a b s t r a c t

Objectives: Cardiac arrest is a leading cause of death in the United States, with Pulseless electrical activity as a common initial arrest rhythm. We sought to determine if rate of electrical activity and QRS width correlate with survival in patients who present with PEA out-of-hospital cardiac arrest.

Methods and results: This is a retrospective review of patients with PEA out-of-hospital cardiac arrest with first documented cardiac rhythm of PEA from January 2010 to September 2013. Demographic, arrest and initial rhythm characteristics, and patient outcome were abstracted via systematic chart review. The initial 20 seconds of each rhythm strip were used to ascertain electrical rate and QRS width. Primary outcome was survival to hospital discharge. Four hundred fourteen patients were eligible for the study. One hundred fifty-two patients did not have sufficient data for analysis. Two hundred sixty-two patients were included in the final analysis with mean age, 66 years. There were 23 (8.8%) survivors and 17 (6.5%) Neurologically intact survivors. Mean heart rate was 58 (confidence interval, 54-63) beats per minute, and mean QRS interval was 100 (confidence interval, 95-106) milliseconds. Twenty-nine point seven percent of patients had wide QRS complexes, and 70.3% were narrow. There was no difference in survival in patients based on heart rate (13.1% vs 7.4%, P = .16) or QRS interval (8.7% vs 7.7%, P = .79).

Conclusions: In this single emergency medical services agency study, neither PEA electrical rate nor QRS width correlated with survival or neurologic outcome.

(C) 2015

Introduction

Approximately 300000 Out-of-hospital cardiac arrests occur annually in the United States with survival around 8%. [1]. Two-thirds of OHCA have an initial Non-shockable rhythm of PEA or asystole with an in- creasing incidence compared with initial Shockable rhythms (ventricular fi- brillation and pulseless ventricular tachycardia) [2,3]. Pulseless electrical activity occurs in approximately 20% to 30% of cardiac arrest victims [4] and has a poor prognosis when compared with shockable arrest rhythms [4-10]. Even when a patient is converted from a non-shockable to shockable rhythm during resuscitation, survival to hospital discharge does not im- prove [3,11]. Thus, a need exists to further risk stratify cardiac arrest pa- tients with initial PEA rhythm.

The definition of PEA is generally accepted as organized cardiac electrical activity without associated mechanical activity [12]. Pulseless electrical activity may be the presenting rhythm in a variety of acutely

? Disclosures: none.

?? Funding sources: none.

? Presented at American College of Emergency Physicians Scientific Assembly, October

27, 2014.

* Corresponding author at: 1000 Blythe Blvd, MEB 3rd floor, Department of Emergency Medicine, Charlotte, NC 28203. Tel.: +1 704 355 3658; fax: +1 704 355 7047.

E-mail address: [email protected] (D.A. Pearson).

reversible diseases processes including hypovolemia, tachydysrhythmias, cardiomyopathy, pulmonary embolism, cardiac tamponade, tension pneu- mothorax, and electrolyte abnormalities [12]. In contrast, unorganized PEA may represent a final common preterminal electrical rhythm. Advanced Cardiac Life Support protocol recommends rapid search of re- versible causes of PEA but does not discriminate PEA characteristics [13]. However, some have postulated that the PEA rhythm might better identify etiology and subsequent treatment strategies [14,15].

As PEA is a disease process with multiple etiologies, effective treat- ment likely includes reversing the cause of cardiac arrest. Although etiol- ogies such as exsanguination from trauma may be apparent upon initial examination, often the etiology of PEA is unknown. With history and physical examination often limited and unhelpful, the rhythm strip is 1 piece of data that can be quickly and easily obtained by prehospital pro- viders and may provide Prehospital providers and emergency physicians insight into the cause of arrest and guide Treatment decisions during re- suscitation. In addition, the characteristics of the PEA arrest rhythm may help with determining who would benefit from aggressive postcardiac care interventions such as therapeutic hypothermia [16-19].

