Automated External Defibrillation

### **Chapter 5**

## AED: Optimal Use of Automated External Defribilators in BLS and ILS

*Tudor Ovidiu Popa, Mihaela Corlade-Andrei, Paul Nedelea, Emilian Manolescu, Alexandra Hauta and Diana Cimpoesu*

#### **Abstract**

The use of Automatic External Defibrillators (AED) present in public access defibrillation programs (PAD) in cardiopulmonary resuscitation (CPR) is a challenge in the effective treatment of cardiac arrest, especially for adult patients. It is already known that the majority of adult cases of out-of-hospital cardiac arrest arise from ventricular fibrillation (VF). The most important factor in determining survival from VF is the time from collapse to defibrillation. If laypersons are trained to perform Basic Life Support (BLS) and to attempt defibrillation using an automatic external defibrillator before the emergency medical services arrive, the survival rate of an out-of-hospital cardiac arrest can be increased. In many countries, the number of public access AEDs has increased but implementation of AED use and CPR performed by public bystanders has not been sufficiently frequent. In fact, only a minority of individuals demonstrate sufficient knowledge and willingness to operate an AED, suggesting that the public is not yet sufficiently prepared. It is also very important to support the permanent campaign of training as many laypersons, starting from school, to properly use such defibrillators in public places. Considering these facts, PAD is an effective way and may be a cost-effective way to improve outcomes in cardiac arrest.

**Keywords:** automatic external Defibrilator (AED), BLS, ILS, defibrillation, CPR, bystanders, cardiac arrest, education

#### **1. Introduction**

Defibrillation is an essential link in the chain of survival in case of ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT).

For every minute that passes without applying defibrillation, the chance of the patient to respond to this maneuver is decreasing by 7–10%, decreasing also the chance of surviving.

Automated external defibrillators (AEDs) are portable smart life savings devices, designed to administer the necessary treatment for people experiencing sudden cardiac arrest, a medical condition in which the heart stops beating suddenly and unexpectedly when VF or pVT is present.

Public access AEDs can be found in airports, community centers, schools, government buildings, and other crowded public locations. They are intended to be used by lay people who have received minimal or no training.

AEDs are a type of computerized defibrillator that automatically analyzes the heart rhythm in people who are suffering cardiac arrest. When appropriate, it delivers an external electric shock to the heart muscle, the goal being to restore its normal sinusal rhythm.

The combination of cardiopulmonary resuscitation (CPR) and early defibrillation is effective in saving lives when used in the first few minutes following a collapse from sudden cardiac arrest, if the victim presents a cardiac arrest rhythm that requires defibrillation, like ventricular fibrillation or ventricular tachycardia without a pulse.

The AED devices include some accessories, such as pads (electrodes), that are necessary for the AED to detect and interpret a person's heart rhythm and also necessary to deliver an external electric shock if it is needed. There are two main types of AEDs: public access and professional use.

Professional use AEDs are used by first responders, such as emergency medical technicians (EMTs) and paramedics, who receive additional AED training.

Automated defibrillators analyze the heart's rhythm, and if an abnormal heart rhythm is detected, that requires a shock, then the device prompts the user to press a button to deliver a defibrillation shock.

A defibrillator should be used as soon as possible when a person is found in cardiac arrest. CPR should be performed until a defibrillator is brought on the scene.

#### **2. Defibrillation**

Defibrillation is an essential link in the chain of survival, in the case of cardiac arrest produced by ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT). After the onset of cardiac arrest, the circulation is absent and the hypoxic brain injury begins to appear after 3 minutes, if in this interval nobody starts to perform chest compressions.

Defibrillation maneuver can stop cardiac arrest produced by VF/pVT by applying an external electric asynchronous shock, at up to 5 seconds after its application, by depolarizing the myocardium and restoring normal electrical activity, compatible with the presence of a pulse.

Although defibrillation is the most important in the management of patients with shockable rhythms (VF/pVT), also continuous, high quality uninterrupted external chest compressions are required to optimize the chances of successful resuscitation [1–3].

The success of defibrillation depends on the transmission of the energy to the myocardium and the following conditions are involved:


#### *AED: Optimal Use of Automated External Defribilators in BLS and ILS DOI: http://dx.doi.org/10.5772/intechopen.111907*

In the case of cardiac arrest produced in the pre-hospital, the emergency medical personnel must ensure good quality resuscitation throughout the interval of bringing, applying, and charging the defibrillator. A predetermined duration (for example, two minutes) of CPR before rhythm analysis and shock delivery is no longer recommended, the defibrillator should be used as soon as this is available.

During resuscitation, different types of defibrillators are used depending on the place where the cardiac arrest occurred, the training of the resuscitation team, technical possibilities, and economic resources [2, 4, 5].

