Ablation of atrial fibrillation
When is this procedure indicated?
In recent years, the indications for the ablation of AF through CPVA have expanded widely, based on the results of numerous clinical trials. The procedure is primarily indicated in symptomatic patients with atrial fibrillation refractory to antiarrhythmic drug therapy. Currently the procedure is recommended at an early stage of the disease, independently of the refractoriness of antiarrhythmic drugs. In recent years, the indication has also extended to patients with heart failure and valvulopathies, and also in older subjects, in subjects with permanent AF and / or mitral or aortic mechanical valve prostheses. A low ejection fraction of the left ventricle does not represent an absolute contraindication to CPVA. Indeed studies, such as CASTLE-AF, have shown that these patients also benefit from ablation. Recent studies have highlighted the usefulness of continuing antiarrhythmic therapy after ablation. Therefore therapy with antiarrhythmic drugs is generally continued after ablation, and dosages are generally progressively reduced. Anticoagulant therapy is also generally continued after ablation, and is suspended on a case-by-case basis after AF ablation.
How is it performed?
Usually in our Electrophysiology laboratory, we use the CARTO mapping systems (BiosenseWebster, Diamond Bar, CA, USA) and the EnSiteNavX (St. Jude Medical, St. Paul, MN, USA), which have significantly shortened the time of fluoroscopy, improving the safety profile of the procedure. The early adoption by our group of the CARTO mapping system has allowed an accurate reconstruction of the complex left atrial anatomy and is now accepted by the entire electrophysiology community that performs AF ablation. The CARTO system continuously locates the position of the catheter using three very low magnetic fields, while the NavX system is based on electric fields generated by three pairs of skin electrodes orthogonal in three axes: X, Y, and Z. Unlike the CARTO, the new NavX allows to obtain a 3-D reconstruction of both the tip and the body of the catheter, which is particularly useful in “difficult” areas, such as the ostia of the PV, the crest, the mitral annulus and the septal area. The monitoring of the catheter with the NavX system is obtained by a proximity indicator which, based on the color intensity of the tip of the catheter, allows the operator to check the optimal contact of the ablation catheter, a contact that when associated with the abatement of the atrial potential indicates achievement of the goal. During RF applications, cardiac movement, pain and breathing are all factors that affect the stability of the positioning of the catheter, but NavX software allows to minimize the amount of target movement, as well as respiratory artifacts. When the posterior wall is ablated, which is a vulnerable area at greater risk of cardiac perforation, the presence of pain can cause changes in the respiratory rate, and respiratory compensation by the NavX is useful for maintaining catheter stability. Furthermore, Navx technology is able to create separately any desired anatomy for each ablation target which results in a more accurate ablation, in particular of difficult targets, such as the ostia of the PVs, their cavern, the posterior wall, and the CS. Although the NavX Ensite system allows you to collect many points quickly and sequentially, in difficult areas, it is preferred to acquire points manually as in the CARTO system. Another important advantage of the NavX system, compared to the CARTO, is that the patient’s movements during the procedure do not concern the reconstruction of the map, as the reference catheter also moves due to the presence of patches attached to the patient’s body. As for the CARTO system, after ablation, a voltage map is shown by a colorimetric gradient to verify the complete elimination of potentials along and within the lesion lines. Currently, with both electroanatomical systems, in a few minutes we are able to reconstruct the anatomy of the LA and the ablation targets.
