Sudden cardiac arrest (SCA) or sudden cardiac death (SCD) refers to the sudden cessation of cardiac activity with haemodynamic collapse, typically due to sustained ventricular tachycardia and/or ventricular fibrillation. SCA remains a major public health problem that accounts for approximately 60 000 deaths annually in the United Kingdom (Papadakis et al, 2009). In addition, approximately 8 people under the age of 35 years die every week due to sudden cardiac arrest in the UK, with 4.7% of cardiac arrests occurring outside of the hospital environment. About 95% of SCA victims will die before reaching the hospital but early defibrillation can triple a victim's chance of survival, making early and timely defibrillation an important intervention.
Research and clinical observational data seem to suggest that the majority of SCA occurs in patients with atherosclerotic coronary artery disease (El-Sherif et al, 2010), but often there is no identifiable cause. According to Papadakis et al (2009: 2):
‘The majority of sudden cardiac deaths are of ischaemic aetiology secondary to atherosclerotic coronary artery disease and affect the older section (35 years) of the population. In a significant proportion of sudden deaths, no specific cause is identified despite detailed histopathological examination and toxicology screen, and a diagnosis of sudden arrhythmic death syndrome (SADS) is advocated.’
Recent research has linked SCA with coronary heart disease (CHD), diabetes (Siscovick et al, 2010) and genetics (Rubart and Zipes 2005; El-Sherif et al, 2010).
CHD is the most common cause of SCA. Atherosclerosis leads to intracellular myocyte hypoxia which contributes to the development of cardiac arrhythmias and SCA (Mahmoud et al, 2011). Diabetes increases the risk of SCA because it is associated with both microvascular disease (such as atherosclerosis) and autonomic neuropathy (Siscovick et al, 2010). The reason that SCA is more common in patients with diabetic autonomic neuropathy is because in such patients there is a prolonged QT period. This lengthening of the QT interval leads to a disturbance in the autonomic regulation of myocardial repolarisation, leading to life threatening arrhythmias, such as SCA (Bellavere et al, 1988; Adabag et al, 2010; Junttila, 2010).
Concerning the genetic link, there is now compelling evidence that a genetic mechanism may increase a patient's susceptibility to SCA following myocardial infarction (Rubart and Zipes, 2005; Arking et al, 2010), and there is now a clear need for guidelines on the appropriate use of genetic testing for the most common genetic conditions associated with a risk of SCA and SCD (Gollob et al, 2011).
AEDs in the community
Sudden cardiac arrest can be aborted if an intervention (typically defibrillation) or spontaneous reversion restores circulation. In recognition of the fact that early and timely defibrillation can triple a victim's chance of survival in the community, the Department of Health (DH) has a target of placing 3 000 new defibrillators in public places in England. In a similar scheme in Wales, the Welsh Ambulance Service (WAS) has trained over 4 000 volunteers to use community based defibrillators in remote communities across Wales (WAS, 2012). Such defibrillators are usually ‘automated’ and are known as Automated External Defibrillators (AED) (Figures 1,2and3below).
AEDs in resuscitation
An AED device is a defibrillator that can analyse a patient's cardiac rhythm, and advise the resuscitator whether or not the patient is in a shockable rhythm and requires a shock as part of the resuscitation attempt. The AED works like a conventional defibrillator in delivering the shock, but an extensive internal database of arrhythmias aims to eliminate human error in rhythm interpretation, reducing the possibility of inappropriate defibrillation.
The AED uses the same self-adhesive pads used with manual defibrillators, but tends to only have an ‘on/off’ button and ‘shock’ button (Figure 1). This design makes them extremely simple to use competently by both healthcare professionals and out-of-hospital first aiders (Mitchell et al, 2008), as such, AEDs have been introduced in shopping centres and other public places. The introduction of the devices to these areas has consistently shown to significantly improve survival following out-of-hospital cardiac arrest (Hallstrom et al, 2004; Weisfeldt et al, 2010), as first responders are able to attach the AED, follow verbal prompts and deliver a standard shock energy of 150 joules if the patient is in either pulseless ventricular tachycardia (VT) or ventricular fibrillation (VF), as survival rates drop by 10% with every minute delay in delivering a shock.
