Similar susceptibility to halothane, caffeine and ryanodine in vitro reflects pharmacogenetic variability of malignant hyperthermia.

BACKGROUND AND

OBJECTIVE

To analyse the use of standardized application of ryanodine for in vitro muscle contracture testing to define cut-off values separating malignant hyperthermia susceptible from malignant hyperthermia negative subjects. Furthermore, we compared the results of in vitro muscle-contracture tests following the halothane, caffeine and ryanodine challenges.

METHODS

In 113 subjects, halothane, caffeine and ryanodine muscle-contracture tests were performed according to the protocol of the European Malignant Hyperthermia Group.

RESULTS

Malignant hyperthermia susceptible subjects (n = 77) had significantly shorter onset times in the ryanodine in vitro muscle-contracture test (1 micromol ryanodine) compared with malignant hyperthermia negative subjects (n = 36), median 4.8 vs. 20.1 min, respectively, without any influence of age or gender. The best cut-off value was 10 min (sensitivity 0.78 and specificity 0.94, respectively). Shorter cut-off values had greater specificity, but lower sensitivity. Groups could not be separated without an overlap. In susceptible subjects, we found a correlation between onset time and threshold concentrations for halothane and caffeine (p = 0.47 and 0.52, respectively). In addition, muscle bundles with high susceptibility to halothane and caffeine also showed high susceptibility to ryanodine.

CONCLUSIONS

The ryanodine in vitro muscle-contracture test confirmed the malignant hyperthermia status that was determined using the halothane and caffeine in vitro muscle-contracture tests. Due to an overlap between the two groups, discrimination ability was not always perfect and short cut-off values with higher specificity had reduced sensitivity and vice versa. The correlation of contractures following the halothane, caffeine and ryanodine challenges points towards a similar individual pharmacogenetic effect rather than a specific, different pharmacological action between the three agents.