Section: New Board Review Category: Vascular

Microvascular Dysfunction-more than Small Vessel Disease

Charles Andersen, MD

Charles Anderson, MD discusses the differences between microvascular disease and microvascular dysfunction, how nephropathy and diabetes complicates vascular disease, as well as the podiatric surgeon’s role with management.

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Goals and Objectives
  1. Compare the differences between microvascular disease vs microvascular dysfunction
  2. Review diabetic nephropathy and its affects on vascular disease
  3. Describe the role of a podiatric surgeon in the management of arterial disease in the diabetic population.
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  • CPME (Credits: 0.5)

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    Release Date: 12/27/2018 Expiration Date: 12/31/2020

  • Author
  • Charles Andersen, MD

    Chief of Vascular-Endovascular-Limb Preservation Service and Medical Director of the Wound Care Clinic at Madigan Army Medical Center
    Tacoma, Washington
    Clinical Professor of Surgery at the University of Washington and the Uniformed Services University of Health Sciences

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  • Lecture Transcript
  • TAPE STARTS – [00:00]


    Speaker: So we are going to kind of continue on with that vascular theme and talk about microvascular dysfunction. It's more than small vessel disease. Again, no disclosure information, the same bias and disclosure and learning objections. We are going to discuss the difference between microvascular disease and microvascular dysfunction. So when you see this patient the question is, is this macrovascular disease, is this microvascular disease, is it a combination of both, can it be treated? That big mistake and let me reiterate this, the big mistake is to assume that this patient has microvascular disease that the patient cannot be treated and send that patient for a major amputation. These patients can be treated. They have macrovascular disease. Even if you can't salvage those toes, if you improve flow, then you may end up with a more minor, more functional amputation. The background of this question goes back to 1959 when Goldberg studied amputated lower extremity or lower extremities in diabetic and non-diabetic extremties and based on light microscopy felt that there was an increased deposition in the arterials in patients with diabetes. And this led to the concept of small vessel disease in patients with diabetes. And unfortunately has led to a lot of unnecessary amputations. So in patients with diabetes, the microvascular circulation, there is microvascular disease more prominent actually in the medium-sized arterials, but there is microvascular dysfunction and we are going to talk about what that really means.

    [02:07]

    Some microvascular changes are fairly unique to patients with diabetes. There is reduction in the capillary size with basement membrane thickening. The patients with microvascular dysfunction have increased vascular permeability, impaired auto-regulation and increased arterial AV shunting. So that can influence the perfusion to the skin in the patients with diabetes and certainly there is another risk factor for ulceration or if it's ulceration from repetitive trauma, a risk factor for poor healing in the patient with diabetes. So endothelial dysfunction, so there is imbalance between vasodilatation, vasoconstriction and that plays again important role in the pathogenesis of vascular complication in diabetes. The risk of developing microvascular complications in patients with diabetes depends on how long the patients have had diabetes and severity of their diabetes. We know now unfortunately that many of these patients have microvascular changes before they are clinically identified as having diabetes. So the "prediabetic state", we have a lot patients that are already undergoing microvascular changes before they are ever undergoing treatment for their diabetes. It really redefines diabetes, is diabetes when somebody requires treatment for hyperglycemia? Is diabetes when somebody has an elevated hemoglobin A1c?

    [04:12]

    So the definition of what diabetes or certainly onset of diabetes is being redefined. So as I mentioned that those changes may occur prior to the diagnosis of diabetes. The microvascular dysfunction can affect skin integrity and wound healing. Both macrovascular disease and microvascular dysfunction are important contributors to amputation. Don't just assume that it's the microvascular treat the macrovascular as the recurring message. So there are complications associated with the macrovascular disease. We have mentioned that it's the systemic disease, coronary artery disease, carotid arterial disease, PAD, which we spent last hour talking about. The coronary artery disease and carotid disease often times are very tightly linked and there's a direct correlation as the peripheral arterial disease progresses coronary artery disease is progressing in a parallel fashion. So the more severe the peripheral arterial disease, the more severe the coronary artery disease and the more chance of a perioperative myocardial infarction. Microvascular dysfunction in patients with diabetes leads to retinopathy, the nephrology, the neuropathy and also is present in other organ systems, for example, in heart, in the GI, patients with diabetes often times have silent MIs.

    [06:02]

    And their only manifestation of an MI may be perioperative the nausea and we tell our residents, any of our patients that have nausea in the postop period even if there is no chest pain that those patients to be considered and need to be ruled out for a postoperative myocardial infarction. Likewise, in the GI tract, this can lead to gastric paresis. They can get a big distended stomach again, which can cause postop problem. Nephropathy, again when we are treating those patients with peripheral arterial disease, to be aware that they have or can have significant nephropathy, we mentioned that if you are considering a CTA, for example, given that 200 mL of contrast may worsen the associated nephropathy associated with these patients that have diabetes. The interesting thing when you look at these microvascular manifestations of diabetes that there is evidence now that more aggressive treatment of the diabetes can decrease the progression of these microvascular disease state. So very, very important to be very aggressive in treating the diabetes. Retinopathy can certain lead to blindness. Neuropathy, all of us involved in podiatric care understand the sensory neuropathy. Oftentimes, it's not as well understood that there are really three faces of the neuropathy.