Automatic external defibrillation can be used by bystanders, paramedics, nonmedical personnel, or personnel with medical training who intervene in situations of cardiorespiratory arrest out of the hospital and in some situations in the hospital. Regarding manual defibrillation, this is performed only by medically trained personnel who have the theoretical and practical knowledge necessary to recognize and defibrillate correctly a shockable rhythm [2, 4, 5].

#### **3. Use of automated external defibrillator**

AEDs are safe and effective when used by lay people without or with minimal knowledge of defibrillation.

AEDs make defibrillation possible with many minutes before the arrival of qualified medical help. Resuscitators should focus on voice commands as soon as they begin, especially resuming CPR as soon as possible and minimizing the interruption of chest compressions.

Standard AEDs are suitable for use in children over 8 years of age. Pediatric selfadhesive paddles are used for children between 1 and 8 years old [1].

The use of the automatic external defibrillator by EMS in the pre-hospital settings.

In the case of out-of-hospital cardiac arrest, the emergency medical personnel must ensure good quality resuscitation during the entire interval of bringing, applying, and loading the defibrillator. For emergency medical services that have implemented a predetermined period of chest compressions before defibrillation, due to the lack of convincing data, it is reasonable for these services to continue this practice [1, 2].

Below is the guide for using the AED which does not require knowledge of electrocardiography, physiopathology of ventricular fibrillation, or defibrillation energy.

Instead, there is essential knowledge about the device and how to use it, following verbal instructions, knowledge of safety measures in defibrillation, and CPR measures.

The device is equipped with self-adhesive pads, which are placed above the level of the apex of the heart and on the right, subclavicular, or antero-posterior presternal and interscapular.

For patients with implantable medical devices (pacemaker for permanent electrical cardiostimulation, implantable defibrillator), electrodes of defibrillation will be placed at a distance from the device (at least 8 cm) or will use an alternative positioning (antero-lateral, antero-posterior).

Also, the transdermal patches should be removed and cleaned the area before applying the self-adhesive electrodes.

Defibrillation should be performed with minimal interruption of chest compressions (less than 5 seconds, actual recommendation being 3 seconds). Thus, the pause in chest compression can be reduced to less than 5 seconds by continuing chest

#### **Figure 1.**

*BLS algorithm. (https://www.cprguidelines.eu/assets/posters/BLS-Algorithms-portrait.pdf).*

compressions during charging of the defibrillator and by effective coordination of the resuscitation team, and minimizing pause.

After each schock, immediately resuming chest compressions is extremely important, this strategy should be applied after each shock administration.

In **Figure 1**, we present the BLS and AED algorithm steps from the Basic Life Support algorithm, accordingly to European Resuscitation Council Guideline 2021.

#### **4. Types of energy used in defibrillation**

Defibrillation requires the release of sufficient energy to depolarize a critical mass in the myocardium, to stop the chaotic electrical activity and to allow the normal activity of the natural pacemaker to be resumed.

The use of monophasic defibrillators for almost 30 years has brought many benefits, but it also allowed the myocardial injury to be highlighted, produced by the passage of the defibrillation current through the heart.

The monophasic defibrillators, which currently are no longer produced, but continue to be in use, release a unipolar current, which crosses the heart in one direction. There are two types of monophasic current: attenuated sinusoidal current and truncated exponential current.

Modern biphasic defibrillators are designed to deliver a current that crosses the myocardium in both directions: positive and negative. There are also two types of current delivered by this defibrillator: truncated biphasic current and rectilinear biphasic current.

*AED: Optimal Use of Automated External Defribilators in BLS and ILS DOI: http://dx.doi.org/10.5772/intechopen.111907*

The advantages of biphasic defibrillators are:


Clinical studies have proven the superiority of defibrillation with defibrillators biphasic, the myocardial injury being minimal, and the efficiency maximal.

#### **5. The automatic external defibrillator**

The automatic external defibrillator is a computerized device with the ability to recognize automatically a heart rhythm that requires an external electric shock and to give the indication to apply the external electric shock (in the case of VF/pVT). The sensitivity of the device to recognize a shockable rhythm is very high, AEDs are designed such that they have a very high specificity (>99%) in detecting shockable rhythms.

The device is provided with self-adhesive electrodes (pads), which are placed anteriorly at the apex of the heart and at right, subclavicular position, or antero-posterior (presternal and interscapular, if the situation requires this, for example, wounds present an apex level). To facilitate the positioning of the pads over the chest, on each of them is drawn the place where should be applied.

The presence of a transdermal drug patch on the patient's chest may prevent good contact and may cause electrical arcing and burns if self-adhesive pads are placed over them. Place the pads in an alternative position that avoids the patch or remove the patches and dry the skin area. If an implantable device is present(pacemaker), the pads should be placed at least 8 cm distance.

According to the new recommendations of the Advance Life Support 2021 published by the European Resuscitation Council, defibrillation must be performed with minimal interruption, this should be performed in less than 3 seconds [2–4].

