Background: In previous studies comparing regional 201Tl (201Tl) and 18fluorodeoxyglucose (FDG) activity in patients with chronic coronary artery disease and left ventricular dysfunction, we hypothesized that regions with mild-to-moderate reduction in FDG activity and regions with mild-to-moderate irreversible 201Tl defects after 3- to 4-hour redistribution represent viable myocardium. In the present study, regional FDG and 201Tl activities were compared with regional systolic wall thickening by gated magnetic resonance imaging (MRI) to confirm the presence of viable myocardium in these territories.
Methods and results: Twenty-five patients with chronic stable coronary artery disease and left ventricular dysfunction (ejection fraction, 28 +/- 10) underwent exercise 201Tl tomographic imaging (SPECT), using a reinjection protocol, positron emission tomography (PET) with FDG and H2(15)O, and gated MRI. Matched SPECT, PET, and MRI tomograms were analyzed. From the PET data, 105 regions had matched reduction in FDG and blood flow, of which 69 regions had moderately reduced FDG uptake (50-79% uptake relative to a normal reference region) and 36 had severely reduced FDG uptake (less than 50% of normal activity). Regions with moderately reduced as compared with severely reduced FDG activity had greater end-diastolic wall thickness (9.4 +/- 2.6 versus 8.0 +/- 3.7 mm; p less than 0.05) and regional systolic wall thickening (1.7 +/- 2.7 versus -0.7 +/- 2.1 mm; p less than 0.01). From the SPECT data, 169 irreversible 201Tl defects after 3-4 hour redistribution were identified, of which 70 were mild (greater than 65 to less than 85% of maximal 201Tl activity), 52 were moderate (50-65% of maximal activity), and 47 were severe (less than 50% of maximal activity). Regional systolic wall thickening was greater in regions with normal 201Tl uptake (3.3 +/- 2.3 mm) as compared with all other regions. Regions showing only mild or moderate irreversible defects at redistribution, however, showed wall thickening (2.4 +/- 2.4 and 2.2 +/- 2.5 mm, respectively), which was similar to that observed in regions with reversible 201Tl defects (2.1 +/- 2.2 mm). Only regions with severe irreversible defects at redistribution showed absence of thickening (-0.1 +/- 2.9 mm, p less than 0.01 versus all other groups). After 201Tl reinjection, 12 of 47 (26%) regions with severe irreversible defects showed enhanced 201Tl uptake. The impairment in regional systolic wall thickening was not significantly different between 201Tl defects with and without enhanced 201Tl uptake after reinjection. FDG activity, however, was present in all 12 regions (100%) with enhanced 201Tl uptake after reinjection as compared with only five of 35 (14%) that were unchanged after reinjection (p less than 0.01).
Conclusions: Therefore, preserved wall thickness and systolic wall thickening in regions with moderate reduction in blood flow and FDG activity, and in irreversible 201Tl defects that are only mild-to-moderate, provide additional evidence that such regions represent viable myocardium. Moreover, the finding of metabolic activity and 201Tl uptake in regions with reduced blood flow and absent wall thickening provides clinical evidence of hibernating myocardium in humans.