Defibrillation During Mechanical Chest Compressions Should Be Avoided During The Downstroke Phase Of The Chest Compression Cycle

Introduction: CPR guidelines emphasize minimizing pre-shock chest compression (cc) pauses. Animal studies indicate higher shock success rates for shocks delivered during the upstroke phase of the cc cycle. In the Circulation Improving Resuscitation Care (CIRC) trial, providers delivered shocks during mechanical cc with Load Distributing Band (LDB). This is the first clinical study investigating shock success related to different cc cycle phases. Methods: Patients who received LDB cc were included. The first and up to three shocks were studied separately for initial shockable rhythms. Electronic defibrillator data with transthoracic impedance were used to determine when in the cc cycle (downstroke, upstroke, decompressed) a shock was delivered, and to identify control group cases with a pre-shock cc pause. Shock success was defined as termination of fibrillation/pulseless VT five seconds post-shock (TOF) and return of organized rhythm 60 seconds post-shock (ROOR). TOF and ROOR were compared between the different LDB cc cycle phases and the control group using Chi-Square tests. P Results: Of 1130 shocks during LDB cc, 164 could not be categorized to the different cc phases and were excluded. TOF was lower in the downstroke phase for all shocks and initial rhythms, and for shockable initial rhythms first up to three shocks, compared with the control group. There were no significant TOF differences for other cc phases. ROOR was independent of where in the LDB cc cycle the shock hit, irrespective of initial rhythm. Conclusion: Defibrillation attempts should be avoided during the downstroke phase of the continuous LDB cc cycle. Shocks during continuous LDB cc do not increase shock success compared to pre-shock LDB cc pause prior to shock.