2 January 2019

‘It is difficult to make predictions, particularly about the future.’ Old Danish proverb

The hallmark of a great scientific hypothesis is prediction. Einstein’s theory of special relativity predicted that gravitational fields could be demonstrated to bend light – and he was proven right during observations made during a total eclipse of the sun.

Unfortunately, things are rarely as black and white as that. Even if you understand almost all of the factors at play, it can be extremely difficult to predict certain events, particularly the timing. Earthquakes, hurricanes, which flu virus will be active next year? There are so many variables interacting with each other that things get very complex. When will San Francisco suffer the next major earthquake? According to the best predictions – about twenty years ago.

Chaos theory can also play its part. A very small change in one part of a system can trigger massive downstream effects. A butterfly flaps its wings in Africa, and two weeks later a hurricane devastates Florida.

So, what of predicting your future risk of cardiovascular disease? How good are the current models? Are they of any use at all?

In the US, the calculator that is most widely used was put together by the American Heart Association and American College of Cardiology.(AHA/ACC). It is called the ‘cvriskcalculator’ It can be found on-line here http://www.cvriskcalculator.com/ It asks you to provide data on ten different parameters:

Age

Sex

Race

Total cholesterol

HDL (good) cholesterol

Systolic blood pressure

Diastolic blood pressure

Treated for blood pressure: yes or no

Diabetes: yes or no

Smoker: yes or no

After you input your data, an algorithm kicks into action to work out your cardiovascular future. If it calculates that your risk of suffering a CV event is greater than 7.5%, within the next ten years, you will be recommended to start on a statin. This, you will have to take for the rest of your life.

One word of warning, all men by age of fifty-five – even men with no other risk factors at all – will have a risk greater than 7.5%. At least they will, using ‘cvrisk’. Because age is by far the most powerful risk factor of all – at least it is on ‘cvrisk’.

In the UK, a more complex risk factor calculator has been developed. In truth, it is only more complex in that it has an additional ten risk factors to consider. It is called Qrisk3. It uses twenty different factors to calculate risk https://qrisk.org/three/: They are, in no particular order:

Age

Sex

Smoking

Diabetes

Total cholesterol/HDL ratio

Raised blood pressure

Variation in two blood pressure readings

BMI

Chronic kidney disease

Rheumatoid arthritis

Systemic Lupus Erythematosus (SLE)

History of migraines

Severe mental illness

On atypical antipsychotic medication

Using steroid tablets

Atrial fibrillation

Diagnosis of erectile dysfunction

Angina, or heart attack in first degree relative under the age of 60

Ethnicity

Postcode

How good are they at predicting a future event? A study was carried out in the US to analyse, in retrospect, how accurate the cvriskcalculator had been. They looked at the historical risk scores of several thousand people, then tracked forward in time to see what actually happened.

In the study they looked at CVD over five years, not ten, so all figures should be doubled to establish the ten-year risk that is used in most calculators:

‘A widely recommended risk calculator for predicting a person’s chance of experiencing a cardiovascular disease event — such as heart attack, ischemic stroke or dying from coronary artery disease — has been found to substantially overestimate the actual five-year risk in adults overall and across all sociodemographic subgroups. The study by Kaiser Permanente was published today in the Journal of the American College of Cardiology.

The actual incidence of atherosclerotic cardiovascular disease events over five years was substantially lower than the predicted risk in each category of the ACC/AHA Pooled Cohort equation:

For predicted risk less than 2.5 percent, actual incidence was 0.2 percent

For predicted risk between 2.5 and 3.74 percent, actual incidence was 0.65 percent

For predicted risk between 3.75 and 4.99 percent, actual incidence was 0.9 percent

For predicted risk equal to or greater than 5 percent, actual incidence was 1.85 percent

“From a relative standpoint, the overestimation is approximately five- to six-fold,” explained Dr. Go” 1

What this means is that you carefully input your parameters into a risk calculator, which took many years of painstaking work to develop, using data carefully gathered by experts from the world of cardiology, and it overestimates your risk by five to six-fold. (I.e., 400 – 500% exaggeration!)

Excellent. Just for starters, this means that millions upon millions of people have been told to take a statin based on a calculation that is so wildly inaccurate as to be virtually meaningless. How so, Dr Go?

On a similar note, a group of researchers in the UK decided to look at data gathered on 378,256 patients from UK general practices. They wanted to establish which factors were most important in predicting future risk. The paper was called ‘Can machine-learning improve cardiovascular risk prediction using routine clinical data?’ 2

If the ACC/AHA and Qrisk3 calculators truly are looking at the most important variables, then we should see all the same factors appearing in this UK study. Below, just to remind you, are the ten factors used in the ACC/AHA calculator:

Age

Sex

Race

Total cholesterol

HDL (good) cholesterol

Systolic blood pressure

Diastolic blood pressure

Treated for blood pressure: yes or no

Diabetes: yes or no

Smoker: yes or no

Here is what the UK researchers found to be the top ten risk factors for CVD, in order, with number one being highest risk and number ten lowest risk:

Chronic Obstructive Pulmonary Disease (usually a result of smoking) Oral corticosteroid prescribed Age Severe mental illness Ethnicity South Asian Immunosuppressant prescribed Socio-economic-status quintile 3 Socio-economic status quintile 4 Chronic Kidney Disease Socio-economic status quintile 2

Compare and contrast, as they say. Do these lists look remotely the same? As you can see, there are only two factors on the ACC/AHA list that were replicated by the UK researchers. One of them is age – which you can do nothing about, and the other is ethnicity – which you can do nothing about. As for the rest. Where have they gone?

