Left ventricular geometry immediately following defibrillation: Shock-induced relaxation
A previous two-dimensional (2D) ultrasound study suggested that there is relaxation of the myocardium after defibrillation. The 2D study could not measure activity occurring within the first 33 ms after the shock, a period that may be critical for discriminating between shock- and excitation-induced relaxation. The objective of our study was to determine the left ventricular (LV) geometry during the first 33 ms after defibrillation. Biphasic defibrillation shocks were delivered 5-50 s after the induction of ventricular fibrillation in each of the seven dogs. One-dimensional, short-axis ultrasound images of the LV cavity were acquired at a rate of 250 samples/s. The LV cavity diameter was computed from 32 ms before to 32 ms after the shock. Preshock and postshock percent changes in LV diameter were analyzed as a function of time with the use of regression analysis. The normalized mean pre- and postshock slopes (0.2 ± 2.2 and 3.3 ± 7.9% per 10 ms) were significantly different (P < 0.01). The postshock slope was positive (P < 0.005). Our results confirm that the bulk of the myocardium is relaxing immediately after defibrillation.
American Journal of Physiology - Heart and Circulatory Physiology
De Jongh, A., Ramanathan, V., Hoffmeister, B., & Malkin, R. (2003). Left ventricular geometry immediately following defibrillation: Shock-induced relaxation. American Journal of Physiology - Heart and Circulatory Physiology, 284 (3 53-3) https://doi.org/10.1152/ajpheart.00093.2002