[Abstract] OBJECTIVE: To explore the strategy in the ablation of special left-sided bypass radiofrequency catheters. METHODS: There were 288 patients with left-sided bypass who underwent radiofrequency catheter ablation in our hospital from January 2013 to December 2013, among which 11 cases had some special features in ablation, including 6 cases with fissure phenomenon, 3 cases with left-sided slow bypass, 1 case with combined pediatric palsy patients with severe tortuous peripheral vascularization, and 1 case with paroxysmal atrial fibrillation and atrial flutter combined with atrioventricular dominant bypass. Radiofrequency ablation was performed via retrograde aortic route on the mitral ventricular side, through septal route on the mitral atrioventricular side and in the coronary sinus. RESULTS: All 11 patients were successfully ablated, 6 on the ventricular side of the mitral valve via the retrograde aortic route and 4 on the atrial side of the mitral valve via the septal puncture.
One case was successfully ablated via coronary vein sinus. In 6 patients, there was no ventricular retrograde transmission at low frequency (above 400 ms in circumference) stimulation, but at high frequency (below 350 ms in circumference) stimulation, there was bypass retrograde transmission, and the ventricular retrograde transmission showed cleft phenomenon. 3 cases were left-sided slow bypass, and the VA interval was significantly prolonged during ventricular retrograde transmission, and the VA at the target point was not fused. 1 case was combined with poliomyelitis, and the peripheral vasculature was severely In one case, the atrioventricular dominant bypass was combined with paroxysmal atrial fibrillation and atrial flutter. After successful isolation of the pulmonary vein potential and blocking of the tricuspid annular isthmus line, ablation was successful at the root of the left auricle and the distal end of the coronary sinus at a distance of about 175 px from the coronary sinus opening. Conclusion: When there are special cases of radiofrequency ablation of the left atrioventricular bypass catheter, careful identification is needed, and a high success rate can still be obtained through different methods and routes of ablation.
【Key words】：Radiofrequency ablation, atrioventricular bypass, fissure phenomenon
Atrioventricular bypass is caused by the presence of a myocardial bundle connecting atria and ventricles in the atrioventricular valve annulus, which causes antegrade and retrograde conduction of atria and ventricles, and is the main cause of atrioventricular folding tachycardia, accounting for 50% of supraventricular tachycardia.1 Radiofrequency catheter ablation to block atrioventricular bypass is the main method to cure atrioventricular folding tachycardia, and the success rate of the procedure can reach more than 95%.2 However, some special circumstances may occur during the ablation of atrioventricular bypass. Some special circumstances may occur during the ablation of AV bypass, and the special phenomena in the ablation of left-sided AV bypass in our hospital are summarized as follows.
1. Information and methods
1.1 Clinical data: From January 2012 to December 2013, 353 patients with atrioventricular tachycardia caused by atrioventricular bypass were treated with radiofrequency ablation surgery in the Department of Cardiology of Shenyang Military Region General Hospital, including 288 cases of left-sided bypass and 65 cases of right-sided bypass. 11 patients had special left-sided atrioventricular bypass, including 6 cases of atrioventricular bypass with cleft phenomenon, 3 cases of left-sided slow bypass, 1 case of combined peripheral vascular There were 6 cases of atrioventricular bypass with cleft phenomenon, 3 cases of left-sided slow bypass, 1 case of severe tortuous peripheral blood vessels, and 1 patient with atrial fibrillation and atrial flutter.
1.2 Methods.
① Preoperative informed consent was signed, antiarrhythmic drugs were discontinued for more than 5 half-lives, and routine biochemical, coagulation and blood analysis examinations were performed. Chest X-ray, cardiac ultrasound, and abdominal ultrasound examination all indicated no organic heart disease and other serious cardiovascular and cerebrovascular diseases. Patients with combined atrial fibrillation and atrial flutter were routinely anticoagulated for 7 days before surgery. Preoperative esophageal ultrasonography was performed to exclude atrial thrombus, and CT and 3D reconstruction of pulmonary veins were performed.
②Electrophysiological examination and catheter ablation: The right femoral vein and right internal jugular vein or left subclavian vein were routinely punctured, and 10-pole coronary sinus electrodes and HIS electrodes (Biosense, Webster, Johnson & Johnson, USA) were implanted. If the septum was punctured, 100 IU/Kg of normal heparin was given after successful puncture and the prothrombin time (ACT) was monitored to maintain between 250-350s. Programmed ventricular stimulation was performed at 500ms-280ms to detect the presence or absence of atrial retrograde bypass. Patients with atrial fibrillation and atrial flutter were preceded by pulmonary vein isolation and linear ablation of the tricuspid isthmus. In the absence of decremental conduction in ventricular atrial pre-stimulation, the retrograde A’ wave of the distal CS electrode was the earliest in advance in ventricular retrograde transmission, and the retrograde A’ wave of the distal CS electrode was also the earliest in advance in induced tachycardia, or there was atrioventricular pre-stimulation, and the CS1,2 V wave was the earliest in sinus rhythm. Diagnosis: left free wall dominant or occult bypass with AVRT.