We sought to determine if electrical rate and/or QRS complex width during PEA arrest correlated with outcome, specifically survival to hospital discharge as well as survival with Good neurologic outcome, defined as cerebral performance score of 1 or 2. We hypothesize

http://dx.doi.org/10.1016/j.ajem.2015.03.050

0735-6757/(C) 2015

892 M. Hauck et al. / American Journal of Emergency Medicine 33 (2015) 891–894

that patients with fast rates and narrow complex QRS will have better outcomes.

Methods

Study design and setting

This study was a retrospective chart review performed at a single urban emergency medical services (EMS) agency. The study was reviewed and approved by our institutional review board.

Selection of participants

Patients who presented to our local EMS agency in cardiac arrest from January 2010 to September 2013 were identified as eligible for the study. The Cardiac Arrest Registry to Enhance Survival (CARES), which currently collects prehospital data in cardiac arrest patients, was used to gather demographic as well as outcome data. This registry was queried for patients age 18 years and older who presented in cardi- ac arrest with an initial rhythm of PEA. Patients were excluded for Initial shockable rhythm, if outcome data were unavailable or not recorded and also if initial rhythm strip data were not interpretable.

Methods and measurements

Once eligible participants were identified, demographic, arrest char- acteristic, and outcome data were collected via the CARES registry. Each patient’s initial rhythm strip was also analyzed using the electronically captured rhythm as stored in event review software associated with the prehospital cardiac management system. The first 20 seconds of each rhythm strip were analyzed. The number of QRS complexes in the first 20 seconds was used to determine the heart rate in QRS com- plexes per minute. The width of the first QRS complexes was measured using calipers in the event review software and averaged to obtain an average QRS complex width in milliseconds. QRS complexes that were less than 120 milliseconds were defined as narrow, and QRS complexes 120 milliseconds and greater were defined as wide. Patients for which no rhythm strip was available, patients with unmeasurable data due to artifact, sinusoidal rhythms (QRS N 200 milliseconds or unmeasur- able), and features consistent with an initial shockable rhythm were ex- cluded. These data were entered into a Microsoft Excel spreadsheet. This data collection was performed by 1 author (MH) with unclear rhythms confirmed by another author (DP).

Outcomes

The primary outcome was defined as survival to hospital discharge, and secondary outcome was Neurologically intact survival, defined as a cerebral performance category of 1 or 2 [20].

Analysis

For the statistical analysis, categorical variables were assessed with the ?² or Fisher exact tests for small counts. Two-sample t tests and Wilcoxon rank sum tests were used for continuous data, depending upon the distribution of the data. Two-sided P values less than 0.05 were considered statistically significant. All analyses were conducted using SAS statistical software version 9.2 (SAS Institute, Cary, NC).

Results

to September 2013. One hundred fifty-two patients did not have suffi- cient data for analysis. Patient exclusions included missing rhythm strip data in the EventPro system (117), missing outcome data from the CARES registry [1], missing both CARES and EventPro data [14], un- measurable QRS complexes and/or electrical rates on rhythm strips largely due to artifact on the rhythm strip [1], ventricular fibrillation [12], ventricular tachycardia [12], and sinusoidal pattern, which did not allow for accurate measurement of the QRS complex [20]. A total of 262 patients were included in the final analysis.

3.2. Main results

Our patient cohort had a mean age of 67 years with 52% male and 51% White. Sixty-nine percent of arrests were witnessed, and 15% of patients received at least 1 defibrillation. Seventy-seven percent of patients received cold intravenous fluids in the prehospital setting. Of the 94 patients who survived to hospital admission, 45 (48%) underwent therapeutic hypothermia.

There were 23 (8.8%) patients who survived to hospital discharge and 17 (6.5%) who survived neurologically intact. Demographic data, ar- rest characteristics, heart rate, and QRS interval were not statistically different between survivors and nonsurvivors of cardiac arrest. Table 1 shows demographic information about the cohort, and Table 2 shows arrest characteristics. Mean heart rate was 58 (confidence interval [CI], 54-63) beats per minute, and mean QRS interval was 100 (CI, 95-106) milliseconds. Twenty-nine point seven percent of patients had wide QRS complexes, and 70.3% were narrow. There was no difference in sur- vival in patients with slow (b 60) or normal (60-100) heart rates (13.1% vs 7.4%, P = .16). Only 1 patient had a heart rate greater than 100, and this patient did not survive. No difference in survival was found be- tween patients with narrow and wide QRS intervals (8.7% vs 7.7%, P =

.79). Table 3 below describes rhythm strip characteristics.

