69 ARTERIAL INSUFFICIENCY
Mark Nehler M.D., William C. Krupski M.D.

1. Describe claudication and its physiology.

Show answer
Intermittent claudication consists of reproducible lower extremity muscular pain induced by exercise and relieved by short periods of rest. It is caused by arterial obstruction to affected muscular beds, which restricts the normal exercise-induced increase in blood flow, producing transient muscle ischemia. Studies have shown that more than half of patients with intermittent claudication have never complained of this symptom to their physicians, assuming that difficulty with walking is a normal consequence of aging.

2. List the different nonoperative therapies for intermittent claudication.

Show answer
Risk factor modification, exercise, and pharmacologic therapies. Smoking cessation reliably doubles walking distances, and the need for eventual amputation in patient’s with lower extremity arterial occlusive disease decreases after smoking cessation. Exercise (defined as walking until onset of leg pain, resting, and then resuming walking) for 30-60 minutes, 3 days per week for 6 months has also been demonstrated in multiple randomized trials to increase walking distance by more than 100%. Currently, the only Food and Drug Administration (FDA)-approved drugs for the treatment of claudication are pentoxifylline (minimally effective) and cilostazol (appears more effective).

3. Define critical limb ischemia.

Show answer
Critical limb ischemia potentially threatens the viability of the limb. Symptoms include rest pain (e.g., foot pain at rest) typically occurring at night when the patient is supine and the gravity contribution to foot arterial pressure is no longer present. This pain is relieved with foot dependency or short periods of ambulation. Poor tissue circulation does not heal minor skin breakdown caused by incidental trauma. These ischemic ulcers are frequently painful and can progress to gangrene.

4. What is the ankle brachial index (ABI)?

Show answer
ABI is the highest ankle pressure (anterior tibial or posterior tibial artery) divided by the higher of the two brachial pressures. The normal ABI is slightly > 1 (1.10). An ABI of 1.0-0.5 is typical of patients with claudication. Patients with rest pain have an ABI < 0.5, and patients with tissue necrosis often have an ABI much lower.

5. Describe the natural history of claudication.

Show answer
Multiple natural history studies have documented the benign nature of claudication. The cumulative 10-year amputation rate is 10%. One third of patients experience symptom deterioration, and half of these patients require some sort of revascularization. Continued smoking and diabetes are major risk factors for progression.

6. Describe the natural history of critical limb ischemia.

Show answer

In the past, it was commonly believed that chronic ischemic rest pain or necrosis inevitably led to either reconstruction or major amputation. This is both simplistic and inaccurate. Clearly, continuous ischemic rest pain or progressive gangrenous changes are unstable conditions that require therapy. However, the control groups from several pharmacologic trials for critical limb ischemia noted improvement over time in 40%. Vascular disease is a systemic disease, and 50% of patients with critical limb ischemia succumb to cardiac disease within 5 years.

7. What are segmental limb pressures? How are they used?

Show answer
Just as the ABI is recorded at the ankle, cuffs at the high thigh, above knee, and below knee level can record pressures. Noting the location of decreases in arterial pressure can determine the level of the vascular obstruction.

8. Describe the natural history of graft occlusions.

Show answer
Although bypass grafts can dramatically improve lower extremity circulation, they have a limited life expectancy. When these grafts fail, the limb involved is frequently in worse circulatory trouble than before the bypass. This is because of division of major arterial collateral pathways during the operation and thrombus propagation or embolization to occlude distal arteries at the time of graft occlusion.

9. What is the prognosis of young patients with vascular disease?

Show answer
Significant atherosclerosis in young patients (age < 40 years) is infrequent. These patients are almost exclusively heavy smokers with a high incidence of hypercoaguable states (defective fibrinolysis, anticardiolipin antibodies, homocysteinemia, or deficiencies in natural anticoagulants). Those with limb-threatening conditions frequently progress to limb loss despite attempts at revascularization. Reconstructive procedures have limited longevity and require frequent revision in this population.