(iii) Ablation strategy: left-sided bypass was ablated using the retrograde transaortic method, the through septal approach and the intracoronary distal. Postoperatively, programmed ventricular stimulation was still taken for 500ms – 280ms to confirm the absence of atrioventricular antegrade and retrograde transmission.
2. Results
2.1 Six cases in electrophysiological examination showed cleft phenomenon, i.e., no ventricular atrial retrograde transmission at 500ms, 450ms, and 400ms, while bypass retrograde transmission occurred at 350ms, 300ms, and 280ms stimulation of the ventricle, and the earliest point of atrial excitation was distal to the coronary sinus, which was diagnosed as left free wall occult bypass. The retrograde pathway through the aorta crossed the aortic valve to the sub mitral valve, left ventricular free wall, the ablation electrode was labeled to small A large V, good VA fusion at retrograde transmission, the bypass retrograde transmission disappeared with 61°C 50w discharge for 3-5 seconds, consolidation discharge for 120s, no atrial retrograde transmission, the procedure was successful.
2.2 Three cases of slow left free wall bypass: electrophysiological examination confirmed the left free wall bypass, but the VA (at CS1,2) was far away during tachycardia, advancement of A wave was seen in the ventricle (RS2) in advance of the Hirschsprung’s bundle nonphase, and ventricular towing also confirmed the atrioventricular bypass. The ablation catheter was passed through the retrograde aortic pathway under the mitral valve and distal to the coronary sinus at 125px from the sinus orifice, and the retrograde A wave was marked and measured to advance the A wave distal to the coronary sinus electrode, but the VA did not fuse, and the VA distance was 192ms (Figure 2) and 198ms, which was used as the ablation target, and the bypass retrograde transmission was interrupted and the procedure was successful.
2.3 One case of severe peripheral vascular tortuosity: the patient was a male, 59 years old, with poliomyelitis and severe S-shaped spinal curvature, accompanied by severe vascular curvature. The ablation catheter was delivered to the left ventricle via the retrograde aortic route, and the ideal target could not be marked under the mitral valve because the catheter rotation was very difficult. The septal puncture was performed, and the ideal target was detected on the mitral valve of the left atrium, and the ablation was successful.
2.4 One case of combined paroxysmal atrial fibrillation and atrial flutter was diagnosed with recurrent atrial fibrillation with pre-excitation, and the electrical resuscitation could not be terminated. After preoperative preparation according to atrial fibrillation and atrial flutter, frequent episodes of atrial fibrillation and atrial flutter still occurred intraoperatively. After electrical isolation of the right and left pulmonary veins by septal puncture, the pulmonary vein potential disappeared and atrial fibrillation was terminated. The ablation catheter was withdrawn from the left atrium and linear ablation of the tricuspid isthmus was performed. After confirming the bidirectional block, the ablation catheter was sent to the left atrium again, and the AV fusion was repeatedly marked at the CS1,2AV fusion, and good AV fusion and bypass potential were marked at about 175px from the coronary sinus orifice, and ablation was performed at 45℃,40W. The atrioventricular bypass forward transmission was interrupted, but it was quickly restored, and repeatedly marked ablation was unsuccessful. The ablation catheter was withdrawn from the left atrium, and the target point was ablated successfully at 45℃,30W through the coronary sinus opening to the distal coronary vein, which corresponds to the atrial side.
3. Discussion
Atrioventricular bypass has the characteristics of fast conduction speed, long non-response period and non-decreasing conduction. However, in a few cases, cleft phenomenon, long conduction time and decremental characteristics can occur. Various difficulties and problems may occur during ablation. In this study, some special cases of left AV bypass and problems arising during ablation are summarized to further improve the success rate of the procedure.
