Article, Emergency Medicine

The NACA score as a predictor of ventricular cardiac arrhythmias – A retrospective six-year study

a b s t r a c t

Background: Helicopter Emergency Medical Service (HEMS) conducts the evaluation of a patient’s condition using NACA score before transporting the patient to hospital. The conditions inside the rescue helicopter limit or even make it impossible to conduct some medical procedures. An appropriate classification of the patient may lead to a lower possibility of occurrence of adverse events during the flight. The aim of the research was to evaluate the correlation of NACA score with the cardiac arrhythmia that may be life threatening.

Methods: A retrospective observational study included a group of 47,131 patients, who were transported by HEMS services between 2012 and 2017. The research was conducted using the analysis of variance ANOVA run- ning a post hoc test. In order to calculate the correlation of variables, Kruskal-Wallis and r-Pearson tests were car- ried out, interpreting the results according to J. Gilville’s scale. The significance level was set at ? = 0,05.

Results: The average number of points using NACA score for the studied group was 4,06 (SD +- 1,38). Twelve heart rhythms were selected while evaluating correlations using NACA score. There was a significant relation between the ECG variable and NACA score (p = 0,003). There was a very strong correlation between NACA score and the following: VF/pVT (r-Pearson = 0,856; p = 0,006), PEA (r-Pearson = 0,810; p = 0,015) and Asystole (r-Pearson

= 0,728; p = 0,026).

Conclusions: NACA score allows to predict the risk of occurrence of ventricular arrhythmia of the myocardium as well as cardiac arrest. The possibility of occurrence of a life-threatening rhythm is significantly higher in patients classified as NACA IV or higher.

(C) 2020 The Authors. This is an open access article under the CC BY-NC-ND license (http://

creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

The main reasons of Out of Hospital Cardiac Arrest – OHCA are pres- ent cardiac diseases [1]. Life-saving procedures, such as resuscitation performed by medical rescue teams are improved all the time, however,

Abbreviations: HEMS, Helicopter Emergency Medical Service; OHCA, Out of Hospital Cardiac Arrest; NACA, National Advisory Committee for Aeronautics; PEA, pulseless electrical activity; VF, ventricular fibrillation; pVT, pulseless ventricular tachycardia; AV block, atrial/ventricular block; sVT, supraventricular tachycardia; VES, ventricular extrasystoles; sVES, supraventricular extrasystoles; AF, atrial fibrillation; AT, atrial flutter; NSR, normal sinus rhythm; ICD, International Statistical Classification of Diseases and Related Health Problems.

* Corresponding author at: Faculty of Medical Sciences and Health Sciences, Siedlce University of Natural Sciences and Humanities, ul. Boleslawa Prusa 14, 08-110 Siedlce, Poland.

E-mail address: [email protected] (P. Leszczynski).

1 The idea and the planning of the study.

2 Gathering and listing data.

3 The data analysis and interpretation.

4 Writing the article.

5 Final approval of the article.

6 Critical review of the article.

predicting Life-threatening arrhythmias is very difficult. Ventricular ar- rhythmias have complex causes and mechanisms [2]. Serious incidents of diseases, body injuries but also changes in electrical properties of a single myocyte may trigger the occurrence of ventricular arrhythmia in patients by influencing early or delayed after depolarization [3].

There are generally four groups or causes of cardiac arrest (Asystole, PEA, VF/pVT). Despite standardized rescue procedures and the fact that newer and newer medical equipment is used, Out of Hospital Cardiac Arrest (OHCA) survivability is still on a quite low level [4]. Even in prehospital conditions, the survival threshold is on average 10%. Chances of experiencing a patient under the care of medical staff in the hospital reach up to 20% [5]. Thus, proper diagnostics and preventive measures may prevent cardiac arrest from occurring both at the scene and during transportation to hospital.

