Could a new blood test help rule out a heart attack more quickly?
Between 60 and 80 percent of patients who complain of severe chest pain have not suffered a heart attack. On admission to hospital an electrocardiogram (ECG) shows diagnostic changes in only a minority of those who have had an attack, so that test is supplemented by blood tests for cardiac troponins, proteins that are released from damaged heart muscle.
The European Society for Cardiology summarised recent research on the diagnostic use of the high-sensitivity troponins hs-cTnT and hs-cTnI in patients with non-diagnostic ECG findings in the European Heart Journal on 14 January 2016. They specified high and low troponin concentrations in admission specimens taken at least three hours after the onset of chest pain that would allow a heart attack to be ruled in or out with confidence. In the same year the results of a “proof of concept” study of another heart muscle protein released after heart damage, cardiac myosin-binding protein C (cMyC), was published. Its serum concentration was found to rise and fall more rapidly than those of hs-cTnT and hs-cTnI, suggesting it might provide earlier diagnosis.
The authors of the “proof of concept” study led a European multi-centre evaluation of serum cMyC that was published online in the journal Circulation on 26 September 2017. All 1954 patients studied presented to hospital with chest pain and had an ECG and measurement of serum cMyC and troponin concentrations on admission. Their final diagnoses were determined independently, using all available clinical information from presentation to 90 days follow-up, including all subsequent serial troponin concentrations but no cMyC concentrations. Heart attack was diagnosed in 340 of the 1954 patients. The final diagnoses of a random 30% of all patients (586) was used to derive “rule-in” and “rule-out” values from their cMyC concentrations. These values were then applied to the initial cMyC concentrations of the remaining 1368 patients.
cMyC concentrations correctly allocated more patients to “rule-in” or “rule-out” groups than either hs-cTnI or hs-cTnT. The initial cMyC concentrations correctly classified 443 (32.4%) of the 1368 patients as “rule-out” with a negative predictive value of 99.8%, while the better of the two troponin tests, hs-cTnT, classified significantly fewer (326, 28.3%) as “rule out” with a negative predictive value of 99.7%.
The authors of the study suggested that fewer patients would have needed further measurements and the new test could have facilitated the early discharge of low-risk patients. Dr Tom Kaier, one of the lead researchers at St Thomas' Hospital, London told the BMJ: "Our research shows that the new test has the potential to reassure many thousands more patients with a single test, improving their experience and freeing up valuable hospital beds in A&E departments and wards across the country."
The problem that remains to be resolved is that the laboratory analysis time of current methods for cMyC is more than three hours. The potential of the test will not be realised unless the laboratory turnaround time can be reduced to minutes rather than hours.
The research was supported by grants from the Medical Research Council, the British Heart Foundation and a wide range of charitable, academic and industrial sources.