Atrial septal puncture is not an emerging technique; it has been in clinical use for decades, and now with the widespread use of radiofrequency ablation of atrial fibrillation catheters, clinicians urgently need to re-enforce this technique. I have visited some important foreign AF centers and observed surgical demonstrations by some top experts. Although they lead the trend of AF ablation procedure, we Chinese physicians have our own characteristics for the basic step of AF catheter ablation – atrial septal puncture.
1. Anatomy of the interatrial septum and the fossa ovalis
The atrial septum is located between the left and right atria and consists of two layers of endocardium sandwiched by a small amount of myocardium and connective tissue, with a thickness of about 3-4 mm, and its anterior edge is opposite to the central part of the ascending aorta, and the posterior edge is in line with the interatrial sulcus. The septal plane is at an average angle of (45±8)º (30-75) º to the sagittal plane and (45±8)º (25-60) º to the coronal plane, and the right atrial plane, the septum is composed of a “bladed” parietal ridge pointing toward the superior vena cava, the anterior and inferior edges. The apex of the “blade” points toward the superior vena cava, and the anterior edge is concave and follows the course of the ascending aorta, ending in a fibrous triangle behind the membrane of the septum, with a smooth section of right atrial wall tissue between the anterior edge and the right auricle. The posterior margin is solitary and ends at the coronary sinus orifice around the posterior edge of the fossa ovalis. The inferior margin is short and runs from near the coronary sinus orifice to a fibrous triangle behind the septal membrane. The inferior border is separated from the tricuspid annulus by the right atrial endocardium and the septal membrane. When viewed from the left atrial plane, the upper edge of the septum follows the same course as the posterior edge of the ascending aorta, and the wide, smooth left atrial free wall separates the septum from the superior edge of the septum from the left aorta. The posterior edge of the interatrial septum was curved downward along the medial side of the right pulmonary vein, and the right upper pulmonary vein was close to the parietal ridge of the posterior edge of the interatrial septum. The anterior edge of the interatrial septum was composed of the mitral annulus, and there was a shallow concavity in the lower and middle part of the right side of the interatrial septum, called the oval fossa, where the tissue was thinnest and its central part was only about 1 mm thick. The edge of the fossa ovalis is elevated, mostly in an inverted “U” shape, and is called the edge of the fossa ovalis. The midpoint of the fossa ovalis is (28±8)mm from the superior vena cava orifice, (24±8)mm from the inferior vena cava orifice, 19mm from the midpoint of the coronary sinus orifice, 25mm from the midpoint of the tricuspid septum, and 24mm from the midpoint of the base of the aortic ramus, with the anterior edge nearest to the ascending aorta (12±5)mm and the posterior edge to the atrial wall corresponding to the interatrial sulcus (3±3). The distance between the center of the fossa ovalis and the contralateral atrial wall (28.4±6.4) mm was reached by puncturing horizontally from the center of the fossa ovalis. posterior anterior radiographic fluoroscopy of the midpoint of the fossa ovalis was mostly located on the right side of the median spine, with 67% projecting in the lower 1/3 segment of the 7th thoracic vertebra, 17% in the upper 1/3 segment, and 17% in the middle segment.
2, Right anterior oblique position 45 º fluoroscopy guided the basic operation of septal puncture
In 1959, Rosst and Cope reported almost simultaneously as the first pioneers of atrial septal puncture. Since then, after the improvement and refinement by Brockenbrough, Mullins, Groft, Inoue, Jackman and other scholars, the atrial septal puncture has continued to mature. In China, scholars such as Li Huatai and Ma Changsheng further enriched the methodology of atrial septal puncture and simplified the puncture procedure on the basis of foreign experience (see Figure 1 for right anterior oblique 45 ºfluoroscopy-guided atrial septal puncture), which has become one of the mainstream atrial septal puncture methods in China because of its simple procedure, easy to master and few complications.
2.1 Anatomical basis of the operations related to atrial septal puncture
The coronary sinus electrode’s turning point represents the coronary sinus orifice, the upper part of the Hirschsprung’s bundle electrode is usually the corresponding part of the aorta without coronary sinus in the atrial septum, the part of the coronary sinus electrode body in the right atrium adjacent to the superior vena cava is usually equivalent to the posterior wall of the right atrium, and the distal course of the left anterior oblique coronary sinus represents the free wall of the left atrium.
