Doppler Evaluation of TIPS Shunts - SD

Introduction

Hi, I'm Mark Cleaver.

I'm a professor of radiology at the University of Wisconsin in Madison in the United States.

And I'll be talking about Doppler examination of TIPS shunts, Doppler evaluation of TIPS shunts.

I'm gonna take this topic in four steps.

First, talk a little bit about portal hypertension, the reason why most TIPS shunts are placed.

Then a little bit about placement and maintenance of the shunt.

Finally, some principles of Doppler surveillance.

And finally, some problems or caveats that you might have to deal with when you do ultrasound of these devices.

Portal Hypertension

Most TIPS shunts are done in people with cirrhosis in the United States.

The vast majority of people with cirrhosis acquire the disease from either an alcoholic or viral etiology, biliary cirrhosis, hemochromatosis makeup of smaller minority, and then there's a host of other things that can cause that worldwide.

However, viral causes take up more preeminent position.

The physiology of portal hypertension is such that the liver disease impedes blood flow through the liver, which increases portal venous pressure.

As a result, portal systemic collaterals will develop by definition, when the portal pressure exceeds 12 millimeters mercury, the patient is diagnosed with portal hypertension.

Portal pressure is defined by the portal vein pressure minus the pressure in the inferior vena cava.

There are three complications of portal hypertension, intractable ascites, variceal bleeding, and hepatic encephalopathy and TIPS shunts are used to address these, and particularly the first two complications of portal hypertension.

The performance of TIPS shunts has been remarkable over the last 10 or 20 years.

TIPS have demonstrated to significantly improved the quality of life of recipients and they perform as well or better than other ways of treating variceal bleeding and ascites.

There are several things that can be done for the treatment of hypertension.

Certainly diuretics are used to treat fluid overload.

Surgical shunts can be placed.

Sclerotherapy has been used on occasion and now TIPS shunts have taken an important position in the treatment of this disease.

Placement and Maintenance of TIPS Shunts

This is what a typical TIPS shunt looks like.

TIPS stands for transjugular intrahepatic portal systemic shunt because these shunts are placed typically through the jugular vein into the right hepatic vein.

And then this conduit is established between the portal system and the right hepatic vein.

Typically, the shunt extends from the right hepatic vein to the right portal vein, and the technical success of this procedure is now greater than 90%.

Here is an MR study showing the connection between or the distance between the right portal vein and the right hepatic vein.

So a relatively small amount of liver tissue is actually traversed.

Here again, is the TIPS shunt in place, and you can see this schematic drawing the connection between the right portal and the right hepatic veins.

Here's a patient with intractable ascites prior to the placement of the TIPS shunt, and here is the desired result.

The TIPS shunt has resulted in the complete resolution of the abdominal fluid.

Complications of TIPS Shunts

There are complications associated with the TIPS shunt.

Certainly the patency of the shunt is of most interest.

This slide illustrates the reason why Doppler surveillance is so important.

The one year patency rate without surveillance is as low as 25%, but with Doppler surveillance, that shunt can be kept open at a rate of about 85%.

So there's a strong incentive to monitor these shunts.

What are some of the complications?

Well, certainly stent thrombosis.

Stent stenosis, and by that I mean there you get a proliferation of pseudo-intima, or what's called pseudo-intimal hyperplasia.

You can get stenosis of the draining hepatic vein, and of course, you can get complete occlusion when identified promptly stenosis or thrombosis can be successfully treated with interventional techniques, particularly balloon angioplasty.

Here is an example of pseudo-intimal hyperplasia that has clogged this TIPS shunt.

You see it, it's a kind of fibro fatty deposition.

So once an abnormality is identified on Doppler, these patients will go on to venography or portal venography.

This is the gold standard of course, however it is an invasive procedure and requires a contrast injection.

So this is not the kind of technique that would be used routinely.

Here's an example of a portovenogram.

A catheter is threaded from the jugular vein through the stent demonstrating this stenosis of the distal stent as shown here by the circle.

A balloon then can be placed at the area of stenosis and inflated.

And here is the result of the balloon angioplasty, reestablishment of the full lumen of the TIPS shunt.

Principles of Doppler Surveillance

So let's talk about some principles of Doppler surveillance.

First of all, TIPS shunts are not always the easiest things to monitor.

There are a couple perspectives that we have found useful at our institution, either the high lateral intercostal approach.

The low intercostal approach or the subcostal subxiphoid approach should demonstrate the length of the shunt.

