Individual differences in fear-potentiated startle as a function of resting heart rate variability: implications for panic disorder.

BACKGROUND Anticipatory anxiety, which can be indexed by the startle potentiation to a threat of shock, has been implicated in the development of panic disorder. Large individual differences exist in startle potentiation to threat of shock but few differences have been found between panic patients in general and non-anxious controls. The present studies explored resting heart rate variability (HRV) as a source of individual differences in startle potentiation in students at risk for panic disorder and in unmedicated panic patients. METHODS Participants in Study 1 were 22 students high and 21 students low in anxiety sensitivity (AS). Nine unmedicated panic patients and 15 matched non-anxious controls were included in Study 2. Startle potentiation to the threat of shock was examined as a function of AS (Study 1) and diagnostic category (Study 2) as well as resting HRV. RESULTS Whereas no differences in startle potentiation were found as a function of AS or panic disorder diagnosis in general, both studies revealed that low resting HRV was associated with exaggerated startle responses to the threat of shock. CONCLUSIONS The present results replicate and extend the sparse literature on fear-potentiated startle in panic disorder. Low HRV was associated with more pronounced startle potentiation to both explicit and contextual cues. Thus, low HRV may be a useful endophenotype for at least some anxiety disorders.