The protocol for using the automatic/semi-automatic defibrillator:


Immediately after applying the external shock, restart CPR (30 chest compressions: 2 ventilations). Repeat these steps after 2 minutes of CPR if VF/pVT is present [1, 2].

#### **6. Use of AED in the hospital**

In every medical facility should be available a defibrillator which can be used in maximum 3 minutes in case of a cardiac arrest occur in a patient. Depending on the partcularityes of each medical facility and the presence of the trained personnel this could be an AED or a manual defibrillator.

There are no published randomized clinical trials comparing the utility of AEDs and manual defibrillators in the hospital. Three observational studies have shown that there is no improvement in the survival of adult patients at discharge following a cardiac arrest when using an AED, compared to a manual defibrillator.

A large observational study showed that in-hospital use of AED was associated with lower survival compared to the one who were defibrillated with a manual defibrillator, suggesting that AED may cause delays in starting CPR or stopping chest compressions in patients with non-shockable rhythm. The goal is to attempt defibrillation within 3 minutes of collapse [1, 5].

According to the recommendations of the resuscitation guide of the European Council of Resuscitation, up to three successive external electric shocks can be used if ventricular fibrillation/pulseless ventricular tachycardia (VF/VT) occurs during cardiac catheterization or immediately in the postoperative period after cardiac surgery. This three shock strategy can also be considered in case of cardiac arrest assisted by VF/pVT when the patient is already monitored with a manual defibrillator or AED.

Throughout resuscitation and defibrillation, it is important to minimize the duration of the pre- and post-shock pauses, the continuity of chest compressions are recommended during defibrillator charging and rapid resumption of chest compressions after each defibrillation.

During resuscitation, different types of defibrillators are used, depending on multiple factors like the place where the cardiac arrest occurred, the training of the resuscitation team, but also the technical possibilities, the economic resources, and the health programs of each community.

Automated external defibrillation is used by paramedical staff, non-medical, or with medium medical training that intervenes in situations of cardiorespiratory arrest in the prehospital settings, but also in some situations even in the hospital.

In **Table 1**, we present the guidance for using AED:


*AED: Optimal Use of Automated External Defribilators in BLS and ILS DOI: http://dx.doi.org/10.5772/intechopen.111907*


**Table 1.** *Guidelines for using AED in hospital.*

### **7. Recommendation for semi-automated defibrillator**

Semi-automated defibrillators are more complex devices that can be utilized in two modes, as an AED or as a manual defibrillator, depending on the medical personnel.

Manual defibrillation should only be performed by medical personnel, personnel who have the necessary theoretical and practical knowledge in recognition of a shockable rhythm.

Manual defibrillation involves, on the part of the operator:


It is recommended to use self-adhesive electrodes for the defibrillation! Safety rules:


Defibrillation technique:

A single shock will be applied after every two minutes of resuscitation maneuvers:

• The older models of external defibrillators delivered a monophasic type of waveform. Biphasic defibrillation alternates the direction of the pulses, requires a low level of energy necessary for successful defibrillation, and decreases the risk of myocardial damage.

The first, as well as the following monophasic shocks will be delivered with 360 J;


Manual defibrillation protocol:


#### **8. Public access defibrillator programs**

Regarding all the advantages of using AED in the first moments of cardiac arrest, there is a large consensus for the implementation of public access to defibrillators. Placement of AEDs in areas where a cardiac arrest can be recorded every 5 years is considered cost-effective and comparable to other medical interventions. Registering the AED for public access so the dispatcher can direct the resuscitator to a nearby AED can also help to optimize the response.

The effectiveness of AED use for victims at home is limited. The proportion of patients with FV is lower at home than in public places, however, the number of potential patients who could be treated at home is greater. Public access to defibrillators (PADs) rarely reaches patients at home.

Lay resuscitators performing CPR and directing to an AED can improve the chances of CPR and help reduce the time to defibrillation.

Universal AED Sign ILCOR has designed a simple and clear AED sign that can be recognized worldwide and is recommended to indicate the location of an AED.

Defibrillation programs with public access have the role of improving survival after cardiac arrest if they are established in locations where a cardiac arrest is likely to occur.

Suitable places may include airports, train stations, theaters, and sports facilities. Approximately 80% of prehospital cardiac arrests occur in private or residential settings. This inevitably limits the overall impact that PAD programs can have on survival rates [2, 5].

AED should be placed in public places (airports, train stations, theaters, stadiums) where there is an increased risk of cardiac arrest occurring with VF/pVT due to the high density of adults and can be used in various technical variants in defibrillation programs for the population—public access defibrillation—PAD.

Within the public programs for defibrillation, ILCOR created a universal sign (**Figure 2**) to indicate the location of an AED, a sign that can be recognized at the international level.

**Figure 2.** *ILCOR AED sign.*

It is indicated that the entity or person who purchases the automatic external defibrillator to inform the emergency medical services about its existence; a physician should supervise it in order to ensure quality control and if there are persons responsible for using the automatic external defibrillator they should be trained on its correct use.

