123 I- m IBG Scintigraphy to Predict Inducibility of Ventricular Arrhythmias on Cardiac Electrophysiology Testing

Abstract

Background— Disturbances of autonomic function after infarction are associated with both total mortality and sudden death. Although many imaging techniques for assessing the cardiac autonomic nervous system have been studied, the clinical usefulness of these techniques remains uncertain. This exploratory pilot study examined the relationship between abnormalities of ventricular sympathetic innervation delineated by scintigraphic imaging with 123 I- m IBG and inducible ventricular tachyarrhythmias in patients with left ventricular dysfunction and previous myocardial infarction. Methods and Results— Fifty patients underwent electrophysiological (EP) testing and 15-minute and 4-hour planar and single photon emission computed tomography (SPECT) imaging with 123 I- m IBG and SPECT imaging with 99m Tc-tetrofosmin. The primary efficacy variables were the 4-hour heart:mediastinum ratio (H/M) and the 123 I- m IBG/ 99m Tc-tetrofosmin SPECT mismatch score. EP studies were categorized as positive (EP + ) or negative (EP − ) for inducibility of sustained (>30 seconds) ventricular tachyarrhythmias. Thirty patients were EP + , and 20 were EP − . There were no significant differences in the 4-hour H/M ratios or 123 I- m IBG/ 99m Tc-tetrofosmin SPECT mismatch scores between the two groups. In a multivariable analysis using all 123 I- m IBG and 99m Tc-tetrofosmin SPECT measurements, the only variable that showed a significant difference between EP + and EP − patients was the 4-hour 123 I- m IBG SPECT defect score. A 4-hour 123 I- m IBG SPECT defect score of ≥37 yielded a sensitivity of 77% and specificity of 75% for predicting EP results. Conclusions— The standard indices of 123 I- m IBG imaging (H/M and innervation-perfusion mismatch score) are not predictive of EP test results. The association of 123 I- m IBG SPECT defect severity with EP test inducibility in this exploratory study will require confirmation in a larger cohort of patients.