Defibrillation external cardioversion

External Cardioversion or Defibrillation. The energy surge from direct current external cardioversion or defibrillation has the potential to damage the pulse generator or cause a bum at the electrode-tissue interface due to flow of current through the leads (69,70). Protective measures, such as serially placed... 

The presence of the epicardial patches can also be potentially problematic by insulating the heart from external shocks. Should an external cardioversion/defibrillation be needed, the external patches need to be placed so as to have an appropriate shocking vector (anterior-posterior in this case). 

Ventricular tachycardia (VT) is the result of uncontrolled electrical activity in the ventricle. This activity may be coordinated or uncoordinated. The definitive therapy for Ventricular is external stimulation by an electric field sufficiently large to reset the electrical activity of most ventricular cells. This ends the previous (uncontrolled) electrical activity and allows the reestablishment of normal cardiac activity. As explained earlier, this requires depolarization of a critical mass of tissue by a high-voltage discharge. When high-voltage therapy is delivered, an attempt is made to synchronize the delivery with a detected R-wave. A synchronized shock is termed cardioversion, whereas an unsynchronized shock is termed defibrillation because VF has no coherent electrical activity, and therefore no basis for synchronization (Figure 15.6). 

The introduction and manipulation of pacing leads are frequently associated with both tachyarrhythmias and bradyarrhythmias as a lead negotiates the chambers of the right heart. Ventricular tachycardia is extremely common as the pacing electrode or guidewire contacts the right ventricular myocardium. Simple withdrawal of these objects usually terminates the arrhythmia. In extreme cases, sustained monomorphic ventricular tachycardia and even ventricular fibrillation may occur. Some institutions have instituted a policy of placing external defibrillation pads prophylactically in anticipation of required cardioversion. 

---