Comparison of SPECT RNA phase analysis amplitude values and left ventricular lateral wall scar size

Objectives Phase analysis has previously been investigated for its potential at predicting the outcome of cardiac resynchronization therapy (CRT). Amplitude, defined as the extent of contraction of a sector, is obtained from phase analysis but has not been investigated to the same extent as phase-based parameters. Furthermore, the extent of scar present in the lateral wall of the left ventricle (LV) has been shown in some studies to predict response to CRT. A scarred heart segment will not contract properly which may correspond to reduced amplitude values. Our objective is to determine the correlation between amplitude and scar size and to evaluate amplitude as a surrogate for scar in predicting response to CRT.

Methods 46 LBBB patients (LVEF<30%, QRS>120 ms) underwent a baseline FDG PET scan and SPECT radionuclide angiography (RNA) scan prior to undergoing CRT. Scar size was obtained from the PET scan using a 5 segment model and phase analysis was performed on the SPECT RNA data. From the SPECT RNA data, 568 normalized LV amplitude values were acquired for each patient. Lateral wall scar size was then compared to average amplitude in that segment for both ischemic (N=26) and non-ischemic patients using a Pearson correlation coefficient (r). The ability of lateral amplitude to predict response was also investigated.

Results Amplitude showed a strong correlation with scar size in all but non-ischemic responders, as shown below. Lateral amplitude did not present any significant differences between responders (N=30) and non-responders (p>0.05). Though all patients with no lateral scar (N=9) were responders, these patients had variable lateral amplitude similar to non-responders.

Conclusions Amplitude obtained from SPECT phase analysis provides good correlation with scar size, but does not prove to be a suitable surrogate marker for response to CRT. This is likely due to differences in average amplitudes observed in patients with no lateral scar

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