#### **9. The factors that affect the success of defibrillation**

Increased chest impedance reduces the level of energy delivered through the heart and decreases the chance of successful defibrillation. This is influenced by the contract between the pads and the skin, by the size of the pads, but also by the breathing phase, impedance being increased during inspiration(inhale) time.

The current recommendations are that the surface of the defibrillation electrode should be at least 150 cm2 , and the diameter should be 8–12 cm [1, 4, 6, 7].

#### **10. Safety**

The defibrillation attempt must be carried out without risk to the members of the resuscitation team. The main risk is represented by the accidentally direct or indirect electrocution of someone of the persons near the victim To minimize this risk, the best solution is to use self-adhesive pads *versus* paddles and by wearing gloves by the members of the medical team [1, 4, 6].

If an external electrical asynchronous shock is administered to someone who is not in VF or pulseless VT, it is possible some time to be applied exactly during the relative refractory period. If a shock is administered at this vulnerable moment of electric activity of the heart, it is a high chance to induce VF. Because of this, the defibrillation should only be performed for patients who present VF or pulseless VT [1, 4].

#### **11. Conclusions**

Regarding the use of the AED, it is certain that to save a life you need to know minimal things that are very helpful even if you are not a person in the medical field. And if you know from where to bring the defibrillator to the victim, you are still part of the chain of survival because you help the person providing first aid to do his job quickly and save time for the victim's life.

The importance of the interaction between the medical dispatcher, the witness who initiates CPR, including resuscitation maneuvers and timely use of automatic external defibrillator should be stressed.

Essentially, the coordinated community response, which attracts these elements, is essential for improving patient survival, if patient installs cardiorespiratory arrest outside the hospital.

The witness who is trained in Basic Life Support techniques and is available, must assess the victim quickly to determine if the victim is unconscious and not breathing normally, and then to alert the emergency services immediately.

The interaction between the medical dispatcher, the witness initiating CPR and the use of an AED are the essential elements for improving survival in case of cardiac arrest outside the hospital.

*AED: Optimal Use of Automated External Defribilators in BLS and ILS DOI: http://dx.doi.org/10.5772/intechopen.111907*

The victim who is unresponsive and not breathing normally is in cardiac arrest and requires CPR.

Witnesses and medical dispatchers must suspect cardiac arrest in any patient presenting with seizures and should carefully assess whether the victim breathing normally or not.

Rescuers trained in CPR should combine chest compressions with ventilations.

Conducting high-quality CPR remains essential for the improvement of the results.

Trained rescuers should provide chest compressions with an adequate depth (of at least 5 cm, but not more than 6 cm), with a frequency of 100–120 compressions per min. After each compression allow the chest to return, minimize interruptions during compressions.

When the savior performs breaths/ventilations for 1 second perform insufflation with a sufficient volume to ensure the expansion of the victim's chest.

Chest compression ratio and ventilation is 30:2. Do not stop chest compressions for more than 10 seconds to achieve ventilation.

Defibrillation performed within 3–5 minutes from the debut of cardiac arrest may increase the survival rate by more than 50–70%.

Early defibrillation can be achieved by the rescuer who initiates CPR using the automatic defibrillator external.

AEDs should be implemented in all spaces and public areas where there is a high population density.

We stress again the importance of implementing national programs for Basic Life Support and AED, to give access to defibrillators to the general public population. With these programs, the time from collapse to defibrillation can be greatly reduced.

#### **Conflict of interest**

The authors declare no conflict of interest.

### **Author details**

Tudor Ovidiu Popa1,2, Mihaela Corlade-Andrei1,2\*, Paul Nedelea1,2, Emilian Manolescu1,2, Alexandra Hauta1,2 and Diana Cimpoesu1,2

1 Emergency Medicine Department, University of Medicine and Pharmacy Grigore T. Popa, Iasi, Romania

2 Clinical County Hospital St. Spiridon – Emergency Department, Iasi, Romania

\*Address all correspondence to: corladeandrei.mihaela@gmail.com

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

[1] Perkins GD, Olasveengen TM, Maconochie I, Soar J, Wyllie J, Greif R, et al. European resuscitation council guidelines for resuscitation: 2017 update. Resuscitation. 2018;**123**:43-50

[2] Exel W, Peran D, Jiménez FC. Advanced Life Support: Provider Manual. Emile Vanderveldelaan, Belgium: European Resuscitation Council vzw; 2021

[3] Liddle R, Davies CS, Colquhoun M, Handley AJ. The automated external defibrillator. BMJ. 2003;**327**(7425):1216

[4] Soar J, Böttiger BW, Carli P, Couper K, Deakin CD, Djärv T, et al. European resuscitation council guidelines 2021: Adult advanced life support. Resuscitation. 2021;**161**:115-151

