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.