Your chest hurts, you go to the hospital (good move), you get rushed through and a nurse takes some blood and measures the electrical activity of your heart. A doctor asks you some questions. While she does so, the blood is being tested – the results are back already! Yeah, they are negative and everything else is OK, it’s not a heart attack – you can go home. This is the likely scenario in the near future thanks to new blood test technology which we, in Christchurch hospital’s Emergency Department, have been fortunate to be the first in the world to trial in patients. The results of our pilot study have now been published ( in a Journal of the American Medical Association (JAMA Cardiology).
About 65,000 patients a year are investigated for heart attacks in New Zealand emergency departments, yet only about 15% of them are actually having a heart attack. New Zealand leads the world in having become the first country in the world in which all patients are assessed by an accelerated diagnostic pathway that enables rapid evaluation of the patients and can send people home after two blood tests taken two to three hours apart (see here for more). This means many patients who once-upon-a-time would have been admitted to hospital overnight, are now able to be reassured after 4-6 hours that they are not having a heart attack and can go home. Nevertheless, there are enormous advantages for both patient and health system to being able to come to the conclusion that the pain isn’t life threatening earlier. The cork in the bottle preventing this happening is the time it takes for a blood sample to be analysed for signs of damage to the heart. These blood tests typically take 1 to 2 hours from the time of sampling (within ~15 minutes of arrival in the ED) until the results are available for the doctor to review. Because doctors are dealing with multiple patients at a time, their review and decisions around whether to allow the patient to go home, or to be admitted for more investigation, are further delayed. A point-of-care test is one that happens with a small machine near the bedside and can produce results available to the doctor even while they are still examining the patient. Until now, though, the precision of these machines has not been good enough to be used in emergency departments. When one manufacturer told us that their new technology may now have sufficient precision we were keen to test it, so we, in a first-in-the-world study, undertook a study in patients entering the emergency department of Christchurch hospital whom the attending doctor was investigating for a possible heart attack.
Thanks to the volunteer patients (I love volunteers) who gave some extra blood we measured the troponin concentration by this new point-of-care test (called the next generation point of care troponin I: TnI-Nx). Troponin comes from the heart muscle and is released into the blood during a heart attack. When the troponin concentrations in the blood are very very low we can be confident that the source of the patient’s discomfort is not a heart attack. Low concentrations require a very precise measurement test. Often, a very low concentration means the patient can safely go home. In 354 volunteers we measured troponin with the TnI-Nx assay when they first came to the emergency department. Their treatment didn’t change, and all clinical decisions were based on the normal laboratory based troponin (measured on entry to the emergency department and again 2 hours later). From the blood samples we collected and measurements we made, we could work out what could have happened if we had used the TnI-Nx results instead.
In our study the TnI-Nx troponin measurement was as good as, and possibly slightly better, than the laboratory based troponin measurement at ruling-out a heart attack. We found 57% of the patients being investigated had troponin concentrations measured with TnI-Nx below a threshold at which we could be confident that they were not having a heart-attack. All 57 patients who were actually having a heart attack had higher concentrations.
When implemented our results may mean that instead of waiting 3-6 hours for a results, half of patients being investigated could know within about 30 minutes of arriving at the ED whether they are having a heart attack or not. This early reassurance would be a relief to many, as well as reducing over-crowding in the emergency department and freeing up staff for other tasks. But before we implement the new test, we must validate it in more patients – this is a study we are carrying out now. Validation will enable us to more precisely determine a threshold concentration for TnI-Nx for clinical use which we can, with a very high degree of certainty, safely use to rule-out a heart attack.
The test also should allow people living in rural areas to get just as good care as in emergency departments because it could be deployed in rural hospital and general practices. This would save many lengthy, worrying, and expensive trips for people to an urban emergency department.
This study was carried out by the Christchurch Emergency Department research group (director and senior author Dr Martin Than) in conjunction with the Christchurch Heart Institute (University of Otago Christchurch). My colleague, Dr Joanna Young did much of the hard yards, and we thank our clinical research nurses and assistant for all they did to take blood samples, collect data, and lend a hand around the ED. The manufacturer of the blood test, Abbott Point-of-care, provided the tests free of charge, but they were blinded to the results and all analysis was conducted independent of them.
How we envisage TnI-Nx may be used in the future to allow very early rule out of heart attacks
Please note – patients experiencing sudden onset chest-pain should always seek immediate medical attention.
I am fortunate to hold a Senior Research Fellowship in Acute Care sponsored by the Canterbury Medical Research Foundation, the Emergency Care Foundation, and the Canterbury District Health Board which enables me to participate in these studies.
ps. You’ll have to read some of my older posts if you want to know why “Cheesecake files”
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