MYOCARDIAL INFARCT SCAN

INDICATIONS:

1. Detect myocardial damage when enzyme determination and the. electrocardiogram are inconclusive.
2. To differentiate acute from old infarction.
3. Localize and estimate the size of myocardial infarcts and contusions.
4. Peri-operative infarct detection.

PATIENT PREPARATION:

None.

RADIOPHARMACEUTICAL:

Technetium-99m pyrophosphate (PyP), 20-25 mCi is given I.V. The bladder is the critical organ (0.1-0.2 rad/mCi).

SCANNING TIME:

Scanning is performed 3 to 4 hours after injection. Up to four views may be required (ANT, 45· LAO, 70·LAO, LT LAT) for a total imaging time of 45 minutes.

OTHER CONSIDERATIONS:

Timing is critical for the successful use of this study. Scans may be negative if done in the first 12 to 24 hours after the onset of symptoms. In most cases, scans become increasingly positive from 24 to 72 hours after the cardiac insult. After this time, uptake diminishes and generally reverts to negative by 10 days to 2 weeks post infarction. A rare patient may not develop a positive scan for 4 or 5 days after the onset of symptoms. In general, optimal scan time is 24 to 72 hours after the acute event.

RATIONALE:

Tc-99m PyP is taken up by necrotic myocardial cells; its deposition in acute myocardial infarction parallels the accumulation of calcium in damaged tissue. PyP images are most likely to be positive when calcium deposition is most active (this is why timing is important). In addition, perfusion to at least the periphery of the injury must be preserved or re-established for accumulation of the radiopharmaceutical.