Background: The TACTICS-TIMI 18 trial showed that an early invasive strategy in beneficial in selected patients with unstable angina or non-ST-elevation myocardial infarction (NSTEMI). These positive findings contrasted the findings from some earlier studies.
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The British Heart Foundation RITA 3 randomized trial sought to compare invasive vs conservative strategy in patients with unstable angina or NSTEMI, similar to the trial question of TACTICS-TIMI 18.
Patients: Eligible patients had suspected cardiac chest pain at rest with at least one of the following: Evidence of ischemia on electrocardiogram (ST depression, transient ST elevation, old left bundle branch block, or T wave inversion), pathologic Q waves suggesting previous myocardial infarction, or documented coronary artery disease on prior coronary angiogram.
Patients were excluded if they had evolving myocardial infarction in which reperfusion therapy was indicated. Patients were also excluded if creatine kinase or creatine kinase MB concentrations were twice the upper limit of normal before randomization, if they had myocardial infarction within a month, had percutaneous coronary intervention (PCI) in the previous 12 months, or coronary artery bypass grafting (CABG) at any time.
Baseline characteristics: The trial randomized 1,810 patients – 895 randomized to the invasive strategy and 915 randomized to conservative strategy. Patients were recruited from 45 hospitals in England and Scotland.
The average age of patients was 63 years and 62% were men. Approximately 35% had hypertension on drugs, 13% had diabetes and 28% had prior myocardial infarction.
The majority (92%) of the patients were enrolled because they met the criteria for evidence of ischemia on electrocardiogram.
Procedures: Patients were randomly assigned in a 1:1 ratio to undergo invasive vs conservative strategy.
In the conservative arm, patients received aspirin and enoxaparin 1mg/kg subcutaneously twice a day for 2-8 days. Beta-blockers, other antiplatelets and glycoprotein IIb/IIIa inhibitors could also be used. Coronary angiography could be performed if patients had anginal symptoms at rest or with minimal exertion despite appropriate therapy or if they had ischemia on stress testing.
Patients in the invasive strategy arm received similar medical therapy to the conservative arm. Coronary angiogram was to be performed as soon as possible after randomization and ideally within 72 hours. Revascularization was recommended for lesions of at least 70% stenosis or 50% or more if left main.
Endpoints: The trial had two co-primary outcomes. The first was a composite of death from any cause, nonfatal myocardial infarction, or refractory angina at 4 months. The second was a composite of death from any cause or nonfatal myocardial infarction at 1 year.
Analysis was performed based on the intention-to-treat principle. The estimated sample size to provide 80% power at 5% alpha, was 1,770 patients. This assumed that 12% of the patients in the conservative arm would experience the outcome of death or non-fatal myocardial infarction at 1-year, and that the invasive strategy would result in 33% relative risk reduction in this outcome.
Results: In the invasive strategy, 97% of the patients underwent coronary angiogram at a median of 2 days after randomization, and 55.3% underwent PCI or CABG. In the conservative arm, 10.3% had revascularization during the index admission, and 17.3% had revascularization at 1-year. The median follow time was 2 years and 97% of the patients had at least 1-year of follow up.
The first primary composite outcome of death from any cause, nonfatal myocardial infarction, or refractory angina at 4 months was lower with the invasive strategy (9.6% vs 14.5%, HR: 0.66, 95% CI: 0.51 – 0.85; p= 0.001). The second primary composite outcome of death from any cause or nonfatal myocardial infarction at 1 year was not significantly different between both groups (7.6% with invasive vs 8.3% with conservative, HR: 0.91, 95% CI: 0.67 – 1.25; p= 0.58). At 1-year, 4.6% patients died in the invasive arm compared to 3.9% in the conservative arm, and this was not statistically significant. Myocardial infarction at 1-year occurred in 3.8% of the patients in the invasive arm compared to 4.8% in the conservative arm, and this was not statistically significant as well.
All bleeding occurred in 8.2% in the invasive arm and 3.5% in the conservative arm.
Subgroup analysis showed that men benefited from an invasive strategy while women did not (p for interaction= 0.011). The endpoint of death or myocardial infarction at 1-year, in women, was 5.1% in the conservative arm and 8.6% in the invasive arm, while in men, the incidence of this endpoint was 10.1% in the conservative arm and 7.0% in the invasive arm.
Conclusion: In patients with unstable angina or NSTEMI, an invasive strategy compared to conservative strategy, reduced refractory angina but not myocardial infarction or death at 1-year.
The reduction in angina is a subjective endpoint, prone to bias and faith healing, as we have previously discussed in other trials of PCI. The reduction in this endpoint alone should not justify widespread adoption of invasive strategy for unstable angina or NSTEMI.
A key distinction between this trial and TACTICS-TIMI 18—which demonstrated a reduction in myocardial infarction with an invasive approach—is that this study included patients with smaller myocardial infarctions. Only 41% of participants had ST depression or transient ST elevation, and patients were excluded if creatine kinase or creatine kinase MB levels were more than twice the upper limit of normal before randomization. This highlights the heterogeneity among patients with unstable angina and NSTEMI, where baseline risk and the extent of myocardial necrosis influence treatment effects. We encourage you to read again the subgroup interactions of TACTICS-TIMI 18.
Additionally, in the current era, high-sensitivity troponin assays enable the detection of smaller myocardial infarctions, potentially limiting the applicability of older trial results to all present NSTEMI patients.
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