The Journal of Thoracic and Cardiovascular Surgery, Vol 92, 755-765, Copyright © 1986 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
The effects of cardioplegic potassium concentration and myocardial temperature on electrical activity in the heart during elective cardioplegic arrest
TB Ferguson Jr, PK Smith, GK Lofland, WL Holman, MA Helms and JL Cox
A major objective of cardioplegic arrest for protection of the heart during
cardiac operations is total electromechanical quiescence. Recent studies
from our laboratory in which we used multiple bipolar intracardiac and
unipolar intramural electrodes have detected the presence of electrical
activity in the lower atrial septum, the atrioventricular node-His bundle
complex, and in ventricular myocardium during elective cardioplegic arrest
that cannot be detected on the limb- lead electrocardiogram. Moreover, this
low-amplitude electrical activity is not associated with visible mechanical
activity of the heart and occurs at ventricular septal temperatures
previously thought to be adequate for myocardial protection. The present
study was designed to determine the effect of cardioplegic solution
potassium concentration and myocardial temperature on the occurrence and
duration of low-amplitude electrical activity during elective cardioplegic
arrest. Fifty adult mongrel dogs were subjected to two consecutive 20
minute periods of cardioplegic arrest. The animals were divided into six
groups, depending upon the cardioplegic solution potassium concentration
they received and on whether or not topical cooling techniques were
employed. The probability of occurrence of low- amplitude electrical
activity during the arrest interval was significantly decreased by
application of topical hypothermic techniques and reinfusion of
hyperkalemic, as compared to normokalemic, cardioplegic solution. These
effects of hyperkalemic cardioplegic solution and myocardial hypothermia
acted synergistically, but independently, to decrease the likelihood of
low-amplitude electrical activity occurring during the period of
cardioplegic arrest. Nevertheless, low-amplitude electrical activity did
occur in all groups after each cardioplegic solution administration and was
not detected by routine monitoring techniques. This suggests that
low-amplitude electrical activity may represent a fundamental type of
metabolic activity that can be recorded from the heart during arrest and
may be responsible for the temporary depression in ventricular function
that frequently follows a period of elective cardioplegic arrest.