10. Describe the anatomic distribution of vascular disease in diabetes.

Show answer
Diabetic patients are unique. They have a predilection for calcification of the arterial wall, rendering diagnostic studies (ankle pressure, ABI) unreliable because of false elevation. The digital arteries are usually spared, and the great toe pressure can be used to approximate the ankle pressure. The inflow arteries (i.e., aorta, iliacs, common femorals) are usually spared. Intermittent disease is often present in the superficial femoral and popliteal arteries. Significant occlusive disease most commonly affects the profunda femoris, posterior and anterior tibials, and pedal arteries, with relative sparing of the peroneal artery.

11. What are the implications of renal failure on outcomes?

Show answer
Patients with end-stage renal failure who have critical limb ischemia are at the end of life, with 3 year survival rates < 30%, similar to patients with metastatic cancer. In addition, the healing potential for partial foot amputations after successful revascularization is limited. Reconstructions in these patients are technically difficult because of calcified distal targets. The combination of these problems has caused many vascular surgeons to discourage vascular reconstructions in these patients.

12. Discuss the concept of inflow versus outflow.

Show answer
The limb is thought of as a separate circulation network when planning revascularization procedures. Adequate leg circulation requires blood to enter the leg from the heart (inflow) and reach the foot from the thigh (outflow). In the normal limb, the inflow to the leg is via the aorta and iliacs, and common and deep femoral arteries. The normal outflow to the foot is the popliteal and three tibial arteries (anterior, posterior, and peroneal). For bypasses to work, they need adequate inflow (i.e., blood coming into them) and outflow (i.e., a vascular bed to supply).

13. What are the choices for autogenous conduits?

Show answer
The success of infrainguinal bypass is highly dependent on the conduit (what the graft is made of). The best choices for conduit in order of preference would be a single segment greater saphenous vein, spliced pieces of saphenous vein, spliced lesser saphenous veins, arm veins, spliced arm veins, and prosthetic material with a distal vein cuff. Cryopreserved cadaver veins are expensive and are generally of limited durability. Prosthetic grafts are best used for above-the-knee popliteal targets, because the bend at the knee joint and the size mismatch at more distal arteries decrease their longevity in these positions markedly.

14. What are the indications for arteriography?

Show answer
Arteriography is only performed in order to plan future operations or interventions. Diagnostic arteriography without intervention is rarely used in lower extremity occlusive disease. Arteriography is expensive and carries a finite risk of bleeding, arterial injury with thrombosis, and renal failure from contrast agent toxicity (combined 3%).

15. What are the patency rates of inflow procedures?

Show answer
The durability of vascular reconstructions is measured by patency. Patency has three types, all measured via a life table method, which accounts for the moderate number of deaths (primarily cardiac origin) occurring in vascular patients over time. Patency can be primary (the graft has remained functioning without any intervention), assisted primary (the graft has never thrombosed but has required some intervention to keep it functioning), or secondary patency (the graft has thrombosed, but an intervention has reopened it and it is again functioning). The four most common procedures to improve inflow are iliac angioplasty, aortofemoral bypass, femorofemoral bypass, and axillofemoral bypass. The most durable is the aortofemoral bypass, which has a 10-year primary patency of 80%. Five-year primary patency rates for iliac angioplasty, axillofemoral, and femorofemoral bypass are 65%, 70%, and 70%, respectively.

16. What are the patency rates of infrainguinal bypass procedures?

Show answer
Infrainguinal bypasses include grafts to the above-knee popliteal, below-knee popliteal, the tibials, and the pedal arteries. Five-year primary patency rates for above-knee popliteal grafts with saphenous vein and prosthetic are 80% and 65%, respectively. Five-year primary patency rates for below-knee saphenous vein popliteal grafts are 75%. Five-year primary patency rates for tibial bypasses are 65%. Five-year primary patency rate for pedal bypass is 50%.

