Advantage of optimizing V-V timing in cardiac resynchronization therapy devices. 
There is little consensus as to the benefits of interventricular (V-V) timing optimization in cardiac resynchronization therapy (CRT).  A variety of parameters are currently used to optimize device timing.  This study was designed to investigate the potential advantage of using 3D ejection fraction (EF) and aortic velocity-time integral (VTI) as measures of global left ventricular (LV) function to optimize ventricular activation in CRT devices.  Seventy-four patients seen in the Optimization Clinic with adequate echocardiographic images were included.  Three aortic VTI and two 3D EF values were recorded at five V-V settings and the average value used.  Aortic VTI and 3D EF were classified as the best, worst, and simultaneous setting values.  Data were analyzed using a two-tailed paired t-test.  Comparing the best to worst V-V timing settings, VTI improved by 4.7 ± 7.5 cm (P < 0.0001) and 3D EF by 9.9%± 5.7% (P < 0.0001).  Comparing the simultaneous setting to the best V-V timing setting, VTI improved by 2.4 ± 2.1 cm (P < 0.0001) and 3D EF by 3.8%± 4.9% (P < 0.0001).  Aortic VTI improved in 85% of patients and 3D EF improved in 72%.  However, only 26% of the patients had the same optimal setting using aortic VTI and 3D EF yielding an r(2) value of 0.003.  Individualized echocardiographic V-V optimization of CRT devices improves global LV function as measured by aortic VTI and 3D EF.  Substantial differences in function were seen over an 80-ms range of V-V timing and optimization resulted in improved LV function in the majority of patients.