4 DISCUSSION
LBBAP is the most consistent with physiological pacing[7][9, 10], because the distribution of the pacing electrode is consistent with the anatomical and physiological walking of the left bundle branch, but it still lacks a specific electrode safe pacing range. This study not only measured the specific distance from the pacing electrode to each coronary artery, but also provided a safe pacing range for the pacing electrode. Due to the beam hardening and motion artifacts of metal pacing electrodes in cardiac computed tomography, the accuracy of the measurement accuracy is easily affected[11]. At the same time, Becker et al.[4] reported that the period when the electrode compressed the coronary arteries was the systolic phase. Therefore, systolic CAG was used for analysis in this study.
This study found that the average distance from the tip of the median electrode to the anterior descending branch was the smallest, and the average distance from the electrode to the anterior descending branch was similar in other positions, suggesting that the risk of damage to the anterior descending branch by pacing electrodes was highest in the median position. This is similar to the average distance (18.9 mm) measured by Pang B et al.[12] using cardiac computed tomography in patients with RVP. This study also found that the average distance from the tip of the PI to the posterior descending branch and the posterior branch of the left ventricle was the smallest, and the average distance from the tip of the PM electrode to the posterior descending branch and the posterior branch of the left ventricle was the largest, suggesting that the posterior descending electrode and the posterior branch of the left ventricle were at the highest risk of injury from the PI electrode. In summary, the distance from the PM electrode to each of the coronary arteries was always at its maximum, suggesting that this is a safe pacing electrode location.
In addition, LBBAP electrodes are at increased risk of damage to the ventricular septal branch on the basis of their anatomical site. Previously, Qi P et al.[2] found that ventricular septal vessels were developed during the injection of a contrast agent into the C315 His sheath to assess the depth of electrode implantation in LBBAP surgery. In addition, it may be a coronary venous vessel. Therefore, in this study, intrathecal angiography of C315 His was used to observe the damage to the ventricular septal branch. Although 38 patients underwent intrathecal angiography, no development of the ventricular septal artery or hematoma formation was observed. As the diameter, length, number and distribution of the anterior and posterior ventricular septal branches observed in each position vary from person to person, they are extremely inconsistent. Therefore, we were unable to measure the precise distance from the tip of the electrode to a certain anterior or posterior ventricular septal branch. It was impossible to quantify the risk of injury to the ventricular septal branch. However, it is recommended that intrathecal angiography with CAG should be completed during the LBBAP surgery to identify the damage to the ventricular septal branches.
Apart from this, anatomical abnormalities in the coronary arteries may be more likely to cause blood vessels to be damaged by pacing electrodes[13]. Pacing electrodes are more likely to damage the arterial blood vessels in patients with myocardial bridges. In this study, coronary angiography of 5 patients showed that the anterior descending artery had different degrees of myocardial bridging phenomenon, as shown in Figure 6. Myocardial fibers compressed the anterior descending artery during systole, and the blood flow of the arterial vessels returned to normal during diastole, which should be distinguished from the compression of the anterior descending artery by the pacing electrode. From multiple angles, there was no compression of the tip of the pacing electrode in the coronary artery of the myocardial bridge during systole. Moreover, there was no obvious chest tightness or chest pain, dynamic ST-T changes in the ECG, and no elevated markers of myocardial injury during or after surgery.