EBCT: no consensus at all

Harvey S Hecht MDDirector, Cardiac ImagingDirector, Atherosclerosis Detection and Preventive Treatment CenterArizona Heart InstitutePhoenix, AZ

Electron beam computed tomography (EBCT or EBT) is a screening tool for cardiovascular disease.

The recently published American College of Cardiology/American Heart Association consensus document recommended

that EBCT not be used as an early screen for coronary artery disease

that the test should not be made available to asymptomatic people in the general population without a physician’s request

Screening for cardiovascular disease

EBCT

O’Rourke RA, et al. Circulation 2000;102:126-140 O’Rourke RA, et al. J Am Coll Cardiol 2000;36(1):326-40

Consensus document

Although EBCT was not designed to detect obstructive coronary disease, the consensus panel emphasized

the high false-positive rate for prediction of obstructive disease

the inaccuracy of EBCT in predicting obstructive coronary artery disease, suggesting that it leads to unnecessary angiography and stress testing

Fundamental misunderstanding

Non-contrast EBCT scans The base of the heart

Left Main

LAD

LCX

Ao

LA

PA

No calcification Severe calcification

Prevention vs intervention

EBCT is about prevention not intervention.

EBCT can detect coronary disease at its earliest stages by detecting calcified plaque in asymptomatic people.

Aggressive preventive techniques can keep people identified as high risk out of the catheterization laboratory.

The discovery of obstructive disease as a result of EBCT testing is an incidental finding.

For detecting calcified plaque, EBCT is unparalleled in its power.

Overlooked paper

Annual event rate in asymptomatic people

0.11% per year for people with a calcium score of 0

2.1% per year for people with a calcium score of 1–99

4.1% per year for people with a calcium score of 100–400

4.8% per year for people with a calcium score >400

People with a score >400 are 45 times more likely to suffer a cardiac event in the next 3 years than people with a score of 0

Prognostic value of EBCT supported

Raggi P, et al. Circulation 2000;101:850-855

EBCT supported

Group A: 172 patients underwent EBCT imaging within 60 days of suffering an unheralded myocardial infarction.

Group B: 632 patients screened by EBCT were followed for a mean of 32±7 months for the development of acute myocardial infarction or cardiac death.

The mean patient age (53±8 vs 52±9 years) and prevalence of coronary calcification (96% each) were similar in the 2 groups.

Use in asymptomatic patients

Raggi P, et al. Circulation 2000;101:850-855

EBCT supported

Group B

Group An=172

Eventn=27

No Eventn=605

Calcium score 0 7 (4%) 1 (4%) 291 (48%)

1–99 58 (34%) 12 (44%) 207 (34%)

100–400 60 (35%) 8 (30%) 66 (11%)

>400 47 (27%) 6 (22%) 41 (6%)

Calcium percentile > 50th 150 (87%) 23 (85%) 258 (43%)

> 75th 121 (70%) 19 (70%) 162 (27%)

> 90th 72 (42%) 11 (41%) 82 (14%)

Raggi P, et al. Circulation 2000;101:850-855

Results

Heart disease

For more than 300 000 people every year, the first symptom of heart disease is the last symptom.

We know that 2/3 of heart attacks occur in people who have less than a 50% narrowing, which is undetectable by any kind of stress test.

Narrowing of less than 50% is only detectable by EBCT.

The incidence cardiac events without any coronary calcium in the arteries is no more than 5%.

Detecting symptoms

Calcified plaque

Calcified plaque is present in 95% of people who have a cardiac event.

The likelihood of having a cardiac event is much greater among people who have more plaque than among those who have less plaque.

The calcium scale

The calcium scale is a linear scale with 4 calcium score categories:

0: no calcification 1–99: mild calcification 100–400: moderate calcification >400: severe calcification

As the amount of calcium increases, the likelihood of an event increases, as does the likelihood of having obstructive disease.

EBCT vs stress testing

Study design

97 patients with symptoms suggestive of coronary artery disease underwent technetium stress testing, treadmill-ECG, and EBCT coronary scanning within 3 months of coronary angiography for the evaluation of chest pain.

Study conclusions

EBCT has a higher diagnostic ability than either treadmill-ECG or technetium-stress for the detection of obstructive angiographic CAD.

EBCT is an accurate and noninvasive alternative to traditional stress testing for the detection of obstructive CAD in symptomatic patients.

Shavelle DM, et al. J Am Coll Cardiol 2000;36(1):32-38

Detecting obstructive CAD

Sensitivity SpecificityRelative

risk†

Treadmill 76% 60% 1.72

Stress test 78% 47% 1.96

EBCT 96% 47%‡ 4.53

EBCT + treadmill 72% 83%* 2.10

*p<0.05†the ratio of the incidence of CAD for patients with a positive test to the incidence of CAD for patients with a negative test‡the low specificity of EBCT alone was improved by the addition of treadmill-ECG (p<0.05)

The ability of each test to predict obstructive angiographic CAD

Shavelle DM, et al. J Am Coll Cardiol 2000;36(1):32-38

EBCT vs stress testingResults

The calcium score

The calcium score is a measure of the amount of calcified plaque, which is linearly related to the total plaque burden.

If there is a small amount of calcified plaque, there is a small amount of total plaque; if there is a large amount of calcified plaque, there is a large amount of total plaque.

The more calcified plaque there is, the more likely there is to be obstructive coronary disease.

