Summary
Uneven distribution of temperature and the persistence of electro-mechanical activity
after aortic cross-clamping are 2 factors limiting the myocardial protection during
cardioplegic arrest, especially in hypertrophied hearts which are known to be extremely
vulnerable to ischemia.
In the present study regional myocardial temperature (T) was continuously controlled,
and the time until arrest occurred (&;t) was determined in 61 patients undergoing
aortic valve replacement. In addition, the myocardial Contents of high energy phosphates
and lactate were assessed.
Three different cardioplegic Solutions were employed: In the first group we used Bretschneider
Solution (Br), in the second group St. Thomas' solution (St), and in the third group
the so-called “Hamburg cardioplegia” (H). During cardiac arrest the regional myocardial
temperature was adjusted to temperatures not exceeding 15 °C by intermittent infusions
of cold cardioplegic Solution. We found a positive correlation between left ventricular
muscle mass (LVMM) and &;t. A negative correlation existed between LVMM and adenosine
triphosphate (ATP) contents at the end of the ischemic period. The cooling characteristics
and At were significantly longer and the cooling to 15 °C was less rapid when H was
used. Adenosine-triphosphate contents were well preserved during ischemia in all 3
groups.
We conclude that all 3 cardioplegic Solutions tested protect the hypertrophied myocardium
adequately if the regional myocardial temperature does not increase above 15 °C during
cardiac arrest. Hearts with a higher LVMM showed a decreased myocardial ATP content
at the end of the ischemic period. Therefore, the LVMM may limit myocardial protection.
Key words
Cardioplegia - Cardiac arrest - Hypothermia - Myocardial hypertrophy - High energy
phosphates
