Assessment of ¹²³I-mIBG and ^99mTc-tetrofosmin single-photon emission computed tomographic images for the prediction of arrhythmic events in patients with ischemic heart failure: Intermediate severity innervation defects are associated with higher arrhythmic risk

Rationale: ¹²³I-mIBG planar image heart-to-mediastinum ratios effectively risk-stratify heart failure (HF) patients. The value of single-photon emission computed tomographic (SPECT) imaging for identifying increased risk of ventricular arrhythmias is less clear. This study sought to determine if findings from simultaneous interpretation of ¹²³I-mIBG and ^99mTc-tetrofosmin SPECT are predictive of arrhythmic events (ArEs). Methods: ¹²³I-mIBG SPECT images from 622 patients with ischemic HF were presented in standard displays alongside ^99mTc-tetrofosmin images. Consensus interpretations using a 17-segment model produced summed scores. Cox proportional hazards analyses related findings to adjudicated ArEs over 2 years. Results: 471 patients had images adequate for total 17-segment scoring. There were 48 ArEs (10.2%). Neither ¹²³I-mIBG nor ^99mTc-tetrofosmin SPECT summed scores were univariate predictors. On multivariate proportional hazards analysis, the ¹²³I-mIBG SPECT score was independently predictive of ArEs (HR: 0.975, 95% CI 0.951-0.999, P = 0.042), but HR<1 indicated that risk decreased with increasing score. This occurred because patients with intermediately abnormal SPECT studies had a higher likelihood of ArEs compared to patients with extensive abnormalities. Conclusions: The presumption of a monotonic increase in ArE risk with increasing summed ¹²³I-mIBG SPECT score may not be correct as ischemic HF patients with abnormalities of intermediate extent appear at highest risk.