An asymptomatic patient would never go directly from an EBCT test to the catheterization laboratory; they would first undergo a stress test.

An absolute measure

Follow-up testing

EBCT testing will not lead to unnecessary testing; in fact, the use of EBCT testing to stratify patients will decrease costs by preventing unnecessary testing.

Calcium score >400A patient whose calcium score is >400 should have a nuclear stress test.

Calcium score <400An asymptomatic patient whose score is <400 does not need a nuclear stress test because the likelihood of having a positive test is no more than 10%.

Calcium score <100The likelihood of a patient with a calcium score <100 having a positive stress test is 1%–2% at most.

The vulnerable patient

Myocardial infarctions result from the rupture of a vulnerable plaque, and that vulnerable portion of the plaque is often not the calcified portion.

Although EBCT does not quantify soft, noncalicified plaque, where there is calcified plaque, there is almost invariably associated soft plaque.

EBCT may not identify the vulnerable portion of the coronary artery that is going to rupture, but it does identify the vulnerable person.

Calcified vs noncalcified plaque

The calcium percentile

The calcium percentile normalizes the calcium score against people of the same age and sex.

A 70-year-old man with a calcium percentile of 60 would be in the 20th percentile — less plaque than 80% of men in that age group, and more plaque than 19%.

A 35-year-old man with a calcium percentile of 60 would be in the 95th percentile — less plaque than 5% of men in that age group, and more plaque than 94%.

An assessment of risk based solely on the amount of plaque blocking the artery is not an accurate assessment of risk.

A relative measure

Score vs percentile

The calcium score — an index of the amount of plaque

The calcium percentile — an indication of how premature that plaque is

These 2 elements will affect decisions about whether or not to proceed to a stress test and how vigorously to treat the cholesterol.

Cholesterol values

Cholesterol values are very poorly predictive of the presence or amount of plaque.

Some people with normal cholesterol levels are in fact at extraordinarily high risk.

EBCT is exponentially more accurate in identifying patients who are at risk than standard cholesterol guidelines are.

Poorly predictive of risk

Framingham risk score

The biggest contribution to the Framingham risk score is age, but chronological age is different than physiological age.

A 50-year-old can have the coronary arteries of an 80-year-old and, conversely, an 80-year-old can have the coronary arteries of a 50-year-old.

To assign an arbitrary risk to a patient simply because of their age totally ignores individual variation.

The EBCT calcium score and calcium percentile can be used to modify the contribution that age makes to the Framingham risk score.

You are as old as your arteries

Grundy SM. Am J Cardiol 1999;83(10):1455-1457

Risk scores

Any general score is based on mean values derived from large groups of patients.

An EBCT test will tell precisely how much calcified plaque a person has and where that person stands in relation to other people of the same age.

Rather than extrapolating a number from a population of thousands, the EBCT represents individual risk.

Individual variations

Healthcare in the US

The US health system spends a higher portion of its gross domestic product than any other country but ranks 37 out of 191 countries according to its performance.The World Health Report 2000 — Health systems: improving

performance

According to the AHA, the cost of cardiac disease in the US is $280 billion per year.

In the US, disease is treated, not prevented.

Identifying patients who are at risk and taking preventive measures will lower overall healthcare costs.

WHO report

Geneva, Switzerland: World Health Organization; 2000

EBCT: for and against

Arguments against EBCT

To screen a large population with EBCT would be very costly to insurance companies and Medicare.

By making EBCT available as a routine screen, millions of people who were unaware they were at risk will be uncovered; these people will then require expensive treatment.

Arguments for EBCT

As soon as EBCT is approved as a routine screen and is implemented on a national level, the cost will plummet; mammography is now much less expensive than when it first came out; the same will happen with EBCT.

Cost of EBCT

The long-term view

Giving patients with high calcium scores stress testing may then lead to angiography, stenting, or bypass surgery — all costly propositions.

But, by preventing coronary events and saving lives, the cost to society in terms of lives and productivity lost as a result of cardiac disease will be reduced.

The short-term view

Average duration of enrolment in one HMO is 3 years; the person currently in one HMO may be a another HMO when a future coronary event occurs.

It is a common pool of patients in this country and they have to be treated as such.

Short term vs long term

The future of EBCT

The cost effectiveness of the longer-range view will eventually be appreciated by the insurance companies.

Scientific data, which are emerging on a monthly basis, will confirm the value of EBCT; it will be universally incorporated as a screening tool in the next consensus statement

Public pressure will call for universal access to EBCT; it will no longer be available only to those who can pay for it.

Cost effective in the long term

Advertising EBCT

Advertising is currently the most effective way to get the information out to the public — the most responsive segment of the population

Physicians may not be aware of the benefits of EBCT and therefore may not order it as a routine screening test.

All advertising will cease as soon as the cost of EBCT is fully covered by the insurance companies.

Getting the message out

Evidence-based medicine

Scientific data supporting the use of EBCT are appearing in all the major peer-reviewed journals, but there is currently only 1 long-term EBCT study planned — and it has design flaws.

There are no evidence-based data that angioplasty, stenting, bypass surgery save lives or decrease coronary events.

We can’t afford to wait until stringent, evidence-based data are available.

8 times as many women die every year from coronary disease as die from breast cancer

more women than men die on an annual basis of coronary disease

Waiting for long-term results