The approach to any cardiac arrest is identical, with early effective CPR shown to improve patient survival (Christenson et al, 2009). This involves compressing the chest at the lower half of the sternum to 5–6 cm at a rate of 100–120 compressions a minute, at a ratio of 30 compressions to 2 breaths (Resuscitation Council, 2011). These compressions should be performed with minimal interruption in order to maintain coronary artery perfusion. This means that other interventions should occur simultaneously, such as application of defibrillation pads, which should occur in every resuscitation attempt. Delays of as little as 5–10 seconds has shown to reduce the incidence of successful defibrillation (Edelson et al, 2006). It is only when this has occurred that the resuscitator can determine if the arrest is due to a shockable or non-shockable rhythm following verbal prompts by the AED. In order for this to occur the self-adhesive pads must be applied correctly. There are multiple possible positions for pad application, with the standard pattern being one electrode placed inferior to the right clavicle, with the other placed in the left axilla in the V6 position. Alternative patterns that are feasible on the deceased patient is the biaxillary, with pads applied to both left and right axilla. Anterior-posterior position one electrode is placed directly anterior over the heart and the other placed posteriorly on the left scapula. If the patient has body hair this should be shaved to allow application of the pad, likewise, any fluid on the patient's trunk must be dried to ensure good adhesion. Furthermore, this area is considered the zone of defibrillation and failure to carry out the latter could mean the rescuer sustains a shock when the defibrillator is discharged.
Safety and training issues
While trained paramedics are performing CPR there is an expectation to ventilate a patient with supplementary oxygen at 15 L/min via a self-inflating bag. This results in a potentially oxygen rich environment, posing a risk of ignition. This is particularly relevant when passing an electrical current through the patient with an AED, the advent of self-adhesive electrodes has significantly minimised this risk, as historical reposts of ignition resulting in significant burns to the patient was due to poorly applied paddles (Hummel et al, 1988). To ensure patient safety, it is therefore recommended that any unsealed oxygen delivery devices are removed from the patient prior to defibrillation and maintained at a distance of one metre while defibrillation is carried out (Deakin et al, 2012). Exceptions to this principle would be if the patient was intubated with an endotracheal tube and connected to an artificial ventilator.
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However, paramedics are likely to be working in poorly ventilated areas, such as small bedrooms or bathrooms, meaning the oxygen vented via the ventilator exhaust could potentially enrich the environment with oxygen. It is recommended that clinical judgement is exercised at the scene, with safety being the highest priority.
It has long been known that safety considerations should be borne in mind when the patient has transdermal patches and requires defibrillation, meaning any patches in the area of electrodes should be removed. This is due to reported cases where transdermal patches have exploded and caused burns when they have been left under electrodes, and shocks delivered through the patch due to aluminium foil being used in the structure of these patches (Wrenn, 1990; Panacek et al, 1992). The paramedic should also ensure the patient does not have a pacemaker implanted under the electrode site; while most pacemakers are implanted around the left clavicle, and so have sufficiently clear room for standard electrode positions, any scars around the anticipated electrode site should be investigated to exclude the possibility of delivering the shock directly above a pacemaker.
Correctly applying the self-adhesive pads also reduces transthoracic impedance. This is a phenomenon whereby the current discharged from the defibrillator is lost to the thoracic cavity, thereby reducing the charge that actually crosses through the heart (Resuscitation Council, 2011), rendering the shock ineffective in terminating the VT or VF.
Once the pads are correctly applied and plugged into the AED the resuscitator can switch the AED on. The verbal prompt will ask that no one touches the patient as it analyses the cardiac rhythm. This does mean CPR is interrupted, but research suggests this has not decreased survival in out-of-hospital cardiac arrest, as Berdowski et al (2010) demonstrated that survival rates decreased when advanced life support trained paramedics took over from paramedics using AEDs. They suggested this was due to delays in delivering shocks due to the time spent analysing the cardiac rhythm. Once the AED has determined the cardiac rhythm it will advise the delivery of a shock in the case of VT/VF, or no shock if pulseless electrical activity or asystole was detected. Regardless of the announcement to shock or not, CPR should be restarted while the AED charges. Once the AED has charged, the chest compression should be stopped and rescuers must stand clear of the patient. The paramedic operating the AED should perform a rapid visual check around the patient to confirm that everyone is safely clear and unsealed oxygen delivery devices are moved one metre clear. Only then can they and declare they are delivering the shock and press the shock delivery button. Once the shock has been delivered CPR should be restarted immediately without checking for a pulse. Pulse checks should be performed every two minutes, the AED will time two minutes from the delivery of each rhythm analysis or shock, and prompt the rescuers to stand clear while it analyses the present cardiac rhythm.
