A simplified M-Mode index of intraventricular asynchrony has been recently developed: the septal-to-posterior wall motion delay (SPWMD), demonstrating an excellent prognostic value in patients (pts) treated with cardiac resynchronizatien therapy (JACC 2005; 45:65). This index however shows some significant limitations: in particular septal motion is often not measurable in clinical practice. Methods: In a population with different degrees of left bundle branch block(LBBB) we tested

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... a new index: the posterior wall motion-to-aortic valve closure delay (PWMACD) based on the simple difference between the time QRSto-posterior wall motion recorded in M-Mode and QRS-to-aortic valve closure as assessed by PW Doppler in the left ventricular outflow tract. Theoretically in normal subjects this interval should be negative. The study population consists of 109 pts with heart failure (mean EF 444-10%) and broad distribution of QRS duration (mean value 1424-41 ms). Pts with right bundle branch block were excluded. Three classes of QRS duration were considered: <120 ms (42 pts); 120-150 (22 pts); > 150 ms (45 pts). Results: SPWMD was feasible only in 68 pts (62%). PWMACD was measurable in all cases. Linear correlation SPWMD-PWMACD was r--0.65 (p<0.O001). Linear correlations between QRS duration and SPWMD and PWMACD were respectively r=0.54 and r=0.45 (p130 ms with good accuracy (area under the ROC curve 0.78; sensitivity 67%, specificity 89%; best cut-off 59 ms). Conclusions: The SPWMD, a well validated index of intraventricular delay, is not feasible in 38% of pts with different degrees of LBBB. The PWMACD is a simple index, feasible virtually in all pts, and shows a good correlation with the previously validated SPWMD. Further studies are needed to assess the additional prognostic value of PWMACD in pts candidates to resynchronization therapy.