This study was aimed at determining whether the (201)Tl SPECT abnormalities documented in patients with dilated cardiomyopathy are related to a local excess in wall stress, which might act against the diastolic perfusion of myocardium.
Methods: We included 6 healthy volunteers and 7 patients with idiopathic dilated cardiomyopathy who underwent (201)Tl SPECT at rest. On a 13-segment division of the left ventricle, indices of wall stress and tension were calculated at end-diastole by applying Laplace's law, with thickness and curvature radii being determined for each segment on 2 orthogonal MRI slices.
Results: Among all patients, 21 analyzed segments had (201)Tl SPECT defects (D+) and 67 had none (D-). Myocardial thickness was lower in D+ (0.88 +/- 0.30 cm) than in D- (1.23 +/- 0.33 cm, P = 0.0002) or in segments from healthy volunteers (0.99 +/- 0.15 cm, P = 0.04). The index of end-diastolic wall tension was also lower in D+ (2.5 +/- 1.0 N.m(-1).mm Hg(-1)) than in D- (3.3 +/- 1.1 N.m(-1).mm Hg(-1), P = 0.02) or in segments from healthy volunteers (3.2 +/- 1.2 .m(-1).mm Hg(-1)) P = 0.04). Last, the index of end-diastolic wall stress, determined by the ratio of wall tension index to myocardial thickness, was equivalent in D+, in D-, and in segments from healthy volunteers (respectively, 3.0 +/- 1.4, 2.8 +/- 1.2, and 3.2 +/- 1.6 hN.m(-2).mm Hg(-1)).
Conclusion: In patients with dilated cardiomyopathy, the abnormalities documented by (201)Tl SPECT at rest are related to a lower than normal wall thickness and not to an excess in wall stress or tension. Therefore, partial-volume effects are likely to induce these abnormalities, and they may be unrelated to any insufficiency of myocardial perfusion.