Rescue medicine uses various scales to evaluate the patient’s condi- tion both in hospital conditions and out of hospital. One of them is the NACA score developed by the National Advisory Committee for Aero- nautics. The classification is widely used in Helicopter Emergency Med- ical Services (HEMS) at international level. It contains a nominal scale with incremental values from 0 to 7 (with the Roman numerals). A gen- eral condition of a patient is determined based on the scale starting from

https://doi.org/10.1016/j.ajem.2019.12.044

0735-6757/(C) 2020 The Authors. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

minor injuries and slight diseases to cardiac arrest and death. NACA score at 0 and 1 are sometimes applied together.

NACA score is a subjective evaluation of an injured patient which was initially used only to analyse changes of the patient’s condition dur- ing the first 24 h of hospitalisation. In the 1980s it was modified in such a way to take into account pre-hospital conditions. Despite the lack of a specific system of measuring NACA score on the basis of vital signs, cou- ple of studies that have shown a correlation between NACA score and outcome (Raatiniemi, Weiss, Bonatti) [6]. In Poland it is applied only in Helicopter Emergency Medical Service. The helicopter carries highly

Table 1

NACA score.

Category Description

NACA 0 No or slight injury/disease. NACA I Minor disturbance.

NACA II Slight to moderate disturbance.

NACA III Moderate to severe but not life-threatening disorder.

NACA IV Serious incident where rapid development into a life-threatening condition can not be excluded.

NACA V Acute danger

NACA VI Respiratory and/or cardiac arrest

specialized medical equipment with digital interfaces. The LIFEPAK 15 monitor/defibrillator or other of such a type are used to monitor the cir- culatory system [7]. HEMS is a State institution nationwide having 23 helicopters at its disposal, some of which are on duty at 24-h cycles. A

NACA VII

Death

three-person helicopter rescue team consists of a doctor, a paramedic or a nurse and a pilot. Each member of the rescue team has to have a university degree, adequate years of service, qualifications and obliga- tory further training to be the part of HEMS [8,9]. Due to the fact that there is little space inside the helicopter, some of the medical activities cannot be performed during the flight. Intubation, re-examination and resuscitation are procedures that can be hard to perform on board a EC135P2+ rescue helicopter [10]. Therefore, HEMS team should always secure and monitor the patient before taking a decision to take off. An appropriate evaluation and qualification of the patient on the basis of the scales available may allow to avoid adverse events during air trans- port. The equipment and training of HEMS personnel allows for a thor- ough physical examination of the patient, e.g. by non-invasive measurement of carboxyhemoglobin, which allows the introduction of effective procedures in cases of mass events with suspected carbon monoxide poisoning [11]. An appropriate evaluation and qualification of the patient on the basis of the scales available may allow to avoid ad- verse events during air transport. Because NACA is based on subjective assessment of vital signs, the authors were inspired by demonstrating the correlation of the scale with the occurrence of specific arrhythmias. The aim of the research was to analyse NACA score as a predictive factor for the occurrence of adverse cardiological events (arrhythmia

and cardiac arrest) during HEMS treatment.

Methods

Study group

The study was conducted on patients suffering from body injuries or a sudden illness who had a HEMS rescue helicopter sent either at the scene or as an interhospital transport. Suggested rephrasing period of time was from 2012 to 2017 and dealt with activities taking place within Poland. The study included all flights accepted by the dispatcher and realized. No canceled missions enabled. Data was acquired in De- cember 2018. The study was approved by the Commission for Research Ethics (11/2018 UPH Siedlce). Written consent was obtained from the institution holding the medical records used in the study.

Research tool

A retrospective observational study of HEMS medical documenta- tion was made taking into account the age and gender of the patients, illness recognition according to the International Statistical Classifica- tion of Diseases and Related Health Problems (ICD), assigned score in accordance with the 8 categories of the NACA score, occurrence of car- diac arrest during transport as well as the initial ECG monitoring. NACA (Table 1) patient assessment was performed by the physician at the place of the incident before transport. Rhythms were divided into 12 groups (Asystole, AV blok, Bradycardia, AF/AT, PEA, NSR, Pacemaker, sVES, VT, sVT, VES, VF/pVT). Each time the doctor evaluated the ECG re- cord alone, and the rhythm recorded in the documentation was the

leading one at the time of the NACA assessment. Six of which are classi-

fied as ventricular disorders of cardiac activities:

Second-degree and third-degree atrioventricular blocks;
  • Ventricular extrasystoles;
  • Ventricular tachycardia;
  • Pulseless electrical activity (cardiac arrest);
  • Ventricular fibrillation. and pulseless ventricular tachycardia (car- diac arrest);
  • Asystole (cardiac arrest).

