Authors: Singh DP et al.
Anesthesiology. December 2025.
Summary
This exploratory validation study evaluated a novel diagnostic technique for malignant hyperthermia (MH) susceptibility based on direct measurement of calcium release dynamics in single skeletal muscle fibers. The current gold standard for MH diagnosis, the in-vitro contracture test (IVCT), is invasive, resource-intensive, and limited to specialized centers. The authors investigated whether a single-fiber Ca²⁺ wave frequency assay (CaWFa) could provide a reliable, more physiologically targeted alternative.
Muscle samples obtained during routine IVCT biopsies from 30 patients were used to isolate mechanically skinned single muscle fibers. Using calcium-dependent fluorescence and confocal microscopy, the investigators assessed ryanodine receptor (RyR1) sensitivity by exposing fibers to graded concentrations of halothane and caffeine. The generation and frequency of regenerative intracellular Ca²⁺ waves were quantified and compared with IVCT classification as MH-susceptible (MHS) or MH-negative (MHN).
Muscle fibers from MHS patients demonstrated a markedly higher proportion of regenerative Ca²⁺ wave responses when exposed to halothane compared with MHN fibers. Wave frequency was consistently higher in MHS fibers across all halothane concentrations tested, indicating heightened RyR1 sensitivity. In contrast, caffeine exposure did not discriminate between MHS and MHN fibers with respect to wave onset or frequency. Using a diagnostic threshold combining halothane concentration and Ca²⁺ wave frequency, the CaWFa achieved high sensitivity and specificity, comparable to IVCT performance.
These findings suggest that CaWFa directly interrogates the pathophysiologic mechanism underlying MH—abnormal RyR1-mediated calcium release—rather than relying on secondary contractile responses. The authors propose that CaWFa may represent a promising, less invasive alternative to IVCT for MH diagnosis, pending further validation in larger cohorts.
Key Points
The Ca²⁺ wave frequency assay directly measures RyR1-mediated calcium release in single muscle fibers.
Halothane-induced Ca²⁺ wave frequency reliably distinguished MH-susceptible from MH-negative muscle.
Caffeine exposure did not discriminate between MH phenotypes in this assay.
CaWFa demonstrated diagnostic sensitivity and specificity comparable to the IVCT.
This technique shows potential as a less invasive, mechanism-based diagnostic tool for MH susceptibility.
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