SPECT gated blood pool phase analysis of lateral wall motion for prediction of CRT response.

Amplitude, defined as the magnitude of contraction of the myocardium, is obtained from phase analysis but has not been investigated to the same extent as phase-based parameters for predicting the outcome of cardiac resynchronization therapy (CRT). The size of scar present in the lateral wall of the left ventricle (LV) has been shown in some studies to predict response to CRT. Scar is associated with impaired regional LV wall motion and is expected to result in a reduction in the corresponding amplitude values derived from phase analysis. Our objective was to determine the correlation between amplitude and scar, and to evaluate amplitude parameters as surrogates for scar in predicting response to CRT. 49 patients underwent a single photon emission computed tomography (SPECT) radionuclide angiography (RNA) scan as well as FDG viability and Rubidium-82 perfusion PET scans prior to undergoing CRT. Phase analysis was performed on the SPECT RNA data to extract amplitude values used to define amplitude size (AmpSize) and amplitude score (AmpScore) parameters. Scar size and scar score were obtained from the PET scans based on a 5 segment model. Scar parameters were then compared to amplitude parameters in the lateral wall for the whole population as well as both ischemic (N = 27) and non-ischemic (N = 22) populations using Pearson correlation. The ability of amplitude parameters to predict response to CRT was also investigated and compared to scar parameters. The largest ROC AUC values were obtained in the ischemic population where values of 0.67 and 0.68 were observed for lateral wall AmpSize and AmpScore respectively. Both parameters produced the same sensitivity and specificity values of 83 and 67 %. Amplitude size in the lateral wall showed significant correlation with lateral wall scar size in all patients (r = 0.51), which was further strengthened in the ischemic patient sub-group (r = 0.64). Lateral wall amplitude-based parameters obtained from SPECT RNA phase analysis produced an overall accuracy in predicting CRT response in ischemic patients that was not significantly different to that of PET lateral wall scar parameters. A significant correlation existed between amplitude size and scar size in the lateral wall.