    Statistical analysis

  • Before conducting a statistical analysis, the normality of variable dis- tribution was confirmed using Levene’s test to determine the fulfillment of essential assumptions to carry out Analysis of variance (ANOVA). The Kruskal-Wallis test and Pearson’s r were used to calculate the signifi- cance of the correlation of variables interpreting the results by applying

    J. Guilford’s model. Post-hoc tests were conducted to compare the corre- lations between the variables in a detailed way.

    Paleontological Statistics Software Package PAST version 3.20 was used to carry out data analysis. The level of significance was set a priori at ? = 0,05 for all the analyses.

    Results

    Characteristics of the studied group

    The study was conducted on 47,131 patients who were helped by Polish Medical Air Rescue in 2012-2017, both as a transports between hospitals and directly to the site of the accident. The research group consisted of 31,165 males, 15,619 females and the gender of 347 pa- tients was not determined. The mean age was 46,89 (SD +- 25,91). The most frequent diagnosis according to ICD classification were acci- dents, intoxications and body injuries (n = 22,950) as well as cardiovas- cular diseases (n = 16,658). Mortality at the scene and during the flight was 5.89% (n = 2778). The number of cases in subsequent years under examination was: 2012 n = 7164, 2013 n = 7237, 2014 n = 7875, 2015 n = 8140, 2016 n = 7686, 2017 n = 9029.

    Arrhythmias

    Twelve heart rhythms (Asystole, AV blok, Bradycardia, AF/AT, PEA, NSR, Pacemaker, sVES, VT, sVT, VES, VF/pVT) were observed in the stud- ied group. The most frequent type was sinus rhythm (n = 37,858), atrial fibrillation and/or atrial flutter AF/AT (n = 2676) and supraventricular tachycardia sVT (n = 2511). Rhythms leading to cardiac arrest include: pulseless electrical activity PEA (n = 525), Ventricular fibrillation. and pulseless ventricular tachycardia VF/pVT (n = 319), Asystole (n = 2054). Other ECG records presented atrioventricular blocks (n = 201), Sinus bradycardia (n = 444), cardiac pacemaker (n = 267), ventricular extrasystoles VES (n = 117), supraventricular extrasystoles sVES (n = 50) and ventricular tachycardia VT (n = 109). In the analysed period

    of time, cardiac arrest took place 339 time during air transport and there was a necessity to defibrillate inside the rescue helicopter in 107 cases.

    NACA score

    The average number of NACA points for the studied group amounted to 4,06 (SD +- 1,38). Almost half of the patients (45,98%) was classified at the level of NACA IV. The rarest interventions concerned NACA I pa- tients (0,91%). The relation of NACA score and the number of patients is presented in Fig. 1.

    In the lowest NACA score (0 and 1), ECG record mostly consisted of a regular sinus rhythm (n = 1575), whereas in the most serious cases and the ones ending in death (NACA VI and VII) Asystole was observed most often (n = 1892). A compilation of ventricular arrhythmias depending on NACA score is presented in Fig. 2.

    NACA correlations

    Six ECG records directly connected with ventricular activities (AV block, VT, VES, VF/pVT, PEA, Asystole) leading to life-threatening situa- tions or cardiac arrest were taken into account. Fulfillment of essential assumptions to carry out the analysis of variance (ANOVA) was con- firmed (Levene’s test at p = 0,000). The variables were nonparametric, therefore the Kruskal-Wallis test was used, which showed a significant relationship between the variable ECG (Asystole, PEA, VF,pVT, VES, VT, AV block) and the NACA result (p = 0.003). Significant differences were confirmed by Welch’s t-test (F = 4278; df = 16,78; p = 0,007). Multiple comparisons post-hoc showed that there was a significant cor- relation between NACA 4 and ventricular heart disorders. Table 2 shows statistical significance in correlations at NACA IV, V, VI, and a detailed summary of the medians for the NACA scale is illustrated in Fig. 3.

