Monday, October 31, 2011

CORONARY ANGIOGRAM. WHAT IS NORMAL? MILD? SIGNIFICANT?

You may be surprise to find that after about 56 years of doing coronary angiography ( or arteriography ), cardiologist are still struggling to define significant coronary artery disease. At what point of luminal narrowing do we consider as significant or important? Some use a cut-off of 50% while others use 70%. All the time we know that coronary angiogram is a 2D picture, so it must also be the 50% or 70% on the severest orthogonal view. Some views may show 50% from one angle, and be 30% on another angle. Some cardiologist use 0% as normal, while others use <50% as normal.
So you can see that such a basic thing like coronary angiography do not even have a full agreement by cardiologist after 56 years.
All this is important, because the degree of stenosis ( or narrowing ), in many ways decide on the form of therapy, be it medical therapy, balloon angioplasty ( PCI ) or CABG ( by-pass surgery ). Here again, the cardiac surgeon will take a position that any heart artery with a narrowing of >50% or more should be by-passed.
Recently, a group called the Cardiac Care Network ( an NGO ), decided to do a survey. Led by Dr Jon David Schwalm of McMaster University, Hamilton, Ontario, they send out 188 survey forms, each containing 13 questions on defining significant CAD, to 18 major cardiac centers in Ontario. They received a 64% respond rate.

This is what they found.
Definition of single-vessel disease

Extent of disease
1 major epicardial vessel >70%
1 major epicardial vessel >50%
Responders (%)
65
35
Definition of double-vessel disease

Extent of disease
2 major epicardial vessels, each >70%
2 major epicardial vessels >50%
Responders (%)
58
37
Definition of triple-vessel disease

Extent of disease
3 major epicardial vessels, each >70%
3 major epicardial vessels >50%
Responders (%)
60
36

Moreover, 41% of respondents defined "mild" disease as <30% stenosis, while 35% used a cutoff of <50% stenosis. A full 69% of responders had very strict definitions of "normal": 0% stenosis and no luminal irregularities.

Can you see the confusion? They also found that ( upon breaking down the survey forms ), those cardiologist with <10 years experience tend to have a stricter definition of significant narrowing, while those of >10 years experience tended to have a less strict definition of significant disease.

Translated, it would mean that some are doing more revascularisation, then others. It is so difficult to see who is right and who is wrong. Whats is most interesting is the fact that a lot of work is now done to see if the anatomical narrowing is functionally significant, meaning that what may appear as an important narrowing, is not actually causing "problems" as evidence by improved outcome upon revascularisation. I was at a meeting in Beijing last March, when I saw data presented by the Koreans which showed that even some 90% narrowing angiographically, corresponded to non-ischemia producing by FFR. Of course, this data was derived from the FAME study, which I am waiting to see duplicated.

I am very concerned about patients being brought into the angio room for evaluation, based on CCTA. These patients may have no symptoms, no stress induced reversible ischemia. They are healthy, every day Joe, with a questionable CCTA, and subjected to coronary arteriography, and based on what is seen, subjected to re-vascularisation.

As for my own philosophy, I would like to take someone to the angio room when they have evidence of ischemia, either from a positive stress ECG or clinical chest pains. I feel that if these two are present, then whatever disease seen may be deemed as significant, if they are 70% or more narrowing in the severest orthogonal view. I feel that this is proper and supported by a large body of evidence. If the patient is going for by-pass surgery, as it is a major undertaking, all disease 50% or more should receive a by-pass graft because of the possibility of disease narrowing worsening, in the ensuing few years.

I suspect that over the coming years, more and more data will come out supporting the use of the FFR ( functional flow reserve ), as a means of defining a significant narrowing. This can be used non-invasively ( FFRCT ), and invasively. That would be good, but again, cost will rise.

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