[5] Soar J, Nolan JP, Böttiger BW, Perkins GD, Lott C, Carli P, et al. European resuscitation council guidelines for resuscitation 2015: Section 3. Adult advanced life support. Resuscitation. 2015;**95**:100-147

[6] Knight BP. Basic principles and technique of external electrical cardioversion and defibrillation. In: Post TW editor. UpToDate. Waltham, MA: UpToDate; 2023 [Accessed on June 06, 2023]

[7] Cimpoesu D, Popa O, Corlade M, et al. Guidelines and Algoritms in Emergency Medicine. Iasi: UMF "Gr. T. Popa" Publishing House; 2019

### **Chapter 6**

## The Influence of Transthoracic Impedance on Electrical Cardioversion and Defibrillation: Current Data

*Adam Pal-Jakab, Bettina Nagy, Boldizsar Kiss and Endre Zima*

### **Abstract**

Sudden cardiac death (SCD) is a leading cause of death globally, often caused by malignant ventricular arrhythmias. Rapid termination by direct current defibrillation (DF) is the best way to treat pulseless ventricular tachycardia and ventricular fibrillation. Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice. External cardioversion (ECV) is an immediate, effective, and safe procedure for the treatment of arrhythmias with high ventricular rate, for example, AF. The success of both ECV and DF is dependent on the delivery of sufficient current, influenced by energy and transthoracic impedance (TTI). TTI depends on patient characteristics, and the exact factors affecting it are still a matter of debate. Influencing factors such as respiration phase, contact pressure, coupling agent, and total energy delivered are commonly identified. However, there are multiple studies with controversial results concerning the effect of age, gender, body mass index, hemoglobin concentration, the presence of chronic heart failure, and fluid accumulation as independent predictors of TTI. The review emphasizes refining energy dosage during ECV and while minimizing complications caused by an unnecessarily high energy delivery. The value of TTI should be predicted to optimize the energy dosage and the number of shocks for successful ECV and DF.

**Keywords:** transthoracic impedance, defibrillation, cardioversion, electric current, delivered energy

#### **1. Introduction**

#### **1.1 Sudden cardiac arrest and atrial fibrillation**

Sudden cardiac death (SCD) is a major cause of death worldwide and the third leading cause of death in Europe [1]. In the European Union, there are 155,000– 343,000 estimated SCD cases annually, with an incidence rate of 48.6 per 100,000 inhabitants. The number of SCD cases accounts for approximately 70% of the total annual expected number of Out-of-Hospital Cardiac Arrest (OHCA) cases in the

European Union [2]. In the United States, SCD accounts for 7–18% of all deaths, or between 185,000 and 450,000 fatalities annually [3, 4].

The electrophysiological causes of SCD include shockable rhythms such as ventricular tachycardia (VT), ventricular fibrillation (VF), and other nonshockable rhythms. Ventricular arrhythmia therapy and SCD prevention involve managing underlying and concomitant conditions and diseases while preventing acute and progressive worsening [5]. In most cases, pharmacological therapy only has not been shown to be effective therapy enough; therefore, the proper consideration and implementation of device and pharmacological therapy are of paramount importance in the management of ventricular arrhythmias. The most effective device-assisted method of treating malignant ventricular tachycardias is the rapid termination by direct current defibrillation (DF).

Atrial fibrillation is the most common sustained cardiac arrhythmia, with a prevalence of up to 4% in the population over 20 years old. Treatment options include both pharmacological and nonpharmacological methods. In hemodynamically unstable patients with atrial fibrillation, an emergency electrical cardioversion (ECV) should be the preferred choice, while in stable patients, antiarrhythmic drugs preceding ECV can also be attempted. The benefits of rhythm control therapy include improving hemodynamics and quality of life, as well as reducing the time in arrhythmia, therefore the risk of potential thromboembolism, beside pharmacological therapeutic measures [6].

The success of both ECV and DF is dependent on the delivery of sufficient current. Current is determined by energy and transthoracic impedance (TTI). TTI largely depends on the patient's characteristics, and the exact factors affecting it are still a matter of debate.

#### **1.2 Relevance of the chapter**

Accurate identification of the exact influencing factors of TTI may lead to an increase in the efficacy of ECV and DF while minimizing the risk of complications. Adjusting the delivered energy according to identified clinical variables that independently influence the thoracic electrical impedance and hence the trans-myocardial current might result in more adequate defibrillation strategies, thus, better defibrillators in the future.

The importance of TTI is further supported by a recent meta-analysis, concluding that skeletal muscles shunt away 82% of the electrical current while lung tissue shunts away 14% of the heart so that only 4% of the total level of electrical current reaches the heart [7]. This, besides raising some clinical questions, reinforces the need to gain a better understanding and insight into the factors that influence the level of TTI, hence the extent of electric current flow.

