The challenge and importance of defining critical limb ischemia

Spinal cord stimulation for ischemic heart disease and peripheral vascular disease

Ischemic disease (ID) is now an important indication for electrical neuromodulation (NM), particularly in chronic pain conditions. NM is defined as a therapeutic modality that aims to restore functions of the nervous system or modulate neural structures involved in the dysfunction of organ systems. One of the NM methods used is chronic electrical stimulation of the spinal cord (spinal cord stimulation: SCS). SCS in ID, as applied to ischemic heart disease (IHD) and peripheral vascular disease (PVD), started in Europe in the 1970s and 1980s, respectively. Patients with ID are eligible for SCS when they experience disabling pain, resulting from ischaemia. This pain should be considered therapeutically refractory to standard treatment intended to decrease metabolic demand or following revascularization procedures. Several studies have demonstrated the beneficial effect of SCS on IHD and PVD by improving the quality of life of this group of severely disabled patients, without adversely influencing mortality and morbidity. SCS used as additional treatment for IHD reduces angina pectoris (AP) in its frequency and intensity, increases exercise capacity, and does not seem to mask the warning signs of a myocardial infarction. Besides the analgesic effect, different studies have demonstrated an anti-ischemic effect, as expressed by different cardiac indices such as exercise duration, ambulatory ECG recording, coronary flow measurements, and PET scans. SCS can be considered as an alternative to open heart bypass grafting (CABG) for patients at high risk from surgical procedures. Moreover, SCS appears to be more efficacious than transcutaneous electrical nerve stimulation (TENS). The SCS implantation technique is relatively simple: implanting an epidural electrode under local anesthesia (supervised by the anesthesist) with the tip at T1, covering the painful area with paraesthesia by external stimulation (pulse width 210, rate 85 Hz), and connecting this electrode to a subcutaneously implanted pulse generator. In PVD the pain may manifest itself at rest or during walking (claudication), disabling the patient severely. Most of the patients suffer from atherosclerotic critical limb ischemia. All patients should be therapeutically refractory (medication and revascularization) to become eligible for SCS. Ulcers on the extremities should be minimal. In PVD the same implantation technique is used as in IHD except that the tip of the electrode is positioned at T10-11. In PVD the majority of the patients show significant reduction in pain and more than half of the patients show improvement of circulatory indices, as shown by Doppler, thermography, and oximetry studies. Limb salvage studies show variable results depending on the stage of the trophic changes. The underlying mechanisms of action of SCS in PVD require further elucidation.

The Prevalence of Chronic Critical Lower Limb Ischaemia in a Population of 20,000 Subjects 40–69 Years of Age

OBJECTIVE

To study the prevalence and possible risk factors for chronic critical lower limb ischaemia (CLI) in an unselected population of 20,291 Norwegian men and women 40-69 years of age.

METHODS

Between 1995 and 1997, all residents 20 years or older in Nord-Trøndelag County, Norway, were invited to participate in a population study (the HUNT 2 Study). Among the 71.2% who attended, 20,291 participants 40-69 years of age responded to questions specifically aimed at identifying CLI. Chronic critical ischaemia was suspected if participants indicated: (1) ulcers on toes, foot or ankle that had failed to heal and/or; (2) persistent pain in the forefoot while in the supine position, but with relief of this pain when standing up. Using logistic regression analyses, we estimated the association between the prevalence of CLI and smoking, diabetes mellitus, previous cardiovascular events, blood lipids and glucose levels, and body mass index (BMI).

RESULTS

The age-adjusted prevalence of CLI was 0.26% among men and 0.24% among women, and there was no gender difference in any age group (age-adjusted OR = 0.91, 95% CI = 0.52-1.58). The presence of increased age, diabetes mellitus, angina pectoris, high triglyceride levels, and high BMI were all independently associated with higher prevalence of CLI.

CONCLUSION

The prevalence of CLI was 0.24%, similar for both genders, and increased with age. Risk factors usually seen in atherosclerotic patients were associated with suspected CLI.

