How to diagnose a heart attack...
Most people are aware of the pressures that face Accident and Emergency Departments, and a significant workload for emergency doctors is the assessment of patients with chest pain. Now this can be one sign of a heart attack; so it’s important to take seriously; but this takes a long time, and the majority of people coming in to hospital with chest pains aren’t actually having heart attacks, meaning that acute care beds can be occupied for long periods of time unnecessarily. Chris Smith spoke to Tom Kaier, from St Thomas’s Hospital in London, who has developed a new blood test that might be able to help speed things up. Plus, Addenbrooke's cardiologists, Tian Zhao and Sharon Wilson, explain the different between a heart attack and a cardiac arrest.
Tom - My name is Tom Kaier. I’m a British Heart Foundation Clinical Research Fellow, and I work at St Thomas’s Hospital in central London.
We’re looking at the diagnosis of myocardial infarction, so in layman's terms a heart attack. It’s a huge public problem; it affects about 2.2 million people a year that present with chest pain to the emergency department in England alone. And only 10 percent of them actually have myocardial infarctions, so have a heart attack that warrants further treatment.
Chris - But the other 90 percent, because they’ve got the symptom, might end up with a whole bunch of unnecessary investigations and possibly even treatments?
Tom - Exactly. Big heart attacks show themselves on the heart trace, but the heart trace abnormalities are only present in about a third of all patients with a heart attack. And the two third of patients that don’t have any ECG abnormalities, we have to perform blood tests in the Emergency Department and often admit them to hospital for ongoing observation and treatment. As you can imagine, because 90 percent of people have actually presented with chest pains do not have a heart attack, it places a huge burden on the health cares system. But, more importantly, also for the patients who sit in an Emergency Department and simply want to have an answer to the question: did I have a heart attack or not?
Chris - The present generation of blood tests that we have, are they not any good?
Tom - The blood tests we use at the moment, which is cardiac troponin, is excellent. It helps us diagnose a heart attack very clearly. The problem with cardiac troponin is that it comes out from the heart muscle at a relatively late stage. So if you look at the guidelines that many of us use, they advocate the use of those blood tests only in patients that had symptoms for more than three hours.
Chris - What’s the new test?
Tom - The new test is called “cardiac myosin-binding protein C.” It’s a mouthful; we abbreviate to MyC. It’s similar to troponin; it’s a protein that forms part of the heart muscle.
Chris - What, and that comes out of injured heart muscles? So when someone has a real heart attack, damage to the muscle releases that into the bloodstream and you can pick it up?
Tom - Exactly. Any sort of damage to the heart muscle would release these proteins. But, in particular, in patients with a heart muscle injury due to a heart attack we see very high levels of MyC. We also see high levels of cardiac troponin but at a later stage. So by having a protein that comes up in the bloodstream much earlier we can, in essence, test more patients and give them an earlier answer.
Chris - How quickly does the concentration of the MyC come up in these people, and how much faster is it than the existing troponin test you do?
Tom - You probably have a twice as quick release of the MyC protein comparing it with troponin. If you look at the time until you can safely make a discharge decision, that is also brought down to probably two hours rather than three hours with the cardiac troponin I’d say. Using MyC, we have shown that we can tell about 17 percent more patients, double the amount of patients than with cardiac troponin, that they didn’t have a heart attack with the first blood test at presentation to the emergency department, and, therefore these patients can be already reassured that they don’t require any further assessment.
Chris - I was thinking also, it might be very useful in primary care settings like General Practice? Because lots of people don’t go straight to the hospital when they have chest pain, they go and see their GP and say: oh, by the way, been up all night with indigestion do you think this could be a heart attack? And the GP then has to make a decision and this could help them?
Tom - It certainly could. The problem we have at the moment is that to bring this to a handheld device is very complicated. You’re trying to detect the equivalent of a few molecules of a protein in the finger prick blood sample, for example, which so far, no handheld troponin device has managed to achieve. Because there is so much more of MyC in the heart muscle, and it rises to much higher levels after the injury to the heart muscle, we are confident that we could translate the MyC onto a handheld device and, therefore, allow the measurement in a primary care environment like at the GP. But also be done by paramedics when they get called out to patients who are complaining of chest pain they could essentially do a risk assessment then and there with a finger prick blood test.
Chris - Tom Kaier. He’s based at St Thomas’s Hospital, in London.
Now also with me today are two heart specialists, or cardiologists. They’re Tian Zhao and Sharon Wilson; they’re both based at Cambridge’s Addenbrooke’s Hospital.
In a moment we’ll hear about how salt can affect your blood pressure, but first, Tian, can you just tell us when Tom was referring to chest pain there, why do people with heart problem classically get chest pain?
Tian - The reason is the heart, like any other muscle in the body, needs blood for it to function. And the three vessels supplying the heart with blood, and if there’s a narrowing in any of these blood vessels, the blood can’t get through and you don’t get enough oxygen and energy to the heart and it gets, essentially, like a cramp-like state where it can’t function well enough. The reflection of that is you get chest tightness; it may go down your arm and it may go up your neck and that’s what classically people call Angina.
Chris - Why does it go all over the place: neck arm and so on if it’s happening in your heart in the centre of your chest?
Tian - The organs in your body aren’t supplied by nerves that feel like the skin does. So sometimes when you get distress in the heart the body perceives it in different ways; for example, in heart patients they perceive it up the neck, in the left arm, and across the chest.
Chris - That pain is classically referred to as Angina. Does angina mean though that you’re actually having a heart attack or is it possible to have that pain and not actually be doing heart attack damage to your heart?
Tian - Exactly. Angina is typically pain that is rather predictable. So, for example, if you walk too briskly or you’re rushing upstairs you get chest tightness and also going up into your arm, but it you stop that goes away. Or if you use a puff of GTN which is a drug that…
Chris - Glycerin trinitrate?
Tian - Yeah. That relieves the pain. A heart attack is when you get chest pain that doesn’t go away, and it’s continuous, and it lasts for a long time or often at rest as well.
Chris - Sharon, when someone has a cardiac arrest, how does that relate to this story? What is one of those?
Sharon - A cardiac arrest is an electrical fault of the heart rather than a heart attack which is a plumbing problem.
If you’re having a cardiac arrest, your heart electrically has stopped. For the patient, who’s usually unconscious, they will not have a pulse that you can feel and this is a more significantly serious situation because you don’t have time.
If you have had a patient who's had a heart attack, you’ve still got blood supply to other parts of the heart and they can get to a hospital or to medical safety, but a cardiac arrest you need to respond to in a more urgent way.
Chris - So you can have a heart attack but not necessarily have a cardiac arrest? But you might do if you have a very serious heart attack and it causes an electrical problem in the heart?
Sharon - Yes. If it’s a significant heart attack it can cause damage to the main pumping chamber of the heart, which actually causes the heart to get into a stunned state. It doesn’t pump effectively and then you go and have a cardiac arrest. Or you can have a heart attack which causes direct damage to the electrical circuits within the heart which can cause a cardiac arrest.
But you can also have a cardiac arrest without having a heart attack. So people who’ve had previous damage to their heart can get abnormal electrical circuits within the left ventricle which can cause some problems and they can go on and have cardiac arrests without having a heart attack at the specific time.
Chris - And Tian, after someone’s had a heart attack how does the heart recover, and is the damage to it permanent or does it get better?
Tian - Unfortunately, the heart does not regenerate itself, so the cells that have died or have become permanently damaged usually stay that way and become scar tissue. Some parts of the heart which have been partially damaged can recover so you do get some recovery of the heart but, unfortunately, a large part of it is permanent.