Walking exercise is the most effective non-invasive therapy for improving maximal and pain free walking distances in people with lower extremity peripheral artery disease (PAD).^1-3 While both home-based and supervised treadmill walking exercise have been shown to improve pain-free and maximal walking distance in PAD,^3-5 most randomized trials of walking exercise in patients with PAD have studied supervised treadmill exercise.

A meta-analysis by Fakhry et al. summarized 25 randomized clinical trials of supervised walking therapy (including 19 of supervised treadmill exercise) for patients with PAD and intermittent claudication.⁵ The meta-analysis included 1,054 patients with PAD and intermittent claudication symptoms who were randomized to either supervised walking exercise or a control group without exercise.⁵ Seventy-six percent of participants were male and mean age was 66.6 + 7.0 years. Most of the trials ranged from 12 to 26 weeks' duration. The meta-analysis results showed that supervised exercise significantly improved maximal treadmill walking distance by 180 meters and pain-free walking distance by 128 meters, relative to the control group.⁵ Of the 21 trials that reported absolute data for change in maximal treadmill walking distance, 15 (71%) reported more than 50% improvement and five (21%) reported more than 100% improvement in maximal treadmill walking distance. Among the control groups, only one (5%) reported more than 50% improvement and none reported more than 100% improvement in maximal treadmill walking distance. In comparison, cilostazol, the only FDA approved medication for treating intermittent claudication symptoms that is currently recommended by clinical practice guidelines, provides approximately 25-40% improvement in treadmill walking distance.¹

When compared directly with endovascular revascularization, supervised treadmill exercise either had greater benefit or was not significantly different from endovascular revascularization for improving maximal treadmill walking distance in patients with PAD.^6,7 For example, the CLEVER (Claudication: Exercise Versus Endoluminal Revascularization) trial was a multi-center trial conducted in the United States that randomized 111 PAD patients with aortoiliac disease and claudication to six-months of either supervised treadmill exercise, aortoiliac stenting, or a control group.⁶ At 6-month follow-up, supervised exercise and the endovascular intervention each significantly improved the primary outcome of maximal treadmill walking time, compared to the control group (+5.8+4.6, +3.7+4.9, and +1.2+2.6 for the supervised exercise, endovascular revascularization, and control groups, respectively). At 6-month follow-up, maximal treadmill walking distance improved more in the supervised treadmill exercise group than in the endovascular intervention group, while most of the patients reported measures of walking ability and quality of life improved more in the endovascular intervention group than in the supervised exercise group.⁶

Until recently, a significant barrier to PAD patients' participation in supervised treadmill exercise programs was lack of medical insurance coverage for this therapy. However, beginning in 2017, the Center for Medicare and Medicaid Services (CMS) provides coverage for supervised treadmill exercise therapy for PAD patients with ischemic leg symptoms. This newly available reimbursement improves access to supervised treadmill therapy and is expected to increase participation in supervised treadmill exercise programs by patients with PAD. Clinicians should be prepared to refer patients with PAD for supervised treadmill exercise and should be familiar with characteristics of effective exercise programs. Clinicians should also be familiar with CMS policies regarding coverage of supervised treadmill exercise for patients with PAD.

The Center for Medicare and Medicaid Services will provide coverage for symptomatic PAD that consists of three exercise sessions per week with 30-60 minutes of exercise per session. The program must be prescribed by a physician after a face-to-face meeting with the patient in which the physician counsels the patient regarding cardiovascular disease prevention and PAD risk factor reduction. This counseling could include education, counseling, behavioral interventions, or risk factor reduction. The exercise program proposed for coverage by CMS must be located in an outpatient hospital setting and delivered by qualified personnel trained in basic and advanced life support and in exercise therapy for PAD. The exercise program must be supervised by a physician, physician's assistant, or a nurse practitioner/clinical nurse specialist trained in basic and advanced life support methods. CS provides coverage for 36 exercise sessions over 12 weeks. An additional 36 sessions may be requested by the referring physician and carried out over an extended period of time.