    While evaluating the correlation between the variables, it was ob- served that there was a very high correlation between NACA score and VF/pVT (r-Pearson = 0,856; p = 0,006), PEA (r-Pearson = 0,810; p = 0,015) and Asystole (r-Pearson = 0,728; p = 0,026) (applying J. Guilford’s model). Other variable such as AV block (r-Pearson = 0,293; p = 0,480), VT (r-Pearson = 0,478; p = 0,230) and VES (r-Pear-

    son = 0,288; p = 0,488) had poor correlation with NACA score.

    Statistically significant relation between NACA score and the cases of cardiac arrest during air transport (correlation = 0,106), patients’ age

    (correlation = 0,069) or other recorded ECG rhythms was not observed (correlation = 0,422).

    Discussion

    Polish Medical Air Rescue is increasingly used for medical transport. In the analysed 6-year period of time, the number of HEMS mission in- creased by almost two thousand per year. The observed tendency sug- gests that the number of patients who will use air medical rescue service increase as it makes it possible to transport patients in a very fast and professional way directly from the place of accident or from one hospital to a higher reference medical centre. There are, however, some contraindications that make it impossible for the patient to be transported by air [10]. These include among others a general condition of a patient and the circumstances of the event, for instance, a woman with advanced pregnancy (due to lack of possibility of medical inter- vention in a helicopter when the labour starts) or a sudden cardiac ar- rest (due to space limitations during resuscitation).

    The risk of deterioration of the patient’s condition during the flight is determined by HEMS doctor who performs clinical and physical exam- ination. Various scales are used to do that (for example Glasgow Coma Scale, Revised Trauma Score). Air medical service commonly applies NACA score to evaluate general condition of a patient. Despite years of experience in using it, there is no scientific research into the relation be- tween NACA score and the occurrence of short-term complications in pre-hospital conditions. The scale is applied not only in air rescue ser- vice but also in other pre-hospital activities (for example medical secu- rity for mass events) [12].

    Cardiac arrests of non-Cardiac origin constitute only 28% of OHCA cases [13]. Other factors leading to cardiac arrest concern sudden cardi- ological conditions (for example arrhythmias). Due to limited diagnos- tic possibilities at the site of the event, there is a necessity to look for parameters predisposing a patient to the occurrence of cardiovascular disorders to take appropriate decisions concerning therapy and trans- port [14,15]. Clearly, the increased activity of the sympathetic nerves during physiological stress (such as post-trauma pain or situational re- action) has a big influence on electrical and systolic heart functions [16]. It may lead to Ventricular tachyarrhythmias and sudden death [17]. Therefore, an attempt was made to evaluate NACA score as a

    Fig. 1. A compilation of the number of patients depending on NACA score. Figure legend: NN – sex unknown.

    Fig. 2. Ventricular arrhythmias depending on NACA score. Figure legends: PEA – pulseless electrical activity; VF – ventricular fibrillation; pVT – pulseless ventricular tachycardia; AV block –

    atrial/ventricular block; VT – supraventricular tachycardia; VES – ventricular extrasystoles.

    predictive factor for the occurrence of arrhythmias which are life- threatening.

    Both in adult patients and in children, an early rhythm evaluation al- lows the implementation of advanced resuscitation activities [18]. The conducted research did not confirm a frequent occurrence of OHCA in VF/pVT rhythm compared to asystole and PEA [19]. Ventricular arrhyth- mia (VES, VT, AV block) which did not cause cardiac arrest during air transport constituted 0,91% (n = 427) of all the patients. A significant tendency of the increase of arrhythmia from NACA IV to NACA VI was observed (Fig. 2). It concerned mainly second-degree and third-degree atrioventricular blocks. This group of patients also indicated a higher risk of cardiac arrest, mostly in the mechanism of Asystole (57,25% of OHCA rhythms).

