Assessment of Pacing Stimulus Conduction and Latency Measurements in CRT-D Patients

Inclusion Criteria: * Patient has been implanted with a CRT-D device by BIOTRONIK at least 4 weeks before enrollment date * Patient successfully implanted with a left ventricular lead * High likelihood of LV latency ≥ 40 ms * LV lead in lateral or postero-lateral position in the coronary venous system * Patient is able to understand the nature of the clinical investigation * Patient is willing to undergo the required measurements at the investigation site * Patient provides written informed consent * Age ≥ 18 years Exclusion Criteria: * Patients with irregular ventricular rhythm due to atrial tachycardia * Pregnant or breast-feeding women * Participation in an interventional clinical investigation