Description
The aim in both is to deliver electrical energy to the heart to stun the heart momentarily and thus allow a normal sinus rhythm to kick in via the heart's normal pacemaker, ie the sinoatrial node. Show
This article will discuss defibrillation and cardioversion. See also the separate Implantable Cardioverter Defibrillators article. What is defibrillation?At the end of the 18th century two physiologists, Prévost and Batelli, performed shock experiments on the hearts of dogs. They applied electrical shocks and discovered that small shocks put the dogs' hearts into VF and this was successfully reversed with a larger shock. It was first used in humans by Claude Beck, a cardiothoracic surgeon - on a boy aged 14 years who was undergoing cardiothoracic surgery for congenital heart disease. Electrodes were placed across the open heart. Closed chest defibrillation was not implemented until the 1950s in Russia. But it was not until 1959 that Bernard Lown designed the modern-day monophasic defibrillator. This is based on the charging of capacitors and then delivering of a shock by paddles over a few milliseconds. In the 1980s the biphasic waveform was discovered. This provided a shock at lower levels of energy which were just as efficacious as monophasic shocks. Differences between monophasic and biphasic systems
Types of defibrillators
Paddles versus adhesive patches
Energy levels for defibrillation[7]For adults, a range of defibrillation energy levels has been recommended by manufacturers and previous guidelines, ranging from 120-360 J. In the absence of any clear evidence for the optimal initial and subsequent energy levels, any energy level within this range is acceptable for the initial shock, followed by a fixed or escalating strategy up to maximum output of the defibrillator. The Biphasic Trial in 2007 compared lower fixed (150, 150, 150 J) and gradually increasing energy (200, 300, 360 J) shocks for out-of-hospital cardiac arrests.[8] Escalating energy shocks were associated with more frequent conversion and termination of VF as opposed to low-level fixed shocks. This applied to patients who remained in VF after the first shock. The COACHED mnemonic is used to help safe defibrillation and stands for: Continue chest compressions Paediatric defibrillation
What is cardioversion?Uses
In cardioversion the shock has to be properly timed, so that it does not occur during the vulnerable period, ie during the T wave. If this occurs then VT can be triggered. Atrial fibrillation
See also the separate article on Atrial Fibrillation. How to cardiovert
Which arrhythmias can be defibrillated?It is the treatment for immediately life-threatening arrhythmias with which the patient does not have a pulse, ie ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT).
Which of the following is a possible arrhythmia that an AED will detect?Which heart rhythms can be treated with an Automated External Defibrillator AED. VF is the most frequent rhythm in cardiac arrest, but it isn't the only one. The AED is designed to treat VF (Ventricular Fibrillation) or VT (ventricular tachycardia), which is a very weak but fast heart rhythm.
Which of the following rhythms are shockable by an AED?The two shockable rhythms are: Ventricular Fibrillation, or VFib. Pulseless ventricular tachycardia, or V-tach.
What are the four heart rhythms that an AED will shock?Shockable Rhythms: Ventricular Tachycardia, Ventricular Fibrillation, Supraventricular Tachycardia. Much of Advanced Cardiac Life Support (ACLS) is about determining the right medication to use at the appropriate time and deciding when to defibrillate.
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