Can nuclear imaging accurately detect scar in ischemic cardiac resynchronization therapy candidates?

Background Accurate scar assessment is crucial in cardiac resynchronization therapy (CRT) candidates, since its presence is a negative predictor for CRT response. Therefore, we assessed the performance of different PET parameters to detect scar in CRT candidates. Methods: Twenty-nine CRT candidates underwent ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG)-PET/computed tomography (CT), resting ¹³N-NH_3-PET/CT and cardiac magnetic resonance (CMR) prior to CRT implantation. Segmental ¹⁸F-FDG uptake, late ¹³N-NH₃ uptake and absolute myocardial blood flow (MBF) were evaluated for scar detection using late gadolinium enhancement (LGE) CMR as reference. A receiver operator characteristic (ROC) area under the curve (AUC) ≥0.8 indicated a good accuracy of the methods evaluated. Results Scar was present in 111 of 464 segments. None of the approaches could reliably identify segments with nontransmural scar, except for ¹⁸F-FDG uptake in the lateral wall (AUC 0.83). Segmental transmural scars could be detected with all methods (AUC ≥ 0.8), except for septal ¹⁸F-FDG uptake and MBF in the inferior wall (AUC < 0.8). Late ¹³N-NH₃ uptake was the best parameter for transmural scar detection, independent of its location, with a sensitivity of 80% and specificity of 92% using a cutoff of 66% of the maximum tracer activity. Conclusions Late ¹³N-NH₃ uptake is superior to ¹³N-NH₃ MBF and ¹⁸F-FDG in detecting transmural scar, independently of its location. However, none of the tested PET parameters was able to accurately detect nontransmural scar.