BACC: Rapid Rule Out Protocol Safe for Acute MI Diagnosis

LONDON, England—Using a rapid rule-out algorithm to diagnose acute MI at 1 hour is safe when based on a high-sensitivity troponin assay, according to results presented on August 30, 2015, at the European Society of Cardiology (ESC) Congress.

For the BACC (Biomarkers in Acute Cardiovascular Care) study, Dirk Westermann, MD, PhD, of Universitäres Herzzentrum Hamburg (Hamburg, Germany), and colleagues compared the effects of a rule-out/rule-in approach when troponin testing was done at 1 hour vs the ESC guideline-recommended 3 hours in 1,045 patients presenting with acute chest pain (mean age 65 years; 64.9% men). Additionally, they looked at a lower cutoff value of 6 ng/L compared with the 99^th percentile value of 27 ng/L in a high-sensitivity troponin T assay (Elecsys; Roche Diagnostics) and a high-sensitivity troponin I assay (STAT hsTnI; Abbott Diagnostics). 

STEMI patients were excluded from the main analysis, but NSTEMI patients (n = 184) were older (70 vs 64 years; P < .001) and had more cardiovascular risk factors including hypertension, diabetes, and a history of CAD or acute MI compared with those without acute MI (n = 793).  

Verifying the Algorithms

Ruling out NSTEMI with hsTnI ≤ 6 ng/L resulted in 402 patients being discharged by 1 hour with no difference compared with waiting 3 hours. Additionally, compared with 6 ng/L, using the 27 ng/L cutoff resulted in a lower negative predictive value (NPV) regardless of the testing time (P < .005 for both) as well as lower sensitivity (table 1).

“We would have missed patients with MI and would have discharged them [if we used the] 99th percentile cutoff,” Dr. Westermann said, adding that the suggested NSTEMI rule-in algorithm should include hsTnI > 6 ng/L after 1 hour with a delta of 12 ng/L compared with the admission value (positive predictive value [PPV] 87.1%; specificity 98.0%).  

These algorithms were verified against 4,009 patients in the European APACE cohort (NPV 99.2% for rule-out; PPV 80.4% for rule-in), which also used a 1-hour algorithm, and the Australian ADAPT cohort (NPV 99.7% for rule-out; 81.5% for rule in).

Over a median follow-up of 183 days, only 3 patients (0.79%) died in the < 6 ng/L rule-out group. However, 12 would have died (1.73%) using the 27 ng/L cutoff (P < .05). Six-month mortality was slightly higher in the rule-in group, but highest among those who did not initially fit into either group. “Therefore, those [gray zone] patients can’t be discharged immediately and probably need specific medical treatment,” Dr. Westermann suggested. “This also implies that elevated troponin I values imply cardiovascular arrest.”  

Lastly, calculations based on a cohort of 74,738 individuals from the BiomarCare Cohort (mean age 51.0 years) without prevalent cardiovascular disease using the 6 vs 27 ng/L cutoff resulted in lower mortality at both 1 and 5 years (P < .001 for both). 

“There’s no need to wait for 3 hours,” Dr. Westermann concluded. “Further studies are needed to test the best cutoff for each troponin assay and to evaluate the 1-hour algorithm, respectively.”   

The ‘Cherry on Top’

Discussing the study, Joseph S. Alpert, MD, of University Medical Center (Tucson, AZ), said the study is “the Maraschino cherry on top of a hot fudge sundae. It really establishes… the usefulness of this protocol.”  

Although high-sensitivity troponin assays are not yet approved by the FDA for use in the United States, Dr. Alpert said he expects them to be used worldwide and incorporated in guidelines in the near future.

However, he warned of the variability among different assays and the effects of environment on cutoff values. “I don't think that one can just accept for the world a 6 ng/L cutoff,” he said. “Each individual hospital is going to have to be careful to study which assay they’re using and what the appropriate cutoffs are for their hospital.”

In a press conference, Kim Allan Williams, MD, of Rush University Medical Center (Chicago, IL), said “it would be nice to compare datasets across many regions of the world.” The age of the BACC population was “quite young,” he said, especially in comparison to typical US patients. “I’m not sure that would change the results, but the comorbid conditions that increase the troponins—whether it’s sepsis or renal failure that we see in the United States—might make it important to focus on that delta.”  

But the inclusion of rapid rule-out protocols in US practice “would be very helpful in terms of the cost of medical care particularly in our [emergency departments (EDs)],” Dr. Williams added.  

Still, American College of Cardiology past president W. Douglas Weaver, MD, of Henry Ford Hospital (Detroit, MI), told TCTMD in an email that “even with 3 hour testing, patients in the United States will spend much more than that in the ED.  

“ED physicians,” he said, “worry about missing any patient with heart attack as it is a frequent cause of lawsuits. They want stress tests and often cardiologist evaluation before releasing any patients to home.”

Source: 
Westermann D. BACC: Accurate and rapid diagnosis of myocardial infarction using a high sensitivity Troponin I 1-hour algorithm. Presented at: European Society of Cardiology Congress; August 30, 2015; London, England.

Disclosures:

• BACC was supported by the German Center of Cardiovascular Research (DZHK), the European Union Seventh Framework Programme, and an unrestricted grant by Abbott Diagnostics. Abbott Diagnostics provided test reagents for high-sensitivity troponin I measurements.
• Drs. Westermann and Weaver report no relevant conflicts of interest.
• Dr. Alpert reports serving as the editor of the American Journal of Medicine.

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