17. Name the primary cause of perioperative mortality.

Show answer
The majority (> 90%) of all peripheral vascular disease patients have underlying coronary artery disease. Because of the ambulatory limitations of their peripheral vascular disease, most of these patients have no overt coronary symptoms. The most common cause of perioperative mortality in vascular surgery is myocardial infarction. The decision to work-up and revascularize (surgically or with angioplasty and stenting) coronary artery disease in these patients before the vascular operation is an area of ongoing controversy.

18. Name the primary cause of perioperative morbidity.

Show answer
Wound complications occur in ≤ 25% of patients undergoing lower extremity bypass for critical limb ischemia. Postoperative lymphedema, ischemic neuropathy, and prolonged (often measured in months rather than weeks) wound healing are all important issues for these patients.

19. What are the causes of graft failure?

Show answer
Early failure (within 30 days) is caused by technical problems with the operation (graft kinking or twisting, narrowing of the anastomosis, bleeding, infection, intimal flaps, or embolization). Graft failure at months 2 through 18 is most often caused by fibrointimal hyperplasia at distal anastomoses or venous valve sites within the graft. Late graft failure (> 18 months) is most frequently caused by recurrent atherosclerosis. Hypercoaguable states are an unusual cause of graft failure.

20. What therapeutic options are available for graft failure?

Show answer
If a vein graft fails immediately postoperatively, the correct approach is to explore the distal anastomosis and to fix the presumed technical problem. If a graft fails weeks to months after implantation, the correct course is somewhat controversial. Exploring the graft to mechanically remove thrombus and repair any stenoses has a poor success rate and is not recommended. Using thrombolytic therapy to open the graft and then repair any underlying stenoses seems attractive, but the longevity of grafts treated in this manner has been poor, with < 50% remaining patent at 1 year. Replacing the vein graft with a new bypass provides the most durable alternative providing it is technically possible and the patient is an operative candidate. Inflow grafts that occlude are usually managed with operative thrombectomy and revision of the distal anastomotic stenosis.
KEY POINTS: ARTERIAL INSUFFICIENCY

1. Ankle-brachial index (ABI) is the highest ankle pressure divided by the higher of the two brachial pressures.
2. Critical limb ischemia potentially threatens the viability of the limb.
3. Patients with end-stage renal failure who have critical limb ischemia are at the end of life, with 3-year survival rates < 30%.
4. If a vein graft fails immediately postoperatively, the correct approach is to explore the distal anastomosis and to fix the presumed technical problem.

21. What method of graft surveillance should be used?

Show answer
Because of the limited options for occluded vein bypass grafts, ultrasound studies are used to detect stenoses within the graft before occlusion. Various criteria have been championed to accurately detect > 50% narrowing within the graft or native inflow and outflow arteries. Natural history data indicate that grafts with > 50% stenoses left untreated have high intermediate-term failure rates. Recurrent symptoms and changes in the ABI are too insensitive to detect these lesions.

22. What therapeutic options are available for graft stenoses?

Show answer
The majority of vein graft stenoses are caused by fibrointimal hyperplasia of sclerotic portions of the graft or valve sites. These lesions are a firm rubber consistency and less amenable to long-term success with percutaneous angioplasty. Open techniques (resection and interposition vein grafting or vein patch angioplasty) are more durable but also cause more patient morbidity.

23. What is the role of iliac angioplasty and stenting?

Show answer
Iliac artery atherosclerotic lesions that respond best to balloon angioplasty are of short length (< 3 cm) and are confined to the common iliac artery. Nondiabetic patients fare better than diabetic patients. Current reports of initial success is > 90%, which has improved with the usage of stents to treat iatrogenic arterial dissections (splitting the arterial wall at the intima or media layers), but their effect on long-term success is still unproven.

