Defibrillation threshold indicates the minimum amount of energy needed to return normal rhythm to a heart that is beating in a
cardiac dysrhythmia. Typical examples are the minimum amount of energy, expressed in
joules
The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied. ...
, delivered by external defibrillator paddles or pads, required to break
atrial fibrillation and restore normal
sinus rhythm. Other common scenarios are restoring normal rhythm from
atrial flutter,
ventricular tachycardia or
ventricular fibrillation.
The defibrillation threshold ranking in these settings, from lowest to highest, would be, in order, ventricular tachycardia, atrial flutter, atrial fibrillation, ventricular fibrillation. The highest amount of energy that an
external defibrillator can deliver at the present time is 360 joules biphasic. In clinical practice, the real threshold can be approximated but not exactly established, since the defibrillating shock can be delivered only once. Certain medications, in particular
sotalol
Sotalol, sold under the brand name Betapace among others, is a medication used to treat and prevent abnormal heart rhythms. It is only recommended in those with significant abnormal heart rhythms due to potentially serious side effects. Evidence ...
, tend to lower such threshold, while others, such as
amiodarone, may increase it.
Defibrillation threshold is a concept also applicable to internal or
implantable cardiac defibrillators.
[Curtis AB:
J Am Coll Cardiol. 2008;52(7):557-558. doi:10.1016/j.jacc.2008.05.016; Defibrillation Threshold Testing in Implantable Cardioverter-Defibrillators
Might Less Be More Than Enough?
] The test needed to establish the defibrillation threshold is often referred to as DFT.
References
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Cardiac electrophysiology