March 2010 429

External cardiac defibrillators

One of the leading players in medical technology, BPL Healthcare has a significantly long presence in the cardiovascular devices segment as the first product launched by the company in 1969 was a single channel electrocardiograph.

In an interview with eHEALTH, Vijay Simha, COO and VP, BPL Healthcare, shares his perspective about the latest technologies and applications of external cardiac defibrillators.

Vijay Simha
COO and VP
BPL Health Management Solutions Group

Managing Sudden Cardiac Death Sudden cardiac death is a prevalent and signifi cant health problem even in developed countries. Sudden cardiac death (SCD) is defi ned as death due to cardiac causes, in which the time and mode of death is unexpected, in a person with or without pre-existing cardiac diseases and occurs within 1 hour of the onset of the symptoms. The defi nition is interpreted within combination of the various defi nitions of sudden cardiac death, which vary within the clinical, scientifi c and medico-legal context.

While the number of sudden cardiac deaths have been well documented in certain parts of the world; in India accurately and well collated information on sudden cardiac death do not exist. Estimates in the US put over 300,000 lives claimed by sudden cardiac death, annually. sudden cardiac death is mainly caused by a lethal form of cardiac arrhythmia known as ventricular fi brillation (VF) and has been characterized by a rapid, disorganized and asynchronized contraction of the ventricular muscle which compromises the circulation of blood in the body leading to organ failure causing death within minutes. Terminating Ventricular Fibrillation using a powerful electric shock and maintaining the fl ow of blood from the heart through manual heart massage has proved beneficial in bringing many people back to normal life.

Across the world, the awareness of giving prompt medical attention and conducting Cardio Pulmonary Resuscitation with an Automated Defi brillator has become a well established practice with paramedical, security and lay persons being trained to perform basic emergency CPR thus potentially having created an environment for saving an individual affi cted by Sudden Cardiac Death.

The Technology of Defibrillators

Defibrillators deliver a controlled and powerful enough electric shock to the heart so as to immobilize the heart muscle by depolarizing it. A number of hypothesis in the electrophysiology of ventricular fi brillation have been put since 1914 and current research has also rejected the so called “electrical paralysis hypothesis” proposed by Dudel (1968), where very strong shocks that were recommended were seen to cause extensive electroporation (rupture of the heart muscle cells) and permanent damage to heart tissue. Current thinking requires the depolarization of a “critical mass” in order to get the best outcomes (effective cardioversion, in this case) and various forms of electrical waveforms and critical parameter settings such as current density and energy settings have been the focus of research into defi brillator design.

Important findings reported strongly indicate the preference of a biphasic waveform with a controlled current density being applied. In externally used defi brillators this is achieved by assessing the victims impedence across the chest electrodes and delivering a predefi ned current vs time profi le.

The Battle of Waveforms 

Biphasic waveforms have been the subject matter of a number of outcome research. Currently divided into 2 schools of thought – the free discharge biphasically  switched waveform also called the Truncated Exponential Biphasic Waveform versus the controlled current waveform  also called rectilinear biphasic waveform. Patient impedence adjustments were present implicitly in a constant current source; the truncated exponential biphasic waveform needed special current sensing in order to control the discharge. The American Heart Association recommends a maximum energy of 200 J for biphasic external defi brillators and 360J for monophasic external defibrillators.

Out of Hospital Use of Defibrillators 

Automatic External Defi brillators (AED) and Public Access Defi brillators (PAD) are being widely recommended by various health authorities and public organizations to improve overall survivability of individuals suffering from sudden cardiac death. This requires adequately aware and trained public service personnel, and “Good Samaritans” to act within the fi rst 10-18 minutes of the occurrence of sudden cardiac arrest where chances for successful cardioversion is high. Afterwhich, the chances for cardioversion begins to drop very rapidly.

Designed and manufactured by BPL, this public access defi brillator is advanced-yet-easy to use, by any Good Samaritan. In order to be used by common public, this product features some relevant features such as Audio & Visual prompts in localized languages (Hindi/English), self-test protocols for “always-ready” usage, The constant current bi-phasic waveform technology is used in the Phoenix to minimize cardiac tissue damage and provide better outcomes. Past-event history review, Light weight & Long battery life make this product suitable for locating in public places.

Training and certifi cation of laypersons, professional paramedics and police/fi re rescue personnel would create an environment where awareness and speed of attention is possible. However, there are precautions in which rescuers need to keep in mind that they are exposed to the laws that are not friendly to “Good Samaritans” . Most AEDs and PADs however, are built in with a number of failsafe features and incorporate an intelligence backed by a substantial database to recognize ventricular fi brillation and prevent the device from delivering a shock on a normal heart. Moreover, the attending paramedic should also ensure that the procedure of CPR is appreciated and followed to ensure the overall success of resuscitation. He has also to ensure the safety of the bystanders during the process of resuscitation

Managing Public Access Defibrillators 

Public Access Defi brillators are located in public places and are available for use in case an emergency arises. Distributed across various important locations; they should be accessible in minutes for use. However, it is important to also manage these defi brillators on an ongoing basis so as to ensure that they are functional when they are most needed. A number of local management strategies as  well as networked strategies are implemented using wired/wireless systems monitoring of PAD health as well as by individual inspection on a regular basis. AEDs and PADs need to be maintenance friendly incorporating automatic self checks and functionality checks as well as automatic enunciators to indicate  fault conditions.

Also the PADs which are driven by voice commands should provide clear and understandable commands understandable by the population at large. The pronunciation and clarity of diction, possibly even in vernacular languages would make  these devices more user friendly.

A Public Access Defi brillator deployed at public places such as railway stations, bus stations,  shopping malls, airports, apartment complexes should clearly display the status of its functioning, purpose,  and availability so as to facilitate speed of attention. Primary health centers, physician’s clinics, sports stadia having a PAD will go a long way in saving lives.

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