The key to atrial septal puncture is the judgment of the direction of puncture, which is simply summarized as “the posterior-anterior position sets the height and the right-anterior oblique position sets the direction”. The posterior-anterior pull down will point the puncture catheter and puncture needle to the left posterior direction, from the superior vena cava back to the level of the fossa ovalis, regardless of the size of the left atrium, generally above the lower edge of the left atrium about a vertebral height, right anterior oblique fluoroscopy is routinely taken 45 º, at this time, the visual direction is left posterior 45 º, the puncture point is generally at the lower edge of the atrial shadow or 2 to 3mm in front of the spine (about a vertebral height), if If the top of the puncture needle bend disappears (parallel to the line of sight) and is straight, this is the ideal penetration point.
2.2 Positioning of the interatrial septal puncture point
Preliminary positioning: Under posteroanterior fluoroscopy, send the atrial septal puncture sheath to the superior vena cava: send the atrial septal puncture needle through the sheath (the head end does not exceed the sheath): the puncture needle indicator points to the 12 o’clock position, then rotate the puncture needle and sheath to the 4 o’clock position in the clockwise direction, and retract the puncture device simultaneously, most of the latter has a sense of falling in on the image when it crosses the fossa ovalis, which is the preliminary positioning of the puncture point, and in the posteroanterior position The height of the puncture point is adjusted appropriately under posteroanterior fluoroscopy.
Precise positioning: 1 height along the left atrial shadow inferior border of the midline of the spine under posteroanterior fluoroscopy, with a maximum range of 0.5 to 1.5 vertebral body heights, 45 º the puncture point under right anterior oblique fluoroscopy is located within a certain range in front of the posterior border of the cardiac shadow, with the anterior border of this range being the midpoint of the posterior border of the cardiac shadow and the atrioventricular sulcus shadow, the posterior border from the posterior border of the cardiac shadow and the midpoint of the atrioventricular sulcus shadow, and the posterior border from the posterior border of the cardiac shadow equivalent to The height of one vertebral body in the upright position. The puncture needle and the distal segment of the sheath arc disappear in a straight or nearly straight shape The puncture needle points to the left posterior 45 º.
2.3 Judgment of the puncture needle tip into the left atrium
The left hand fixes the atrial septal puncture sheath and gently sends it forward to hold the oval fossa, while the right hand pushes the puncture needle in a short amplitude; push the contrast agent, and if the contrast agent is ejected in a linear pattern, it is confirmed to have penetrated into the left atrium.
2.4 Method of repositioning the puncture point after a failed one-needle puncture
Fine adjustment of the puncture point: withdraw the puncture needle into the sheath toward the right anterior oblique position of 45 º fluoroscopy to ensure that the anterior segment is straightened and lifted, rotate the sheath appropriately, adjust the position of the puncture point and puncture again. The sheath is delivered to the superior vena cava under guidance of the guidewire; the sheath is withdrawn to the lower right atrium and the penetrating needle is withdrawn, and the guidewire is fed through the sheath to the superior vena cava and re-punctured. Directly send the sheath and the puncture needle to the superior vena cava: withdraw the sheath to the middle of the right atrium, ensure that the head end of the puncture needle is withdrawn into the sheath, rotate the sheath and the puncture needle simultaneously so that the direction indicator points to the 12 o’clock direction (sternal direction), and then swing the sheath and the puncture needle from side to side, push the injection of contrast agent while pushing in the direction of superior vena cava static, in order to avoid or timely find that the sheath pierces the atrial wall.
2.5 Precautions for atrial septal puncture
During atrial septal puncture, when the needle tip has already entered the left atrium, in order to avoid perforation of the posterior wall of the left atrium during continued anterior delivery of the dilatation tube and the exocannula and sheath tube, it is usually necessary to gently rotate the catheter counterclockwise to make the needle tip more anterior to the left side of the left atrium, so that there will be more space for anterior-like penetration of the septal device. Congenital failure of the fossa ovalis is seen in approximately 10% of patients. Although the catheter can enter the left atrium directly without puncture, because the unclosed foramen ovale is located anteriorly above the septum, the catheter entering the left atrium through this foramen may cause difficulties in subsequent catheterization (e.g., atrial fibrillation ablation), and the anterior wall of the left atrium should be carefully guarded against perforation when delivering the catheter through this foramen ovale.
