Scar imaging in the dyssynchronous left ventricle: Accuracy of myocardial metabolism by positron emission tomography and function by echocardiographic strain.

Response to cardiac resynchronization therapy (CRT) is reduced in patients with high left ventricular (LV) scar burden, in particular when scar is located in the LV lateral wall or septum. Late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) can identity scar, but is not feasible in all patients. This study investigates if myocardial metabolism by 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) and contractile function by echocardiographic strain are alternatives to LGE-CMR. In a prospective multicenter study, 132 CRT candidates (91% with left bundle branch block) were studied by speckle tracking strain echocardiography, and 53 of these by FDG-PET. Regional myocardial FDG metabolism and peak systolic strain were compared to LGE-CMR as reference method. Reduced FDG metabolism (<70% relative) precisely identified transmural scars (≥50% of myocardial volume) in the LV lateral wall, with area under the curve (AUC) 0.96 (95% confidence interval (CI) 0.90–1.00). Reduced contractile function by strain identified transmural scars in the LV lateral wall with only moderate accuracy (AUC = 0.77, CI 0.71–0.84). However, absolute peak systolic strain >10% could rule out transmural scar with high sensitivity (80%) and high negative predictive value (96%). Neither FDG-PET nor strain identified septal scars (for both, AUC < 0.80). In CRT candidates, FDG-PET is an excellent alternative to LGE-CMR to identify scar in the LV lateral wall. Furthermore, preserved strain in the LV lateral wall has good accuracy to rule out transmural scar. None of the modalities can identify septal scar. The present study is part of the clinical study "Contractile Reserve in Dyssynchrony: A Novel Principle to Identify Candidates for Cardiac Resynchronization Therapy (CRID–CRT)", which was registered at clinicaltrials.gov (identifier NCT02525185). The ability of peak systolic strain by echocardiography and glucose metabolism by FDG-PET to identify transmural LV lateral and septal scar in CRT candidates compared to LGE-CMR, illustrated in three representative patients. LGE-CMR (left images) allows for direct scar identification independent of wall motion, and was used as reference standard for scar. Peak systolic strain by echocardiography (middle images) was generally inconclusive of scar, but absolute strain >10% in the LV lateral wall implies that transmural scar in this region is unlikely. Glucose metabolism by FDG-PET (right images) accurately identified transmural LV lateral wall scar, but was unable to distinguish transmural septal scar from septal hypo-metabolism due to left bundle branch block in itself. FDG-PET = 18F-fluorodeoxyglucose Positron Emission Tomography; LV = left ventricular; CRT = cardiac resynchronization therapy; LGE = late gadolinium enhancement; CMR = cardiac magnetic resonance. [Display omitted] • FDG-PET is a good alternative to CMR to identify transmural left ventricular lateral wall scars in patients referred for CRT. • Strain by echocardiography is only moderately accurate, but relatively preserved strain (>10%) in the lateral wall strain means that transmural scar in this region is unlikely. • Contrary to preserved strain, reduced strain in the lateral wall is inconclusive with regard to scar. • Neither FDG-PET nor echocardiographic strain identifies septal scar. [ABSTRACT FROM AUTHOR]