Discordant electrical and mechanical atrial delays affect intracavitary electrogram-based cardiac resynchronization therapy optimization

AIMS: It has been shown that atrioventricular (AV) delay optimization improves cardiac resynchronization therapy (CRT) response. Recently, an automatic algorithm (QuickOpt™, St Jude Medical), able to quickly identify the individual optimal AV interval, has been developed. The algorithm suggests an AV delay based on atrial intracavitary electrogram (IEGM) duration. We hypothesized that the difference between electrical and mechanical atrial delays could affect the effectiveness of QuickOpt method. The aim of this study was to test this hypothesis in 23 CRT patients who were recipients of St. Jude Medical devices. METHODS AND RESULTS: Using echocardiography, aortic flow velocity time integral (VTI) was evaluated at baseline, at QuickOpt suggested AV delay and after reducing it by 25 and 50%. Mechanical inter-atrial delay (MIAD) derived from echo/Doppler and electrical inter-atrial delay (EIAD) derived from IEGM were also analysed. Optimal AV delay was identified by the maximal VTI. In 11 patients (Group 1) the maximal VTI was achieved at the AV delay suggested by the algorithm, in 6 patients (Group 2) after a 25% reduction, and in 6 patients (Group 3) after a 50% reduction. While EIAD was similar among the three groups, MIAD was significantly different (P< 0.001). MIAD was longer than EIAD in Group 1 (P= 0.028) and shorter than EIAD in Groups 2 (P= 0.028) and 3. (P< 0.001). Mechanical inter-atrial delay was the only independent predictor of the AV interval associated with the best VTI (R(2) = 0.77; P< 0.001). CONCLUSION: Our results show that MIAD plays the main role in determining the optimal AV delay, thus caution should be taken when optimizing AV by IEGM-based methods.