Introduction: Quantitative waveform measures are a surrogate of the acute physiological status of the myocardium and predict survival following ventricular fibrillation out-of-hospital cardiac arrest (OHCA). We investigated whether the amplitude spectrum area (AMSA) waveform measure mediates the adverse relationship between increasing burden of chronic health conditions and lower likelihood of survival.
Methods: We performed a cohort investigation of persons > = 18 years who suffered ventricular fibrillation OHCA between 2008-2015 in a metropolitan emergency medical service (EMS) system. The count of chronic health conditions was determined using the Charlson Comorbidity Index (CCI). AMSA was calculated just prior to the initial shock. We used multivariable logistic regression to assess the relationship between CCI and survival-to-discharge in models first without and then with AMSA to determine the extent to which AMSA attenuated the CCI-survival association.
Results: Of the 716 eligible patients, 422/716 (59%) had at least one chronic health condition; 21.8% with one, 19.6% with two, 10.3% with 3, and 7.3% with ≥4. Survival-to-discharge was 45% (324/716). In the multivariable model adjusted for traditional Utstein characteristics, increasing CCI was associated with lower odds of survival (Odds ratio (OR) (95% confidence interval] = 0.82 [0.72, 0.93] for each additional chronic health condition). The addition of AMSA to the model only modestly attenuated the CCI-survival association (OR = 0.85 [0.74,0.98]).
Conclusion: The waveform measure AMSA - a surrogate for the physiological status of the myocardium - mediated only a modest portion of the association between increasing burden of chronic health conditions and lower likelihood of survival following ventricular fibrillation OHCA.
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