This is an interesting strip as it illustrates several important points.This is an interesting strip as it illustrates several important points.
The patient had an SVT or slow atrial flutter with 2:1 block. The first shock was 52 joules and synchronized to the QRS. (note the markers on the bottom of the tracing) The shock converts the patient not into sinus rhythm but an irregular rhythm which is probably atrial fibrillation. This failure to achieve sinus rhythm is more commonly seen with lower energy shocks.
The second point to note is that the second shock of 103 joules is not synchronized to the QRS. This is an operator error and reflects a "safety" feature of the defibrillator which switches to a non-synchronized mode after each shock, just in case VF is induced and non-synchronized defibrillation is needed. It is probable that most cardioverter/defibrillators will not shock a patient when the patient is in VF and the operator has the machine in the synchronized mode. Clearly in this case the "safety" feature was not safe, as T wave shocks are used to induce VF.
Finally note the change in the change in the T wave and ST segment after the shock.