[Previously posted over here]
This paper deserves a rant, just for the sake of its ridiculous use of numbers
Most people who come to an Emergency Dept. with chest pain do absolutely fine in the long run
A small number will be having/had a heart attack. we can usually pick up these pretty well.
Some people have chest pain but not heart attack but go on to have a big heart attack over the next few months. These are the tricky ones (and unfortunately there’s a lot of them). They look well, their tests tell us they haven’t had a heart attack but the question is are they at big risk for having one in the next few months.
We have no good test for this. No matter what people might say, we don’t.
Our gold-standard test has become the angiogram, where we use dye and x-rays to look at the lining of arteries to see if they’re narrowed. While useful, it still doesn’t tell us if someone is going to have a heart attack in 2 months.
So in this slightly grey area we have to work out what’s best to do.
There is big, big money in this for someone who can work it out. And we’re already throwing big money at it.
One of the tests that has been around for a while now is the exercise stress test (EST) where we get people to run on a treadmill while we take an ECG to see if we can induce angina. Hardly the most hi-tech but hey…
It certainly is +ve more often if the person is going to have a heart attack in the next 30 days, but it’s not good enough for us to make a decision on. If all the test gives us is enough info to guess, then maybe we’re just better guessing without the test – in other words clinical judgement.
This paper took 170 of the kind of patients we’re interested in. In the ED with chest pain and an ECG that doesn’t make a decision for us and a troponin that tells us they haven’t had a heart attack.
They all got an EST and they used the Duke scoring system to stratify them low, medium and high risk.
They followed them (not in a creepy way) for 30 days to see if they had an adverse event.
And this is where it gets a bit dubious. I care about whether the patient dies or has a heart attack in the next 30 days. And they measured that, but they also measured if people got an angiogram and 1) that’s not really an adverse event in the same sense, and 2) it’s a bit subjective; someone has to decide to do the angio, it’s not like it just happens spontaneously as part of the natural history of the disease
So this skews all their figures. They found a 3.5% adverse event rate and guess what – it was largely made of angios. Only 2 people had an MI in the next 30 days.
Especially seeing as most of the angios occurred while the patient was in hospital not when they were rushed back in a week later
With such a low adverse event rate it makes a farce of going on to calculate sensitivity and specificity, which they do anyhow.
Even more farcical is the dreaded -ve predictive value. Very basically this is the percentage chance after the test that nothing bad will happen to the patient.
They calculate it as 99.2%.
Which is nonsense. In their cohort if you simply sent them all home without the EST the percentage chance of them not having a heart attack in the next 30 days would have been 98.8%
Beware the -ve predictive value
They conclude wonderful things about their results and suggest that the EST is useful.
Did I mention that it was sponsored by a medical diagnostics company…
Pingback: Beware the negative predictive value | Emergency Medicine Ireland