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The Journal of Thoracic and Cardiovascular Surgery, Vol 91, 115-122, Copyright © 1986 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
EL Bove and AH Stammers
The immature myocardium has a greater tolerance for ischemia than does the
mature heart. The effect of ischemia when combined with hypothermia on the
newborn heart is poorly understood but has important clinical applications.
This study examined the metabolic and functional recovery after 90 minutes
of global ischemia at 20 degrees C in neonatal (1 week), immature (1
month), and mature (4 month) isolated working rabbit hearts. Following
ischemia, aortic flow, cardiac output, heart rate, and stroke work remained
at baseline values for neonatal hearts. Only coronary flow was
significantly reduced from a control level of 4.5 +/- 1.4 (standard error
of the mean) to 3.3 +/- 1.1 ml/min, p less than 0.05. In the immature
group, hemodynamic parameters were below baseline, although no statistical
differences were noted. Among mature hearts, however, all hemodynamic
values were significantly below preischemic control. Water content was
significantly higher in immature (73.2% +/- 1.4%) and mature (75.3% +/-
2.5%) hearts when compared with the neonatal group (46.8% +/- 4.6%), p less
than 0.001. Coronary sinus creatine kinase was unchanged from baseline at
10 and 30 minutes following ischemia in the neonatal group. Although
demonstrating substantial increases from baseline, statistical significance
was not seen in the immature group because of the wide variation about the
mean. In the mature group, creatine kinase rose significantly from
preischemic levels of 15.4 +/- 4.3 IU/L/gm to 184.2 +/- 51.6 IU/L/gm at 10
minutes (p less than 0.01) and 123.7 +/- 31.9 IU/L/gm at 30 minutes (p less
than 0.05). This study demonstrated improved tolerance to prolonged
hypothermic ischemia in neonatal rabbit hearts when compared with older
hearts subjected to the same conditions. The role of cardioplegic solutions
in protecting the neonatal heart during cardiac operations when deep
hypothermia is used may be of lesser importance than in the older patient.
ARTICLES
Recovery of left ventricular function after hypothermic global ischemia. Age-related differences in the isolated working rabbit heart
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