invasive or conservative strategies in acute coronary syndromes without ST elevation it is still a matter of controversy. We performed a meta-analysis in order to have both a wider and stricter scope of the available information, and to provide clues for decision-making in the clinical setting.

Material and methods

We selected the four randomized clinical trials that prospectively compared initial invasive with conservative strategies: TIMI IIIB, VANQWISH, FRISCII, and TACTICS. We analyzed clinical characteristics, therapeutic interventions and complication rates. Selected endpoints were: death, myocardial infarction or both at 30 days and 6-12 months.

Results

Our meta-analysis included 7070 patients. a) General considerations:both inclusion criteria and initial treatment were different among studies (the VANQWISH trial only included non-Q-wave myocardial infarction; FRISC II only considered for inclusion asymptomatic patients after 48 hours on dalteparin; in TACTICS all patients received tirofiban). Invasive treatment rates also differed among studies: from 71% and 9% in FRISC II for the invasive and conservative arms respectively, to similar rates in the VANQWISH (44% versus 33%)Angioplasty-associated mortality was low in all studies (0.15%to 1.25% in hospital, and 1.9% at 30days). Surgical mortality varied from 2% to7.7%. b) Meta-analysis (Table) (...)

Heterogeneity analyses: 1) Mortality: we found homogeneity among studies. 2) Infarction rates: there was heterogeneity in the acute phase (p< 0.01); theTACTICS, a study that considered a different diagnostic criterion for myocardial infarction definition (minimal enzymatic rise), was the only one that reported a reduction in myocardial infarction rate. Myocardial infarction was homogeneously reduced in the invasive arm during follow-up. 3) We found heterogeneity for the reduction of the combined endpoint death or myocardial infarction, during acute phase and at 1 year (p < 0.01). Surgical mortality influenced the general mortality:TACTICS (3.9%) no effects; VANQWISH (7.7%),increased mortality rate in the invasive arm; FRISCII (< 2%), increased survival rate in the invasive arm. Subgroup analysis showed that the greater benefit was confined to patients with raised troponin levels at study entry, those > 65 years old and showing ST segment deviation.

Conclusions

The invasive strategy did not offer advantages in terms of mortality; even more, it was associated with a tendency to a worse initial evolution. However, in the long-term follow-up, it reduced the incidence of both myocardial infarction and the combined endpoint (myocardial infarction. or death). We believe results of this meta-analysis about myocardial infarction rate should be interpreted cautiously: small variations in the definition of MI may lead to an over diagnoses due to a low cut-off value for myocardial enzymes raise (microinfarction). A three-fold increase in infarction rate may be seen, without clinical relevance. Moreover, the clinical and statistical heterogeneity among the results of the different studies, makes it difficult to obtain a unique and firm "meta-analysis based" conclusion regarding medical decision-making in the setting of the acute coronary syndrome without ST elevation. For the management of the individual patient, clinical cardiologists should balance clinical risks and the morbimortality risks associated with the invasive strategy in their own institutions; this is because, based in this meta-analysis, there are not significant evolutive differences between initial invasive or conservative strategies for the treatment of patients with acute coronary syndromes with-out ST segment elevation.