High Sensitivity Troponin T Assay Shows Strong Prognostic Ability in STEMI Patients

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In patients presenting with ST-elevation myocardial infarction (STEMI), elevated levels of high-sensitivity (hs) troponin T predict short- and long-term risk of adverse events and death, according to the results of a study published online February 27, 2014, ahead of print in the European Heart Journal: Acute Cardiovascular Care. The biomarker’s prognostic value is maintained even after adjustment for potential confounding variables.

Timothy Watson, MD, of Auckland City Hospital (Auckland, New Zealand), and colleagues studied 173 STEMI patients admitted to their institution between October 2010 and September 2011. All had hs-troponin T levels measured at admission.

The median time from symptom onset to index troponin T meas­urement (symptom to first hospital contact) was 2.5 hours. Median admission level was 59 ng/L (IQR, 19-310). Patients presenting with ST-elevation vs left bundle branch block MI demonstrated no differences in median levels (P = 0.895).

The median time from troponin T measurement to revascularization was 1.6 hours. In most cases, culprit artery TIMI (Thrombolysis in Myocardial Infarction) flow prior to intervention was grade 0. Overall, 84% of patients underwent PCI with 60% receiving DES.

High Predictive Ability

Rates of MACE (death, MI, and revascularization) were 10% at 30 days and 18% at 1 year. Analysis of admission troponin T by quartiles showed significant predictive ability for freedom from both MACE and all-cause mortality up to 12 months from the index event (log-rank P < 0.001 for both).

In receiver operating characteristic analysis, C-statistics for the ability of troponin T admission testing to predict MACE at 30 days and 1 year were 0.800 (95% CI 0.696-0.904) and 0.750 (95% CI 0.655-0.845), respectively. The optimal threshold for prediction was 225 ng/L for MACE and 465 ng/L for all-cause mortality.

Among patients presenting within 60 minutes of symptom onset, 52.9% had elevated troponin T, while 89.3% of those presenting within 3 to 6 hours showed elevated levels of the biomarker.

On multivariate analysis, independent predictors of precatheterization troponin T levels above the 225 ng/L threshold were:

• Age (OR 1.03; P = 0.049)
• Maori or Pacific ethnicity (OR 6.01; P = 0.003)
• Chronic respiratory disease (OR 10.9; P = 0.010)

In addition, admission troponin T level was an independent predictor of MACE at both 30 days (HR 5.16) and 1 year (HR 2.88; both P < 0.001) even after adjustment for time from symptom onset and multiple demographic variables. No association was seen between troponin T measurements and pre-intervention TIMI scores.

Advantages Over Traditional Troponin Test

According to the authors, the increasing adoption of the high-sensitivity troponin T assay in clinical practice highlights the impor­tance of evaluating its correlation with patient outcomes. This newer troponin test detects myocar­dial necrosis at lower levels and permits more rapid diagnosis than traditional troponin testing alone, they observe. “These characteristics may provide an addi­tional advantage for routine use of [hs troponin T] as a prognostic marker in STEMI where there is broad variability in the symptom to revascularization time and where the extent of myocardial injury can be difficult to quantify,” the investigators say, adding that the results suggest that the newer assay “may be considered a potential surrogate for symptom-to-revascularization time.”

As for clinical relevance, Dr. Watson and colleagues say incorporation of biomarkers such as troponin could help to further refine risk-stratification algorithms and improve their applicability in contemporary practice.

“This may help determine where interventions such as titration of drug therapy, revasculari­zation of nonculprit disease, and early implantable cardio­verter defibrillator therapy may improve outcome,” they say. “Whether addition of [hs troponin T] to such algorithms intended for this purpose is useful has yet to be tested.”

Potential Usefulness Unclear

In an email with TCTMD, Stephen G. Ellis, MD, of the Cleveland Clinic (Cleveland, OH), said it was not surprising that peak hs troponin T, which reflects the amount of infarcted heart muscle, is related to prognosis. However, he said the “tightness” of the relationship as assessed by C-statistic was perhaps “unexpected.”

“Since patients come to the hospital at somewhat varied times after the start of their heart attack, one might expect that this relation would be a little ‘blurred.’ This is true especially because the median time to [troponin T] [measurement] was only 2.5 hours after symptom onset (presumably too early in some patients to even catch the beginning of the [troponin T] rise)” he said.

Also, he explained that it is unclear how the findings might change practice, noting that patients with large infarcts are typically readily identified by low ejection fraction. The paper does not provide details as to whether LVEF was included in the multivariate analysis, he added.

Availability of Assay ‘Imminent’

“In the United States, we’re all pretty interested in the imminent availability of the high-sensitivity troponin tests and what that means for us,” said Christopher Granger, MD, of Duke University (Durham, NC), in a telephone interview with TCTMD.

He agreed with Dr. Ellis that the clinical significance of its use in STEMI remains to be seen, but said the high-degree of prognostic ability as shown in the study is interesting nonetheless.

“We already knew that CK-MB and the old troponin had some prognostic importance at presentation with STEMI, so it is important that this is showing [strong correlation] with the [hs troponin T],” Dr. Granger said. “The relationship that they demonstrate with time is another important aspect of this study. People who come in earlier [after symptom onset] have lower [hs troponin T], which may be another example of why getting people to present early after symptom onset is important.”

When the high-sensitivity assay does become available in the United States, which Dr. Granger said is expected to be sometime later this year, its primary use will be in the emergency department in non-STEMI.

Study Details 

The mean age of patients was 64 ± 12 years, and 73% were male. Twenty-four (14%) patients presented with car­diogenic shock and 22 (13%) with cardiac arrest prior to arrival in the cath lab.

 

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Source:
Wang TKM, Snow TAC, Chen Y, et al. High-sensitivity troponin level pre-catheterization predicts adverse cardiovascular outcomes after primary angioplasty for ST-elevation myocardial infarction. Eur Heart J: Acute Cardiovasc Care. 2014;Epub ahead of print.

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