#### **1.3 Definition and background of transthoracic impedance**

The history of electrical defibrillation dates back to 1956, when a patient was successfully treated for ventricular fibrillation. A few years later, the delivery of an electric shock proved to be effective in atrial fibrillation and atrial flutter [8, 9].

Several factors have been investigated to make defibrillation therapy more effective, highlighting the paramount importance of the current application and the current delivery distribution [10]. Effective defibrillation is based on the delivery of *The Influence of Transthoracic Impedance on Electrical Cardioversion and Defibrillation… DOI: http://dx.doi.org/10.5772/intechopen.112538*

an electrical shock to a critical amount of myocardial cells, which is determined by the flow of electrical current that is influenced by the shock energy modified according to the measured TTI. If the electrical current is too low, defibrillation will fail, so the objective should be to reduce the level of TTI as much as possible [11].

With the development of cardiac implantable devices, it has become possible to measure a variety of parameters, enabling healthcare specialists to provide telemedical treatment and monitoring. One of these parameters is the monitoring of the intrathoracic impedance in a special setup of implantable cardioverter defibrillators (ICDs) to monitor fluid overload in chronic heart failure patients. A recent metaanalysis has shown that reduced intrathoracic impedance is a significant risk factor for developing both atrial and ventricular arrhythmias [12]. However, in the present chapter, we focus on the factors affecting transthoracic impedance and do not address intrathoracic impedance because of the different measurement characteristics.

The factors that influence TTI can be divided into two subgroups, modifiable (extrinsic) and nonmodifiable (intrinsic) factors. Although the latter are not alterable, knowledge of them allows us to approximate the value of a TTI more accurately.

#### **1.4 Methodology of transthoracic impedance measurements**

The available datasets involving TTI measurements are derived mainly from implantable defibrillator devices and external defibrillators in the setting of electrophysiological conditions requiring the delivery of an electric shock to patients. The other technique is high-frequency impedance estimation. This is a built-in feature of all modern defibrillator devices, estimating what the current TTI value might be according to the so-called test-pulse method by delivering a minimum current electrical pulse.

#### **2. Factors influencing transthoracic impedance**

#### **2.1 Paddle force, contact pressure**

Several studies have examined the influence of electrode contact on the TTI, highlighting an inverse relation between electrode pressure and TTI [13–18]. When holding conventional, hand-held defibrillator paddles, by increasing the pressure force, the electrical contact surface at the electrode-skin contact level increases, while the air volume in the lungs may decrease [15]. The optimal paddle force is different for adults and children: 8 kilogram-force (kgf) for adults, 5 kgf for children, and 3 kgf for infants [13, 14].

Since 2020, the ERC guidelines have recommended the use of self-adhesive defibrillation pads instead of defibrillation paddles to improve defibrillation performance and increase the safety of the providers [19]. Although the importance of paddle force has been marginalized by the widespread use of defibrillation pads, studies indicate that the force applied to self-adhesive defibrillation pads may as well contribute to reduced TTI [17, 18, 20].

In addition to the absolute force applied, the size of the defibrillator electrode is also important, as it is a key element in the distribution of the pressure. This may be especially important in the case of defibrillating infants and children weighing less than 10 kg [7].

#### **2.2 Pad/paddle placement**

Human studies have failed to prove the role of the pad position as a determinant of Return of spontaneous circulation (ROSC) in the setting of ventricular tachycardias [19]. According to the ILCOR 2020 systematic review, trans-myocardial electrical flow is highest when the fibrillating myocardial area is located between the defibrillator electrodes. This indicates that the optimal position of the electrodes is the region located close to the left ventricle in cases of ventricular arrhythmia. Where feasible, anterolateral (sternal-apical) positioning is recommended; however, anteroposterior, bi-axillary, and right posterior-apical positionings are also acceptable. In largebreasted individuals, the electrode may be shifted to the lateral or inferior side, selecting the one closest to the optimal placement if possible [19, 21]. Deakin et al. found that the use of the apical defibrillation paddle in a longitudinal orientation resulted in a significantly lower TTI compared to the transverse placement during shocks in cardioversion [22].

#### **2.3 Repeated shocks**

The change in TTI during multiple shocks is also a topic of debate [23]. In their study, Deakin et al. conducted electrical cardioversion on 58 patients. TTI significantly decreased with each consecutive shock, initially averaging 92.2 Ohms, while for patients receiving five shocks, the average was 85.0 Ohms [24]. Similarly, Fumagalli and colleagues found a significant difference in TTI, which decreased by 6.2% after 2 or more shocks from the starting value [25]. However, Walker and colleagues analyzed data from 863 out-of-hospital cardiac arrest patients treated with AED shocks for ventricular fibrillation and found no significant change in TTI between consecutive shocks. In the study, they examined both the high-frequency impedance and the shock impedance; all patients were initially administered 200 J for their first shocks, with the second shocks being either 200 J or 300 J, using preprogrammed AEDs by the local protocols [26]. Niemann and colleagues also found similar results in their animal model, as TTI did not change significantly in animals receiving 4 or more shocks compared to the first shock to eliminate ventricular fibrillation [27].

