Technetium-99m-pyrophosphate uptake as an indicator of myocardial injury without infarct

Technetium-99m-pyrophosphate (PYP) is bound to calcium in necrotic myocardium and has been used clinically to evaluate myocardial infarction. Technetium-99m-PYP is also reported to accumulate in myocardium with unstable angina pectoris and it is speculated that severe ischemia with noninfarcted tissue may also increase uptake of 99mTc-PYP. In this paper, 99mTc-PYP uptake was determined in various models of myocardial ischemia of short duration to examine its applicability to the assessment of myocardial viability.

In 23 open-chest dogs under anesthesia, models of ischemia-reperfusion of the left anterior descending artery (LAD) subjected to ischemia for 10, 30 or 60 min were produced. Wall motion was examined by echocardiography and myocardial blood flow was calculated using colored microspheres. Technetium-99m-PYP was injected after each ischemic intervention and reperfusion.

Technetium-99m-PYP showed 1.18 +/- 0.009 in the uptake ratio (ischemic area/normal area) following 10-min ischemia (11 dogs). The uptake ratio following 30-min ischemia (8 dogs) showed a significantly higher increase than that following 10-min ischemia (4.09 +/- 1.75; p < 0.05), permitting in vivo and ex vivo imaging. After 60-min ischemia resulting in infarction (4 dogs), 99mTc-PYP uptake of the ischemic area showed an uptake ten times that of the normal area (transmural: 12.2 +/- 2.9, epicardium: 7.5 +/- 1.9, endocardium: 16.8 +/- 4.1).

These findings indicate that since 99mTc-PYP accumulates in injured myocardium, its concurrent use with blood flow imaging is useful for the assessment of severity of ischemia, injured area and myocardial viability.