But of course, there are still problems.

These shunts tend to be deeply situated.

So where imaging at considerable depth, there's often a limited window suboptimal sound transmission.

As the cirrhosis itself causes sound attenuation, there's often a moving target cause many of these patients are unable to hold their breath adequately.

And also the orientation of the shunt relative to the sound beam is often perpendicular, which of course limits the amount of Doppler signal that can be obtained.

In general, we tend to use a low frequency probe for its advantages with penetration post TIPS.

The portal pressure then should decline, but hepatic resistance remains elevated as a result.

Flow in the portal venous branches and in particular the left portal venous branch will tend to reverse.

It will go away from the liver and towards the shunt in a hepatofugal orientation, subsequent portal vein branch.

Then if it reverses and goes towards the liver and away from the shunt, which is to say hepatopedal, that indicates stenosis of the shunt and is an important indicator of early shunt dysfunction.

Here's an example of normal portal venous flow.

Here is the flow that occurs.

Post TIPS, you see that the connection is made between the right portal vein and the right hepatic vein and the flow within the left portal branch and also the right portal vein branch distal to the shunt reverses.

Here is an example of that.

You can see the Doppler examination on your left showing flow through the TIPS.

And on the right you can see the blue color of the left portal branch indicating flow away from the liver and towards the shunt.

Studies of TIPS thrombosis have demonstrated that Doppler sonography is very sensitive and specific for complete occlusion in excess with sensitivities and specificities well in excess of 95 96 percentile.

Here's an example of complete occlusion.

You can see that with power Doppler, no flow signal is seen within the shunt.

And if you put spectral Doppler on, all you get is this transmitted pulsation from the aorta.

Identification of TIPS stenosis is more problematic and there is no uniform agreement on the parameters to identify the malfunctioning shunt.

As a result, eight different parameters have been developed and proposed.

There are three parameters that you can look for pre shunt, four parameters within the shunt and one post shunt.

Pre-Shunt Parameters

The pre shunt parameters are these direction of flow in the left portal vein branch, which is what I just discussed, the reappearance of collateral veins and a main portal vein velocity lower than 30 centimeters per second.

Here's a schematic demonstrating the flow in the left portal vein branch going towards the liver and away from the shunt indicating shunt dysfunction or stenosis.

Here's an example of a patient who had flow going towards the shunt at one period and later developed flow going away from the shunt indicated by the red color away from the shunt and towards the liver, indicating that the flow through the shunt was no longer the path of least resistance.

Here's an example of a patient who redeveloped a periumbilical venous collateral indicating that the shunt is no longer serving as the principle path of blood flow through the liver.

Parameters Within the Shunt

Within the shunt, four parameters have been elaborated.

There can be a visible narrowing by color or power Doppler, particularly in the distal shunt.

You can get absolute velocities within the shunt outside the 90 to 190 centimeters per second range.

You can get a temporal change in velocities exceeding 50 centimeters per second.

And by that I mean a change in the absolute velocity from one study to the next.

That exceeds 50 centimeters per second.

Or you can see a focal velocity elevation within the shunt during the performance of a single examination.

So as you're stepping through the shunt, you get a velocity elevation in excess of a hundred centimeters per second.

Here is an example of an absolute velocity in this shunt less than 90 centimeters per second.

And you can see the visible narrowing on color Doppler.

Here is an example of slow flow relatively slow flow in the mid shunt of approximately 77 centimeters per second.

That increases to 227 centimeters per second just beyond an area of stenosis.

Here is another example of a visible narrowing of the color Doppler signal in the distal shunt caused by pseudo-intimal hyperplasia.

Almost all stenosis do occur in the distal shunt that is at the hepatic venous end.

Post-Shunt Parameters

In the post shunt. One criteria is used in the draining hepatic vein.

A stenosis can occur, which will result in blood flow instead of traveling to the inferior vena cava for it to reverse in the right hepatic vein and go towards the liver.

So reversal of flow in the draining hepatic vein, usually the right hepatic vein indicates stenosis.

Here is an example of a stenosis in the area of the draining hepatic vein here, and you can see that after intervention that that flow has been reestablished using these eight criteria.

The sensitivity of Doppler for shunt stenosis is approximately 94% with a positive predictive value in a screen population of 96%.

Here is a table adopted from the reference by Kneman et al this came out in the AJR in 1997 and is widely used, but you can see that the sensitivities and specificities of the various criteria and that the overall impression, you tend to be more sensitive than specific, which is the way it should be by and large.

