DETECTION OF SKELETAL-MUSCLE FATIGUE IN PATIENTS WITH HEART-FAILURE USING ELECTROMYOGRAPHY

Patients with heart failure frequently report that leg fatigue limits maximal exercise capacity. However, objective documentation of muscle fatigue has not been obtained in such patients. In normal subjects, muscle fatigue during constant work load exercise is associated with an increase in electrical activity generated per contraction due to use of additional muscle fibers to compensate for fiber fatigue. The present study was performed to determine if this approach can be used to document muscle fatigue in patients with heart failure. Vastus lateralis surface electromyograms were monitored in 8 ambulatory patients with nonedematous heart failure and 6 normal subjects during maximal bicycle exercise (20 W increments every 2 minutes). The electromyogram was stored on tape and subsequently analyzed for integrated root-mean-square voltage/contraction (iRMSV). At each work load, the iRMSV of the first and last 30 seconds of the work load were compared. The maximal work load achieved by patients with heart failure was significantly lower (73 +/- 22 W) than that by normal subjects (150 +/- 15 W; p <0.01). Both groups had no significant difference between the initial and final iRMSV at submaximal work loads. However, during the 2 highest work loads, both groups reported leg fatigue and had significant increases in iRMSV, consistent with muscle fiber fatigue (maximal work load: 259 +/- 59 to 279 +/- 58 mv . ms [normals] vs 258 =/- 94 to 283 +/- 93 mv . ms [heart failure]; p <0.03). The data indicate that the surface electromyogram can be used to detect skeletal muscle fatigue in patients with heart failure. This approach provides an objective method of assessing exertional fatigue in such patients and may be useful for assessing the efficacy of therapeutic interventions.