A TACTICAL Approach to Myocardial Infarction
Abstract & Commentary
Synopsis: This study suggests that the initial troponin level may be a useful determinant in deciding which patients should receive early invasive therapy.
Source: Morrow DA, et al. JAMA. 2001;286:2405-2412.
The TACTICS trial randomized 2220 patients with acute coronary syndrome to receive either invasive therapy (angioplasty or stent plus tirofiban) or medical management. Patients were followed for 6 months for a primary end point of a composite of death, myocardial infarction, or rehospitalization. Early invasive therapy resulted in an 18% relative reduction of the composite index.
Patients in both groups were stratified according to their troponin I and T levels. There was no difference between the 2 treatment strategies in patients who had a troponin I level of less than 0.1 ng/mL. Patients who had a troponin I level higher than this level had a 39% relative risk reduction if they received invasive management. The absolute risk reduction was 10%; the number needed to treat was 10.
Patients assigned to medical management who had a troponin I level of greater than 0.1 ng/mL had a 6-fold increase risk of recurrent myocardial infarction, rehospitalization, or death when compared to those with a troponin less than 0.1 ng/mL (OR, 6; CI, 3-13; P = 0.02). This increased risk was attenuated by the invasive strategy; those who had a troponin I level of greater than 0.1 ng/mL who received invasive therapy had a risk similar to those with lower troponin levels (OR, 1.7; CI, 0.8-3.4).
Similar findings were observed with troponin T, but at a cutoff level of 0.01 ng/mL.
Comment by Jeff Wiese, MD
Elevated troponin levels are predictive of a greater obstruction to coronary flow, more complicated thrombosis, and greater tissue injury.1 Previous trials have established that therapy for acute coronary syndrome is most effective in patients with elevated troponin levels.2,3 This study suggests that the initial troponin level may be a useful determinant in deciding which patients should receive early invasive therapy (those with a troponin I > 0.1 ng/mL) and which should receive medical management (troponin I < 0.1 ng/mL).
Caution should be exercised prior to using this algorithm in clinical practice. There is great variability among the commercially available troponin assays. Furthermore, the cutoff used in this study (> 1.0 ng/mL) is at the lower end of detection; all assays have less precision at this level. Clinicians should be aware that at this level there may be large sample to sample variability.
The results of this study should not replace good clinical reasoning in determining therapy for myocardial infarction. Angioplasty or stent placement was shown to be beneficial, but it also has potential side effects. Complication rates vary according to the hospital center, and physicians should integrate this into their decision. Where the complication rate appears high, as in centers where few procedures are performed or in high-risk patients, the physician should have a higher threshold for initiating invasive therapy. An isolated troponin I > 1.0 ng/mL should not prompt aggressive intervention unless the pretest probability of having myocardial ischemia exceeds this treatment threshold. Physicians should be aware of causes of false-positive results, including jaundice, rhabdomyolysis, and renal failure.
Dr. Wiese, Chief of Medicine, Charity, and University Hospitals, Associate Chairman of Medicine, Tulane Health Sciences Center, is Associate Editor of Internal Medicine Alert.
References
1. Gibson CM, et al. Circulation. 2001;104:2778-2783.
2. Wallentin L, et al. Lancet. 2000;356:9-16.
3. Heeschen C, et al. Lancet. 1999;354:1757-1762.
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