Discussion

This study showed that neither electrical rate nor QRS width on a car- diac monitor rhythm strip during PEA cardiac arrest was associated with survival or neurologic outcome. However, there was a nonstatistically significant trend toward improved survival in bradycardic electrical rates when compared with normal electrical rates. To our knowledge, this is the only study exploring the association of cardiac rhythm charac- teristics and outcome after PEA cardiac arrest.

Pulseless electrical activity is a disease with high mortality and di- verse etiologies [4-10]. Often, a standardized treatment algorithm is de- ployed that is the same for each patient in PEA regardless of the etiology, particularly in the prehospital setting, due to the time critical nature of the disease and lack of a clear identifiable etiology during resuscitation [13]. With the vast Potential causes of PEA, diagnostic tests with rapid results to help guide the resuscitation optimal therapeutic algorithms are needed. Cardiac monitor rhythm strips is one potential rapid test [21]. In this study, we wanted to explore the potential role of initial cardi- ac rhythm strip and its association with outcomes after PEA arrest, as it is readily available test for prehospital resuscitators [22]. It has been proposed that QRS width may assist with classifying PEA arrest etiology than the American Heart Association’s conventionally taught ACLS algorithm that includes the 5 H’s and 5 T’s mnemonic and guide

Table 1

Demographics

Survivors Nonsurvivors

Age (mean) 62.2 (CI:, 57.4-67.2) y 67.2 (CI, 65.5-69.0) y

3.1. Characteristics of study subjects

The CARES registry identified 414 patients who had OHCA with ini- tial rhythm of PEA documented by our EMS system from January 2010

QRS (mean) 94.8 (CI, 79-110.6)

milliseconds

Heart rate (mean) 51 (CI, 38.8-63.2) beats per minute

101.4 (CI, 95.3-107.4)

milliseconds

59.2 (CI, 54.8-63.6)

beats per minute

M. Hauck et al. / American Journal of Emergency Medicine 33 (2015) 891–894 893

Table 2

Arrest characteristics

		Survivors	Nonsurvivors	P
Race	White	13 (9.9%)	121 (90.1%)	.71
	Other	9 (8.8%)	117 (91.2%)
Sex	Female	13(10%)	112 (90%)	.64
	Male	12 (8.7%)	125 (91.3%)
witnessed arrest	Yes	18 (9.8%)	164 (90.2%)	.61
	No	7 (8.2%)	73 (91.8%)
Defibrillation	Yes	2 (4.9%)	38 (95.1%)	.2
	No	22 (10.1%)	200 (89.9%)
Prehospital cold intravenous fluids	Yes	21 (10.3%)	182 (89.7%)	.58
	No	7 (12.7%)	52 (87.3%)
Therapeutic hypothermia	Yes	13 (28.9%)	32 (71.1%)	.16
	No	21 (42.9%)	28 (57.1%)

Resuscitative efforts [23]. Narrow complex QRS PEA more often is sec- ondary to a mechanical problem due to right ventricle inflow or outflow obstruction (cardiac tamponade, Tension pneumothorax, mechanical lung hyperinflation, and pulmonary embolism), whereas wide complex QRS PEA is more likely due to a metabolic issue (hyperkalemia and so- dium channel blocker overdose), left ventricular failure (due to ische- mia), or an agonal rhythm, for which there are no effective treatments [14]. Although this algorithm has not been validated, it does use the car- diac rhythm to quickly identify and guide therapy for the possible causes of PEA [24]. Although in our study we did not correlate QRS rhythm with etiology, we did not find an association between QRS width and survival [25]. Our study showed that 30% of patients had an initial wide QRS width, with 70% having a narrow QRS width without an associated difference in outcomes. This is a notable finding, as given the large proportion of narrow and wide QRS width, this allows an opportunity for further development and validation of the treatment algorithm described by Littman et al [14] in the management of PEA arrest.

