Introduction
Cardiac resynchronization therapy (CRT) has been shown to prevent hospitalizations for heart failure and improve mortality in patients with severe left ventricular (LV) dysfunction and inter-ventricular or intra-ventricular electromechanical dyssynchrony (1-8). However, LV lead placement (LV-LP) in the target branch of the coronary sinus (CS) tributaries can be difficult due to variations in coronary venous anatomy (9) despite the recent advances in delivery systems for LV-LP (10-14).This is one of the causes of non-response to CRT. In general, 9Fr or 10Fr outer guiding catheters (Outer-Cath) with a variety of curves and shapes are initially selected for CS cannulation to serve as backup force for LV lead delivery to a target vein. At other times, a subselection inner catheter (Inner-Cath) may be used adjunctively to guide the Outer-Cath into the CS more safely, especially in difficult cases of CS cannulations, which can lead to complications such as CS dissection or perforation (15, 16). However, efficacy and safety of the LV-LP using only the smaller 7Fr Inner-Cath for CRT implantation has never been investigated before. The aim of this study was to investigate the feasibility, efficacy, and safety of LV-LP guided only by an Inner-Cath as a first-line approach to CRT implantation.