P975 Echocardiography and nuclear medicine imaging techniques are insufficient for scar detection in patients referred for cardiac resynchronization therapy
Authors: Kjellstad Larsen C , Galli E , Duchenne J , Aalen J M , Stokke C , Degtiarova G , Fjeld J G , Gheysens O , Saberniak J , Kongsgaard E , Penicka M , Voigt J-U , Donal E , Smiseth O A , Hopp E 
Published: January 2020

Abstract

Funding Acknowledgements
The study was supported by Center for Cardiological Innovation

Background
Many patients referred for cardiac resynchronization therapy (CRT) do not respond to the treatment. Scar either in septum or the left ventricular (LV) lateral wall, as well as global scar burden, influence the outcome negatively. Preoperative scar assessment is therefore recommended in this patient group. Late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) is considered reference standard for scar detection, but is not always available.

Purpose
To investigate the ability of advanced echocardiographic and nuclear imaging techniques to detect septal and left ventricular (LV) lateral wall scar in patients referred for CRT, compared to late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR).

Methods
Scar was quantified as percentage segmental LGE in 131 patients (age 66 ± 10, 66% male, QRS-width 164 ± 17ms) referred for CRT, 92% with left bundle branch block (LBBB). Longitudinal strain was assessed by speckle tracking echocardiography in 130 patients (641 septal and 630 LV lateral wall segments). Wall motion score index (WMSI) was assessed visually in all patients by an experienced operator, and graded from one to four. Glucose metabolism was assessed by 18F-fluorodeoxyglucose (FDG) Positron Emission Tomography (PET) in 52 patients. Perfusion was assessed in 46 patients by either 13N-ammonia PET (n = 32) or Single Photon Emission Computed Tomography (SPECT) (n = 14). Metabolism and perfusion were reported as percentages of the segment with maximum tracer uptake. The ability of each parameter to identify scar was evaluated with receiver operating characteristic (ROC) curves with calculation of area under the curve (AUC) and 95% confidence interval (CI). AUC≥0.800 was considered reasonable agreement with LGE.

Results
Scar was present in 574 of total 2090 interpretable segments (79% ischemic etiology). Globally, perfusion (AUC = 0.845, 95% CI 0.777-0.914) and glucose metabolism (AUC = 0.807, 95% CI 0.758-0.855) adequately detected transmural scars, but not smaller scars (all AUC &lt; 0.800). Echocardiographic parameters failed to detect global scars irrespective of size (all AUC &lt; 0.800). However, the associations between echocardiographic/nuclear parameters and scars were highly dependent on myocardial region. In the LV lateral wall, glucose metabolism precisely detected transmural scars (AUC = 0.958, 95% CI 0.902-1.00) and WMSI proved reasonable agreement (AUC = 0.812, 95% CI 0.737-0.887), while the rest of the parameters did not (all AUC &lt; 0.800). Smaller scars in this region was not detected by any parameter tested (all AUC &lt; 0.800). No parameter adequately detected septal scars, not even those with transmural involvement (all AUC &lt; 0.800) (Figure).

Conclusions
Neither echocardiographic nor nuclear imaging techniques can replace LGE-CMR in scar assessment prior to CRT. Septum is especially challenging, explained by LBBB-induced reduction in strain, metabolism and perfusion in this region.
Abstract P975 Figure. Detection of transmural septal scar