During the resuscitation process it is clear that clear and effective communication is paramount for numerous reasons, particularly to ensure interventions are performed promptly and of course to ensure the safety of the patient, paramedic team and lay bystanders. Commands and/or requests should be clear and assertive, but polite, as frantic and aggressive communication will adversely affect team performance and potentially degrade the quality of care (Soar et al, 2010).
There are obvious risks in using an AED on patients, bystanders and the paramedic, with this in mind a paramedic must be properly trained before using the device on patients. Training in their use can be achieved through training courses run by local resuscitation departments or by completing a Resuscitation Council approved course such as Intermediate Life Support (ILS).
These courses will ensure the paramedic had a good level of understanding about correct electrode application, use of the AED, and defibrillator safety. They can also enable the paramedic to rapidly recognise cardiac arrest and be able to deliver an effective shock early in the resuscitation attempt (Resuscitation Council, 2008).
Paediatric defibrillation
The approach to paediatric defibrillation is identical to that of an adult, with principles of pad application, effective compressions and minimal interruptions to CPR advocated. Atkins et al (2009) state the incidence of VT/VF cardiac arrest is far lower in children, 7–15% compared to 25–30% in adults, but survival rates to discharge was higher in those children who presented with an initial shockable rhythm. The most common causes for these cardiac arrests are congenital heart disease, hypothermia and drug overdose (Deakin et al, 2010). Adult pads can be used with children over 8-years-old, while specific paediatric pads should be used for children less than 8-years-old (Resuscitation Council, 2011). When these pads are inserted into the AED it will automatically detect paediatric pads and reduce the standard energy down to 50 joules. However, products such as the iPAD range allow the use of standard pads in paediactric defibrillation due to their having an adult and child mode that can be easily switched between. In the event of a cardiac arrest of a child under 1 year, the use of an AED is not advocated due to the highly limited ability to adjust energy settings (Deakin et al, 2010).
Psychological impact of resuscitation for the paramedic
Resuscitation attempts on any patient is potentially stressful and emotionally damaging over time. This is particularly pertinent to paramedic practice, where the practitioner attends the victim at the scene, sometimes within horrific circumstances. Steen et al (1997) conducted a study in Oslo exploring paramedic decisions during cardiac arrest; however, the interviewed paramedics regularly discussed other aspects of the situation that held a high priority for them. This included care of the relatives following a cardiac arrest; these were relatives of patients through all age ranges. The study revealed high levels of stress and emotional burnout in paramedics, this was attributed to a ‘cope with anything’ culture, where formal debriefings following traumatic events did not exist, leaving the paramedic team to debrief each other on an ad-hoc basis. This left many with years of pent up emotions and reactions they were unable to process, resulting in relationship problems and occupational burn-out. These findings concur with those of James (1989), demonstrating an ongoing and historical problem.
More up-to-date research by Williams (2013) exploring student paramedics’ ability to deal with the emotions elicited by the job found they experienced difficulty in processing their emotions following distressing situations. Again, there were few formal support mechanisms in place specifically to deal with emotional turmoil. They tended to turn to friends, relatives and colleges on an ad-hoc basis, but did have the advantage of a clinical mentor to discuss their issues. However, attitudes echoed those found by Steen et al (1997) of ‘getting on with it’ and using humour to dispel emotional issues, demonstrating a historical and ongoing failure to provide paramedics with much needed support in what could be argued as one of the most stressful roles in healthcare.
Conclusions
SCA is a leading cause of death in the UK. Although it is often the case that no identifiable cause can be ascertained, the condition is linked to CHD, diabetes and has a strong genetic component. Early intervention, such as defibrillation via an AED, can reverse life threatening cardiac arrhythmias and if they are used correctly by appropriately trained paramedics they can improve patient survival.