Vol. 284, Issue 3, H815-H819, March 2003
Left ventricular geometry immediately following
defibrillation: shock-induced relaxation
Amy L.
De
Jongh1,
Vijaya
Ramanathan1,
Brent K.
Hoffmeister2, and
Robert A.
Malkin1
1 Joint Graduate Program in Biomedical Engineering,
The University of Memphis and University of Tennessee Health
Sciences Center, Memphis 38152; and 2 Department of
Physics, Rhodes College, Memphis, Tennessee 38112
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.
deexcitation; ultrasound; cardiac mechanics
