Automated external defibrillators (AEDs) provide an important component of the early cardioversion link in the chain of survival promoted by the American Heart Association (AHA).1,2 There have been many efforts to place AEDs in common public areas and buildings–one of those efforts has targeted schools,3 since early defibrillation is also recommended for pediatric cardiac arrests4 in children 1 year old and greater.5
Although AEDs have been shown to be very reliable and almost foolproof, a case presented whereby an AED recognized an instance of supraventricular tachycardia (SVT) and recommended cardioversion at 200 joules for an awake 9-year-old boy.
PEDIATRIC PAIN
The boy presented to his school’s registered nurse with the chief complaint of abdominal pain, which began while he was playing basketball during recess. The RN, who was trained in BLS,6 observed that the patient’s pulse seemed fast. He was also noted to be alert, oriented and talkative. The nurse wasn’t aware of any past medical problems.
According to an unwritten but verbal policy implemented by the local school district, school nurses are required to place AEDs on any patients suspected of manifesting irregular heart rates or rhythms. Specifically, AED pads are placed on the patient and the AED is powered on with the goal of potentially identifying a serious etiology.
This policy was prompted by an anecdotal incident where an adult teacher wasn’t feeling well and an AED was placed on him. No shock was advised but a download of the data showed a serious sinus bradycardia and led to the placement of a pacemaker.
The nurse attached AED pads to the 9-year-old and, after initial rhythm interpretation, the AED advised the nurse to deliver a cardioversion and initiate CPR. The AED was the Cardiac Science Powerheart–a unit intended for both layperson and trained provider use.
According to the device’s analysis algorithm overview, the device determines the heart rate by measuring between eight consecutive QRS complexes; two outliers are disregarded and the remaining six QRS rates are averaged. If this calculation is greater than the programmed threshold rate for v fib or v tach, cardioversion is advised. The factory default rate for v fib or v tach, which can be customized, is 160 beats per minute.
All presenting rhythms are analyzed via threshold rate determination, and can be visualized on the AED screen. Following rhythm determination and shock analysis, the Powerheart AED determines whether cardioversion or synchronized cardioversion is more appropriate for the presenting rhythm.
The “automatic synchronization feature” attempts synchronization with the R wave for one second. If an R wave is detected, the underlying rhythm likely represents v tach or supraventricular tachycardia (SVT) and synchronized cardioversion occurs. If an R wave isn’t detected, the rhythm is likely v fib and cardioversion occurs.
Another feature–and one unique to the Powerheart AED–is the SVT discrimination function, which differentiates SVT from v fib and v tach
A maximum SVT rate (factory default rate is 200 beats per minute) is programmed at a higher rate than the v fib or v tach detection rate. Synchronized cardioversion is always advised when the maximum SVT rate is exceeded. However, SVT rates between the detection rate and the maximum SVT rate are classified as nonshockable.
Rhythm analysis anteceding AED cardioversion was consistent with SVT at a rate of 240 beats per minute, presumably secondary to underlying Wolff-Parkinson-White (WPW) syndrome. However, the AED was inappropriately applied to the conscious and breathing young patient, who wasn’t suffering from cardiac arrest, because of the verbal school policy.
It appears the “automatic synchronization feature” detected R waves, and synchronized cardioversion was delivered rather than defibrillation. Although the nurse took a full 14 seconds between the AED advice to “push the button,” the patient was cardioverted while conscious, breathing and hemodynamically stable. This occurred just prior to first response and ALS ambulance arrival.
No sedation or analgesia was administered to the patient prior to the procedure. Immediately afterward the patient said that he felt better.
Figure 1: Post-cardioversion 12-lead ECG
The ECG pattern is consistent with WPW syndrome. Note the shortened PR interval, prolonged QRS complex and delta wave.
According to the EMS report, the patient was alert and oriented to person, place and time. He was also asymptomatic and noted resolution of previous symptoms. Heart rate was 101 beats per minute and the remaining physical exam features were unremarkable. A 12-lead ECG performed on-scene suggested WPW syndrome with sinus tachycardia. (See Figure 1).
IV access was established by EMS and supplemental oxygen was administered to the patient during transport to the regional, pediatric, tertiary care hospital.
HOSPITAL CARE & FOLLOW UP
Hospital records revealed a previous WPW syndrome diagnosis and a previously scheduled electrophysiological intervention. The ED course was uneventful and no adverse outcomes were noted in the 30 days following the event.
A multidisciplinary team, including members from EMS, the school nurse, school district officials, ED personnel and the patient’s cardiologist, reviewed the case. It was determined the nurse was following school district policy when she inappropriately utilized the AED.
Following discussions with the school district, the policy on AED utilization was edited to exclude conscious patients from having AEDs attached.
Although the patient didn’t experience an adverse outcome, the scenario provides an opportunity to emphasize several key points:
>> As with other medical interventions, a risk—benefit analysis should occur before AED application. But AEDs should only be applied to patients thought to be in cardiac arrest, which is consistent with national guidelines.1
>> AEDs shouldn’t be used as cardiac monitors in non-cardiac arrest patients unless the individual caring for the patient has been trained to interpret the cardiac rhythm displayed on the AED monitor.
>> Operator error is the most common etiology of false-positive shock advisories,1 but has been noted to be a rare occurrence (< 0.1%).7
>> Medical providers should combine clinical information with the AED’s shock analysis before delivering a defibrillation or cardioversion.
>> The benefits of public access defibrillation with AEDs are definitive. However, rare instances of inadvertent utilization may occur. Organizations and EMS agencies promoting public access defibrillation share a responsibility to educate the public.
More Case of the Month from JEMS.com.
REFERENCES
1. Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Part 4: the automated external defibrillator: Key link in the chain of survival. The American Heart Association in Collaboration with the International Liaison Committee on Resuscitation. Circulation. 2000;102 (8 Suppl):I60—I76.
2. Cummins RO, Ornato JP, Thies WH, et al. Improving survival from sudden cardiac arrest: The “chain of survival” concept. A statement for health professions from the Advanced Cardiac Life Support Subcommittee and the Emergency Cardiac Care Committee, American Heart Association.Circulation. 1991;83(5):1832—1847.
3. Olympia RP, Wan E, Avner JR. The preparedness of schools to respond to emergencies in children: A national survey of school nurses. Pediatrics. 2005;116(6):e738—e745.
4. Kleinman ME, Chameides L, Schexnayder SM, et al. Part 14: Pediatric advanced life support: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care science.Circulation. 2010;122(18 Suppl 3):S876—S908
5. Atkinson E, Mikysa B, Conway JA, et al. Specificity and sensitivity of automated external defibrillator rhythm analysis in infants and children. Ann Emerg Med. 2003;42(2):185—196.
6. Boudreaux S, Broussard L. Sudden cardiac arrest in schools: The role of the school nurse in AED program implementation. Issues Compr Pediatr Nurs. 2012;35(3—4):143—152.
7. Sedgwick ML, Watson J, Dalziel K, et al. Efficacy of out of hospital defibrillation by ambulance technicians using automated external defibrillators: The Heartstart Scotland Project. Resuscitation. 1992;24(1):73—87.
