Uncovering phantom shocks in cardiac patients with an implantable cardioverter defibrillator

Background Implantable cardioverter defibrillator recipients sometimes report "phantom shocks" (PSs), defined as a reported shock lacking objective evidence. The aim of this study was to describe the subjective experience of PSs and their psychosocial correlates using a mixed methods approach. Methods PS participants were matched on sex and age with individuals who received objective shocks only (OSO). Participants were interviewed and completed measures of posttraumatic stress disorder (PTSD Checklist - Civilian Version), depression and anxiety (Hospital Anxiety and Depression Scale), disease-specific distress (Cardiac Anxiety Questionnaire - CAQ), and social desirability (Socially Desirable Response Set - SDRS). Interviews were analyzed using interpretative phenomenological analysis (IPA). Results Seventeen male patients participated (PS: n = 9; OSO: n = 8). Three themes emerged from IPA: (1) PS as a somatic experience, (2) the emotional impact of PSs, and (3) searching for meaning. Quantitative analyses showed that both groups exhibited elevated trauma and anxiety levels. Effect size differences (ESD) suggested a medium ESD on depression (P = 0.176, η_p² = 0.118) and PTSD (avoidance: P = 0.383, η_p² = 0.055, numbing: P = 0.311, η_p² = 0.068), and a large ESD on SDRS (P = 0.081, η_p² = 0.189), where PS participants, comparatively, exhibited elevated levels. A medium ESD was detected on CAQ-fear (P = 0.237, η_p² = 0.092) where OSO participants exhibited greater heart-focused worry. Conclusion The qualitative and quantitative findings of this mixed method study show convergence in terms of the emotional factors associated with the experience of PSs. PSs are often reported to be indistinguishable from objective shocks, evoking alarm, frustration, and confusion, forcing the individual to face the uncertainties of what to them is a novel and confusing experience.