3. Complications of septal puncture and countermeasures
3.1 Small left atrial internal diameter
The left atrial diameter is too small, and it is easy to accidentally perforate the adjacent structures around the fossa, so the puncture point should be carefully selected to avoid attempted puncture. After the needle tip is pierced into the left atrium, extra care should be taken during the forward delivery of the puncture device to avoid the needle tip piercing the posterior wall of the left atrium.
3.2 Significant increase in left atrial internal diameter
The left atrial septum and fossa ovalis are convex to the right atrium when the internal diameter of the left atrium is increased. At this point, the septal puncture is similar to puncture on a spherical surface, and the inlet catheter slides easily forward toward the aorta-atrial septal space, backward toward the posterior wall of the right atrium-atrial septal space, or above the septum. In the posterior-anterior position, during the retraction of the catheter from the superior vena cava, most of the catheters have no obvious characteristic movement below the location of the conventional puncture point, that is, above the inferior edge of the left atrial shadow, where the puncture point is sometimes even located at the right edge of the spine, and the direction of the puncture needle at the successful puncture point refers to 5 to 6 points. Because of the low puncture position in the atrium, one should be alert to the wrong coronary vein. The puncture point site should not be too far back, otherwise it is easy to pass through the right atrium into the left atrium, thus leading to cardiac compression.
3.3 Significant dilatation of the aortic root
It is common in patients with aortic stenosis, Marfan syndrome, and severe hypertension. A clear diagnosis should be made preoperatively, and a full understanding of the morphology and degree of dilatation is beneficial for guiding intraoperative puncture. Due to the squeezing and pushing effect of the dilated aortic root (located behind the anterior part of the atrial septum) on the atrial septum, the septal plane and the sagittal plane become smaller, or close to vertical in severe cases. Therefore, the direction of the needle tip refers to pumping 2-3 o’clock more often.
3.4 When the right atrium is huge (such as severe tricuspid regurgitation), the needle tip is often difficult to adhere to the atrial septum, and when the angle between the inferior vena cava and the right atrium is too large, the catheter is withdrawn along the 4 o’clock direction, and the puncture needle is drawn in the direction of the distal curvature of the atrial septal puncture needle.
3.5 Significant dilatation of the coronary sinus orifice
It is particularly common in patients with permanent left superior vena cava. The deformity is easily detected by puncture of the left subclavian vein, and the puncture sheath enters the coronary sinus with the same characteristic oscillation as the coronary sinus electrode. Therefore, the needle is held off for suspicious cases and fluoroscopic observation is performed in the left anterior oblique position. In the case of the permanent superior vena cava, it should be imaged before the septal puncture to determine the location of the opening.
3.6 Tissue thickening at the fossa ovalis
It is common to find that the septum is difficult to penetrate with the puncture needle after partial cardiac surgery, when epileptic scar formation is present in the septum. In this case, as long as the puncture point is selected and the direction of needle entry is correct, and the pushing force is increased appropriately, the operator should pay attention to the amplitude of pushing the puncture needle forward. In the case where the tip of the needle has entered the left atrium, but it is difficult to follow up with the bowing tube, pushing the puncture device with force increases the chance of passing the bowing tube, but also increases the risk of perforation of the posterior wall of the left atrium, so the left atrial guiding wire (commonly known as “two and a half turns” wire), which is used in percutaneous mitral balloon dilatation, can be fed through the bowing tube to assist in passing the bowing tube. The wire is hard and has good support, and the puncture hole can be dilated by sending the dilatation tube forward several times with a small amount of force, and the tube can be placed in the left atrium.
When the puncture needle enters the ascending aorta or pericardium, there are characteristic changes.
Pulmonary venous atrial angiography and interpretation
There are many catheter ablation procedures for the treatment of atrial fibrillation, but most of them are related to the pulmonary veins, and the complications associated with ablation therapy are also related to the pulmonary veins and their left atrial junction. Therefore, it is important to be familiar with the opening of the pulmonary vein and its relationship with the left atrium.
