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Advisory algorithm/automation feature to inhibit inappropriate use of shock synchronization during cardioversion and defibrillation Disclosure Number: IPCOM000124611D
Publication Date: 2005-Apr-29
Document File: 5 page(s) / 37K

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A defibrillator is provided with prompted or automatic deselection of the synchronization function, and prompted or automatic adjustment of the cardioversion energy selection, when a rhythm is encountered that meets certain criteria contraindicating use of lower energy synchronized shocks.

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“No Sync Advised” advisory/automation feature to inhibit inappropriate use of shock synchronization during cardioversion and defibrillation

The idea described herein relates to prevention of inappropriate or mistaken use of the shock synchronization feature on manual external defibrillators during cardioversion and defibrillation.  It aims to minimize the risk of user error causing the use of shock synchronization when it is contraindicated or inadvertently enabled.  The idea addresses two issues that may lead to inappropriate use of a manual external defibrillator’s shock synchronization mode. 

The first issue relates to training and practice in clinical protocols for treatment of VT.  The AHA Guidelines 2000 (“Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care”, Supplement to Circulation, Vol. 102, Number 8, August 22, 2000) say that “monomorphic VT” should be treated with lower energy synchronized shocks, while “polymorphic VT” should be treated like ventricular fibrillation (VF) (i.e. with non-synchronized shocks at higher energy levels.).

Diagnostic criteria to be employed to distinguish between monomorphic and polymorphic VT are not well defined.  How to distinguish between “monomorphic” and “polymorphic” is left to the professional judgment of the user, an emergency medical care provider with clinical training.  However, the underlying electrophysiologic behavior of different tachycardias that might indicate or contra-indicate use of shock synchronization is not emphasized in clinical training, and in fact may not be included at all in the clinical training of many emergency medical care providers. 

In practice, it appears that ECG rhythms determined to be a VT rhythm are typically treated as candidates for synchronized cardioversion.  However, there is a risk within a subset of these rhythms, as in circuitous conduction the gap between depolarization and repolarization in the cardiac cycle becomes too short, the risk of a cardioversion shock converting the patient rhythm into VF becomes greater.  The risk stems from two factors: the energy used for cardioversion and the nature of unstable ventricular tachycardias.

Cardioversion protocols usually use escalating energies beginning at about 50 J.  Energies in this range are below the upper limit of vulnerability.  This range is high enough to initiate conduction in the heart, but too low to stop normal conduction.  The interaction between intrinsic conduction and induced wavefronts produces a risk of inducing fibrillation in the heart.  Increasing the energy above the upper limit of vulnerability, about 75 to 100 J (or below the lower limit of vulnerability, something less than 1 J) removes the risk of inducing VF.

The interaction is possible during the vulnerable period in the cardiac cycle, normally just prior to the peak of the T wave.  This is the interval in which conduction is actively occurring through the ve...