Left ventricular geometry immediately following defibrillation-strength shocks

A previous 2D ultrasound study suggested that there is relaxation of the myocardium after defibrillation. However, that 2D study could not measure activity occurring within the first 33 ms following the shock. Thus, the objective of our study is to determine the left ventricular (LV) geometry during this period. Biphasic defibrillation shocks were delivered in seven dogs. One-dimensional, short-axis ultrasound images of the LV cavity were acquired, the boundary of the anterior and posterior endocardial walls was extracted, and the distance between them computed from 32 ms before to 32 ms after the shock. The normalized mean pre- and post-shock slopes are 0.2 +/- 2.2 and 3.3 +/- 7.9 %/10 ms, respectively. The post-shock LV diameter slope is positive in the first 32 ms following both successful and unsuccessful defibrillation shocks (p<0.05). Therefore, our results confirm that the bulk of the myocardium is relaxing immediately after defibrillation shocks.