Anatomical characteristics of the pulmonary veins
The pulmonary veins are responsible for the return of oxygenated blood from the lungs to the left atrium. Generally, in humans, there are four pulmonary veins that converge into the left atrium from the posterior part of the heart like the “four corners of the pillow”, namely the left superior pulmonary vein (LSPV), the left inferior pulmonary vein (LIPV), the right superior pulmonary vein (RSPV), and the right inferior pulmonary vein (RIPV) (Figure 1). However, there is some variation, and there can be more or less than 4. There is no valve present at the connection between the pulmonary veins and the left atrium.
1.Characteristics of the anatomical relationship between the pulmonary veins and the atria
(1)The position and angle of the pulmonary veins into the left atrium. The position of the left pulmonary vein converging into the left atrium will be relatively higher than the convergence position of the right pulmonary vein. The inferior pulmonary veins converge into the left atrium more posteriorly than the superior pulmonary veins. The superior pulmonary vein generally joins the left atrium at 45°-60° to the horizontal, while the inferior pulmonary vein generally joins the left atrium at 30°-45° to the horizontal (Figure 2), and this difference makes it relatively difficult to attach and fix the inferior pulmonary vein catheter during the clinical marking and ablation of the pulmonary vein opening.
(2) The course of the pulmonary veins. The right superior pulmonary vein passes posterior to the connection between the superior vena cava (SVC) and the right atrium, the right inferior pulmonary vein travels posterior to the right atrium, and the left superior pulmonary vein travels posterior to the left auricle (Figure 3). Therefore, the far-field potentials of the atria measured by different pulmonary veins are different during clinical measurements.
(3) The way the pulmonary veins converge into the left atrium. The pulmonary veins converge into the left atrium in various ways, including lateral, vertical, oblique, and post-convergence co-opening types. It has been found that the post-convergence common opening can reach 25% and is more common in the left side. In addition, there are other pulmonary veins that open directly into the left atrium, usually the right pulmonary vein, such as the right middle pulmonary vein that opens directly into the left atrium without converging to the right superior pulmonary vein, and the left lingual pulmonary vein that opens directly into the left atrium without converging to the left superior pulmonary vein. Moreover, some of the pulmonary veins may have branches at 3 cm from the left atrial opening, which may also affect the shape of the opening. Therefore, the shape and number of pulmonary vein openings in the left atrium are highly variable among patients. In dogs, the pulmonary veins open in the posterior wall of the left atrium, although some pulmonary veins also have convergent posterior openings before entering the left atrium, five to six pulmonary vein openings can often be seen. In pigs, there are generally only two pulmonary vein openings, i.e., the left and right pulmonary vein systems have converged before entering the left atrium.
2.About the pulmonary vein openings
Because of the large variation of pulmonary vein opening in the left atrium, the diameter of pulmonary vein opening, the shape of opening and the distance between pulmonary vein openings are highly variable.
(1)The geometry of pulmonary vein opening. Most of the pulmonary vein openings are round or oval in shape, and retrograde pulmonary venography is more commonly used to determine them clinically. Fred et al. found that the left pulmonary vein openings were more oval in shape, and the maximum and minimum diameters of the same pulmonary vein were different; the right pulmonary vein was relatively round. Even some of the pulmonary vein openings that were shown to be thick on retrograde pulmonary venography were shown to be narrower on MRI, which may be related to the limited angle of projection during imaging. Therefore, some scholars believe that MRI or CT scan is necessary to determine the shape of the pulmonary vein opening before the pulmonary vein isolation procedure in order to help determine the shape of the pulmonary vein opening and thus help select the type of Lasso electrode and the fixation of the electrode catheter to avoid the occurrence of pulmonary vein stenosis.
(2) Relationship between pulmonary vein openings. The relationship between pulmonary vein openings is clearly related to the way in which the pulmonary veins converge into the left atrium as described above. ho et al. found that in ipsilateral pulmonary veins, the distance between pulmonary vein openings with non-common openings could vary from less than 3 mm to 7.3 mm. 8 of the 20 patients studied had pulmonary vein openings less than 3 mm apart.
