The RAMER Reviews: Initial Defibrillator Pad Position and Outcomes for Shockable Out-of-Hospital Cardiac Arrest
Written By David Poloway, DO; Edited by Timothy Khowong, MD, MSEd
Background:
Out of hospital cardiac arrest (OHCA) is a leading cause of mortality. In the emergency department, we often receive patients in the middle of a resuscitation from OHCA. Patients who are in shockable rhythms either have ventricular fibrillation or pulseless ventricular tachycardia. The optimal pad positioning for defibrillators has been discussed before in many studies, with differing guidelines being published from organizations such as the European Resuscitation Council and the American Heart Association. This paper aims to determine the association between initial defibrillator pad placement and outcomes in patients with shockable rhythms during OHCA.
The Study:
The study was designed as a prospective cohort study which analyzed data from 255 patients with shockable OHCA rhythms (VF or pVT) treated by a single emergency medical service (EMS) agency between July 2019 and June 2023. Patients were categorized based on initial pad placement for the defibrillator: AP (158 patients) or AL (97 patients). The primary outcome was return of spontaneous circulation (ROSC) at any time, while secondary outcomes included pulses present at emergency department arrival, survival to hospital admission, and functional survival at discharge.
Results indicated that patients who were initially defibrillated with AP pad placement had a 2.64 times greater odds of achieving ROSC compared to those with AL pad placement, suggesting that AP may be superior to AL as initial pad positioning. While there was a significant difference in the primary outcome, there was no significant difference in any of the secondary outcomes such as survival rate or neurological function at discharge.
Discussion:
These results show that AP pad placement could be superior to AL pad placement in OHCA patients in pVT or VF. Now, this study was done in an out-of-hospital setting, so may not be clinically significant for physicians who practice within the hospital setting. When it comes to the actual study, some limitations/biases could be affecting the study and its outcome. Pad placement was left to the discretion of individual EMS crews, the authors admitted the study was underpowered, and the study was done with one single EMS company. They also used EMS-estimated weights to stratify patients as opposed to hospital measured weights which may add bias. Additionally, their definition of ROSC was at the discretion of EMS which may provide confounders as this is typically measured by palpation of a pulse which we know has its limitations as manual palpation has been shown to not be reliable (especially in obese patients).
We often run codes in the ED. Our normal habit is to place AP pads which based on this study is valid. Given that in-hospital cardiac arrest typically has better outcomes than OHCA, one would assume that AP placement would also lead to higher rates of ROSC in the ED as well. Using what we know about anatomy and physiology, one would venture to guess that the higher rates of ROSC are likely secondary to a higher amount of electrical vector going through the heart itself.
The common quote “the definition of insanity is doing the same thing over and over again expecting different results” rings true here. If ROSC has not been achieved after multiple shocks, this study should serve as another reminder to consider changing pad placement in order to change or enhance the electrical vector through the heart.
References:
Lupton JR, Newgard CD, Dennis D, et al. Initial Defibrillator Pad Position and Outcomes for Shockable Out-of-Hospital Cardiac Arrest. JAMA Netw Open. 2024;7(9):e2431673. doi:10.1001/jamanetworkopen.2024.31673