CLINICIAN'S CAPSULE
What is known about the topic?
Shorter time to initial defibrillation in patients with ventricular fibrillation/tachycardia arrests increases favourable neurologic survival.
What did the study ask?
Does routine application of defibrillation pads in prehospital ST-elevation myocardial infarction (STEMI) patients decrease time to initial defibrillation in out-of-hospital cardiac arrest?
What did the study find?
Mean time to initial defibrillation was 17.7 seconds in the “pads-on protocol,” compared with 72.7 seconds in routine care.
Why does this study matter to clinicians?
Routinely applying defibrillation pads to STEMI patients decreases time to initial defibrillation, which has been found to increase survival in out-of-hospital cardiac arrest.
INTRODUCTION
Annually, there are approximately 400,000 out-of-hospital cardiac arrests (OHCA) in North America, with an average survival rate of 10%–12%.Reference Benjamin, Muntner and Alonso1 Ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT) is the initial rhythm in approximately 20% of these patients. Studies have demonstrated that the probability of survival in VF/VT OHCA decreases as time to initial defibrillation increases. Patients with witnessed VF/VT OHCA have greater rates of functional neurologic survival when times from onset to initial defibrillation are shorter.Reference Drennan, Lin, Thorpe and Morrison2–Reference Berdowski, ten Haaf, Tijssen, Chapman and Koster5
Observational studies suggest that up to 4% of all ST-elevation myocardial infarctions (STEMI) are complicated by OHCA.Reference Lettieri, Savonitto and De Servi6,Reference Mylotte, Morice and Eltchaninoff7 Commonly, paramedics responded to such events by applying defibrillation pads at the time of arrest and defibrillating as quickly as possible. A case report of a “pads-on” protocol describes a case in which defibrillation pads were applied to a patient with STEMI with the aim of decreasing time to potential initial defibrillation.Reference Osei-Ampofo, Cheskes and Byers8 Two cases of STEMI complicated by VF were reported. The time to initial defibrillation was 2 minutes 43 seconds for the patient who required application of pads following arrest, but the time to initial first defibrillation was only 27 seconds in the “pads-on” protocol patient.
The purpose of this study was to evaluate the difference in time to initial defibrillation in patients with STEMI who experience OHCA after implementation of a “pads-on” protocol and describe the effects of this protocol on outcomes including survival to hospital discharge.
METHODS
Study design and time period
This was a health records review of patients with STEMI diagnosed in the prehospital setting pre- (Jan 2012 to May 2014) and post- (Jun 2014 to Jul 2016) implementation of a new protocol. In June 2014, paramedics began routinely applying defibrillation pads to patients with presumed STEMI. All patients with STEMI treated by Middlesex-London Paramedic Service Primary Care and Advanced Care Paramedics between January 2012 and July 2016 were included. This study was approved by the research ethics board of Western University.
Population
Patients were identified by searching all ambulance call reports during the study period with any of the following data codes: “STEMI,” “CPR,” or “defibrillation.” Cases of patients ≥18 years of age were reviewed if diagnosed with prehospital STEMI, and the diagnosis was confirmed on review of prehospital ECGs. STEMI was defined as at least 2 mm of ST elevation in leads V1–V3 in or at least 1 mm of ST elevation in any other leads, with the presence of ST elevation in at least two anatomically contiguous leads. Patients were included if they subsequently experienced a VF/VT arrest while in paramedic care. Patients were excluded if they arrested prior to a prehospital STEMI diagnosis or if they had a valid “do not resuscitate” order.
Data abstraction and analysis
Ambulance call reports of included patients were reviewed for patient demographics, event features (e.g., number of defibrillations, length of transport, doses of epinephrine, and airway interventions), and time to initial defibrillation. Other secondary outcomes were obtained from hospital records including intensive care unit (ICU) admission, admission duration, survival to hospital discharge, and discharge disposition. Time to defibrillation was tested for normality, and a t-test was used to assess the difference in time to initial defibrillation between the two groups.
RESULTS
Between January 2012 and July 2016, 446 patients were diagnosed with prehospital STEMI. Eleven of these patients experienced a paramedic-witnessed VF/VT arrest. The mean (standard deviation [SD]) age was 66.0 (9.3) years, and 55% were female. Seven patients underwent application of defibrillation pads following arrest with a mean (SD) time to initial defibrillation of 72.7 (34.9) seconds. In the four patients treated with the “pads-on” protocol, the mean (SD) time to initial defibrillation was 17.7 (4.2) seconds. The mean difference between the two groups was 55.0 seconds (95% confidence interval [CI] 22.7–87.2).
