e406 Article Type Correspondence To the Editor: We read with interest the opposite viewpoints of McDermott et al 1 and Hiatt et al 2 about the best functional test for measuring response to interventions in peripheral artery disease (PAD). Community-based global positioning system (GPS) measurement has been recently proposed to assess outdoor walking capacity in PAD patients, that is, under conditions expected to be closer to real life. 3–5 Although an emerging approach, GPS assessment provides some interesting insights, adding arguments to the aforementioned controversies. In their articles, authors present evidence to determine whether the 6-minute walk test (6MWT) or the treadmill walking test (TWT) is a better surrogate of real-life daily walking or daily ambulatory activity. 1,2 As a theoretical prerequisite, it is fundamental to under- line that walking capacity is conceptually different from physi- cal activity. Thus, measuring walking capacity does not imply that we are measuring a surrogate of (daily) physical activity and vice versa. Considering that an optimal functional test should directly correlate with patient-reported physical limitations, a recent study showed that patient-reported measures of walking limitation tended to correlate better with a GPS assessment of the maximal walking distance (MWD) than they do with the 6MWT and a graded TWT. 3 Regarding the agreement between GPS assessment and both TWT and 6MWT, available studies reported that GPS maximal 5 or total 4 walking distance was correlated to both TWT (r=0.81, P<0.001) and 6MWT (r=0.78, P<0.001). Median GPS MWD was reported to be on average 4.1 times higher than MWD from TWT. 5 This is an average coefficient, but a wider discrepancy exists for some PAD patients, suggesting that TWT could importantly underestimate real-life out- door walking capacity. From the same study, median GPS MWD was on average 2.2 times higher than the 6MWT total walked distance. 5 Should we thus consider that the 6MWT is a better surrogate of real- life walking capacity? One main limitation of the 6MWT is that the test is limited to a relatively short total duration. Thus, this is expected to induce a ceiling effect that could potentially lead to an underesti- mation of the walking capacity in PAD patients with mild to moder- ate limitation. This probably explains why responses to intervention assessed with the 6MWT seem blunted compared with the TWT. In addition, because the testing procedure enables PAD patients to have different walking strategies when performing the 6MWT, not con- trolling (at least measuring) walking speed during the 6MWT could lead to a misinterpretation of the functional results on the sole basis of the total walking distance covered. By the way, some supposed asymptomatic PAD patients are in fact symptom limited during the 6MWT, whereas others are not. With the use of GPS, it has been shown that a large short-term walking capacity variability exists, and rest duration before walking bouts has been suggested to be a major determinant of this variability. Because patients are allowed to rest during the 6MWT, this could also influence the total distance walked. Futures studies should be conducted to compare the 6MWT, TWT, and community-based GPS procedure to determine the best func- tional outcome measure in PAD. Disclosures None. A. Le Faucheur, PhD Movement, Sport, and Health Laboratory University of Rennes 2 Rennes, France Department of Sport Sciences and Physical Education ENS Rennes Bruz, France INSERM Centre d’Investigation Clinique, CIC 1414 Rennes, France P.-Y. de Müllenheim, BSc Movement, Sport, and Health Laboratory University of Rennes 2 Rennes, France G. Mahé, MD, PhD INSERM Centre d’Investigation Clinique, CIC 1414 Rennes, France CHU Rennes Imagerie Coeur-Vaisseaux Rennes, France References 1. 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;130:61–68. doi: 10.1161/CIRCULATIONAHA.114.007002. 2. Hiatt WR, Rogers RK, Brass EP. The treadmill is a better functional test than the 6-minute walk test in therapeutic trials of patients with peripheral artery disease. Circulation. 2014;130:69–78. doi: 10.1161/ CIRCULATIONAHA.113.007003. 3. Tew G, Copeland R, Le Faucheur A, Gernigon M, Nawaz S, Abraham P. Feasibility and validity of self-reported walking capacity in patients with intermittent claudication. J Vasc Surg. 2013;57:1227–1234. doi: 10.1016/j. jvs.2012.02.073. 4. Nordanstig J, Broeren M, Hensäter M, Perlander A, Osterberg K, Jivegård L. Six-minute walk test closely correlates to “real-life” outdoor walking capacity and quality of life in patients with intermittent claudication. J Vasc Surg. 2014;60:404–409. doi: 10.1016/j.jvs.2014.03.003. 5. Le Faucheur A, Abraham P, Jaquinandi V, Bouyé P, Saumet JL, Noury- Desvaux B. Measurement of walking distance and speed in patients with peripheral arterial disease: a novel method using a global posi- tioning system. Circulation. 2008;117:897–904. doi: 10.1161/ CIRCULATIONAHA.107.725994. (Circulation. 2015;131:e406. DOI: 10.1161/CIRCULATIONAHA.114.012389.) © 2015 American Heart Association, Inc. Circulation is available at http://circ.ahajournals.org DOI: 10.1161/CIRCULATIONAHA.114.012389 Letter by Le Faucheur et al Regarding Articles, “Six-Minute Walk Is a Better Outcome Measure Than Treadmill Walking Tests in Therapeutic Trials of Patients With Peripheral Artery Disease” and “The Treadmill Is a Better Functional Test Than the 6-Minute Walk Test in Therapeutic Trials of Patients With Peripheral Artery Disease” by guest on July 19, 2018 http://circ.ahajournals.org/ Downloaded from