The Journal of Thoracic and Cardiovascular Surgery, Vol 94, 104-109, Copyright © 1987 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Recognition of reversible and irreversible myocardial injury by technetium pyrophosphate extraction kinetics
R Silva, YF Chen, TL Sell, JE Lowe and RH Jones
The need for a more accurate method of detecting episodes of myocardial
ischemia during cardiac operations, particularly during the ischemic arrest
interval, prompted us to investigate the usefulness of measuring the active
extraction of technetium pyrophosphate in identifying and quantitating
ischemic injury. Twenty-four adult mongrel dogs were subjected to
cardiopulmonary bypass, and normothermic global ischemia was induced by
cross-clamping the proximal aorta. Technetium pyrophosphate (1 mCi) was
injected through a standard cardioplegia line with normal saline,
simulating administration of cardioplegic solution, upon placement of the
aortic cross-clamp (time 0), at 15, 30, 45, and 60 minutes of global
ischemia, and with the onset and completion of ischemic contracture.
Radioactive counts were recorded over the heart at 1 second intervals, and
the extraction fraction and half-time of clearance were calculated. The
extraction fraction increased from 0.22 at time 0 to 0.58 at 15 minutes,
0.82 at 30 minutes, 0.85 at 45 minutes, and 0.91 at 60 minutes. The
halftime increased from a baseline of 114 seconds (time 0) to a maximum of
321 seconds at 60 minutes of ischemia. The onset and completion of ischemic
contracture showed a return toward baseline of both the extraction fraction
and halftime of clearance, with an extraction fraction of 0.44 and 0.46 and
a halftime of 135 and 133 seconds, respectively. These data clearly show
that reversible myocardial injury increased the extraction and reduced the
clearance of technetium pyrophosphate and that the magnitude of change
related to the extent of injury. The progression to irreversible myocardial
injury decreased the active extraction of technetium pyrophosphate. This
simple procedure for real-time documentation of myocardial injury promises
to provide easily obtainable endpoints of injury for use during cardiac
operations in humans.
