title: Left ventricular geometry immediately following defibrillation: shock-induced relaxation.
abstract: 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.
authors.affiliation: Joint Graduate Program in Biomedical Engineering, The University of Memphis, Memphis 38152, USA. adejongh@memphis.edu
authors.forename: Amy L
authors.initials: AL
authors.lastname: De Jongh
authors.forename: Vijaya
authors.initials: V
authors.lastname: Ramanathan
authors.forename: Brent K
authors.initials: BK
authors.lastname: Hoffmeister
authors.forename: Robert A
authors.initials: RA
authors.lastname: Malkin
mesh_terms: D000818:Animals; D002306:Cardiac Volume; D004285:Dogs; D004452:Echocardiography; D004554:Electric Countershock; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac / Q000379:methods; D006352:Heart Ventricles / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000000981:diagnostic imaging* / Q000503:physiopathology* / Q000628:therapy