(3) Pulmonary vein opening diameter: Ho and Cabrera et al. found that the diameter of pulmonary vein openings varied from 8 to 21 mm, with an average of about (125±3) mm. in general, the upper pulmonary vein diameter was generally larger than the lower pulmonary vein diameter, and the right lower pulmonary vein diameter was the smallest. Weiss observed 118 pulmonary veins and found that the diameter of the right inferior pulmonary vein was significantly smaller than that of the other three pulmonary veins. The relationship between pulmonary vein diameter and paroxysmal atrial fibrillation remains unclear. It has been shown that the upper pulmonary veins are significantly dilated in patients with atrial fibrillation, and the distribution of focal points of origin of the upper pulmonary veins is statistically higher than that of the lower pulmonary veins. Among them, 85% of the ectopic excitatory foci were found in the largest diameter pulmonary veins, so the difference in pulmonary vein diameter may be one of the reasons for the different distribution of focal points of origin in atrial fibrillation. However, Lin et al. measured the size of pulmonary vein diameters in three groups of patients (the group with atrial fibrillation originating in the pulmonary veins, the group with atrial fibrillation originating in the terminal crest or superior vena cava, and the group without atrial fibrillation) and found that patients in the atrial fibrillation group with ectopic excitation foci in the upper pulmonary veins had larger diameters in the upper pulmonary veins than in the other two groups, while the enlargement of the diameters of the two upper pulmonary veins did not correspond to the distribution of ectopic foci in them, that is, when there was ectopic excitation in the left upper pulmonary vein, it did not necessarily Cheung et al. suggested that atrial fibrillation was not secondary to structural changes in the left atrium, but rather to a rapidly disorganized focal point of excitation at the atrioventricular junction that caused a disordered contraction of the dilator-like structures there, which in turn caused an increase in the diameter of the atrioventricular junction. In contrast, Satoh et al. suggested that the dilated pulmonary vein orifice and its increased traction could alter the electrophysiological properties of the myocardial tissue and thus trigger tachyarrhythmias. Therefore, the causal relationship between pulmonary vein diameter and the development of atrial fibrillation remains to be further investigated.
Evaluation of the pulmonary vein anatomy and its relationship with the atria
The anatomy of the pulmonary veins and their relationship with the atria are of great importance in the clinical study of paroxysmal atrial fibrillation. In addition to anatomical studies in isolation, the anatomy of the pulmonary veins and their course have been studied more frequently in imaging studies. Currently, many clinical centers use interventional retrograde pulmonary venography to determine the anatomical pattern of the pulmonary veins, which can help to define the diameter and course of the pulmonary veins. However, this method is often affected by the limited angle of projection, interference between pulmonary veins and surrounding tissues, and the performance of the x-ray machine. Many centers also use magnetic resonance or spiral CT to visualize the three-dimensional anatomy of the pulmonary veins preoperatively and postoperatively with less interference and higher accuracy. In our center, the 3D reconstruction of the pulmonary veins by spiral CT can accurately and clearly determine the opening, diameter, course and relationship between the pulmonary veins and the atria. Combined with the intraoperative retrograde pulmonary venography, we can have an accurate grasp of the pulmonary vein anatomy, which is helpful for the selection of Lasso electrodes and the accuracy of ablation. Moreover, it can also help to determine the presence of pulmonary vein stenosis after ablation.
1.Multi-layer spiral cr for three-dimensional reconstruction of pulmonary veins For RF ablation of atrial fibrillation pulmonary vein electric isolation treatment, the value of Mscr is mainly reflected in the following two aspects: (1) evaluation of pulmonary vein anatomy and variation. It helps to guide the implementation of radiofrequency ablation pulmonary vein electroisolation for atrial fibrillation (Figure 4). The lumen and wall changes at the entrance site of the pulmonary veins were followed up after the procedure to evaluate the effect of electrical isolation on the pulmonary veins and to provide a basis for the next treatment plan (Figure 5)Q(2) Evaluation of the morphology and structure of the heart. Evaluate whether there is thrombosis in the left atrium; show the size and morphological structure of each atrium of the heart; make a clear diagnosis of certain primary diseases of the heart such as hypertrophic cardiomyopathy.
