Effect of alcohol septal ablation in patients with hypertrophic cardiomyopathy on left-ventricular mechanical dyssynchrony as assessed by phase analysis of gated SPECT myocardial perfusion imaging

Abstract

Patients with hypertrophic cardiomyopathy (HCM) may have delayed septal activation and left ventricular (LV) mechanical dyssynchrony, and may improve after alcohol septal ablation (ASA). This study used phase analysis of gated SPECT myocardial perfusion imaging (MPI) to evaluate septal activation and LV dyssynchrony in HCM patients pre- and post-ASA. Phase analysis was applied to 28 controls, and 32 HCM patients having rest MPI pre- and post-ASA to assess septal-lateral mechanical activation delay (SLD) and consequent LV dyssynchrony. In addition, phase analysis was applied to another group of 30 patients having serial MPI to measure variability of the LV dyssynchrony parameters on serial studies. ASA significantly reduced SLD and improved LV synchrony in the HCM patients with SLD < 0° due to earlier activation of the lateral wall relative to the septum. Based on the measured variability, 12 HCM patients had significant (Z < -1.65, P < 0.05) and 4 had moderate (Z < -1.00, P < 0.15) improvement in LV synchrony post-ASA. SLD < 0° predicted improvement in LV synchrony after ASA with a sensitivity of 81% and a specificity of 88%. SLD and LV dyssynchrony were frequent in HCM patients. HCM patients, whose septal activation became later than lateral activation, had significant reduction in septal activation delay and improvement in LV synchrony after ASA.

Figure 1

Processing steps of phase analysis. The gated SPECT MPI raw data were reconstructed and reoriented using the standard protocol to generate a gated SPECT MPI short-axis image. Regional maximal count detection was performed on the gated SPECT MPI short-axis image in 3D for each temporal frame to generate wall-thickening curves for over 600 LV regions. The wall-thickening curve for each region was approximated by the 1-harmonic function to calculate a phase angle that represented the regional onset of mechanical contraction (OMC). Once the OMC phase angles of all regions were obtained, an OMC phase distribution was generated and displayed as a polar map and a histogram. The standard deviation of the OMC phase distribution (phase standard deviation) and the histogram bandwidth (including 95% of the phase angles over the entire LV) indicated the degree of global LV dyssynchrony.

Figure 2

LV regional activation as assessed by phase analysis of gated SPECT MPI. A 9-segment model was used to automatically segment the phase polar map as shown in the figure. The mean phase angles were automatically calculated for each segment to represent the relative regional activation time. Septal-lateral delay (SLD) was calculated as the difference between the mean phases of the septal and lateral segments. For a normal subject, the septal segment should be activated earlier than the lateral wall, and thus, SLD should be greater than 0.

Figure 3

Patient example. At baseline the patient had reversed septal-lateral activation and significant LV dyssynchrony. ASA reduced the septal activation delay and improved LV dyssynchrony.