    The calculated mean number of NACA points (4,06) for all the pa- tients transported by HEMS during the 6-year-long period of time in Poland is similar to the results described in literature in other countries [20]. The results of the study are confirmed by data from Sweden, where

    NACA was rated as a reliable scale. It was also indicated that HEMS usu- ally transports patients with mean IV NACA [21]. This proves that an in- ternational Air ambulance usually provides assistance to patients in severe condition. Taking into account the condition of a patient who was classified at at least NACA IV, over three-quarters (76,91%) of the missions concerned people with Serious injuries and/or illnesses in the research period. It is a significant number in comparison to data in Norway where flights concerning Serious conditions of the patients con- stitute only one-third of all the interventions [22].

    An accurate evaluation of the patient’s condition using NACA score allows to make appropriate decisions concerning the form, procedure and means of medical transport. This requires appropriate qualifications of the staff [23,24]. While evaluating the patient with the use of NACA score, it is not the ECG record that is taken into account but basic vital signs. The conducted research proved that the achieved score points may indicate coexistence or probability of occurrence of life- threatening arrhythmias. The results confirmed that scores higher

    Table 2

    Dunn’s post hoc NACA vs. ventricular arrhythmias.

    NACA

    NACA 0

    NACA I

    NACA II

    NACA III

    NACA IV

    NACA V

    NACA VI

    NACA VII

    0,9257

    0,5687

    0,351

    0,004984

    0,002397

    0,01049

    0,1083

    0

    0,9257

    0,6336

    0,4013

    0,006631

    0,003253

    0,01366

    0,1303

    1

    0,5687

    0,6336

    0,7169

    0,02521

    0,01366

    0,04665

    0,3001

    2

    0,351

    0,4013

    0,7169

    0,06072

    0,03542

    0,1038

    0,5006

    3

    0,004984

    0,006631

    0,02521

    0,06072

    0,8197

    0,8036

    0,2294

    4

    0,002397

    0,003253

    0,01366

    0,03542

    0,8197

    0,6336

    0,1527

    5

    0,01049

    0,01366

    0,04665

    0,1038

    0,8036

    0,6336

    0,3404

    6

    0,1083

    0,1303

    0,3001

    0,5006

    0,2294

    0,1527

    0,3404

    7

    Fig. 3. The proportion of NACA score in ventricular arrhythmias.

    than NACA III are connected with significantly higher probability of oc- currence of a life-threatening condition [25]. Authors of other papers show that the increase in the NACA scale is closely related to the greater physical and mental strain of medical personnel [26,27]. It is worth tak- ing into account in the assessment of threats resulting from the HEMS work environment.

    Thus, it is necessary to conduct further research whose results may help to determine standards of behavior while dealing with patients de- pending on the assigned category in NACA score. The authors suggest that the study may contribute to the clinical practice the obligation to use the NACA scale also in terrestrial emergency medical services [28].

    Study limitations

    The research was conducted on 47,131 patients whose documenta- tion allowed to carry out analyses. While correlating NACA score with ECG records, twelve basic rhythms were selected. It is a retrospective observational study with all inherent limitations, the NACA score is based on the clinicians subjective evaluation. The long-term survival outcomes of the studied group are not known, as there is no possibility to track the future of patients in such a big number of medical centers. This is the first study that analyzes the correlation of the NACA scale with specific rhythm records, so it is not possible to rely on the results of other authors. The study showed that in patients with NACA IV and higher, circulatory arrest to the non-defibrillation rhythm occurs more frequently. This requires further research into the mechanism of cardiac arrest in pre-hospital conditions.

    Conclusions

    NACA as a reliable digital scale of evaluating general condition of a patient applied in pre-hospital conditions is significantly correlated with the patient’s heart rhythm. It allows to evaluate the risk of occur- rence of ventricular disorders of the myocardium as well as cardiac ar- rest. The probability of occurrence of the life-threatening rhythm increases significantly in patients classified as NACA IV or higher. The scale may be treated as a predictive factor for the occurrence of adverse events during the patient’s air transport to hospital.

    Declaration of competing interest

    None.

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