Myocardial 43K uptake directly correlated with regional myocardial viability and blood flow (r=0.93 for transmural flow), whereas 99mTc-PYP uptake showed no such direct relationship.
In a canine infarct model, potassium-43 uptake directly correlates with myocardial viability and blood flow, whereas technetium-99m stannous pyrophosphate uptake is flow-dependent and maximal at moderately reduced flows rather than in the central infarct zone.
The dual radionuclide myocardial distributions of imaging agents potassium-43 (43K) and technetium-99m stannous pyrophosphate (99mTc-PYP) were studied in a 24-hour closed chest canine infarct preparation. In multiple myocardial biopsies in 20 dogs, tissue levels of both radionuclides were compared to either an index of tissue viability (myocardial creatine phosphokinase CPK depletion), or to estimates of regional myocardial blood flow as measured by the microsphere technique. Myocardial 43K uptake in the ischemic and infarcted zone correlated well with both CPK depletion (r = 0.73) and microsphere estimates of relative blood flow. The correlation with microspheres was excellent in the transmural sample (r = 0.93) as well as endocardial (r = 0.97) and epicardial (r = 0.86) portions. On the other hand, 99mTc-PYP myocardial uptake did not correlate with the extent of CPK depletion. Maximal uptake was frequently noted in border zones with only moderate CPK depletion, while lesser degrees of 99mTc-PYP uptake were noted in the central infarct zone where CPK activity was lowest. The relationship of 99mTc-PYP uptake to microsphere regional flow estimates demonstrated that 99mTc-PYP uptake was maximal at flows of 0.3 to 0.4 of normal. At lower flows, 99mTc-PYP uptake fell toward normal levels. A similar relationship was noted between the distributions of 99mTc-PYP and 43K. In relatively high flow border segments (larger than or equal to 0.80 of normal), abnormal 99mTc-PYP uptake of five to six times normal persisted. The transmural distribution of 99mTc-PYP demonstrated that in low flow regions 99mTc-PYP uptake was primarily epicardial, while in the higher flow ischemic periphery of the infarct endocardial uptake predominated. Thus, while there is a direct correlation between cationic 43K myocardial uptake and regional myocardial viability and blood flow, no such direct relationship exists for 99mTc-PYP. This is in part based on the necessity for delivery of the radioactive tracer to the infarct zone.
Zaret et al. (1976) studied Myocardial infarction (canine model) (n=20). Potassium-43 (43K) and technetium-99m stannous pyrophosphate (99mTc-PYP) imaging was evaluated on Correlation of radionuclide tissue levels with CPK depletion and regional myocardial blood flow. Myocardial 43K uptake directly correlated with regional myocardial viability and blood flow (r=0.93 for transmural flow), whereas 99mTc-PYP uptake showed no such direct relationship.