#### **2.4 Hypothermia**

The beneficial role of induced hypothermia (HT) is still a widely debated issue, mainly as a measure to protect the heart and brain after cardiac arrest following resuscitation. According to Rhee and colleagues, severe HT enhanced the success of transthoracic defibrillation in a swine model. After inducing ventricular fibrillation for 30 s, the pigs were defibrillated using biphasic waveform at various energies in both normothermic and HT conditions. Results showed that severe HT (30°C) led to a higher success rate in terminating ventricular fibrillation compared to normothermia, even though impedance increased and current decreased during HT. No significant differences were found between normothermia and HT in the other groups [28]. Similarly, the moderate HT (33°C) group showed a significant increase in first-shock success, with a trend toward improvement in the severe HT group in another swine model [29]. The rise in defibrillation success despite the increased TTI in hypothermic conditions suggests that other factors besides current delivery may contribute to improved shock success.

*The Influence of Transthoracic Impedance on Electrical Cardioversion and Defibrillation… DOI: http://dx.doi.org/10.5772/intechopen.112538*

#### **2.5 Respiration phase**

Sirna and colleagues observed 28 patients who underwent elective cardioversion and were monitored for 48 h after shock delivery and compared them with 10 control subjects who did not receive a shock. TTI was 9% lower at end-expiration compared to end-inspiration [15]. Kim and colleagues also confirmed that impedance seems to be sensitive to changes in lung volume and body position [30]. According to a study published in 2004, TTI drops as thoracic volume decreases, but this only accounts for a maximum of 16% of the total TTI reduction [31]. Deakin and colleagues also observed that TTI increased linearly with increasing positive end-expiratory pressure [32]. Furthermore, in another study, they examined 10 healthy people while they breathed different respiratory gas mixtures and concluded that TTI is unlikely to be affected by different breathing gases during defibrillation [33].

#### **2.6 Coupling agent**

The proper alignment and connection of electrodes to the skin are vital for achieving accurate TTI measurements. Sirna et al. found that using a salt-free adhesive gel (ultrasound gel) led to a 20% higher TTI compared to a salt-containing gel (Redux paste). When no adhesive was used, TTI was significantly higher than the control [15]. In a study, 80 patients were examined and received 267 shocks using self-adhesive electrode paddles. The researchers compared the effectiveness of these pads to traditional manual electrode paddles. The transthoracic impedance during defibrillation did not significantly differ between the self-adhesive pads and manual pads (75 ± 21 Ohm vs. 67 ± 36 Ohm). The initial shock success rate of 64% for ventricular fibrillation of self-adhesive pads using 150–200 J shock energy was found to be comparably good [34] to the defibrillation rates achieved in a large prospective study that achieved successful first shock in 61% of the total OHCA patients, delivering 175 J shock energy by defibrillation paddles [35]. Thus, self-adhesive pads were found to be effective for both defibrillation and cardioversion [34]. However, Dodd and colleagues found that using manual paddles resulted in lower TTI than using self-adhesive paddles in both the anterior-anterior and anterior-posterior positions [36]. This may be due to the pressure set on the paddles and body by defibrillation providers.

#### **2.7 Age**

The relationship between age and TTI is not well understood, and there is a lack of agreement among experts. Several studies have reported that TTI values are higher in older adults. This can be attributed to a variety of factors, including altered body posture as a result of musculoskeletal diseases associated with aging and decreased lung function [7, 37]. However, in a study by Fumagalli and colleagues, there was no correlation between age and chest impedance. This discrepancy may be explained by their study population being restricted to a narrow age range, with 75% of patients being around 70 years old [38]. Additionally, there was a high prevalence of chronic heart failure in the patient population, which is associated with lower chest impedance. Seung-Young Roh and colleagues performed a total of 683 direct current cardioversions in 466 patients with atrial tachyarrhythmias. In their study, they found that age did not affect TTI [39].

#### **2.8 Gender**

In a meta-analysis, Heyer and colleagues obtained contradictory results regarding the relationship between TTI and gender and found no clear trend. Body fat increases with age, to a greater extent, in women than in men [7]. From this, one might conclude that chest electrical impedance is higher in women; however, many other factors also differ between the two sexes, which makes the picture more nuanced. For example, chest hair also affects TTI. It has been shown that after shaving, chest impedance decreases significantly [40, 41]. In the 2020 ILCOR overview paper, the authors conclude that the removal of chest hair before electrode placement may be considered if it does not delay the shock delivery [42]. Overall, it can be said that factors that affect TTI, such as the amount of subcutaneous fat, or hair, and breast size, also show a high degree of variability within gender and that knowledge of these factors together would be necessary to tailor the delivered shock energy level to the individual.