Our study further explored whether electrical rate on initial rhythm strip was associated with outcome. It is unknown whether heart rate in combination with QRS width is helpful in narrowing down the etiology of PEA arrest or in identification of pseudo-PEA vs true PEA. Our study showed a trend toward improved outcomes with bradycardic rates yet no statistical difference. Larger studies involving multiple EMS agen- cies might be necessary to further elucidate the role of rate and QRS width in prognosis, diagnosis, and treatment of PEA.

Although effective Treatment algorithms that exist for shockable arrest rhythms have led to improved outcomes, little improvement has been made for the resuscitation of patients in a non-shockable car- diac arrest rhythm. In addition, Non-shockable rhythms are becoming more common in cardiac arrest, possibly due to the advances in cardio- vascular disease therapy over the last 3 decades [26]. At present, PEA has no unifying definition but is widely recognized as electrical activity of the heart without adequate cardiac output to generate a pulse. This wide definition encompasses a large number of potential disease pro- cesses. This makes studying PEA problematic, as the model currently used in bench research is asphyxia, which is in reality a very small per- centage of PEA arrests, suggesting that this model may be ineffective in studying this disease process [26].

Interestingly, we found that a notable proportion of patients in our cohort of PEA initial arrest rhythm (15.2%) was defibrillated. We did not assess whether defibrillation was used for a converted rhythm

Table 3

Rhythm strip characteristics (n = 262 patients)

		Survivors	Nonsurvivors	P
QRS	Narrow (n = 184, 70%)	16 (8.7%)	168 (91.3%)	.78
	Wide (n = 78, 30%)	6 (7.6%)	72 (92.3%)
HR	b60 (n = 91, 35%)	12 (13.1%)	79 (86.9%)	.059
	N 60 (n = 171, 65%)	13 (7.3%)	158 (92.7%)

from PEA to shockable, attempted during PEA for questionable rhythms, or if this was an attempt on the part of the prehospital providers to pro- vide another treatment strategy for this disease. Our findings are consis- tent with the study of Thomas et al [3] that showed patients who converted to a shockable rhythm from an initial non-shockable have also not been shown to improve outcome.

For this study, retrospectively interpreting rhythm strips was per- formed to determine initial arrest rhythm as well as rhythm character- istics. Our EMS agency uses a device that records rhythm during compressions. However, due to artifact from compressions, rhythms are often difficult to interpret. During our analysis, 6 patients had rhythms that met criteria for a shockable rhythm (3 ventricular tachycardia and 3 ventricular fibrillation) despite being classified as a PEA arrest. In the prehospital setting, artifact and other factors can make rhythm interpretation difficult. Automated devices such as auto- mated external defibrillators do help this but require providers to take time away from chest compressions. Devices and methods for rhythm interpretations without interruptions for cardiopulmonary resuscita- tion (CPR) are currently undergoing study [27] and may ultimately de- crease errors with rhythm interpretation and increase amount of time of chest compressions during cardiac arrest.

Limitations

First, this study was a retrospective chart review with its inherent limitations. Variables that may have been confounders in our analysis, such as total downtime and Time to return of spontaneous circulation, were not collected. Furthermore, this study was based on the first rhythm captured by EMS, and there were a significant number of pa- tients with either missing or uninterpretable data, which may have been secondary to acquisition technique or artifact from CPR. Because of the obvious acuity of the situation whereby CPR cannot be delayed, this is nevertheless a limitation of the study. This study also only includ- ed patients cared for by a single urban EMS agency with fast Response times, and, thus, these results may not be generalizable to other EMS agencies or patient populations. Finally, although there were a large number of patients included in the study population, there were only a small number of survivors and neurologically intact survivors. Because of this small number, it is difficult to detect an outcome differences be- tween groups with different rates and QRS complex widths, especially with only 1 patient with a rate greater than 100 milliseconds.

Conclusion

In summary, in this single EMS agency study, neither PEA rate nor QRS width correlated with survival or neurologic outcome.

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