2.Pulmonary venography to evaluate the anatomy of pulmonary veins Although the size of each pulmonary vein can be clearly shown by multi-layer spiral CT imaging before surgery, it cannot provide the relative position of pulmonary vein openings during X-ray fluoroscopy, so intraoperative pulmonary venography is usually necessary. The ablation catheter is delivered into the appropriate pulmonary vein as a guide, and the atrial septum is punctured and bowed to the vicinity of the pulmonary vein opening, then the ablation catheter is withdrawn and retrograde imaging is performed. Different pulmonary veins were selected at different fluoroscopic angles for imaging. For the right upper pulmonary vein, the left anterior oblique 45° is chosen. The left upper pulmonary vein is selected at 45° anterior left combined with 30° anterior right oblique. The left anterior 45° projection position for selective left upper pulmonary vein imaging can result in partial overlap of the pulmonary veins with the left auricle (Figure 6). The left inferior pulmonary vein is selected at 45° anterior left oblique. The right inferior pulmonary vein is selected
Application of image fusion technique in atrial fibrillation ablation
Atrial fibrillation (AF) is one of the most common types of refractory arrhythmias. In recent years, the success rate of catheter ablation for atrial fibrillation has been greatly improved with the in-depth research on the electrophysiological mechanism of atrial fibrillation. Currently, the main method of catheter ablation for atrial fibrillation is linear ablation of the circumferential pulmonary vein with electrical isolation of the pulmonary vein as the endpoint, to which additional ablation of other sites will be added according to the condition. Due to the anatomical complexity of the left atrium and pulmonary veins, it is difficult to achieve complete blockage of the ablation line under X-ray fluoroscopy. Although the intraoperative 3D reconstruction of the patient’s left atrium using some 3D scalar systems allows the surgeon to have a three-dimensional view of the atrial structure and catheter position, there are still limitations. Because the constructed atrial model is a simulation, its accuracy is not yet good and may differ from the patient’s atrial morphology. In addition, the anatomical structure of the atrium is complex, and there are many special structures such as venous population, valves, and ears, and the location and relationship of these special structures sometimes cannot be clearly shown under X-ray or on the simulated anatomical pattern, which greatly affects the subsequent ablation treatment.
CT and magnetic resonance imaging techniques have long been used to evaluate the atrial anatomy before AF ablation and to determine the presence or absence of pulmonary vein stenosis after the procedure. Since these radiological images can clearly show the anatomical structures of the left atrium and pulmonary veins, the application of computer technology to fuse the radiological images with the intraoperative 3D simulated images can clearly show the images of each structure of the left atrium and pulmonary veins, and ablation can be performed under the guidance of the patient’s anatomical images, which can shorten the operation time and X-ray exposure time, increase the accuracy of the ablation site, and reduce the operation-related It can shorten the procedure time and X-ray exposure time, increase the accuracy of ablation sites and reduce the complications associated with the procedure. In this paper, we summarize the application of image fusion technology in atrial fibrillation ablation. Since high-precision 32- or 64-row spiral CT has been widely used,6 and its cardiac and vascular imaging accuracy is higher than that of magnetic resonance, we basically apply cr radiography for image fusion.
CT cardiac scan and its left atrial and pulmonary vein image construction
The patient was scanned with CT 1 day before surgery. A retrospective cardiac gating technique was applied to obtain the original images, and the images of atrial diastole were selected for sinus rhythm and the images of QRS wave apex for atrial fibrillation, with a scan interval of 0.625 mm. o After the CT cardiac scan, the CT data were burned into a CD-ROM in DICOM mode, and then imported with image integration After the CT scan was completed, the CT data were burned to a CD-ROM in DICOM mode, and then transferred to an electroanatomical marker system workstation (CARTOXP, Biosense Webster) with image integration software (Carto-MergeTM, Image Integration Module).
