• Sara J Thompson, Sheila Riazi, Natalia Kraeva, Michael D Noseworthy, Tammy E Rayner, Jane E Schneiderman, Barbara Cifra, and Greg D Wells.
• From the *Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Ontario, Canada; †Malignant Hyperthermia Investigation Unit, Toronto General Hospital, Toronto, Ontario, Canada; ‡Department of Anesthesia, University of Toronto, Toronto, Ontario, Canada; §Department of Electrical and Computer Engineering, School of Biomedical Engineering, McMaster University, Hamilton, Ontario, Canada; ‖Department of Diagnostic Imaging, the Hospital for Sick Children, Toronto, Ontario, Canada; ¶Physiology and Experimental Medicine, the Hospital for Sick Children, Toronto, Ontario, Canada; and #Division of Cardiology, the Labatt Family Heart Centre, the Hospital for Sick Children, Toronto, Ontario, Canada.
• Anesth. Analg. 2017 Aug 1; 125 (2): 434441434-441.

BackgroundMalignant hyperthermia (MH), a pharmacogenetic disorder of skeletal muscle, presents with a potentially lethal hypermetabolic reaction to certain anesthetics. However, some MH-susceptible patients experience muscle weakness, fatigue, and exercise intolerance in the absence of anesthetic triggers. The objective of this exploratory study was to elucidate the pathophysiology of exercise intolerance in patients tested positive for MH with the caffeine-halothane contracture test. To this end, we used phosphorus magnetic resonance spectroscopy, blood oxygen level-dependent functional magnetic resonance imaging (MRI), and traditional exercise testing to compare skeletal muscle metabolism in MH-positive patients and healthy controls.MethodsSkeletal muscle metabolism was assessed using phosphorus magnetic resonance spectroscopy and blood oxygen level-dependent functional MRI in 29 MH-positive patients and 20 healthy controls. Traditional measures of physical capacity were employed to measure aerobic capacity, anaerobic capacity, and muscle strength.ResultsDuring 30- and 60-second exercise, MH-positive patients had significantly lower ATP production via the oxidative pathway compared to healthy controls. MH-positive patients also had a longer recovery time with blood oxygen level-dependent functional MRI compared to healthy controls. Exercise testing revealed lower aerobic and anaerobic capacity in MH-positive patients compared to healthy controls.ConclusionsResults of this exploratory study suggest that MH-positive patients have impaired aerobic metabolism compared to healthy individuals. This could explain the exercise intolerance exhibited in MH-susceptible patient population.

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