The reconstruction of the PVs and their hosts represents the first step and is confirmed by the simultaneous use of fluoroscopy, electrograms, and impedance gradients. Typically and simultaneously, once the catheter enters the PV, the tip is seen outside the heart shadow on fluoroscopy, the impedance values significantly increase (over 4 Ohms above the left atrial impedance), and the atrial electrograms disappear. Once the PVs are displayed, a detailed sequential reconstruction of the left atrium is performed, including the rear and front walls, the LAA, the roof, the septum and the mitral annulus with its isthmus. The septum and the channel between LAA and the LSPV often require the acquisition of many more points than in other areas. LAA, which is identified with the presence of unfractionated and large amplitude atrial electrograms and large ventricular electrograms with an electrical activity organized in AF, is one of the last areas that is mapped. The channel between LAA and LSPV shows potentials that are typically smaller than those of LAA but higher and more fractionated than in the rest of the left atrium. If the canal is not accurately rebuilt, the left side of the circumferential lesion can be positioned too close to the LAA or within the PV ostium, which can result in poor efficacy and major complications, such as perforation of the LAA stenosis of the PV. Although roof reconstruction is easier by requiring fewer points to acquire, incorrect interpolation of the roofs should be avoided when using the CARTO system.
Once the left atrium and the main pulmonary veins have been adequately reconstructed, radio frequency energy is supplied, which in our laboratory is the most frequently used type of energy, for the endocardial ablation of the aforementioned electrophysiological and anatomical targets. Over the past three years, we have used an irrigated 4 mm catheter instead of the irrigated 8 mm, which has been shown to have some limitations, including the propensity for clot formation and insufficient energy delivery in areas with low blood flow. The irrigated catheter allows to adequately distribute the energy and to obtain larger lesions, minimizing the embolic risk. In our approach, the effectiveness of radio frequency delivery is and remains important, but we try to moderate the power in risk areas for greater safety. We usually use a lower power setting (30-50 W) and an irrigation flow of 2 ml/min (during mapping) and up to 50 ml/min during ablation (based on the site of delivery of the radio frequencies). For circumferential lesions, radiofrequencies are delivered at a distance of about 1 cm from the ostia (instead of 5 mm), thus reducing the risk of stenosis of the pulmonary veins. If an increase in impedance occurs (> 10 Ohms) or the patient experiences burning pain, the radio frequencies are stopped immediately.
When the ablation starts, the irrigation flow increases from 2 to 17 ml/min, while the impedance and temperature values at the tip of the catheter are constantly monitored. The output energy is limited to 50 W with a maximum temperature of 48 degrees C throughout the procedure, but lower values are used in the posterior wall and in the coronary sinus to reduce the risk of injury to adjacent structures. Usually the circumferential lesion lines are practiced starting from the lateral portion of the tricuspid annulus and moving posteriorly, then anteriorly to the left of the pulmonary veins, passing the ridge between the LSPV and the atrium and going close to the lesion on the posterior wall of the atrium. The right pulmonary veins are isolated in a similar way, and two further lines connecting the two circumferential lines are made posteriorly. The circumferential lines are adapted according to the individual anatomy of the junction between the pulmonary vein and the atrium. A single circumferential line surrounds the two ipsilateral VPs in the presence of ostia less than 20 mm apart, in the presence of a common ostium or an early branch division. If anatomically possible, we also practice a line of injury between the two ostia to further reduce the anatomical and electrophysiological substrate.
Characteristically, in patients with permanent AF and dilated atria, while performing the disconnection of the coronary sinus and before restoring the sinus rhythm, there is a regularization of the cycle with a transformation in CT and a uniform morphology of the P wave. With our approach, there is a restoration of the sinus rhythm (SR) in almost all patients with permanent AF. The restoration to SR occurs immediately or after transformation into AT. The procedure is successful when all endpoints are reached.
In the first two months after the procedure, atrial fibrillation recurrences may occur, however in half of the cases they constitute a transient phenomenon and do not require a second procedure. The long-term efficacy of CPVA is > 90% in patients with paroxysmal atrial fibrillation, and approximately 85% in patients with permanent atrial fibrillation, when it was not possible to induce AF or AT at the end of the procedure. The long-term success rate is higher in patients with paroxysmal atrial fibrillation and local vagal denervation. If there is a recurrence of persistent atrial fibrillation or frequent episodes of symptomatic atrial fibrillation or the presence of a symptomatic right or left atrial flutter, a second procedure is proposed at least six months after the first. The procedure is repeatable for a maximum of three times. The absence of symptoms may not correspond to a stable restoration of the sinus rhythm, and the accuracy of the evaluation of post-ablation recurrences most of the time depends on the duration of the ECG recordings. To assess what the burden of asymptomatic recurrences of arrhythmia is, usually after ablation, patients undergo a loop recorder implant (generally within 45 days of ablation), followed by remote monitoring. Alternatively, patients can undergo Holter ECG recordings after 1, 3, 6 and 12 months and a transtelephonic ECG (cardiotelephone) monitoring.
