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Variations in the size of the ischemic myocardium due to differences in the normal file
1Philadelphia Heart Institute, Presbyterian Medical Center, Philadelphia, PA 19104.
Insights
Using a stress-specific normal file is crucial for accurately measuring myocardial perfusion abnormalities. An exercise-derived file overestimates defect size during pharmacologic stress testing, impacting quantitative analysis.
Area of Science:
- Cardiology
- Nuclear Medicine
- Medical Imaging
Background:
- Myocardial thallium concentration varies between pharmacologic and exercise stress testing.
- Differences in coronary blood flow and cardiac output influence thallium uptake.
- Using a non-specific normal file can lead to inaccurate quantitative measurements of ischemic myocardium.
Purpose of the Study:
- To evaluate the impact of using stress-specific normal files for quantitative measurement of ischemic myocardium.
- To compare the size of perfusion abnormalities using exercise-derived versus adenosine-derived normal files.
- To determine if stress-specific normal files are necessary for accurate assessment in patients with coronary artery disease.
Main Methods:
- 34 patients with isolated left anterior descending coronary artery disease underwent tomographic thallium imaging during adenosine infusion.
- Ischemic myocardium size was measured using polar maps with two normal files: one from exercise stress tests and one from adenosine stress tests.
- Perfusion abnormality extent and severity scores were compared between the two normal file groups.
Main Results:
- The extent of perfusion abnormality was significantly larger using the exercise file (19%) compared to the adenosine file (11%) (P=0.0001).
- Severity scores were also significantly higher with the exercise file (580) versus the adenosine file (310) (P<0.001).
- These discrepancies were observed in patients with both moderate and severe coronary artery stenosis.
Conclusions:
- A stress-specific normal file is essential for accurate sizing of myocardial perfusion abnormalities.
- Employing an exercise-derived normal file overestimates defect size in patients undergoing pharmacologic stress testing.
- Accurate quantitative assessment requires matching the normal file to the specific stress modality used.
Abstract:
The myocardial thallium concentration is different during pharmacologic than exercise stress testing due to differences in coronary blood flow and cardiac output. These differences may affect the quantitative measurement of the size of ischemic myocardium if a stress-specific normal file is not used. This study examined this concept in 34 patients with isolated left anterior descending coronary artery disease. All patients underwent tomographic thallium imaging during adenosine infusion (140 micrograms/kg/min for 6 minutes). The size of the ischemic myocardium was measured from the polar map using two different normal files; one derived from normal subjects undergoing treadmill exercise testing, and the second from normal subjects undergoing adenosine stress testing. The extent perfusion abnormality was 19 +/- 13% using the exercise file, and 11 +/- 10% using adenosine file (difference; 8.1 +/- 1.6%, P = 0.0001), the severity score was 580 +/- 480 using exercise file, and 310 +/- 310 using the adenosine file (P < 0.001). The differences were present in the 20 patients with moderate stenosis (50 to 70% diameter stenosis); 17 +/- 10% versus 7 +/- 7% (P = 0.001), and in the 14 patients with severe stenosis (> 70% diameter stenosis); 24 +/- 16% versus 18 +/- 10% (P = 0.03). Thus, stress-specific normal file should be used for sizing the perfusion abnormality. The use of exercise file overestimates defect size in patients undergoing pharmacologic stress testing.