Major findings
To the best of our knowledge, this is the first study to investigate the feasibility and efficacy of LV-LP guided by Inner-Cath without Outer-Cath as a first-line methodology in CRT implantation. The study results demonstrated that LV-LP guided by Inner-Cath alone was successful in over 95% of the patients undergoing de novo or upgrade CRT implantation without severe complications. The Inner-Cath group had shorter total procedure time and less procedure-related complications. In particular, mechanical CS injury during CS cannulation caused by the guiding catheters was only observed in the Outer-Cath group. Consequently, we consider LV-LP guided by Inner-Cath alone to be safer and more effective compared with conventional methods that use Outer-Cath.