External Cardioversion for Atrial Flutter

These are two continuous strips taken doing a cardioversion for atrial flutter. There are a few interesting points to notice:

• The first rhythm is a narrow complex rhythm at which is slightly irregular. At first glance this would look like atrial fibrillation but this was in fact atrial flutter with variable block.
• The cardioverter was synchronized to the QRS (note ventricle markers below each QRS) and the device discharged on the QRS as expected.
• The flutter does not terminate with the shock but the rate is a little slower with more A/V block.
• A second shock is given but the cardioverter is not synchronized (no vertical bars below the QRS) This was an operator error and increases the chance of VF being induced (see induction of VF with a T wave shock when checking a Defibrillation threshold )
  • this mode switch, is a "safety feature" of this cardioverter. The device switches to a defibrillation mode in case the first shock induces ventricular fibrillation and a rapid defibrillating shock is required. N.B. a cardioverter/defibrillator will not shock a patient in ventricular fibrillation if the device is in a synchronized mode.
• Fortunately the second shock does not fall on the T wave
• The impedance for the first shock was 68 ohms and for the second 63 ohms. This fall is probably is not a measurement error, as the impedance of a first shock is usually higher than those following and may explain the greater efficacy of second shocks.
• The progressive ST segment depression after both the first and the last shock.

Dr. M. Rosengarten