Aims: One of the reasons for patient non-response to cardiac resynchronization therapy (CRT) is a suboptimal left ventricular (LV) pacing site. LV electrical delay has been indicated as a prognostic parameter of CRT response. This study evaluates the LV delay for optimization of LV pacing site.
Methods: Twenty-six consecutive patients (18 male, mean age 71±11 years, LV ejection fraction 31±7%, 14 with ischemic cardiomyopathy, mean QRS 180±27 ms), underwent CRT device implantation. All the available tributary veins of the coronary sinus were tested and LV electrical delay (Q-LV) was measured at each pacing site. The hemodynamic effects of different sites were evaluated by invasive measurement of dP/dtmax at the baseline and during pacing.
Results: An average of 2.8±0.8 different veins and 5.9±2.2 pacing sites were tested. In 25/26 (96%) patients, the highest dP/dtmax coincided with the maximum Q-LV. Q-LV correlated with the increase in dP/dtmax in all patients at every site (R=0.53; p<0.0001). A cut-off value of 95 ms corresponded to a minimum increase of 10% in dP/dtmax in all patients at every pacing site. An inverse correlation between paced QRS and improvement in dP/dtmax was seen in 20 patients (77%).
Conclusions: Pacing the LV at the latest activated site is highly predictive of the maximum increase in contractility, as expressed by an increase of dP/dt_max. A positive correlation between Q-LV and hemodynamic improvement was found in all patients at every pacing site, a cut-off value of 95 ms corresponding to a minimum increase of 10% in dP/dt_max.