Electric shock ventricular fibrillation

The cornerstone of therapy for ventricular fibrillation is electrical deflbrillation. In the acute setting, defibrination is first-line therapy. Intravenous bretylium can occasionally contribute to conversion, but this is infrequent. In the management of out-of-hospital cardiac arrest, high-dose epinephrine (5 mg intravenously) improves the rate of successful resuscitation in patients with asystole, but not in those with ventricular fibrillation, when compared with the standard dose of 1 mg. Vasopressin (40 U intravenously) may more effective than 1 mg intravenous epinephrine in out-of-hospital patients with ventricular fibrillation that is resistant to electrical defibrillation. The OPTIC smdy (see Connolly et al., 2006) showed that amiodarone plus jS-blocker is superior than sotalol or jS-blocker alone for reducing ICD shocks in patients with reduced left ventricular function and history of sustained VT, VF, or cardiac arrest. 

HPI CS is a 5 -year-old man admitted for an anterior Ml. Three days after admission, the patient s nurse found him unresponsive. His vital signs included no detectable blood pressure or pulse. ECG showed VT that progressed to ventricular fibrillation (VF). Immediate electrical defibrillation was applied. Other treatments instituted include airway management, chest compression, and establishment of IV access. After three shocks, 1 mg epinephrine was given and patient was shocked again. However, he was still in VF and amiodarone was administered. 

Vasopressin levels in patients with vasodilatory shock are inappropriately low, and such patients are extraordinarily sensitive to the pressor actions of vasopressin. The combination of vasopressin and norepinephrine is superior to NE alone in the management of catecholamine-resistant vasodilatory shock. Although the efficacy of vasopressin in the resuscitation of patients with ventricular fibrillation or pulseless electrical activity is similar to that of epinephrine, vasopressin followed by Epi appears to be more effective than Epi alone in the treatment of patients with asystole. 

Cardiac defibrillators are electronic devices that have been used for decades to provide a strong electrical shock to a patient in an attempt to convert a very rapid (and often chaotic), ineffective heart rhythm to a slower, coordinated, and more effective rhythm. When used to treat ventricular fibrillation (VF) or very rapid ventricular tachycardia the shock may be lifesaving because the heart output is nil or is too low to sustain life. Occurrence of VF is a medical emergency and rapid treatment (within seconds to minutes) is essential for survival. 

Another use for defibrillators is to shock either atrial flutter or fibrillation, which are abnormally rapid atrial rhythms. These atrial rhythms are much less likely to spontaneously proceed rapidly to death than ventricular arrhythmias. Using electrical shock to treat rapid heart arrhythmias other than VF is usually referred to as cardioversion and hence some users refer to the tachycardia treatment devices as cardioverter—defibrillators. Cardiovertor and defibrillator treatment is different from pacemaker treatment (discussed elsewhere in this book) because a pacemaker stimulates a slowly beating heart and uses much weaker shocks. Pacemaking increases the rate of the relatively healthy heart, which increases blood flow. 

Electrocutions kill an average of 143 construction workers each year. Data from 1992 through 2003 indicates electrical workers suffered the highest number of electrocutions per year, 34 percent of the total deaths caused by electrocution ( Alarming statistics, by D. Bremer, 2007, Electrical Contractor). Direct death from electrical shock results from ventricular fibrillation, paralysis of the respiratory center, or a combination of the two. Electricity can be hazardous to the process employees in a variety of forms. They are ... 

An AED is an electronic device designed to deliver an electric shock to a victim of sudden cardiac arrest. Ventricular fibrillation may be restored to normal rhythm up to 60 percent of the time if treated promptly with an AED, a procedure called defibril-lation. The American Heart Association (AHA) estimates that approximately 890 deaths from coronary heart disease occur outside of the hospital or emergency room every day. According to the Occupational Safety and Health Administration (OSHA) in 2001 and 2002, there were reported 6628 workplace fatalities 1216 from heart attack, 354 from electric shock, and 267 from asphyxia. The AHA and OSHA have estimated that up to 60 percent of these victims might have been saved if automated external defibrillators (AEDs) were immediately available. Chances of survival from sudden cardiac death diminish by 7 to 10 percent for each minute without immediate CPR or defibrillation. After 10 minutes, resuscitation rarely succeeds. See Figure A.7 for an AED provided in a wall-mounted case. 

Institute of Electrical and Electronic Engineers (IEEE) Standard 1048-2003, lEEEGuide for Protective Grounding of Power Lines, provides the following equation for determining the threshold of ventricular fibrillation when the duration of the electric shock is limited ... 

The gross symptoms of cardiac arrest produced by electric shock are an unconscious subject who is not breathing, has no detectable pulse (cardiac arrest), and zero blood pressure. The heart, however, may be in either one of two states standstill or ventricular fibrillation. In standstill, as the name implies, the heart is not beating and the ECG signal is a flat line. In fibrillation, the ventricular muscle... 

Ironically, the treatment for cardiac arrest induced by an electric shock is a massive countershock, which causes the entire heart muscle to contract. The random and uncoordinated ventricular fibrillation contractions (if present) are thus stilled. Under ideal conditions, normal heart rhythm is restored once the shock current ceases. The countershock is generated by a cardiac defibrillator, various portable models of which are available for use by emergency medical technicians and other trained personnel. Although portable defibrillators may be available at industrial sites where there is a high risk of electrical shock to plant personnel, they should be used only by trained personnel. AppHcation of a defibrillator to an unconscious subject whose heart is beating can induce cardiac standstill or ventricular fibrillation, just the conditions that the defibrillator was designed to correct. 

Although the scaffold pole was a poor earth electrode, having a considerable earth resistance, it allowed sufficient current to flow through the labourer to cause fatal electrical injuries. Typical resistances would be 400 ohms for the earth connection and 2000 ohms for the labourer s body, resulting in a shock current of 230/(400 + 2000) = 0.096 A. A hand-to-hand current of 96 mA is sufficient to cause ventricular fibrillation. 

Electric shock can result in death by three different means—respiratory arrest, asph)odation, and ventricular fibrillation—briefly discussed below. 

Ventricular Fibrillation Because only a small amount of current is required to disrupt the natural rhythm of the heart, ventricular fibrillation is considered the most dangerous electric shock hazard. The shock current needs to pass through the heart during the phase when the ventricles are starting to relax after a contraction (Lee 1966). When fibrillation occurs, the effective pumping action of the heart ceases, the pulse disappears, and death usually occurs within minutes. The lower boundary of the threshold of ventricular fibrillation is generally considered to be 50 mA. 

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