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In patients treated with cardiac resynchronization therapy (CRT) for chronic heart failure (CHF), the atrio-ventricular (AV) and interventricular (VV) intervals can be individually optimized by means of echocardiography. We assessed the outcome of 55 consecutive optimization procedures.Methods Fifty-five patients (age 67±12, range 29-87 y) with CHF (LVEDD 66±10 mm, EF 22±7) received a biventricular pacemaker. Forty-three patients were in stable sinus rhythm (SR) and 12 had chronic atrial fibrillation (AF). The etiology of CHF was ischemic cardiomyopathy in 33 and dilated cardiomyopathy in 22 cases. Within 3 months after implantation, the AV-delay was optimized according to the mitral inflow pattern as described by Ritter. If the pacemaker permitted a differential programming of the interventricular delay (n=44), the VVdelay associated with the highest aortic time velocity integral (TVI, mean of 3 cardiac cycles) was considered optimal. Results In patients with SR the average optimal sensed AV-delay was 116±19 ms (range 80-150). In 18 of 43 cases, the optimal sensed AV-delay differed at least 20 ms from the nominal programming suggested by the pacemaker manufacturer (120 ms). The optimal VV interval was 23±18 ms (left ventricular lead paced first). Patients with ICM and DCM yielded an optimal AV-delay of 120±17 and 108±16 ms, respectively (p<0.05). There was no difference between ICM and DCM patients with respect to the VV-delay. Patients with SR had a shorter optimal VV-delay (21±18 ms) compared with AF patients (32±13ms; ns). Conclusion In CRT patients the average optimal AV-delay and VV-delay were close to the nominal programmed values. However, according to echocardiographic evaluation, AV- and VV-delays were changed in a substantial number of patients, suggesting that individual optimization is useful. Furthermore, our findings indicate, that the etiology of CHF might play a role in AV-delay optimization. [ABSTRACT FROM PUBLISHER]