What of cholesterol, and sex, and blood pressure, and smoking, and diabetes. Well, out of a total of forty-eight factors analysed, here is where they ranked in importance. In this analysis factors could either be ranked protective, or causal:

Smoking = 18

Sex/female = 19 (protective)

Total cholesterol = 25

HDL cholesterol = 28 (protective)

Systolic blood pressure = 29

Diabetes = 31

LDL ‘bad’ cholesterol = 46

Yes, LDL ranked 46th out of 48 factors, well, well, who’d a thunk. The only things that scored lower than LDL were FEV1 and AST/ALT ratio. Factors that, unless you are medically trained, you will never have heard of. The first one, FEV1 stands for forced expiratory volume (from your lungs), measured over one second. The other is the ratio of two liver enzymes.

At present, it is true to say that the established risk factors, and the risk calculators, are almost completely useless. Not only that, they get more useless if you try to use them across different countries. If I took Qrisk3, or ‘cvrisk’ to France, whatever risk it calculated, I would then have to divide whatever figure I got, by four.

This is because, for exactly the same set of risk factors, someone in France will have one quarter the rate of CVD as a man in the US, or UK. Which means that the ‘cvrisk’ would actually overestimate risk by twenty-fold in France. Five times too high a calculated risk in the US, multiplied by four times too high a calculated risk in France. 5 x 4 = 20.

So, what should you measure? What can help you to predict your risk of CVD? Coronary calcium score (CAC)? That is, looking at the amount of calcium in your arteries. This is probably the most accurate way to establish your burden of atherosclerosis.

However, a high(er) CAC score does not mean that you are at risk of CVD, it means you have already got CVD, it is already there. The CAC score is just telling you how far along the CVD path you have traveled. So, it is not really predictive, it is more of a historical record.

What you really want is to stop the calcium forming in your arteries in the first place. Or then again, do you? A ‘calcified’ plaque is not, necessarily, a dangerous plaque. A dangerous plaque has an almost liquid core, which is in danger of rupturing. A dangerous plaque is often called a vulnerable plaque, and they don’t show up well, if at all, on a CAC scan.

If you have lots of vulnerable plaque what should you do?

Take a statin. Statins accelerate calcification.

Take warfarin. Warfarin accelerates calcification

Both reduce the risk of dying of CVD – if only by a small amount (at least small with statins). So, you could both increase calcification and reduce your risk of a CV event – simultaneously. What then to make of your CAC score? If you find it is zero, great. If you find it is four hundred?

Logically, a high score only tells you that you have CVD, and already having CVD means you are at higher risk of dying of a CV event. Which comes as no great surprise. What you really need to be able to do is to accurately predict what your CAC score would be – before you did it. And if you could do that, you really would have a scientific hypothesis worthy of the name.

The LDL hypothesis for example. If you could find you someone with an extremely high LDL level, say four to five times average, and a CAC score of zero – at the age of seventy-two then you would remove it as a factor for prediction.

So, here you go – I have blogged about this before – from a paper called: ‘A 72-Year-Old Patient with Longstanding, Untreated Familial Hypercholesterolemia but no Coronary Artery Calcification: A Case Report.’

The subject has a longstanding history of hypercholesterolemia. He was initially diagnosed while in his first or second year as a college student after presenting with corneal arcus and LDL-C levels above 300 mg/dL [7.7mmol/l] 3

He reports that pharmacologic therapy with statins was largely ineffective at reducing his LDL-C levels, with the majority of lab results reporting results above 300 mg/dL and a single lowest value of 260 mg/dL while on combination atorvastatin and niacin. In addition to FH-directed therapy, our subject reports occasionally using baby aspirin (81 mg) and over-the-counter Vitamin D supplements and multivitamins.

In the early 1990s, our patient underwent electron beam computed tomography (EBCT) imaging for CAC following a series of elevated lipid panels. Presence of CAC (coronary artery calcification) was assessed in the left main, left anterior descending, left circumflex, and right coronary arteries and scored using the Agatston score.

His initial score was 0.0, implying a greater than 95% chance of absence of coronary artery disease. Because of this surprising finding, he subsequently undertook four additional EBCT tests from 2006 to 2014 resulting in Agatston scores of 1.6, 2.1, 0.0, and 0.0, suggesting a nearly complete absence of any coronary artery calcification. In February of 2018, he underwent multi-slice CT which revealed a complete absence of coronary artery calcification.

Prediction, prediction. The risk factor calculators cannot do it. LDL levels don’t do it. I cannot do it with perfect accuracy either. I cannot say to anyone that you will not die of CVD. I cannot say to anyone that you will die of CVD. I can only help you to change the odds.

If you are an elderly, depressed, diabetic South Asian man with Chronic Obstructive Pulmonary Disease, taking steroids, with chronic kidney disease, living in a small council house in the UK then your odds of dying of CVD in the next year are pretty damned high. What should such a person do? Write a will, I would think.

Not many of us are at such high risk. Few of us are in such a bleak situation. What can the average person do to shift those odds in your favour? If you have read this blog from start to finish, I would imagine that you already know. If not, I am going to tell you next time. I am going to tell you how to change the odds, but I am unable to tell you how to get them to zero.

1: https://www.eurekalert.org/pub_releases/2016-05/kp-crt042916.php

2: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0174944

3: https://www.cureus.com/articles/11752-a-72-year-old-patient-with-longstanding-untreated-familial-hypercholesterolemia-but-no-coronary-artery-calcification-a-case-report