#### **2.9 Body mass index (BMI)**

The results of the studies suggest that as BMI increases, chest impedance also increases [22, 38, 39, 43, 44]. The exact mechanism behind this is currently unknown. It is believed that increased amounts of fat tissue may lead to higher chest impedance values. Body composition measurement methods (InBody) also utilize this characteristic in their measurements [45].

#### **2.10 Hemoglobin concentration**

Studies have shown a connection between hemoglobin concentration and the electrical properties of blood [46]. Plasma is believed to be the conductive element of blood, with red blood cells interfering with current flow and increasing blood viscosity [47]. The microvascular tree itself alone acts as an electrical insulator due to the presence of endothelial and red blood cells along the capillary wall [48].

Studies have shown a correlation between hemoglobin oxygen saturation and TTI [25, 38]. According to one study, a 1.9 ± 0.6 Ω increase in TTI with higher Hb concentration is related to the electrical properties of blood and the insulating layers around capillaries [38]. Another study found a 0.2 ± 0.1 Ω increase in TTI with higher Hb O2 saturation, partially attributed to Chronic Obstructive Pulmonary Disease symptoms [25]. An animal study observed that hypoxia can affect TTI by changing cytoplasmic resistance and intercellular impedance [49]. Higher Hb O2 saturation results in a small increase in TTI, with clinical significance dependent on other pathological symptoms.

#### **2.11 Presence of chronic heart failure**

In chronic heart failure, transthoracic impedance also changes in parallel with the symptoms of heart failure, such as pulmonary congestion, decreasing the TTI value. Research has found that a decrease in TTI or intrathoracic impedance, as measured by Cardiac resynchronization therapy (CRT) and ICD devices, is linked to the severity of heart failure and the patient's prognosis [38, 50–52]. Measuring TTI can aid in predicting the severity of heart failure and the patient's prognosis, as well as assessing the effectiveness of the treatment (**Table 1**).

*The Influence of Transthoracic Impedance on Electrical Cardioversion and Defibrillation… DOI: http://dx.doi.org/10.5772/intechopen.112538*


*Chapter sections: 2.1. Paddle force, contact pressure, 2.2. Pad/paddle placement, 2.3. Repeated shocks, 2.4. Hypothermia, 2.5. Respiration phase, 2.6. Coupling agent, 2.7. Age, 2.8. Gender, 2.9. Body mass index (BMI), 2.10. Hemoglobin concentration.*

#### **Table 1.**

*Influencing factors of TTI supported by a recent meta-analysis [7].*

#### **3. Conclusion**

Defibrillators are one of the most important devices that can potentially save a person's life in emergency medical situations of SCD or AF by restoring normal heart rhythm. The TTI plays a key role in determining the current flow during defibrillation and should be monitored and used for current modulation, to improve the success and safety of the procedure. In this chapter, we have analyzed and discussed the most important factors that can affect TTI and, thus defibrillation success.

#### **Conflict of interest**

The authors declare no conflict of interest.

#### **Acronyms and abbreviations**


### **Author details**

Adam Pal-Jakab, Bettina Nagy, Boldizsar Kiss and Endre Zima\* Department of Cardiology, Semmelweis University Heart and Vascular Centre, Budapest, Hungary

\*Address all correspondence to: zima.endre@med.semmelweis-univ.hu

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*The Influence of Transthoracic Impedance on Electrical Cardioversion and Defibrillation… DOI: http://dx.doi.org/10.5772/intechopen.112538*

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## *Edited by Endre Zima*

*Updates on Cardiac Defibrillation, Cardioversion and AED Development* delves deeply into the multifaceted world of arrhythmia treatment. Through various approaches, the chapters show a wide array of electrical and pharmacological methods to restore normal sinus rhythm in tachyarrhythmic cases. From the historical perspective of the first use of direct current electrical cardioversion to the effective deployment of Automated External Defibrillators (AEDs) in public-access defibrillation programs, this book underscores the crucial role of timely intervention. Focusing on atrial arrhythmias, the impact of tachyarrhythmia on heart function is highlighted and potential breakthroughs of cardioversion drugs are introduced. In the context of hypertrophic obstructive cardiomyopathy, the book uncovers treatment strategies, emphasizing the innovative cardiac myosin modulation. The chapter on the effectors of transthoracic impedance and their significant influence on electrical intervention success rate urges personalized optimization methods for increased efficiency. Collectively, these chapters provide a comprehensive overview of various aspects of arrhythmia treatment, presenting advancements, challenges, and strategies to enhance patient outcomes in the dynamic landscape of acute cardiology care.

Published in London, UK © 2024 IntechOpen © Bruno Thethe / Unsplash

Updates on Cardiac Defibrillation, Cardioversion and AED Development

Updates on Cardiac

Defibrillation, Cardioversion

and AED Development

*Edited by Endre Zima*