Effect of interval (V-V) optimization in ischemic versus nonischemic patients after cardiac resynchronization therapy

It is with great interest that we read the article published in the November 2009 issue of the Journal by Marsan et al.1 We applaud the authors for the report of acute effect of interventricular pacing interval (V-V) optimization on left ventricular (LV) systolic performance, and dyssynchrony in ischemic versus nonischemic patients received cardiac resynchronization therapy (CRT). The limitations of the work were elucidated by the authors. However, we have some questions about the paper.

First, the authors found that the increase in left ventricular outflow-tract velocity-time interval (LVOT VTI) and LV ejection fraction after implantation was greater in nonischemic as compared with ischemic patients. However, V-V optimization yielded a larger improvement in LV systolic performance in ischemic patients. Consequently, the 2 groups showed comparable response after V-V optimization. The authors have reported that the long-term beneficial effects of CRT were evaluated in 2 subsets of patients (34 ischemic patients vs 40 nonischemic patients).2 Two-year follow-up showed the percentages of responders to CRT were comparable in both groups, but no V-V optimization was undertaken in the patients, at least no such data were noted in that paper. This raises the question of whether ischemic patients who do not receive VV optimization may still get a larger improvement in LV systolic performance as compared to nonischemic patients.

Second, optimized sequential pacing provided a significant improvement in LVOT VTI compared to simultaneous stimulation and was associated with a significant reduction in LV dyssynchrony. The concordance between V-V intervals yielding the highest LVOT VTI and the lowest LV dyssynchrony was excellent. However, in Table II we found that the highest LVOT VTI and the lowest LV dyssynchrony is not always coincident during VV optimization. Which is more important during VV optimization, highest LVOT VTI or lowest LV dyssynchrony?

Third, a significant correlation was observed between LV scar tissue and optimal V-V interval with a larger extent of scar related to a larger level of LV preactivation. The authors have reported that the extent of scar tissue and viable myocardium were directly related to the response to CRT. Furthermore, scar tissue in the LV pacing lead region may prohibit response to CRT.3 And CRT did not reduce LV dyssynchrony in patients with transmural scar tissue in the posterolateral LV segments.4 This raises the question of whether localization of scar tissue is also related to level of LV preactivation, and localization is more important than extent of scar tissue. At the same time, whether V-V optimization can improve LV dyssynchrony in patients with transmural scar tissue in the posterolateral LV segments who received CRT.