Get the LEAD Out

Lower extremity arterial disease affects approximately one third of individuals 66 years of age and older and has a high risk for nonhealing wounds, infection, and limb loss. Much wound care is given by or under the direction of nurses. Therefore, the assessment and management of these patients presents many opportunities and challenges. Assessment is the cornerstone of effective care, but traditional methods of lower extremity arterial assessment, such as pulse palpation and pain history, are insufficient to determine the presence and extent of ischemia. Recently published national guidelines for assessment and management of patients with lower extremity wounds have recommended using noninvasive tests such as the ankle brachial index and toe brachial index to rule out lower extremity arterial disease, which complicates wound healing. However, the ankle brachial index can be falsely elevated in patients with diabetes and renal failure because of calcification of the arteries, which causes them to be incompressible. In these situations, it has been advised to obtain a toe pressure or toe brachial index because digital arteries are usually less affected by calcification. There is a paucity of data about the knowledge of principles and performance of the ankle brachial index/toe brachial index by nurses, particularly in the United States, using pocket-sized portable Doppler equipment. Therefore, the purpose of this article is to provide an overview and synthesis of relevant studies and published expert opinion regarding noninvasive arterial assessment using ankle brachial and toe brachial indexes as a basis for developing protocols for performing the tests and identifying gaps in research where further investigation is needed.

The value of toe pulse waves in determination of risks for limb amputation and death in patients with peripheral arterial disease and skin ulcers or gangrene

OBJECTIVES

The purpose of this study was to determine whether the presence of low amplitude of pulse waves recorded from the toes is related to the risk of subsequent amputation and death in patients with skin ulcers or gangrene and peripheral arterial disease, and how the risk of low wave amplitude relates to the risk associated with low peripheral pressures.

METHODS

A total of 309 patients with 346 limbs with skin lesions and arterial disease referred to the vascular laboratory were followed up for an average of 5 years (range, 1-8 years). Measurements were carried out to obtain ankle and toe pressures, pressure indices, and toe pulse wave amplitude. These variables were related to the risks of major amputation and total and cardiovascular death by means of the Cox proportional hazards model.

RESULTS

Low toe pulse wave amplitude (< or = 4 mm) was associated with increased risk of amputation (relative risks 4.20 in all limbs and 2.63 in those with toe pressure < or = 30 mm Hg; P <.01). Wave amplitude remained significantly associated with increased risk of amputation after controlling for each pressure variable (P <.01). Low pulse wave amplitude and toe/brachial index were associated with increased risks of both total and cardiovascular death in all patients (relative risks ranged from 1.43-1.73; P <.05) and in those with toe pressure of 30 mm Hg or less (relative risks 1.56-1.90; P <.05).

CONCLUSIONS

Low toe pulse wave amplitude is related significantly to increased risks of amputation and death in patients with skin lesions and arterial disease. The presence of low wave amplitude provides significant information in addition to peripheral pressures with respect to the risk of amputation.

Skin perfusion pressure of the foot is a good substitute for toe pressure in the assessment of limb ischemia

PURPOSE

Noninvasive measurements of limb systolic pressures are used routinely in the assessment of the severity of peripheral arterial disease, including the evaluation for critical limb ischemia. However, ankle pressures cannot be measured reliably in patients with medial calcification, which is especially common among patients with diabetes. Skin lesions on the toes or previous digital amputations may preclude the measurement of toe pressures. Measurements of skin perfusion pressure (SPP) are not subject to such limitations and were shown to be useful in the assessment of the severity of peripheral arterial disease. Because toe pressure is often used in the evaluation of severity of arterial disease and in the assessment for critical ischemia, we undertook to study whether there is a sufficient correlation between toe pressure and foot SPP that would allow the use of SPP measurements when toe pressures cannot be measured.

METHODS

Measurements were carried out in 85 limbs of 71 patients referred to the vascular laboratory for evaluation for peripheral arterial disease. Diabetes mellitus was present in 43 patients. Each patient had foot SPP and toe pressure measurements. Toe pressures measured with photoplethysmography were correlated with foot SPP measured with laser Doppler scanning.

RESULTS

There was a strong linear correlation between SPP and toe pressure (r = 0.87; P <.01). Also, significant correlation was found in both the patients with diabetes and the patients without diabetes (r = 0.85 and 0.93, respectively; P <.01 in both cases).

CONCLUSIONS

We concluded that SPP measured in the foot correlates well with toe pressure and can be substituted for toe pressure measurement in patients in whom toe pressures cannot be measured.