How is external synchronized electrical cardioversion administered?

Updated: Nov 28, 2018
  • Author: Sean C Beinart, MD, MSc, FACC, FHRS; Chief Editor: Jose M Dizon, MD  more...
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Answer

Answer

Advanced cardiac (cardiovascular) life support (ACLS) guidelines should be followed as indicated. The key components in preparing the patient are intravenous access as well as the close availability of airway management equipment, sedative drugs, and a cardioverter/defibrillator monitoring device. Note the following:

  • The patient should be adequately sedated with a short-acting agent such as midazolam or propofol. In addition, an opioid analgesic, such as fentanyl, is commonly used. Reversal agents, such as flumazenil and naloxone, should be available.

  • The defibrillator should be placed in the synchronized mode, which permits a search for a large R or S wave. The delivered energy is selected. Most monophasic and biphasic models can deliver up to 360 joules. Manual button depression by the operator causes the defibrillator to discharge an electric current that lasts less than 4 milliseconds and avoids the vulnerable period of cardiac repolarization when ventricular fibrillation (VF, vfib) can be induced. The operator should be aware of this brief delay as the cardioverter searches for a large positive or negative deflection. If the deflections are too small for the defibrillator to synchronize, the clinician can change the leads or place them closer to the patient's chest or heart. If the patient develops ventricular fibrillation, always turn off synchronization to avoid delay in energy delivery.

  • Two options exist for the placement of the paddles on the chest wall. First is the anterolateral position in which a single paddle is placed on the left fourth or fifth intercostal space on the midaxillary line; the other paddle is placed just to the right of the sternal edge on the second or third intercostal space.

  • The second option is the anteroposterior position. A single paddle is placed to the right of the sternum, as above, and the other paddle is placed between the tip of the left scapula and the spine. Conductive gel or pre-gelled pads are commonly used to ensure good contact, because the skin can conduct away a significant portion of the current. Even under ideal circumstances, only 10-30% of the total current reaches the heart.

  • The paddles should be placed firmly against the chest wall to avoid arcing and skin burns. Although there is a risk of receiving a shock if touching the patient or the stretcher, bed, or other equipment in which the patient is in contact, evidence exists showing that continued contact with the patient is safe during biphasic defibrillation. [10]  Pacemakers and implantable cardioverter-defibrillators (ICDs) should be at least 10 cm away from direct contact with the paddles, and these devices should eventually be interrogated for any postcardioversion malfunction. The anteroposterior approach is preferred in patients with implantable devices to avoid shunting the current to the implantable device and damaging the system.

  • Energy requirements for atrial fibrillation (AF, afib) are 100-200 joules initially and 360 joules for subsequent shocks. A study showed good response to higher energy shocks of 720 joules for the treatment of refractory atrial fibrillation. [11] Biphasic shocks require a typical energy level of 75 joules for the correction of atrial fibrillation. Cardioversion of atrial fibrillation secondary to hyperthyroidism is 90% successful. [12] Only 25% of patients with atrial fibrillation caused by severe mitral regurgitation are successfully treated, and half revert in the first 6 months. Atrial flutter and paroxysmal supraventricular tachycardia (PSVT) require less energy: 50 joules initially, then 100 joules if needed. Cardioversion of ventricular tachycardia (VT, vtach) involves shocks of 50-100 joules initially, and then 200 joules if unsuccessful.

  • Either external paddles or stick-on electrode pads may be used to deliver the electric shocks.

  • Applying pressure to the pads using a rolled towel can improve cardioversion success by ensuring pad contact and minimizing skin burns.

  • In particularly difficult cases, two sets of pads and defibrillators can be used simultaneously to achieve synchronized cardioversion. [11]


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