24. How is viability determined in cases of acute ischemia?

Show answer
The five P’s of acute ischemia are pain, pallor, pulselessness, paresthesia, and paralysis. Early findings with acute ischemia include absent pulse, pain, and pallor. Paresthesia and paralysis are later findings. Classical teaching states irreversible muscle ischemia after 6 hours. However, in clinical practice, there are many overlaps. Perhaps the most sensitive finding that indicates limb nonviability is muscle rigor in the calf. The vast majority of ischemic limbs can be managed with initial heparin therapy followed by angiography and surgery or thrombolysis the next day(s).

25. How is thrombus distinguished from embolus in acute ischemia?

Show answer
The diagnosis of acute thrombotic versus embolic lower extremity arterial occlusion is complicated. Findings suggestive of embolus include no history of vascular disease, normal contralateral leg circulation, no history of cardiac arrhythmia or recent myocardial infarction, and no known cardiac thrombus. Patients with embolus frequently have rather profound leg ischemia because of the proximal nature of the occlusion (aortic or femoral bifurcation) and the absence of any developed collaterals. Occasionally, arteriography is required to differentiate between the two.

26. When is thrombolysis indicated?

Show answer
Thrombolytic therapy requires a patient without contraindications (bleeding risks) and a thrombus that can be crossed with a guidewire. The lytic medication (urokinase, streptokinase, or tissue plasminogen activator) needs to be placed directly within the thrombus. Acute native arterial occlusions should not have evidence of patent outflow arteries (e.g., a thrombosed popliteal artery aneurysm). Arterial embolus in an extremity that is not severely ischemic and can tolerate the time course of successful thrombolysis (frequently multiple hours of intra-arterial infusion and repeat trips to the angiography suite for angiograms to help determine optimal catheter repositioning for complete thrombus lysis). The use of thrombolytic therapy for graft occlusions is more controversial because of the relatively poor long-term durability of these grafts after flow is restored.

27. What is compartment syndrome?

Show answer
Reperfusion after acute ischemia can lead to profound tissue swelling in the involved extremity. Edema of the involved muscle can increase the pressure within the fascia bound muscle compartments (i.e., anterior, lateral, deep posterior, and superficial posterior) to a level that exceeds the capillary perfusion pressure (> 30 mmHg). Muscle death is then inevitable unless the pressure is relieved by opening the compartments surgically, a procedure known as fasciotomy. Patients complain of intense pain and swelling, with associated paresthesia. Pedal pulses can remain palpable.

References
WEB SITE
http://www.acssurgery.com
BIBLIOGRAPHY
1. Carter SA: The challenge and importance of defining critical limb ischemia. Vasc Med 2:126-131, 1997. Medline Similar articles
2. Faries P, Morrissey NJ, Teodorescu V, et al: Recent advances in peripheral angioplasty and stenting. Angiology 52:617-626, 2002.
3. Gahtan V: The noninvasive vascular laboratory. Surg Clin North Am 78:507-518, 1998. Medline Similar articles
4. Lau H, Cheng SW, Hui J: Eighteen-year experience with femoro-femoral bypass. Aust N Z J Surg 70:275-278, 2000. Medline Similar articles Full article
5. Nehler MR, Hiatt WR: Exercise therapy for claudication. Ann Vasc Surg 13:109-114, 1999. Medline Similar articles Full article
6. Nehler MR, Taylor LM Jr, Moneta GL, Porter JM: Natural history, nonoperative treatment, and functional assessment in chronic lower extremity ischemia. In Moore W (ed): Vascular Surgery: A Comprehensive Review. Philadelphia, W.B. Saunders, 1998, pp 251-265. Full article
7. Ouriel K, Veith F: Acute lower limb ischemia: Determinants of outcome. Surgery 124:336-342, 1998. Medline Similar articles
8. Pomposelli FB Jr, Arora S, Gibbons GW, et al: Lower extremity arterial reconstruction in the very elderly: Successful outcome preserves not only the limb but also residential status and ambulatory function. J Vasc Surg 28:215-225, 1998. Medline Similar articles