Aims: The relationship between wall thickness, wall thickening, wall motion, and single-photon emission computed tomography (SPECT) results for detection of myocardial infarction has never been systematically evaluated in a clinical setting. In particular, the discussion whether non-ischaemic regional wall motion abnormalities and reduced wall thickness can cause SPECT to be false positive for infarct detection remains unsettled.
Methods and results: We therefore evaluated patients presenting with left bundle branch block (LBBB) and only included them in the analysis if any coronary artery disease (CAD) had been ruled out by angiography. LBBB is known to cause septal wall motion abnormalities as well as to reduce systolic septal wall thickness. Thus, LBBB is a good non-ischaemic clinical model to evaluate the influence of wall thickness and wall motion on the homogeneity of tracer distribution in resting SPECT images. SPECT revealed fixed defects in all 139 patients initially identified for possible enrollment. CAD was found to be present by angiography in 120 patients. The remaining 19 patients without any CAD underwent cardiovascular magnetic resonance (CMR) and were included in the study. Evaluation of SPECT using a 72-segment model revealed septum-related fixed defects in all 19 patients. Every defect was interpreted as myocardial infarction by blinded observers. The comparison of nuclear results to the gold standard CMR demonstrated that none of the fixed SPECT defects did represent myocardial infarcts. Defects, however, exactly matched areas of wall motion abnormalities as well as regions with impaired wall thickness as demonstrated by CMR. On a segmental basis, we found a strong relationship between wall motion and reduced wall thickness on one hand and SPECT defects on the other hand. For example, only 5% of segments with normal wall motion were false positive by SPECT for myocardial infarction, whereas 93% of all dyskinetic segments were found to be false positive (P<0.01). Comparing wall thickness to SPECT results revealed that 58% of segment in which wall thickness was 1 SD below the mean and 93% of segments in which wall thickness was 2 SD below the mean showed fixed defects by SPECT. Conversely, only 0.5% of segments in which wall thickness was above the mean were affected by false positive SPECT results (P<0.01).
Conclusion: Wall motion abnormalities as well as impaired myocardial wall thickening and wall thickness can cause false positive results of resting SPECT myocardial perfusion imaging for detection of myocardial infarction in the absence of myocardial infarct scars and CAD.