QRS complex duration and dipyridamole gated SPECT findings in the left bundle branch block.

Objective: The aim of this study was to investigate the relationship between QRS duration, artifactual perfusion abnormalities, and left ventricular function in patients with left bundle branch block (LBBB) using dipyridamole technetium-99m sestamibi electrocardiography-gated single-photon emission computed tomography (SPECT).
Methods: Twenty-three patients (62 +/- 12.2 years, 18 women, 5 men) with complete LBBB were analyzed. All patients underwent rest-dipyridamole gated SPECT (1-day protocol). To exclude patients with true myocardial ischemia and clearly define artifactual abnormalities owing to LBBB, only patients with normal end-diastolic stress images were involved. Four sets of SPECT images representing ungated rest, ungated stress, and end-diastolic and end-systolic stress images were generated, and the summed defect scores were obtained for each [summed rest score (SRS), summed stress score (SSS), end-diastolic score (EDS), and end-systolic score (ESS), respectively]. QRS durations were measured for both rest and dipyridamole stress.
Results: The patients with perfusion abnormalities on ungated rest, ungated stress, or end-systolic stress images had significantly longer minimum QRS duration at rest. These QRS values correlated with SRS and SSS (r: 0.528, P: 0.01 and r: 0.47, P: 0.024, respectively). Analysis of perfusion and functional data demonstrated an inverse correlation between left ventricular ejection fraction (LVEF) and ESS (r: -0.671, P < 0.0001). The patients with end-systolic perfusion abnormalities had significantly lower LVEF rates when compared with the patients with normal perfusion on end-systolic images.
Conclusions: Our results demonstrated that the presence and severity of artifactual perfusion abnormalities owing to LBBB were significantly related to minimum QRS duration. The magnitude of perfusion abnormalities especially on the end-systolic phase seems to adversely affect systolic function of the left ventricle.