Advantages of LV-LP guided by Inner-Cath
LV-LP guided by Inner-Cath alone has some advantages leading to the high success rate of LV-LP. First, an Inner-Cath can be easily and safely cannulated into the CS regardless of various CS anatomies or size of right atrium (9), especially when using a 5Fr steerable EP catheter (11) as electrophysiologists are familiar with its manipulation. In fact, mechanical injuries of the CS such as dissection and perforation were more frequently observed in the Outer-Cath group. In addition, it is not difficult to advance an Inner-Cath deep inside the target CS tributaries, that may result in shortened procedure time and reduce radiation exposure compared with the Outer-Cath group. Our method makes it unnecessary to select from a variety of Outer-Cath with different shapes and curves. Given the excellent success rate of LV-LP guided by Inner-Cath alone, it appears that an Inner-Cath provides sufficient backup force to deliver LV leads to the target veins in spite of the varied anatomy of CS tributaries. Our results suggest that it is a misconception that use of an Outer-Cath is always necessary to get adequate backup force for LV lead delivery. Our study results also showed that LV threshold was significantly lower in the Inner-Cath group than that of the Outer-Cath group. We surmise that this was due to Inner-Cath superiority to Outer-Cath in terms of enabling selection of optimal CS tributary and LV lead placement site, especially in patients with ICM in whom the LV pacing may be affected by scar location (21). Second, peel-off of the Inner-Cath for removal from the CS may be easier than that of the Outer-Cath. We often experience LV lead dislodgement when peeling off the Outer-Cath, which is caused by a mismatch between the position of the CS ostium or CS trunk and shape of the selected Outer-Cath with different curves. Meanwhile, the LV lead is very unlikely to become dislodged during peel-off of an Inner-Cath because it has a simple shape without complex curves. Third, an Inner-Cath can be repeatedly inserted through a smaller 7 Fr sheath in the subclavian vein unlike the Outer-Cath that requires an 9Fr or 10Fr sheath. The use of a smaller sheath has substantial advantages in terms of avoiding the risk of unnecessary bleeding from the insertion site of the sheath and interference from other sheaths in manipulating a guiding catheter, especially in patients undergoing a CRT upgrade who may have subclavian vein stenosis due to the adhesion of previously inserted leads to a venous wall as shown in Figure 4.