The Journal of Thoracic and Cardiovascular Surgery, Vol 109, Issue 5 981-988, Copyright © 1995 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
NOTE: The fulltext of this article is not available online.
The effects of normothermic and hypothermic cardiopulmonary bypass on defibrillation energy requirements and transmyocardial impedance. Implications for implantable cardioverter-defibrillator implantation
D. Martin, J. Garcia, C. R. Valeri and S. F. Khuri
Department of Cardiology, West Roxbury Veterans Administration Medical Center, MA, USA.
The influence of normothermic and hypothermic cardiopulmonary bypass on
defibrillation energy requirements and transcardiac impedance is not well
characterized. However, this relationship is of clinical importance during
automatic defibrillator implantation done with concomitant cardiac surgery,
and there is anecdotal information that criteria for successful
implantation are harder to achieve after such operations. We studied the
effect of controlled hypothermia on defibrillation energy requirements and
transcardiac impedance in a canine model of cardiopulmonary bypass in which
26 animals underwent right atrial and femoral arterial cannulation, as well
as continuous hemodynamic and intramyocardial temperature monitoring. The
defibrillation energy requirements were evaluated at 60-minute intervals
with an epicardial patch system, and transcardiac impedance was measured
before and after the multiple inductions and terminations of ventricular
fibrillation. In group 1 (n = 10) defibrillation energy requirements were
evaluated immediately after initiation of cardiopulmonary bypass at 37
degrees C (T0), after gradual cooling to 28 degrees C (T1), and after
rewarming to 37 degrees C (T2). Group 2 (n = 16) comprised time controls
that were identically instrumented and studied, but maintained at 37
degrees C throughout. Percent successful defibrillation was plotted against
delivered energy, and the raw data fit by logistic regression. The energy
at which 50% of shocks were successful (E50) was 3.23 +/- 0.89 joules at
T0, 5.12 +/- 1.85 joules at T1, and 4.42 +/- 1.22 joules at T2 in group 1;
this was not significantly different from the corresponding group 2 E50
values, which were 3.11 +/- 1.39 joules, 4.95 +/- 2.47 joules, and 5.59 +/-
3.18 joules, respectively. Both groups demonstrated a significant increase
in E50 during the first hour of cardiopulmonary bypass (mean increase from
T0 to T1 was 1.89 joules in group 1 and 1.84 joules in group 2, p <
0.05). Transmyocardial impedance fell progressively during the group 2
experiments from 73.6 +/- 12.9 omega at the beginning of the T0 shock
series to 61.4 +/- 8.9 omega at the end of the T2 shock series. A similar
reduction in transmyocardial impedance was observed during the course of
all the group 1 experiments; however, at the beginning of the T1 shock
series impedance was significantly elevated to 77.4 +/- 12.3 omega (p
< 0.05 compared with group 2 and with end T0 in group 1). There was
no relationship between defibrillation energy requirements and transcardiac
impedance; there was also no correlation between either of these parameters
and intramyocardial extracellular pH or left ventricular end-diastolic
pressure.(ABSTRACT TRUNCATED AT 400 WORDS)