3.1 It is well known that AV bypass is divided into two types according to conduction characteristics.3-5 One is fast bypass, with fast conduction velocity, long non-reduction period, no decremental characteristics, with all-and-none characteristics, forming tachycardia with short RP interval and forming paroxysmal tachycardia; the other is slow bypass, with decremental conduction characteristics of AV node-like, with slow conduction velocity, forming tachycardia with long RP interval characteristics, often leading to The other is slow bypass, which has AV node-like decremental conduction characteristics and slow conduction speed, resulting in tachycardia with long RP intervals, often leading to restless tachycardia. In this paper, 8 of 13 patients had fast bypass and 3 had slow bypass. Six of the patients in the fast bypass had a cleft phenomenon. The cleft phenomenon is a phenomenon in which the excitation arriving at the distal end of the cardiac cycle cannot be conducted within a certain time frame, but the earlier or later excitation can be conducted due to the large dispersion of the nonconducting period and conduction velocity in different parts of the cardiac conduction system, and this time frame is called the cleft band.5 Electrocardiographic phenomenon: the downward transmission of excitation with a long interphase is blocked, while the downward transmission of excitation with a short interphase is blocked. Possible electrophysiological mechanisms: During preterm contraction, the intercohortic interval is shortened, and the excitation falls into the effective nonstop period at the distal level and is blocked from downward transmission.
When the intercoherent interval of preterm contraction is shortened further, it falls into the relative overload period at the proximal level and the excitation is delayed proximally, when it is transmitted to the distal end. The distal block is already out of the effective nonconducting period, so that the excitation can be down-conducted. Therefore, the mechanism of the cleft phenomenon is not an unexpected improvement of the distal tissue, but a result of the slow downward conduction of the excitation in the proximal tissue into the relative nonphase, which is essentially a pseudo-overlong conduction. The cleft phenomenon is not uncommon during clinical ECG and cardiac electrophysiological examinations and can occur in both forward and reverse conduction of the AV conduction system. The cleft phenomenon is also influenced by various factors such as tachycardia length and antiarrhythmic drugs. Therefore, in electrophysiological examinations, if the ventricle is stimulated at a slower frequency and there is no atrial retrograde conduction, the stimulation perimeter should be gradually shortened so that the S1S1 stimulation perimeter is gradually reduced to 280 ms or even 260 ms to detect the presence of a bypass. After catheter ablation, the bypass was still stimulated with different circumferences of S1S1 to check whether the bypass was completely terminated. In this paper, all six patients showed cleft phenomenon before surgery and no further bypass reversal after surgery, suggesting that atrial and ventricular program stimulation with different perimeters and prephase stimulation should be carefully completed during electrophysiological examination to prevent missed diagnosis and misdiagnosis.
3.2 Most of the slow bypasses were located in the right posterior septum, accounting for about 70.6%6, while the percentage of those in the left free wall was not high, and the slow bypasses in this study accounted for only 0.9% of the bypass ablations. Careful intraoperative identification is required to exclude atrial tachycardia and AV nodal retrograde tachycardia (fast/slow type) by applying late onset ventricular stimulation, early onset ventricular stimulation, and Hitchcock bundle parasternal stimulation. In case of tachycardia or ventricular retrograde transmission, it is difficult to find VA fusion by target point labeling, but atrial waves with earlier retrograde transmission can be labeled, but VA does not fuse and there is a plateau period between VA, and ablation can be successful.
3.3 The conventional ablation route for left-sided bypass is the retrograde aortic approach with ablation under the mitral valve. However, in some special cases, such as severe peripheral vascular tortuosity, presence of thoracoabdominal aortic aneurysm, peripheral arterial occlusive disease, etc., ablation can be performed via the femoral vein route via septal puncture to the left atrium, and ablation can be performed at the atrial side of the supra-micronomic valve to mark the target site.
3.4 In patients with atrial fibrillation combined with preexcitation, is it necessary to ablate only the bypass or also to isolate the pulmonary vein potential? Some studies have shown that atrial fibrillation in patients with preexcitation syndrome combined with ablation to block bypass antegrade or retrograde transmission rarely occurs, but mostly in younger people. In patients older than 50 years, the atrial muscle gradually ages and may become fibrotic, and atrial fibrillation can still occur even after blocking the atrial bypass. Therefore, preexcitation syndrome in the elderly with atrial fibrillation requires both isolation of the pulmonary vein potential and ablation of the atrioventricular bypass. In this patient, atrial fibrillation was terminated after isolation of the pulmonary vein potential. However, the coronary sinus potential showed that the bypass was located in the left free wall, and repeated markings on the mitral valve showed no ideal target, not excluding epicardial bypass, so the ablation catheter was delivered to the distal end of the coronary sinus via the coronary vein route, and the ablation was successful.
In conclusion, radiofrequency catheter ablation is the main treatment for atrioventricular folding tachycardia involving atrioventricular bypass, with a success rate of over 95%. However, various special circumstances may be encountered intraoperatively, and understanding and mastering the identification and ablation skills will further increase the success rate of the procedure and reduce the occurrence of complications.