On the importance of image gating for the assay of left ventricular mechanical dyssynchrony using SPECT

The potential of SPECT for quantifying left ventricular mechanical dyssynchrony is increasingly appreciated. We sought to examine the incidence and impact of image gating errors on this quantification and to test a possible solution for affected studies. Methods: First, to establish whether and how gating error alone could affect the measurement of dyssynchrony, we performed a prospective study in which patients with pacemakers were studied twice: during normal rhythm without gating error and with gating error caused by pacemaker-induced dysrhythmia. Second, to understand the pattern and magnitude of gating error during our typical imaging practice, we retrospectively examined studies from a separate cohort of 64 patients who were referred for dyssynchrony evaluation. Third, to understand whether studies with gating error could be repaired for the purpose of quantifying dyssynchrony, we tested a correction algorithm on the pacemaker-induced dysrhythmia image set to see whether it repaired this set so as to approximate the patients' normal rhythm image data. We subsequently applied this algorithm to the 64-patient cohort. Results: Pacemaker-induced gating error caused a spurious decrease in dyssynchrony magnitude. Among the 64-patient cohort, similar gating errors were common, and an inverse exponential relationship between gating-error magnitude and dyssynchrony magnitude was observed. The correction algorithm accurately repaired the pacemaker-induced dysrhythmia image set; when it was applied to the 64-patient cohort, the magnitude of the postcorrection increase in dyssynchrony magnitude was proportional to the magnitude of the gating error. Conclusion: Gating errors cause a spurious reduction in SPECT assay of dyssynchrony magnitude. In our standard imaging practice, gating errors were common. Post hoc correction appears to be feasible.