Electromyographic evaluation of malignant hyperthermia-susceptible pigs

Electromyography, with the aid of telemetry, was used to examine muscles of 4 young and 4 adult pigs from a genetic line highly susceptible to malignant hyperthermia (MH) and 4 young pigs (controls) from a line with no history of susceptibility to MH. In the young pigs, the intercostales, vastus lateralis, triceps brachii, biceps femoris, and gastrocnemius muscles were examined, whereas in the adult pigs only the latter 3 were examined. Spontaneous electrical activity, such as fibrillation potentials and abnormal insertion activity, was not observed in the electromyograms, indicating that neither denervation nor muscle membrane hyperirritability was associated with MH susceptibility in these pigs. Amplitude and duration of motor unit potentials (MUP) in the young MH-susceptible (MHS) pigs were significantly larger (P less than 0.01) and longer (P less than 0.05), respectively, than these values for MUP in the control pigs. These changes are opposite in direction to those expected in a myopathy. The mean values (+/- SD) for amplitude and duration for all muscles were 300 +/- 160 microV and 3.2 +/- 0.7 ms, respectively, in the control pigs and 555 +/- microV and 3.6 +/- 0.3 ms, respectively, in the young MHS pigs. Mean values for amplitude and duration of MUP for the adult MHS pigs were larger than were those for the young MHS pigs, but the differences were not significant (P greater than 0.05).