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Introduction: AHA guidelines emphasize the importance of limiting pauses during CPR to less than 10 seconds due to the association of interruptions in chest compressions (CC) with adverse outcomes. Previous literature has associated shorter peri-shock pause times with greater odds of survival and longest pause in CC with lower odds of survival, though these analyses were restricted to patients with initial shockable rhythm. The aim of this analysis is to investigate the association between CC pause duration and patient outcomes in all-rhythm OHCA. Methods: OHCA cases from three EMS Agencies in Arizona between Jan 2016-Dec 2016 (n=229) were analyzed. De-identified prehospital patient data were linked to outcome data as part of the state quality program. Pauses calculated from CPR pad accelerometer data were defined by a minimum duration of 1000 ms. Mean pause duration was calculated by case as the average of all pauses, while longest pause duration was defined as the single longest pause in CC. Descriptive statistics and multivariate logistic regression was performed in STATA 15.1. Primary outcome measures defined were ROSC, survival-to-discharge, and favorable neurological outcome (Cerebral Performance Category 1 or 2). Covariates included in the statistical model include time in CPR, age, witnessed arrest, initial shockable rhythm, bystander CPR, and CPR quality. Results: A total of 37.1% of patients (n=85) achieved prehospital ROSC, 12.7% (n=29) survived, and 10.5% (n=24) had favorable neurological outcome. Average mean and longest pause duration was 8.13 + 0.76 s and 24.93 + 2.84 in survivors with favorable neurological outcome compared to 9.21 + 0.47 s and 35.56 + 3.55 s in non-survivors. Mean pause duration was associated with survival (adjusted OR 0.89, 95% CI 0.80-0.99) and favorable neurological outcome (adjusted OR 0.83, 95% CI 0.72-0.97). Longest pause duration was associated with favorable neurological outcome (adjusted OR 0.97, 95% CI 0.94-1.00). Conclusions: Prolonged pauses in CC during prehospital resuscitation was associated with worse survival and neurological function in OHCA patients with all cardiac rhythms. Pause duration should be kept as brief as possible due to the impact upon outcomes regardless of presenting cardiac rhythm.

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Introduction: Pseudo electro-mechanical dissociation (P-EMD) is a cardiac arrest variant characterized by a life-threatening reduction in cardiac output in the presence of organized electrical activity. Synchronization of chest compressions to the R-wave in the ECG may be preferable to the delivery of standard CPR. However, in the bradycardic P-EMD state, synchronization may result in inadequate blood flow due to the low compression/heart rate. This pilot study examined the hemodynamic effect of interposing additional chest compressions between synchronized chest compressions during bradycardic P-EMD to increase the compression rate. Methods: P-EMD was induced via hypoxia in three female swine (~30 kg) and treated with synchronized compressions until the onset of asystole (HR<12 BPM). Interposed compressions were added when the heart rate fell below 60 BPM. A chest compression was classified as synchronized or interposed depending on the presence or absence of a co-incident R-wave. Hemodynamic parameters were integrated or averaged over each compression interval. Results: Synchronized compressions tended to produce larger aortic pressures, larger carotid blood flows, and lower right atrial pressures than interposed compressions. Data from one experiment are shown in Figure 1. The relative hemodynamic benefit of a synchronized chest compression appears to depend on the effectiveness of the underlying heart contraction. The interposed chest compressions generated forward carotid blood flow and increased the compression rate during bradycardia. Discussion: During bradycardic P-EMD, synchronized compressions may generate better hemodynamics than interposed compressions, and the combination of synchronized and interposed compressions may result in more blood flow than the delivery of synchronized compressions alone. Figure 1. Comparison of hemodynamics generated by synchronized compressions (blue) and interposed compressions (red).