Clinicians should also be familiar with characteristics of successful supervised exercise programs. For example, supervised exercise programs should be individualized. Most patients with PAD begin with 10-15 minutes of walking exercise per session. Exercise duration should be increased by approximately five minutes each week until the patient achieves approximately 50 minutes of exercise per session. However, not all patients with PAD will be able to achieve 50 minutes of walking exercise per session. Patients should expect to alternate short periods of walking exercise with short periods of rest. When the patient experiences significant ischemic leg symptoms, they should rest until these symptoms resolve or nearly resolve.

Clinicians and patients with PAD should also be aware of the following characteristics of successful supervised treadmill exercise programs. First, ischemic leg symptoms improve gradually. Patients typically experience improvement in walking ability 4-6 weeks after beginning an exercise program, and peak benefit is typically observed 12 to 26 weeks after initiating the exercise program. Second, benefit requires persistent adherence to exercise sessions three times per week. Third, evidence is unclear regarding whether walking to maximal ischemic leg discomfort during exercise is more beneficial than walking to the onset of ischemic leg discomfort during exercise. The meta-analysis by Fakhry et al. concluded that there was no difference in the magnitude of improvement in treadmill walking distance between trials in which participants with PAD walked to maximal ischemic leg symptoms during exercise versus those in which they walked to the onset of ischemic leg symptoms.⁵ However, no adequately powered randomized trials have compared exercise programs in which patients were asked to exercise to maximal ischemic leg pain versus those in which they were asked to exercise to the onset of ischemic leg pain. An ongoing randomized clinical trial (Low InTensity Exercise Intervention in PAD [LITE], NCT02538900) will determine whether low intensity versus high intensity walking exercise is more beneficial for patients with PAD.

Supervised treadmill exercise programs for patients with PAD are generally safe. Because of the common presence of co-existent coronary artery disease in patients with PAD, an exercise treadmill stress test should be performed prior to beginning a new exercise program. Despite the benefit of supervised exercise for ischemic leg symptoms, there is no evidence from randomized clinical trials that supervised treadmill exercise reduces mortality in patients with PAD.

Additional factors regarding supervised treadmill exercise should be considered. First, few studies have assessed the durability of benefit from supervised treadmill exercise. The CLEVER trial reported that 12 months after a six-month supervised exercise intervention was completed, participants randomized to supervised exercise continued to have better maximal treadmill walking time than the control group that received optimal medical care without exercise (+5.0 minutes +5.4 for supervised exercise vs. +0.20 minutes+2.1 for the control group). However, supervised exercise was not better than endovascular intervention at 18-month follow-up,⁸ though these results were limited by the fact that only 79 of 111 participants (71%) completed 18-month follow-up testing. A separate study of 63 patients with PAD who participated in a 12-week supervised exercise program reported that 12 weeks after the supervised exercise program was completed, only 15/63 (24%) continued to exercise. Patients who complete a supervised treadmill exercise program should be encouraged to continue walking exercise at home after the supervised exercise is completed.

Second, supervised treadmill exercise should be offered in conjunction with lower extremity revascularization. Consistent clinical trial evidence demonstrates that patients who participate in supervised treadmill exercise combined with a revascularization procedure achieve greater improvement in treadmill walking than those who had either individual therapy.^7,9

Third, many patients with PAD may elect not to participate in supervised treadmill exercise. In a report from 23 randomized trials of supervised exercise, 69% of 1,541 eligible PAD participants without critical limb ischemia refused participation in supervised exercise.¹⁰ Many refused due to the burden of traveling to an exercise center multiple times per week.¹⁰ For these patients, home-based walking exercise may be a reasonable alternative.

Fourth, results of randomized trials are inconsistent regarding their effect on physical activity in daily life for patients with PAD. The CLEVER trial reported no significant difference in physical activity in daily life for participants in the supervised exercise group compared to the control group or the endovascular revascularization group. Supervised treadmill exercise improves treadmill walking ability more than any other outcome,¹¹ and further work is needed to identify an exercise intervention that increases all aspects of functioning in daily life for patients with PAD, including physical activity and quality of life.

