Cardiac resynchronization (CRT) therapy is well established for treatment of patients with severe heartfailure, reduced left ventricular (LV) function and ventricular dyssynchrony. Roughly 1/3 of CRT patients do not improve after CRT implant. One possible reason is interruption of biventricular pacing. This might be caused by several conditions, including elevated left ventricular (LV) pacing thresholds or presence of phrenic nerve stimulation (PNS). CRT devices with quadripolar LV leads offer 10 LV pacing vectors to choose from. It's the aim of this prospective observational study to investigate efficacy and reliability of cardiac resynchronization therapy (CRT) with quadripolar left ventricular leads.

Hypothesis: In more than 90% of patients, who received a CRT system with quadripolar LV lead, at least one acceptable LV lead vector is available.

Definition of an acceptable lead vector: Any LV pacing vector that complies in both tested body positions (left lateral position and sitting) with both criteria:

1. Phrenic nerve stimulation threshold is at least twice as high as LV pacing threshold
2. LV pacing threshold is less or equals 2.5Volts (V) @0.5 milliseconds (ms)

Inclusion Criteria:

• Indication for implantation of a CRT-D
• Age >= 18 years
• Written informed consent

Exclusion Criteria:

• Already implanted LV or coronary sinus lead
• Previous unsuccessful LV lead implant attempt
• Patient is eligible for heart transplantation
• Comorbidities that results in life expectancy of less than 12 months
• Known pregnancy
• Inability to provide written patient informed consent
• Participation to another study with active treatment arm (i.e. randomized studies etc...)
• Patient is not willing or is not able to visit the study center for the study assessments within the first 3 months after implant
• Patient is not able to understand or answer the quality of life questionaire

Patients who are planned for being implanted with a cardiac resynchronization therapy implantable cardioverter defibrillator (CRT-D) system in the participating centers.