Home Monitoring of Tissue Perfusion Post-PTA Predicts Clinical Outcome of CLTI Patients

An Interview With Jean-Paul de Vries, MD, PhD

In Thursday's session focusing on the interventional treatment of below-the-knee (BTK) and below-the-ankle (BTA) vessels in diabetics, we heard from Jean-Paul de Vries (Groningen, the Netherlands) who discussed his study of the relationship between home monitoring of tissue perfusion and post-clinical outcomes in chronic limb-threatening ischemia (CLTI) patients.

Speaking to LINC Today, Professor de Vries, who is a vascular surgeon and head of the Department of Surgery of the University Medical Centre in Groningen, outlined the study and its findings, and posits that home monitoring will become an important tool to improve post-clinical outcomes in CLTI patients.

Can you give us an overview of the study and the methods you used? 

This was a study of CLTI patients with severe ischemia of the legs. They need revascularization and they need interventions, so we’ve tended to focus on the bigger arteries. If they are occluded or stenosed we perform a percutaneous transluminal angioplasty (PTA) and say, “OK, the large arteries are open, or they are not stenosed anymore – so this is a success.” That’s one part of a possible successful intervention, but there’s another aspect that we seem to have overlooked, which is whether there is an improvement in the perfusion of the tissue. 

It’s not only the opening of arteries that’s important for a successful outcome, but also adequate improvement of perfusion of the lower limb and the feet. That was the focus of the study. We see patients in the hospital, perform an intervention, and then see the patients 6 weeks later in the outpatient clinic. 
In the interim, there’s a nurse taking care of the patient’s wounds, but we don’t measure if the tissue is really improving. And that’s because we haven’t had a good monitoring system to measure perfusion at home.

Our researchers used, I believe for the first time, a kind of tissue-perfusion measuring camera, and hopefully, it will become standard procedure for wound-care nurses to take a picture with a perfusion camera as part of their home visits.

Can you tell us something about the devices you’ve been using?

We used thermal imaging and hyperspectral imaging. The HyperView (HyperMed Imaging) hyperspectral camera is a hand-held device that allows you to take an image that shows tissue perfusion. Thermal imaging didn’t prove to be that much of an asset, so we mainly used the HyperView camera. 

What were the practicalities? And what’s the relationship between home monitoring of tissue perfusion and predicting clinical outcomes?

This was a feasibility study to see if there was any value in performing the imaging during the initial post-procedural, 6-week follow-up period. We took images with the hyperspectral camera and thermal imaging cameras and measured tissue perfusion just before and just after treatment. The patients then went home, and our researchers measured tissue perfusion at 1 day post-intervention, at 1 week, and at 2 weeks. The researchers kept each patient supine for 15 minutes and then they took the images. The final measurement was at 6 weeks in the outpatient clinic.

When the patients came back to the hospital at 6 weeks, we obtained clinical judgment by the vascular surgeon and the interventional radiologist to see if there was a clinical improvement. We defined a clinical improvement as at least 1-degree improvement on the Rutherford scale.

We then compared all the hyperspectral measurements just after the intervention and during the course of the home monitoring (1, 7, 14 days) and of course at 6 weeks back at the outpatient clinic.

What important insights from tissue perfusion will you share?

We proved that by 7 days, there was already a difference in the hyperspectral imaging and tissue perfusion measurements of patients with clinical improvements, and those with no clinical improvements. That allows us to make an educated guess at 1 and 2 weeks to predict which patients will really have an improvement in perfusion, and therefore who will have clinical improvement, and who will likely not respond to the intervention.

That’s valuable because if you know at 1 or 2 weeks after intervention who is responding and who is not, then you might decide to perform a re-intervention earlier, or you might decide you need a better follow-up. Maybe they don’t respond at all, maybe they have pain, or maybe an amputation is necessary. In all these cases, the more time we have to decide, and the earlier we’re able to act, the better the outcome for the patient.

We proved that with early home monitoring, we can predict in an earlier phase whether there will be a clinical improvement.

What was the control?

The control was that every patient had an intervention and all those patients had pre- and post-intervention measurements. All of them had the 1-week, 2-week, and 6-week measurements. 

At 6 weeks, our study cohort was then deemed either to have a clinical improvement or not have a clinal improvement – according to our definition of improvement as 1 degree on the Rutherford scale. There was no randomization; the entire cohort was measured and their condition at 6 weeks was the endpoint of the study.

What other advantages are there to home monitoring other than the ability to predict clinal outcomes?

In the Netherlands at least, you do an intervention, and you see your patients at 6 weeks in the outpatient clinic. In those first 6 weeks, their wound might be a little bit better, or the pain might be a little bit less. They’ve had an expensive, invasive treatment but there are 6 weeks of ‘downtime’ that could be better used to evaluate decisions to re-intervene, to do an added intervention, or to perform a minor amputation.

In those terms, I think this is a minor breakthrough. It’s not rocket science, it’s a simple addition to an existing care program. This was a feasibility study – there’s a lot more work to be done, and of course, we’ll continue with a larger study group of patients. But every wound-care nurse can use a hyperspectral camera, gather the images, and upload the data.

There are two key points: one, there is a difference in tissue perfusion between a patient with clinical improvement and one without clinical improvement. Secondly, you can monitor a patient’s recovery trend. Let’s say they’ve responded well to treatment in the first few weeks, but on day 22 there is a decline in their hyperspectral imaging and their values are off. That might indicate there is something wrong; there might be an early re-occlusion, for instance. We can pick up problems earlier and deal with them more swiftly.

Conversely, if a patient improves, maybe they don’t need a 6-week follow-up at the outpatient clinic. Home monitoring could allow us to tailor the follow-up to the patient's progress, and of course, this can save time and money.

I think this home monitoring will change the way we conduct outpatient monitoring, for sure. In every European country, there is a real shortage of nursing staff and outpatient clinic time – every little bit helps.

Why hasn’t this been done before?

There are some tissue perfusion measurement systems on the market; the golden standard was transcutaneous oxygen pressure (TcPO₂), but TcPO₂ is rather labor-intensive, and it’s not contact-free. With the HyperView camera, it’s really just like taking a photo with a normal camera – that’s what makes it so suitable for home monitoring.

A few steps further down the road, we might have patients taking their own pictures, but that’s in the future. So, at present, our best resource for home monitoring and predicting outcomes is the wound-care nurses who already visit patients in their own homes.

What are your final thoughts on the study and its potential?

It’s still in its infancy but there is potential benefit, especially for our most frail patients who can be monitored in their own homes. Sure, we need a larger trial, but I think the next step is for wound-care nurses to implement the program. 

That’s when we’ll really be able to determine its value. Training is very straightforward. It’s an easy-to-use technology and methodology that holds a lot of promise for improved patient outcomes.