Supervised treadmill exercise is safe and significantly improves treadmill walking performance in patients with PAD. The recent decision by CMS to pay for supervised treadmill exercise for patients with symptomatic PAD should increase access to this safe and effective therapy for the large and growing number of people disabled by PAD.

Table 1: Characteristics of Center for Medicare and Medicaid Services Coverage for Supervised Exercise in Peripheral Artery Disease¹²

Components and Requirements of Supervised Exercise Programs for PAD Under CMS

Exercise must be prescribed by a physician after a face-to-face meeting with the patient that includes counseling on cardiovascular disease prevention. Prescribed exercise must consist of exercise sessions three times weekly for 12 weeks. An additional 36 sessions may be prescribed, with written justification, after the first 12 weeks are completed and may take place over a longer period of time. The exercise sessions must take place in a physician's office or outpatient hospital-affiliated setting. Exercise must be delivered by qualified personnel with training in basic and advance life support and exercise therapy for PAD. Exercise must be supervised by a physician, physician's assistant, or nurse practitioner/clinical nurse specialist.

References

1. Gerhard-Herman MD, Gornik HL, Barrett C, et al. 2016 AHA/ACC guideline on the management of patients with lower extremity peripheral artery disease: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. J Am Coll Cardiol 2017;69:1465-1508.
2. McDermott MM, Kibbe MR. Improving lower extremity functioning in peripheral artery disease: exercise, endovascular revascularization, or both? JAMA 2017;317:689-90.
3. Gardner AW, Parker DE, Montgomery PS, Blevins SM. Step-monitored home exercise improves ambulation, vascular function, and inflammation in symptomatic patients with peripheral artery disease: a randomized controlled trial. J Am Heart Assoc 2014;3:e001107.
4. McDermott MM, Liu K, Guralnik JM, et al. Home-based walking exercise intervention in peripheral artery disease: a randomized clinical trial. JAMA 2013;310:57-65.
5. Fakhry F, van de Luijtgaarden KM, Bax L, et al. Supervised walking therapy in patients with intermittent claudication. J Vasc Surg 2012;56:1132-42.
6. Murphy TP, Cutlip DE, Regensteiner JG, et al. Supervised exercise versus primary stenting for claudication resulting from aortoiliac peripheral artery disease: six-month outcomes from the claudication: exercise versus endoluminal revascularization (CLEVER) study. Circulation 2012;125:130-9.
7. Mazari FA, Khan JA, Carradice D, et al. Randomized clinical trial of percutaneous transluminal angioplasty, supervised exercise and combined treatment for intermittent claudication due to femoropopliteal arterial disease. Br J Surg 2012;99:39-48.
8. Murphy TP, Cutlip DE, Regensteiner JG, et al. Supervised exercise, stent revascularization, or medical therapy for claudication due to aortoiliac peripheral artery disease: the CLEVER study. J Am Coll Cardiol 2015;65:999-1009.
9. Fakhry F, Spronk S, van der Laan L, et al. Endovascular revascularization and supervised exercise for peripheral artery disease and intermittent claudication: a randomized clinical trial. JAMA 2015;314:1936-44.
10. Harwood AE, Smith GE, Cayton T, Broadbent E, Chetter IC. A systematic review of the uptake and adherence rates to supervised exercise programs in patients with intermittent claudication. Ann Vasc Surg 2016;34:280-9.
11. McDermott MM, Guralnik JM, Criqui MH, Liu K, Kibbe MR, Ferrucci L. Six-minute walk is a better outcome measure than treadmill walking tests in therapeutic trials of patients with peripheral artery disease. Circulation 2014;130:61-8.
12. Centers for Medicare and Medicaid Services. Decision memo for supervised exercise therapy (SET) for symptomatic peripheral artery disease (PAD). Accessed 30 June 2017. https://www.cms.gov/medicare-coverage-database/details/nca-decision-memo.aspx?NCAId=287.

Keywords: Intermittent Claudication, Walking, Exercise Test, Coronary Artery Disease, Risk Factors, Peripheral Arterial Disease, Exercise Therapy, Aneurysm

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