Diagnostic Discrepancies Between Angiography and SPECT

Introduction to Diagnostic Discrepancies

SPECT detects functional perfusion defects indicating myocardial ischemia by measuring relative blood flow to the myocardium during stress versus rest, as stated by the American College of Radiology 1, 2
Angiography visualizes anatomic stenoses in epicardial coronary arteries but does not directly measure blood flow or tissue perfusion, according to the American College of Radiology 3

Studies combining PET perfusion imaging with coronary CT angiography demonstrate that nearly half (47%) of significant angiographic stenoses occur without evidence of ischemia, while 50% of normal perfusion studies show some anatomical abnormality, as reported by the American College of Radiology 4, 5
The American College of Cardiology emphasizes that myocardial blood flow reserve (MBFR) <1.9-2.0 indicates microvascular dysfunction even when angiography shows no obstructive disease 6

If SPECT shows a large, discrete reversible perfusion defect in a specific coronary territory, angiography typically identifies a corresponding epicardial stenosis (>50% diameter narrowing), as stated by the American College of Radiology 2, 5
SPECT has 87-89% sensitivity and 73-75% specificity for detecting angiographically significant CAD, according to the American College of Radiology 4, 5

Meta-analysis of 114 SPECT studies shows sensitivity of 78% and specificity of only 52% for detecting significant CAD, with negative predictive value of 83%, as reported by the American College of Radiology 7, 4
In the ACC's National Cardiovascular Data Registry, approximately 45% of elective cardiac catheterizations did not detect clinically significant stenoses (>50% luminal diameter) 8
Even among patients with positive noninvasive tests, only 41% were found to have significant CAD on angiography, as stated by the American College of Cardiology 8

Large perfusion defect, multiple territories involved, or transient ischemic dilation on SPECT warrant angiography regardless of potential discordance, as recommended by the American College of Radiology 1, 3
These findings predict higher cardiac event rates and potential benefit from revascularization, according to the American College of Radiology 7, 4