At the end of the procedure, we usually use protamine sulphate to allow the removal of the introducers. Subsequently, management includes anticoagulant therapy, while in the past embrication with heparin was used. Currently with DOAC drugs, this is no longer necessary and only oral anticoagulant is continued. The possibility of optimizing the parameters according to the most critical areas allows for a lower incidence rate of major complications. Cardiac tamponade should be excluded in all patients who have post-procedure hypotension. In our experience, however, this complication is very rare if you pay attention to the settings used. Only a few patients required pericardiocentesis following pericardial effusion, and we reported only one case of atrioesophageal fistula. The late onset (6-10 days after ablation) of a febrile state with or without neurological symptoms should always lead to suspicion of esophageal atrium fistula, which should be excluded by means of a spiral CT with contrast. In our extensive experience covering over 15,000 cases of CPVA, there have been no perioperative deaths, or major complications, such as VP stenosis, phrenic nerve injury or coronary artery occlusion. Minor complications are infrequent, while a non-hemodynamically significant pericardial effusion affects about 4% of patients. Pericarditic pain may be present in the early days of the post-procedure and is usually responsive to salicylates.
If all objectives have been achieved during the procedure, post ablation atrial tachycardia develops in less than 5% of cases, and it is usually macro / micro re-entry tachycardia, rather than focal atrial tachycardia. In our experience, these tachycardias should initially be treated conservatively through drug therapy or cardioversion. Only in symptomatic patients is the procedure repeated in order to optimize ablative therapy, and in many cases therapeutic success is achieved. Ablation should be performed not through empirical lesions but after recognition of the underlying mechanism. The morphology of the P wave, its axis, and the continuous activation of the atrium leads to a macro-reorientation mechanism, while the observation of an isoelectric line between the P waves leads to a focal tachycardia. We routinely perform both a voltage and activation map; combining them together with pacing maneuvers for a better result of ablative therapy. Usually the activation map shows the earlier and later activation with a chromatic scale that refers to a time window equal to the tachycardia cycle. The most common post-ablation atrial tachycardia is due to one originating from the mitral annulus. Entering with post-pacing intervals equal to the tachycardia cycle measured at more than three sites around the upper and lower mitral annulus, with an activation time around the tricuspid annulus equal to the tachycardia cycle, strongly suggest a diagnosis of atrial tachycardia originating from the mitral annulus. As in the case of the isthmus-dependent right atrial flutter, the narrowest area of the circuit is located between the VPIS and the annulus. Consequently, the best place to look for the residual gaps and to repeat the ablation is the mitral isthmus. For micro reentrant atrial tachycardias (cycle length less than 80%) originating from the reconnection of the VP ostia, the ablation of the sites with earlier activation that have an occult entrainment proves to be very effective. Frequently the voltage maps show areas of voltage preserved at the early activation sites, suggesting the presence of areas not previously ablated or insufficiently ablated. The re-entry around the right or left pulmonary veins can be demonstrated by pacing from the distal and proximal coronary sinus, from the septum and from the roof of the atrium. Their management requires the use of 3-D activation maps to outline the course of tachycardia and to identify a lesion line that connects the anatomical barriers in order to interrupt the atrial tachycardia circuits. RFs are delivered after having clearly identified the critical isthmuses with a detailed electroanatomical map. Usually only a few RF applications are needed to eliminate tachycardia circuits and their inducibility.