You want to identify early shunt dysfunction with a high degree of sensitivity so that you can avoid the recurrence of either ascites or the reformation of collateral veins because the reformation of some of these collaterals, especially esophageal collaterals, could result in catastrophic bleeding.

Venous Pulsatility Index

One more recent index that has been proposed is so-called venous pulsatility index.

And what is suggested here is that when you get a stenosis in the distal shunt, the hepatic venous end that the cardiac pulsation will be dampened.

And you can measure this VPI venous pulsatility index by taking the velocity maximal minus the velocity minimum over the velocity maximum.

And a value of 0.16 or less is considered bad.

This has been reported to be 94% sensitive and 87% specific.

Basically, a flat line waveform is bad and indicates shunt dysfunction.

This index has not been widely adopted, and these early positive and promising results are difficult to recreate in our laboratory.

But this is the concept.

Here's the cardiac pulsation seen in the TIPS in this patient, which over time is maintained and this is good.

This is a TIPS shunt where you see the cardiac pulsation and later on the monophasic flow or the flat line flow in the TIPS which indicates shunt dysfunction.

So this is bad. So if you see a monophasic flow in the setting of other abnormalities or abnormalities of the other indices, you should suggest shunt dysfunction.

Alternative Imaging Techniques and Pitfalls

There are alternative imaging techniques.

These are not widely used ultrasound contrast agents has more use in Europe and other countries than it is in the United States.

Other people have advocated CT angiography and even MR angiography, but these are very expensive ways of evaluating a shunt can be more effectively evaluated with ultrasound.

And finally, I'm gonna talk about some pitfalls that you might see in the performance of Doppler of TIPS shunts.

First of all, remember that once a shunt is placed in the first few days after placement.

You can get very abnormal hemodynamics and wildly abnormal indices.

This will settle as the hemodynamics of the liver start to settle.

So don't over-interpret abnormalities within the first days, and in particular, you often get intra velocities that are quite high.

Another caveat that you need to be aware of is a Doppler artifact that occurs at the edges of shunts.

What this is, is analogous to the twinkle artifact and this is what it looks like.

You can get what looks to be flow at the periphery of the shunt, which is really just reflection from the very brightly echogenic shunt walls.

This is however, a completely occluded shunt, no flow is seen, is present.

Within the shunt though, you get a power Doppler signal at the walls of the shunt itself.

And here's the color Doppler example of that.

And if you have any doubts about this being real or not real, I encourage you to use spectral Doppler to look at the waveform and you'll see readily that it is simply noise.

Here's another example of noise along the edges of the TIPS shunt.

No flow is seen with color Doppler, and if you put the spectral Doppler on, it will confirm the absence of flow within the shunt itself.

Another thing you should be aware of is that the velocities that you obtain within the shunt are dependent on the phase of respiration.

If you look at the velocities within the TIPS shunt, you'll see that it decreases with Valsalva.

We did a study looking at the effects of patient position and respiratory state on the measurement of Doppler velocities in TIPS.

We looked at three different positions, supine, upright and decubitus, and two respiratory states, quiet respiration and deep inspiration.

Here's an example of some measurements we did.

This is measurements in the TIPS shunt.

And you can see that in deep inspiration, the velocity declined from 104 centimeters per second to 80 centimeters per second.

In a nutshell, the suffice it to say that position was not an important factor in the measurement of these velocities, but respiration certainly was the average velocity.

And quiet respiration was fully 22 centimeters per second.

Greater than that in deep inspiration and deeper inspiration is analogous to the Valsalva maneuver.

Here's another example of a TIPS shunt that was at 70 centimeters per second in quiet breathing that fell to 45 centimeters per second with the Valsalva maneuver.

This is more of the results of that study, but suffice it to say that almost in a third of studies, a decline exceeded 50 centimeters per second, and fell below the 90 to 190 range in almost half of cases.

So this is an important factor when you do these measurements in, it's important, do it the same way.

If you take the initial set of measurements in quiet respiration, you should take all subsequent measurements in the same respiratory state.

And by that I mean that you should standardize your Doppler protocols so that you do it the same way each time or that some notation is made in the report so that the person doing subsequent studies will do it in the same way.

Conclusion

In conclusion, Doppler sonography can be a sensitive and relatively specific indicator for TIPS dysfunction.

The keys to success is that you have to use multiple parameters, at least eight that I described, compare with prior studies and communicate with the clinical team.

Thank you for your time and attention.