Background Methods Results Conclusion Assessment of LV scar burden cardiac magnetic resonance and phase analysis gated SPECT and impact on cardiac resynchronization therapy Walid Kamel BCCh 1; Wael Samy MD; 1 Osama Tayeh MD 1; Noha Behairy MD 2; Alia Abd el Fattah MD 1 1 Critical care department, Cairo University 2 Radiology department, Cairo University Background Cardiac resynchronization therapy (CRT) is an established tool in improving dyssynchrony in chronic heart failure. Scar burden assessment plays an important role in predicting response to CRT implantation. P <.001 Phase analysis Area P value Cut-off Sensitivity specificity Histogram BW 72.2% .045 152 72.7% 63.2% Histogram SD 74.2% .030 54 81.8% Histogram Entropy 78.9% .009 48.5 73.7% Methods 30 Pts  CRT implantation Echocardiographic response, defined as relative increase in LVES or decrease in LVEF by ≥15% CMR: Pre-implantation delayed hyperenhancement cardiac magnetic resonance - Scar burden - Lateral wall involvement. Group A: (0-50% scar thickness) Segments Group B: (>50% scar thickness). Rest 99mTc-MIBI gated SPECT - LV volumes & EF - Rest perfusion defects - Dyssynchrony parameters (Histogram bandwidth BW, Standard deviation SD and entropy) Echocardiography CMR Responder Non-responder P value CMR Scar segments 9.0±3.2 12.2±2.6 0.009 Scarred segment percentage 53±18% 73±15% 0.006 Scar score CMR 20.5±7.5 27.9±5.2 0.008 Scar burden CMR 30±11% 41±8% CRT non-responder Area P value Cut-off Sensitivity Specificity Summed Rest Score .641 .204 15.5 72.7% 57.9% scar burden SPECT .617 .292 23.0% scar score (CMR) .782 .011 25.0 81.8% 68.4% scar burden (CMR) .780 .012 38.5% CMR Responder Non-responder P value Lat. wall scarred segments 1.5±1.2 2.3±.8 0.08 Lat. wall CMR scar score 6.3±4.1 9.2±2.6 0.024 Results 30 Pts CRT (mean age 58.7±9.0, 24 males). Echocardiographic response, was documented in 19 patients (63.3%). There was no statistically significant difference between responders and non-responders for their baseline risk factors, demographics, cardiac imaging data. P .005 R .238, P .206 R .257, P .170 R .364, P .058 Conclusion Gated SPECT LV dyssynchrony depends largely on underlying LV scar substrate. Cardiac Magnetic Resonance could provide an adequate tool to rule out potential CRT non-responders.