Firstly, the image processing software of CARTO XP workstation was applied to maximize the cardiac blood pool of the left atrium and pulmonary veins in the 2D cross-section of the heart in the CT image (Figure 1), distinguish the division between the left atrium and the left ventricle, complete the 3D reconstruction of the cr image, extract the elements of the heart and large blood vessels, and obtain the structures of each heart chamber and large blood vessels. Next, the seeds were planted on each cavity structure, and the segmentation function of the application software was applied to distinguish each cavity structure from the great arteries (Figure 2), and the structures outside the left atrium and the pulmonary veins were hidden. The distal pulmonary vein structures were then removed using the cutting function, leaving the left atrium and pulmonary vein root intact. When the distal left upper pulmonary vein was resected, the upper edge of the preserved pulmonary vein was appropriately longer than the lower edge. Finally, a cut was made at the appropriate site outside the root of the left auricle.
In this way, the junction of the left pulmonary vein and the left auricle can be fully exposed in combination with the resection method of the distal left upper pulmonary vein, which is conducive to guiding the linear ablation at this site (Figure 3). After successful image construction, the above two parts were named as left atrium and left auricle, and the images were exported to Carto XP’s calibration system.
Three-dimensional electroanatomical reconstruction of the left atrium and image fusion
The patient’s preoperative preparation and some specific operations during the procedure are not described. Under the guidance of Carto, the Navistar ablation catheter (saline infusion or 8 mm) was used to construct an approximate left atrial morphology and to mark the mitral annulus by taking points in each wall of the left atrium. When constructing the left atrium, care should be taken that the points taken in different walls of the atrium are relatively uniform, especially in the left and right sides of the left atrium in the vestibule of the circumflex pulmonary veins, so that the fused images do not shift to one side and affect the accuracy of image fusion. Because the anterior wall of the left atrium is the most mobile, too many acquisition points in this area will reduce the accuracy of fusion.
Image fusion can be performed with multiple or single “land markers”. Since single landmark image fusion is easy and requires less time, and the mean value of the distance between the constructed left atrial image and the CT image after fusion is similar to the mean value obtained by the multi-point marker method reported abroad, we currently use single landmark for image fusion. Since the anterior wall of the left atrium is more mobile, the roadmap should be selected from other parts of the left atrium with unique anatomical features. The posterior inferior edge of the right inferior pulmonary vein orifice is used as the anatomical landmark for fusion, because it is relatively unaffected by respiratory motion and cardiac pulsation and can be easily identified under X-ray fluoroscopy.
After determining the roadmap for image fusion on the constructed left atrial image with reference to the pulmonary venogram under fluoroscopy, the site corresponding to the roadmap was selected on the CT left atrial image (Figure 4). If the distance between the constructed left atrium image and some corresponding points of the CT image is larger, for example, more than 5 mm, these points should be removed and the surface fusion should be performed again (Figure 5). After successful fusion, the filling value of the constructed left atrial map was reduced to zero, and the CT images of the left atrium and pulmonary veins could be clearly displayed.
Ablation guided by fusion images
Linear ablation of bilateral circumferential pulmonary veins was performed under the guidance of fusion images, and the ablation site was the vestibular part of bilateral pulmonary veins, combined with the application of annular marker electrodes to achieve electrical isolation of pulmonary veins (Figure 6). For persistent or permanent atrial fibrillation, complex fractionated atrial electrograms (CFAEs) are calibrated and ablated, as well as linear ablation of the left atrial apex or isthmus, depending on the patient.
The CT image fusion of the left atrium and pulmonary veins on the CARTO XP system allows the operator to understand the anatomy of the left atrium and pulmonary veins from multiple perspectives and to fully understand the anatomical pattern and course of the proximal segment of the pulmonary veins. This not only helps to appreciate the various anatomical variations of the left atrium and pulmonary veins, but also facilitates the understanding of the two-dimensional image of the pulmonary venogram, so that the operator has a macroscopic understanding of the anatomy of the left atrium of the patient from the beginning of the septal puncture. The fusion image guided ablation of the circumferential pulmonary veins can avoid the “perfect” ablation loop guided by the pure application of 3D electroanatomy, in which all ablation points on one side of the ablation loop are nearly in one plane and are assumed to be round or oval, which is not consistent with the actual anatomy of the upper and lower pulmonary vestibule. In addition, the ablation plan can be individualized according to the different anatomy and cardiac electrophysiology of each patient, and some additional ablation lines can be designed according to the concave and convexity of the left atrial endocardium and the local voltage.
