**6.4 Summary**

Thus, HB can be accessible for HBP in at least 68% of cases based on the data from the abovementioned study. Unfortunately, no technology nowadays can define the anatomical variant of HB before the lead implantation.

#### **Figure 3.**

*HB of type I. A – Anatomical substrate; B – Graphical representation; AT - attachment of tricuspid valve; AVB - atrioventricular bundle; AVN - atrioventricular node; RB - right branch; MS - membranous part of the interventricular septum (Kawashima and Sasaki [25]).*

*The Evolving Concept of Cardiac Conduction System Pacing DOI: http://dx.doi.org/10.5772/intechopen.99987*

#### **Figure 4.**

*HB of type II. A – Anatomical substrate; B – Graphical representation; AT - attachment of tricuspid valve; AVB - atrioventricular bundle; AVN - atrioventricular node; RB - right branch; MS - membranous part of the interventricular septum; CS - coronary sinus (Kawashima and Sasaki [25]).*

#### **Figure 5.**

*HB of type III. AVB - atrioventricular bundle; AVN - atrioventricular node; RB - right branch; MS membranous part of the interventricular septum (Kawashima and Sasaki [25]).*

#### **7. Practical recommendations for His bundle pacing**

#### **7.1 First stage. Venous access**

For venous access, we preferably puncture left axillary vein. Usually, we enter with a short peel-away regular 7F sheath as it is congruent with advanced further C315 His catheter. While having a C315 catheter in RA, we try to place a guiding wire in RV. It advantages smooth guiding of C315 catheter to RV and avoids tip damaging during tricuspidal valve crossing. Afterward, the system withdrawing to the basal septal region is easier than penetrating forward.

#### **7.2 Second stage. His bundle mapping**

After the lead introducer system is positioned in a supposed projection of HB, signal mapping of HB starts from the distal tip of the lead to register unipolar or bipolar signal. For this purpose, a standard electrophysiological system can be used and/or PSA 3 signal analyzer and Medtronic programmer. It is advised to apply atrial channel for HB mapping as it is more sensitive. The cathode is

**Figure 6.** *HB mapping (total gain – 5000, filtration rate – 500 Hz).*

connected to the distal tip and anode to the skin. After that, an accurate search of HB potentials starts. It is necessary to point out that the distal electrode (Helix) is in an active position what complicates the overall system manipulation; however, it is possible to map with Helix placed slightly inside the lumen of the delivery system (**Figures 6** and **7**).

After HB mapping, it is necessary to know the main maneuvers with C 315 His introducer. For fluoroscopic visualization, RAO 15–30 position is used. Clockwise

**Figure 7.** *HB mapping.*

*The Evolving Concept of Cardiac Conduction System Pacing DOI: http://dx.doi.org/10.5772/intechopen.99987*

introducer rotation with an electrode inside turns its tip forward and upwards relative to the IVS. Counterclockwise introducer rotation directs it backwards, closer to the tricuspid valve.

C 315 His introducer is advanced maximally further through an electrode after identification of the HB signal. It adds additional stability to the system before lead implantation (screwing). His lead implantation is performed after HB signal assessment relative to the atrial and ventricular signals (**Figure 7**).

In a case when it is not possible to register discrete HB potential, the pacemapping technique may be applied beginning with high amplitudes (5–10 V / 1 ms) with identification of the pacing threshold for RV and HB. This technique is especially useful for conducting HBP in patients with AV blocks.

#### **7.3 Third stage. Lead implantation**

Lead implantation starts with both operator's hands for clockwise rotation: 4–5 rotations with slight pressure on lead in a forward direction. Meanwhile assistant supports a delivery system in a necessary position (usually performing anticlockwise movements for pushing introducer and lead perpendicular to the implantation site). Additional rotations may be needed based upon tactic feelings and fluoroscopy. After fixation, the lead is pointed frontward while the introducer is retracted 3–5 cm backward, creating a moderate 'insurance' loop and evaluating lead fixation stability.

In the experimental post-mortem study, M. Jastrzebski et al. distinguished 3 types of lead behavior during deep septal implantation – entanglement, drill-effect, and screwdriver effect [36]. These behaviors depend on endo-myocardial tissue characteristics, positioning angle relative to the cardiac wall, and the way of screwing. Recognition of these behaviors might help to achieve successful penetration without complications and unnecessarily prolong attempts.

#### **7.4 Fourth stage. His bundle pacing testing**

R-wave amplitude test is performed afterward. Because of the thin myocardial layer in this region, acceptable values for appropriate R-wave sensing are more than 1–2 mV, which usually provides enough safety margin from far-field atrial and His signals oversensing. This makes use of pacemakers with maximum ventricular sensing of 0.5 mV more reasonable.

QRS complex assessment in standard 12-lead ECG with relatively high amplitude and duration of the pacing impulse (5 V / 1 ms) is the next step. A threshold test is conducted with a gradual decrease of the pacing impulse amplitude. It is necessary to define the threshold of selective HBP and RV pacing. The acceptable HBP threshold is less than 2.5 V / 1 ms. HBP threshold may decrease within 10–20 mins after implantation due to a decrease in an acute HB fibers traumatic damage.

An important prognostic factor is a change between selective and non-selective HBP in response to different pacing outputs. If decreasing a pacing output lead to a transition from non-selective to selective HBP, it is a strong predictor of a favorable outcome because the active electrode part is within the conduction system. The opposite sequence points out a more remote position from HB, and further considerations should be taken into account.

#### **7.5 Fifth stage. Introducer extraction**

For introducer extraction, a standard set of knives is used. The presence of a "secure" loop is mandatory before the introducer extraction; it provides sustainability to the lead. Extraction is guided by fluoroscopy to control the lead position. Unfortunately, delivery and extraction systems are not the perfect ones. Because of that, it is necessary to be prepared for accurate delivery system dissection with small scissors.

After introducer extraction, there is an additional check of the ventricular signal amplitude and pacing thresholds for bipolar/monopolar configuration. Monopolar sensing is inadvisable in pacemaker-dependent patients (risk of atrial oversensing).
