Diagnostic and prognostic value of gated myocardial perfusion single-photon emission computed tomography in low-risk patients with left bundle-branch block

BACKGROUND: The abnormal left ventricular activation pattern in patients with a left bundle-branch block (LBBB) frequently induces myocardial perfusion defects, decreasing the specificity of noninvasive coronary-risk stratification with stress testing. We assessed the diagnostic and prognostic impact of gated single-photon emission computed tomography (SPECT) in low-risk patients with LBBB. METHODS: A total of 114 patients underwent dual-day protocol Tc-99m sestamibi gated SPECT and were divided into two subsets: without LBBB (group 1, n = 57) and with LBBB (group 2, n = 57). Sixty-eight (60%) patients had negative coronary angiography and 46 (40%) were at a low risk for coronary artery disease. The variables incorporating the extent and severity of perfusion defects were calculated: summed stress score, summed rest score and summed difference score, end-diastolic volume (EDV), end-systolic volume (ESV), and left ventricular ejection fraction. The mean variations in EDV and ESV were computed as follows: rest volume-poststress volume. Cardiac events were classified as major and minor. RESULTS: Gated SPECT was positive in eight (14%) patients of group 1 and 33 (58%) patients of group 2 (P<0.001). The summed stress score was significantly higher in group 2 than in group 1 (4.7 ± 4.8 vs. 0.9 ± 1.8, P<0.001); similarly, EDV and ESV were significantly higher in LBBB patients (P<0.05 in both). The mean variation in EDV was -2.21 ml for group 1 and 1.32 ml for group 2 (P<0.05). After a mean follow-up period of 32 ± 19 months, cardiac events occurred in 22 (23%) patients, six of group 1 and 16 of group 2 (12 vs. 35%, P<0.01). CONCLUSION: Functional and perfusion parameters obtained by gated SPECT are different between patients with and without LBBB. In LBBB patients, the decrease in EDV between rest and poststress could be considered an early marker of diastolic dysfunction that might anticipate left ventricular ejection fraction reduction and may have an impact on prognosis.