Perspectives in Circulation Today

Critical Leg Ischemia?

"Critical Leg Ischemia" Just what is it? The problems with a definition and a recommendation have been made by the Vascular Surgery Society (J Vascular Surgery Part 2, Volume 31 (1), 2000) : The term critical limb ischemia implies, they point out, chronicity and is to be distinguished from acute limb ischemia. In their recommendation 74, they write that trials and reporting standards definition of critical limb ischemia should favor a relatively inclusive entry criterion to ensure that the ulceration, gangrene, or rest pain is indeed caused by peripheral arterial disease and that most would be expected to require a major amputation within the next 6 months to a year in the absence of a significant hemodynamic improvement. To achieve this, they suggest use of absolute pressures of either ankle pressure < 50–70 mm Hg or reduced toe pressure (<30–50 mm Hg) or reduced TCPO 2 (<30–50 mm Hg). Such a recommendation is in keeping with that of the European Working Group on CLI who defined CLI as the presence of ischemic rest pain requiring analgesia for more than two weeks, or ulceration, or gangrene of the lower extremity with an ankle systolic blood pressure <= 50 mmHg and/or toe systolic pressure <= 30 mmHg. More recently, Novo, Coppola and Milio reviewed the problems of CLI along with its natural history (Curr Drug Targets Cardiovasc Haematol Disord 4(3):219-25, 2004). Its incidence is approximately 500 to 1000 per million year, with the highest rates among older subjects, smokers and diabetics. The rate of primary amputation ranges from 10% to 40%, and was performed only when no graftable distal vessels were present, or in neurologically impaired or hopelessly nonambulatory patients. Contrarily, in some highly specialized and aggressive centres about 90% of patients with CLI had an attempted revascularization. Furthermore, patients with critical limb ischemia have an elevated risk of future myocardial infarction, stroke and vascular death, 3-fold higher than patients with intermittent claudication. Therefore, due to its negative impact on the quality of life and the poor prognosis both in terms of limb salvage and survival, critical limb ischemia is a critical public health issue. However, historically most amputations in the diabetic are not due to ischemia.

Such data is in keeping with many other publications. Calhoun et al (Foot and Ankle 9:101-8, 1988), for example, described 355 diabetics with foot infections in whom their team did 805 operations including 130 major amputations and 313 lesser amputations. Only 32 vascular procedures were performed.

What Critical Limb Ischemia Is Not

Misleading Physical Findings

A casual observation of foot temperature may be misleading: a cool foot may feel warm to a cold hand and a normal foot may become cold with prolonged exposure to the air in a cold room. Properly done in a constant temperature room, however, measurement of toe temperatures becomes a powerful tool in documenting significant ischemia (Horwitz O and Abramson DG, Am J Cardiology 6:663, 1960). The absence of palpable pulses does not prove PAD. The dorsalis pedis may be congenitally absent in one leg in 2.9% of the population and absent in both legs in 1.8% (Robertson et al: Ann R Coll Surg Engl 72(2):99-100, 1990). Mowlavi et al found a dorsalis pedis present by palpation in 78% of their patients and in 95% by Doppler (Postgrad Med J 78(926):746-7, 2002), the difference attributed primarily to variability of technique between examiners. They found it helpful to locate the dorsalis pedis pulse by using the dorsal most prominence of the navicular bone as a landmark; the location of the left dorsalis pedis artery was a mean (SD) 9.8 (1.4) mm by palpation and 11.1 (2.1) mm by Doppler ultrasound from the dorsal most prominence of the navicular bone. The right dorsalis pedis artery was 10.4 (3.4) mm by palpation and 11.5 (0.7) mm from the dorsal most prominence of the navicular bone. Even when the pulses are determined by Doppler and ABI's are calculated, variation between the posterior tibial and dorsalis pedis may be expected. Hiatt et al, in The San Luis Valley Diabetes Study (SLVDS)(Circulation 91:1472-1479, 1995), evaluated the prevalence and complications of non–insulin-dependent diabetes mellitus (NIDDM) in a biethnic population comprising 1280 nondiabetic control subjects and 430 patients with NIDDM. The ABI criteria for PAD were developed in 403 healthy individuals with a low risk for cardiovascular disease. In these low-risk subjects, those classified with PAD by the two-vessel criterion had a higher frequency of claudication and the physical finding of an absent pulse compared with subjects without PAD or patients with PAD defined by the one-vessel or exercise criterion. Use of the two-vessel criterion identified an increased risk of PAD with increasing age, NIDDM, smoking, hypertension, and elevated cholesterol levels. In contrast, the one-vessel PAD criterion was associated only with increasing age and smoking, and exercise-diagnosed PAD was not associated with any cardiovascular risk factor except for male sex. Thus, they concluded an abnormal dorsalis pedis and posterior tibial ABI in the same leg at rest should be used for the diagnosis of PAD in epidemiological studies.

Conclusions

Many patients coming to amputations do indeed have CLI, but a minority. Before invasive vascular procedures are contemplated, documentation of the degree of ischemia should be accomplished in a skilled noninvasive vascular laboratory. Localized ischemia due to bacterial arteritis and associated thrombi/hemorrhage is not correctible by large vessel reconstruction procedures. The Circulator Boot Corporation believes it has documented that therapy with the Circulator Boot along with locally administered antibiotics may benefit such patients. Again patients with CLI not amenable to reconstruction procedures may benefit from boot therapy.

Illustrative Case Histories