Application of projection function
When ablation is started, the ablation point projection function and the catheter tip projection function are enabled to clearly show the actual ablation point and the catheter tip position and their projections on the fused cr image. In linear ablation, the ablation point should be linearly connected on the fused CT image, and the ablation line connection of the pure 3D electroanatomical reconstruction (without dragging in the CT image) displayed in another window of the Carto system screen should be used to select the next ablation site, determine the missed site and perform additional ablation. This helps to determine whether the catheter tip is in good contact with the endocardium of the left atrium, avoiding the possible false contact guided by the simple 3D electroanatomical reconstruction, and reducing the invalid discharge. In addition, parameters such as energy output, temperature and impedance between the distal end of the ablation catheter and the tissue during ablation are helpful to determine the contact between the distal end of the ablation catheter and the atrial wall.
Ablation of special sites
The junction between the left pulmonary vein and the left auricle and the junction of the upper and lower pulmonary veins on both sides are often difficult and missing points in ablation. The cut method mentioned above in the CFr left atrial image reconstruction can better expose the left pulmonary vein and the saki between the left auricles. This preserves the base of the pulmonary vein and the left auricle, and the location and opening of the pulmonary vein and the left auricle remain well understood, while avoiding the distal branches or lobes of the pulmonary vein and the left auricle from interfering with the exposure of the streamers between them. In addition, cutting off the distal ends of the pulmonary veins and left auricle also ensures that the constructed left atrium can be satisfactorily integrated with the CT left atrial image without excessive catheter access to the pulmonary veins and left auricle during the 3D reconstruction of the left atrium. If necessary, the CT image of the left auricle can be dragged into the fused left atrial window to guide the ablation.
Most of the saki between the left pulmonary vein and the left auricle are narrow, and there is a lot of myofascicular traffic in this area, which makes the potential at the connection between the left atrium and the pulmonary vein high and makes the successful linear ablation of this area difficult. The narrow streamers make it difficult for the catheter tip to adhere, and it often slips between the base of the left atrium and the pulmonary veins. A well-fused CT image not only shows this structure clearly, but also enables
This can be avoided by precisely locating the catheter tip. The endoscopic function of the image fusion technology allows the position of the ablation catheter in relation to the saki from both the outside and inside of the left atrium, allowing for a more targeted view.
The junction of the superior and inferior pulmonary veins is also an easy area to be missed in ablation, especially in the junction of the left superior and inferior pulmonary veins. The two pulmonary veins are often crossed and overlapped, and the muscular component is relatively thick, which brings inconvenience to the successful continuous linear ablation through the wall in this area; the local unevenness of this area prevents stable apposition to achieve effective discharge. The use of image fusion technology clearly shows these structures, which can be noted during circumferential ablation, and even if a miss occurs, it is more convenient to supplement the ablation under the guidance of circumferential marker electrodes.
Influencing factors
Current image fusion techniques still have limitations in that the anatomical images used to guide the procedure are obtained from preoperative cr scans and are not real-time. The accuracy of the fused images can be affected by the patient’s respiratory and circulatory status both during the preoperative CT scan and intraoperatively, for example, the left atrial volume can be increased to varying degrees in atrial fibrillation compared to sinus rhythm. When a catheter is used for LV image construction, there is a certain amount of tension between the distal end of the catheter and the atrial wall, so that the LV image constructed with the catheter is different from that obtained with Cvr scanning, even under the same physiological state. In addition, the operator’s knowledge of cardiac anatomy and proficiency in catheterization can affect the accuracy of LV image construction and image fusion. To maximize the accuracy of image fusion, it is recommended that the CT scan be performed within 24 hours before surgery, that the patient’s heart rhythm be consistent with that of the CT scan during 3D electroanatomic reconstruction, and that the patient’s breathing be as stable as possible; and that the tension between the distal end of the catheter and the atrial wall be moderate when constructing the left atrium.
In conclusion, the application of image fusion technology to guide the ablation of atrial fibrillation can increase the effectiveness and safety of the procedure, and can increase the confidence of the operator, especially the beginner, shorten the learning curve, and better promote the ablation technique of atrial fibrillation for the benefit of the majority of patients.