Figure 6 Red arrow indicates the myocardial bridge. (A) The middle segment of the anterior descending branch is compressed by myocardial fibers during systolic. (B) There is no compression of the anterior descending artery during diastole and the blood flow is unobstructed.
This study had some limitations. First, the veins that accompany the interventricular septal branch, the anterior descending branch and the posterior descending branch are difficult to detect by CAG when they injured by pacing electrodes[14]. Second, the damage to some small blood vessels of the heart is difficult to cause changes in serum troponin, myocardial enzyme profile and ST-T segment of the ECG[14]. It is not convenient for endurance exercise to increase cardiac troponin[15]. Third, because of the influence of anatomy and physiology, the distribution of electrodes in each of the nine partition positions is not well-proportioned, and the number of pacing electrodes in some positions is small. Therefore, it is necessary to increase the number of cases in further studies. Finally, in this study, the distance between the tip of the pacing electrode and the coronary artery was a rough estimate measured by fluoroscopy, which cannot be equivalent to the actual spatial distance. How to measure the accurate distance between the pacing electrode and the coronary artery is worthy of further study.