Intravascular Ultrasound (IVUS)

A coronary angiogram shows the inside of an artery from the outside, as an outline filled with dye. Intravascular ultrasound goes inside the artery itself. IVUS uses a thin catheter with a small ultrasound probe at its tip to look at the inner structure of a coronary artery through a full 360 degrees. It shows the true diameter of the vessel, how much narrowing there is, the make-up of the plaque in the wall and any calcium, in detail. In stent procedures in particular, that detail changes the decision.

What Is Intravascular Ultrasound?

IVUS stands for intravascular ultrasound.

In an ultrasound scan of the abdomen the probe is moved over the skin. In IVUS the probe is inside the artery. The picture is therefore taken from within, as a cross-section, rather than from outside.

What you see on the screen is a cross-section of the artery: the channel the blood runs through, the layers of the wall, and the plaque sitting within that wall. This is precisely the detail an angiogram cannot show.

Why Is IVUS Needed When There Is an Angiogram?

An angiogram is a shadow picture. It shows the space filled by the contrast dye; it does not show the wall of the artery.

That brings three important limitations with it:

• The wall is not visible. Plaque can build up within the wall, and for a time the artery accommodates it by expanding outwards. The channel looks normal while the disease has advanced.

• The percentage of narrowing is an estimate. It is measured from a two-dimensional shadow and can change with the angle it is viewed from.

• The depth of the calcium is unclear. Whether calcium sits at the surface or deep in the wall decides how the artery has to be prepared.

IVUS shows all three directly. That is why intravascular ultrasound does not replace the angiogram; it completes it.

How Is IVUS Carried Out?

IVUS is not a separate procedure. It is done in the same session as the coronary angiogram or the stent procedure, through the same access point. You do not need to come back a second time.

• Access. Under local anaesthetic, the artery is entered at the wrist (the radial route) or at the groin — the route already opened for the angiogram.

• Advancing the catheter. A catheter a little thicker than a human hair, with an ultrasound probe at its tip, is taken as far as the relevant part of the artery.

• Recording the images. The catheter is drawn back at a steady speed while cross-sections are recorded from one end of the artery to the other. The recording maps the vessel along its length.

• Measurement. The true diameter of the artery, the size of the healthy segment, the length of the narrowing and the make-up of the plaque are worked out on screen.

• The decision. The result is seen straight away. If treatment is needed, the balloon and stent follow in the same session.

What Will You Feel?

You will not feel the catheter moving inside the artery; there are no pain-sensing nerve endings inside blood vessels. The ultrasound waves themselves cause no sensation.

Some people feel brief chest discomfort during the procedure. This usually has to do with the catheter slowing the flow in the artery for a moment, and it passes once the catheter is drawn back. Do tell the team if you are uncomfortable.

How Long Does It Take?

Imaging a single artery usually adds a few minutes to the angiogram. If a second recording is made to check the stent afterwards, it takes a little longer. Your observation afterwards is the same as after an ordinary angiogram.

Stenting with IVUS: What Does It Add?

Stent procedures are where intravascular ultrasound makes the most difference. It contributes at two stages.

Before the Stent Goes In

• The right diameter. The true diameter of the artery is measured. A stent chosen smaller than the vessel does not sit against the wall; one chosen larger strains it.

• The right length. Where the narrowing begins and ends can be seen. The stent has to cover the diseased segment from end to end.

• Preparing the artery. Where there is heavy calcium, a stent will not open fully. Because IVUS shows where the calcium is and how deep it lies, it becomes clear whether the artery needs preparing first. Methods for calcified arteries come into play at this stage.

After the Stent Is In

• Has it opened fully? Whether the stent has reached the intended diameter is measured. A stent that has not opened fully is one of the commonest reasons for narrowing inside a stent later on.

• Is it against the wall? Whether any gap has been left between the struts of the stent and the wall of the artery can be seen.

• Are the edges clean? The points where the stent begins and ends are checked for damage to the artery.

International cardiology guidelines recommend using intravascular imaging in complex coronary procedures. The recommendation stands out particularly in arteries that supply a large area of muscle, such as the left main coronary artery.

Who Is IVUS For?

Intravascular ultrasound is not needed for every angiogram. It is used where the picture alone does not settle the decision, or where the procedure calls for precision:

• Assessing narrowings in the left main coronary artery

• Arteries with marked calcification

• Long narrowings, bifurcations and completely blocked artery (CTO) procedures

• Narrowings where the angiogram remains unclear or questionable

• Narrowing that has developed again in a stent placed earlier, and finding out why

• Situations where as little contrast dye as possible should be used

IVUS Where Kidney Function Is Limited

This is a detail most sources leave out. In an angiogram the picture is produced with contrast dye, and contrast puts a load on the kidneys.

IVUS produces its picture with sound waves and needs no contrast of its own. In people whose kidney function is limited, it can therefore help to reduce the total amount of contrast used during the procedure. Whether it suits you is decided after your existing results have been considered.

How Do IVUS and FFR Differ?

Both are done during the angiogram, but they answer different questions.

• IVUS is an imaging method. It shows what the artery looks like: diameter, the make-up of the plaque, calcium, how a stent is sitting.

• FFR is a pressure measurement. It shows what the artery is doing: is the narrowing genuinely restricting blood flow?

Neither is the alternative to the other. In complex procedures they are often used together: FFR helps decide whether a narrowing should be treated, IVUS helps decide how.

How IVUS and OCT Differ

OCT (optical coherence tomography) is also an intravascular imaging method, but it uses light rather than sound. Its resolution is higher than that of IVUS; in return it cannot see as deep into the wall, and the artery has to be cleared briefly with contrast dye for the picture to be taken.

In short, IVUS shows more depth and OCT shows finer detail. Which is used is decided according to the artery in question and the patient’s situation.

Coronary Imaging with IVUS in Antalya

Prof. Dr. Umuttan Doğan is a cardiologist working in complex coronary procedures. Intravascular ultrasound is carried out in the catheter laboratory at Antalya American Hospital, in the same session as the coronary angiogram or the stent procedure.

If you have had an angiogram and the result is not clear, or if you have a problem with a stent placed earlier, you can be seen at the clinic in Konyaaltı with the images and results you already have. You will find his background and contact details on their own pages.

Frequently Asked Questions

Is IVUS a separate procedure? Will I need a second angiogram?

No. Intravascular ultrasound is done in the same session as the coronary angiogram or the stent procedure, through the same access point. There is no separate appointment and no second procedure.

Will IVUS hurt?

You will not feel the catheter moving inside the artery. Some people have brief chest discomfort, which usually passes once the catheter is drawn back. At the access site, local anaesthetic is used as it is for an angiogram.

I have kidney disease — can IVUS still be done?

IVUS produces its picture with sound waves and needs no contrast dye of its own. That can help reduce the total amount of contrast used during the procedure. The decision is made after your kidney function and your other results have been considered.

Is IVUS used in every stent procedure?

No. For a single, straightforward narrowing it is usually not needed. It comes into play in complex situations such as the left main coronary artery, heavy calcification, long narrowings, bifurcations and complete blockages.

How much longer does IVUS make the angiogram?

Imaging a single artery usually adds a few minutes. If a check recording is made after the stent, it takes a little longer. Your stay in hospital does not change because of it.

The information on this page is for general guidance and does not replace a consultation. Decisions about diagnosis and treatment are made by your doctor after assessing your own situation.