Phase image characterization of ventricular contraction in left anterior hemiblock.

We investigated whether or not left anterior hemiblock is present in patients with left axis deviation using first-harmonic Fourier analysis of gated blood-pool images. Gated blood-pool images were taken in 50 patients without contraction abnormality. They included 14 normal subjects, 8 patients with right bundle branch block (RBBB), 20 with left axis deviation (LAD) and 8 with both RBBB and LAD (RBBB + LAD). ECG gated blood-pool scans were acquired in the anterior and "best septal" left anterior oblique projections. First, the phase images were displayed cinematically as a continuous-loop movie. Next, for quantitative analysis of the phase image, the whole left ventricular and left ventricular high lateral regions of interest were drawn. The "regional phase shift" (RPS) was then defined as (RPS = A-a) where "A" is the mean value of the whole left ventricular phase angles and "a" is that of phase angles in the high lateral region. The left ventricular phase changes and the RPSs in the RBBB and LAD groups were similar to those in the normal group. In the RBBB + LAD group, the latest phase changes occurred in the high anterolateral region. The RPSs of this group were significantly lower than those in the other 3 groups (p less than 0.01). These data suggest that left anterior hemiblock might coexist with RBBB in patients with RBBB + LAD, whereas left anterior hemiblock might not exist in the majority of patients with LAD alone.