Characteristics of the 11 patients with prehospital STEMI who experienced OHCA are detailed in Table 1. Most patients (9 out of 11) presented and maintained normal vital signs prior to their cardiac arrest (defined as systolic blood pressure >100, heart rate [HR] ≥60 and <100, and oxygen saturation ≥95% on room air). Nine of 11 (81.8%) patients experienced return of spontaneous circulation (ROSC) with one defibrillation attempt. After one defibrillation attempt, six of the seven in the pre-intervention group achieved ROSC, and three of the four patients in the “pads-on” group had ROSC (Appendix 1). No patient required invasive airway management by paramedics. All four of the “pads-on” group survived to hospital discharge, and six of the seven in the “pre-intervention” group survived to hospital discharge. Seven of the 11 (63.6%) patients were found to have a culprit left anterior descending artery lesion at the time of angiography. Ten of the 11 patients survived to angiography. Of these 10 patients, all 10 survived to hospital discharge to an independent setting within 14 days of admission.
Table 1. Characteristics of patients with STEMI who experienced VF/VT arrest while in EMS care
ICU = intensive care unit; LAD = left anterior descending artery; RCA = right coronary artery; ROSC = return of spontaneous circulation
DISCUSSION
In this study, routine applications of defibrillation pads in patients with prehospital STEMI who experienced OHCA was associated with a decreased time to initial defibrillation. These findings are in keeping with the case report published by Osei-Ampofo et al.Reference Osei-Ampofo, Cheskes and Byers8 Although causation cannot be assumed in our study, time to defibrillation is a relatively objective measure that should not be unduly influenced by a patient or other event variables. All patients in the “pads-on” protocol group survived to hospital discharge, but one patient in the pre-intervention group did not survive. Although this study was not designed to show a survival benefit, previous studies indicate that each minute delay in the time to initial defibrillation is associated with a 7%–10% decrease in patient survival to hospital discharge.Reference Drennan, Lin, Thorpe and Morrison2–Reference Berdowski, ten Haaf, Tijssen, Chapman and Koster5 In our study, the intervention was able to decrease time to initial defibrillation by 55 seconds.
Of note, there was wide variability in time to first defibrillation in the pre-intervention group and less variability in the “pads-on” group. Factors that may account for this difference in the pre-intervention group can include time required to find pads in bags, connect to monitor, apply to patient, and safely defibrillate during a time of critical stress.
Only 2 of the 11 patients with post-STEMI OHCA had concerning vital signs prior to their arrest, thus indicating that all patients with prehospital STEMI, including those with normal vital signs, may benefit from early application of defibrillation pads. Lethal arrhythmias can occur suddenly in well-looking patients with prehospital STEMI and normal vital signs, thus making it difficult for paramedics to predict which patients will deteriorate into a VF or pulseless VT rhythm.
This study was limited by its small size and not powered to control for variables such as transport time, type of paramedic crew, patient age, and comorbidities that may affect time to initial defibrillation and impact outcomes such as survival. The results are at risk of error because of the reliance of documented event times. However, no patients were excluded because of inadequate or missing data. Furthermore, paramedic delay to recognition of VF/VT could not be controlled for as a confounding factor that might have contributed to longer defibrillation times in the pre-intervention group. Only 2.5% of patients with prehospital STEMI experienced OHCA while in paramedic care during the study period. This is lower than anticipated based on previously documented rates of OHCA in patients with STEMI patients.Reference Lettieri, Savonitto and De Servi6,Reference Mylotte, Morice and Eltchaninoff7 This discrepancy may be attributed to the fact that this study did not capture patients who experienced a cardiac arrest prior to the diagnosis of STEMI. Given that few patients with prehospital STEMI potentially derive benefit, cost-benefit analysis requires consideration. Because of the adherence of removal of expired pads from stock and their general infrequent use, the implementation of this protocol resulted in no additional costs to the paramedic service involved in this study.
CONCLUSION
This study suggests that routinely applying defibrillation pads to patients diagnosed with STEMI in the prehospital setting significantly decreases time to initial defibrillation that has been previously found to be a predictor of increased survival in OHCA. These results would benefit from validation in a prospective setting.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/cem.2019.408.
Acknowledgements
The authors would like to thank Middlesex-London Paramedic Service, Superintendent of Education Mr. Jay Loosley and frontline Middlesex-London paramedics for their involvement with this study and their continued commitment and contributions to high quality care and collaboration in resuscitation research.
Competing interests
None.