    [08:01]

    There is this sensory, the loss of protective sensation, the motor neuropathy is an imbalance between flexors and extensors. So you can end up with hammertoes, end up with equinus foot, biomechanical abnormalities that then can change the pressure distribution and be a risk factor for ulceration. The autonomic dysfunction plays a role in skin perfusion. It also leaves you with dry skin that's prone to fissuring and can be the entry site for the diabetic foot infection. I am vascular surgeon, so I am treading on some perhaps thin water here, but I have spent my career working with podiatric surgeons and I can tell you that podiatric surgeons, more than any other surgeons no matter what their specialty is, understand the biomechanics of the foot. And when you are dealing with reconstruction of the diabetic foot or you are dealing with looking at the etiology of the ulceration or doing for example internal offloading to prevent recurrent ulceration, having an understanding of the biomechanics of that foot is very, very important. I used to think I could do a TMA better than anybody. I can do a good TMA but I don't understand the tendon balancing nearly as well as my podiatric counterpart. So balancing those TMAs, knowing the ability or understanding the biomechanics in the foot is exceedingly important.

    [10:00]

    So in summary, patients with diabetes have both macrovascular disease and microvascular dysfunction. Most patients with critical limb ischemia and macrovascular disease can be treated. So it's not right, it's inappropriate to do an amputation on a patient because of microvascular disease without exploring the presence of macrovascular disease and looking at opportunities now to revascularize those patients. Even with extensive changes in the foot that made lower the level of amputation, so I will give a talk tomorrow morning, couple of talk tomorrow morning, but one is on amputation and there is a big difference between a minor amputation in the foot when you are talking about restoration of function versus a major amputation, a BK or an AK amputation. So if you can revascularize that patient even if you don't save the toes and that patient ends up with a TMA, you have ended up with a much more functional individual. The fact that the diabetes have microvascular dysfunction does not rule out macrovascular disease. Patients with critical limb ischemia should be evaluated for microvascular disease. Even in the presence of microvascular dysfunction, macrovascular disease should be treated and again I have mentioned the reason. So we have four minutes and 45 seconds remaining for questions on all three talks that anybody has a question.

    [12:01}

    Speaker 1: There was a slide where you have talked about restenosis rates being around 50%. Is that the same for plano-balloon angioplasty versus bare metal stent versus drug-eluting stent? And after your endovascular intervention, what is the typical timeframe for restenosis to happen if that was to occur?

    Speaker: The idea behind the drug-eluting stents, drug-eluting balloons and new stent technology and I also didn't mention medical therapy at the same time, so antiplatelet agent is to decrease the chance of restenosis. In terms of when it occurs, that's a very hard thing to predict. It's somewhat dependent on the size of the vessel that you are treating. If you are treating larger vessels, the chance of recurrence and the timing for recurrence is going to be later and there is going to be lower incidence. If you are down treating the vessels in the foot, a much higher incidence and you can have an early incidence of restenosis. Just realize that when you are working with your vascular surgeon, if there has been a procedure performed, that's not the end of the story. You still need to do the podiatric work, the wound care and if things all of a sudden have stopped progressing, you have to have that high index of restenosis and look for it and treat it.

    Speaker 1: Thank you.

    Speaker 2: I wanted to ask you about the timing on referrals. So you know if you have a person you find that you elevate their foot about their heart and their subpapillary venous plexus filling time greater than 6 seconds. Our referrals are supposed to be seen consultation within 30 days and now I am wondering, well, is that soon enough for that situation? I mean they're not infected necessarily or have another urgent matter, but I am wondering is that too long? I thought it was a slower process I guess.

    [14:17]

    Speaker: It can definitely be too long in selected patients. So if you a patient that presents with critical limb ischemia, they have gangrene of one toe and their other toes are dusky and you are not picking up any Doppler signals in the foot, that patient in the matter of weeks can really progress to where all of a sudden you have five ischemic toes. You can get cellulitis and you can miss that opportunity for revascularization.

    Speaker 2: I mean if you are seeing gangrene and dusky toes, that's pretty easy to determine they need to get over there quickly. I am talking about when it's not quite in your face that way?

    Speaker: To answer your question it depends on the degree of disease how urgent the referral is and that's a clinical decision. So we have 1 minute and 17 seconds time for one more question.

    Speaker 3: Yeah, Dr. Anderson, you did mention if you have a complete occlusion, there is a possibility of recanalizing that same vessel like juxtaposition to that actual occlusion. What's the rate of aneurysm at that particular areas and that you made the wall of that vessel much thinner?

    Speaker: Excellent question. Actually, the incidence of aneurysm is very low and the reason is once you have done the reentry and created a new lumen, then that's stented open, so now you have flow through stented area and even though the wall on the outside of that stent may be thinner, the aneurysmal change is not very common at all.


    TAPE ENDS - [16:10]