Veno-Atrial Antral Ablations Achieve Comparable Early Success Rates to Electroanatomical Left Atrial Ablations for Treating Paroxysmal Atrial Fibrillation

Atrial fibrillation is a serious clinical problem with major morbidities. Recently, ablation of both paroxysmal and persistent atrial fibrillation has become an effective therapy for many patients with this arrhythmia. Ablation has become an effective therapy for atrial fibrillation subsequent to the realization that inducers and drivers of atrial fibrillation tend to originate in the pulmonary veins and the posterior wall region of the left atria. Controversy currently exists in the academic electrophysiology community regarding the best approach towards this ablation with both circumferential pulmonary conduit isolation and ostial pulmonary vein isolation being the two predominate techniques to accomplish this ablation. In our laboratory, we have performed atrial fibrillation ablations since 1999 and currently perform over 200 of these procedures annually. We have utilized numerous techniques for these ablations including focal trigger ablations, ostial pulmonary vein isolations and circumferential pulmonary conduit ablations. A recently treated patient illustrates a typical ablation procedure.

Case Presentation

The patient is a 42-year-old man with a three-year history of paroxysmal atrial fibrillation (PAF). He has a history of coronary artery bypass surgery for multi-vessel coronary disease, with paroxysms of fibrillation beginning shortly after this surgery. Antiarrhythmic drug therapy failed to control PAF, and episodes continued, requiring multiple hospital admissions. Episodes were now occurring three to four times a month. The patient s only other medical history was that of hypertension. Echocardiography revealed normal left ventricular function with mild mitral regurgitation and a normal left atrial size of 3.8 cm. The patient was informed of the risks of this ablation including cardiac perforation, stroke and pulmonary vein stenosis and consented to the procedure. In this patient s case, given the relatively normal left atrial (LA) architecture, we elected to perform an ostial isolation procedure. To perform this procedure, the patient was brought to the electrophysiology laboratory and both groins were prepped. Via hemostatic sheaths in the left groin, a standard quadripolar electrophysiology catheter was positioned at the right atrial appendage. In addition, a 4 French (Fr) steerable decapolar recording catheter (Boston Scientific/Irvine Biomedical, Natick, Massachusetts) was passed into the coronary sinus. This smaller decapolar catheter provides us with several advantages when performing atrial fibrillation ablations. Specifically, in order to separate the pulmonary vein potentials from the LA electrograms, pacing in the distal great cardiac vein near the ostia of the targeted pulmonary vein provides the best separation. The 4 Fr decapolar can generally be passed distally into the anterior part of the great cardiac vein, allowing for pacing in closer proximity to the left upper and left lower pulmonary veins. The coronary sinus valve of Viusen s can at times prevent passage of larger steerable catheters distally into the great cardiac vein. The smaller decapole generally can be passed all the way into the anterior interventricular vein, should mapping/pacing require this functionality. This catheter can also be passed into the vein of Marshall if needed and is potentially less traumatic to smaller distal branch veins than a larger mapping catheter could be. To map this patient s left atrium, a double transseptal technique is utilized with both transseptals placed from the right femoral vein. The patient is heparinized to an activated clotting time of 300-350 seconds. A full strength aspirin and 150 mg of Plavix are given two hours prior to the procedure. A heparin drip is started after the heparin boluses, and both sheaths are flushed every 10 minutes with either contrast or heparinized saline. To selectively intubate each of the four pulmonary veins requires pre-shaped sheaths. We generally utilize modified SL-2 sheaths, with SL-2 sizes working for most patients. After the veins are imaged, a circular mapping catheter (Boston Scientific/Irvine Biomedical) is passed into the various venous ostia. The catheter size selected will depend on the veno-atrial ostia sizes seen during venography. If at all possible, a catheter with an expandable helix should be selected. Expandable helixes provide for better myocardial electrode contact and also allow for better positioning near the true veno-atrial junction. A fixed helix size cannot be individually sized to the ostia and more distal pulmonary vein positioning may occur. Once the circular catheter has been placed at the vein ostia, we then start pacing from the mapping catheter placed in the lateral great cardiac vein. Electrograms from the circular mapping catheter will then reveal the various veno-atrial connection points. The circular mapping catheter is pulled as proximally into the ostia of the vein as possible for this mapping and ablation. Although controversy exists in the academic electrophysiology community regarding the best approach to ablations for atrial fibrillation (ostial pulmonary vein isolation versus circumferential electroanatomically mapped left atrial ablations), one incontrovertible fact exists: in order for one to achieve the highest efficacy of ablation of atrial fibrillation with the lowest risk of pulmonary vein stenosis, ablation delivery should remain as proximal to the vein ostia as possible. In addition, delivery of ablation energy in the left atrial antrum of the vein and posterior wall of the atria, proximal to the anatomical ostia of the vein, is thought to improve success rates in these ablations. Although the anatomical venous ostia can usually be easily found fluoroscopically, the true electrophysiological veno-atrial junction may lie in the atria per se. Indeed, the efficacy of circumferential left atrial ablation techniques may in part lie in ablation of these proximal veno-atrial connection sites residing in the left atria. In this particular patient s case, a large common left venous trunkus was seen draining the entire left chest. Common trunki are common, but the proximal segments are often very short, making it difficult to distinguish the body of the left atrium from the short segment of the common trunkus, thus giving the appearance that individual ostia are present. Ablation in this common venous segment may account for the success reported with circumferential ablation techniques. Ablation in the antral region of ostial venous segments will have the net effect of delivering ablation energy to this common venous segment even if it is too short to be easily recognized in a particular fluoroscopic view. When performing ostial isolation, to achieve ablation of these regions, we utilize a 10 mm tipped ablation catheter. During these ablations, distal coronary sinus pacing will reveal veno-atrial connection points along the circular mapping catheter s body. The ablation catheter is positioned at the mapping site of earliest veno-atrial fusion. The ablation catheter is then pulled back to a more proximal location. In this more proximal location, the electrograms from the ablation catheter will often demonstrate a single large potential versus the two individual atrial and pulmonary vein potentials seen in more distal pulmonary vein locations. This potential will often have a high frequency component at its tail end. We try to keep the tip of the catheter just at or outside of the ostia of the vein with the shaft of the catheter lying in the left atrial vestibule region of the vein. Ablation energy is then delivered at these sites. Ablation temperatures are limited to 58 degrees with 100 watts of energy delivered. Higher RF power levels are needed with large tip catheters to achieve similar energy densities as seen with smaller tips. Despite these high power levels, we have not seen a single case of acute or subsequently clinically manifest pulmonary vein stenosis in our experience to date with this technique (43 patients to date). This we attribute to our attempts to limit ablation delivery to proximal sites only and to keep the majority of the ablation catheter in the atria per se.

Discussion

Isolation of individual veins with the use of this larger tipped catheter proves to be quicker than with smaller tip sizes. Generally, isolation of a vein can be accomplished in under 10 minutes of time. During ablation delivery, electrogram height at the ablation catheter will decrease markedly. Usually, 15 to 20 seconds of power delivery will result in a 50-75% decrease in electrogram height. This is often accompanied by a shift in veno-atrial activation pattern, and the ablation catheter is then moved to the next site of earliest vein activation where the technique of proximal/antral ablation is again performed. Veno-atrial disassociation will occur generally with fewer than 10 RF applications per vein. When veno-atrial disassociation occurs, we have seen very large pulmonary vein potentials disassociate from the left atrial potentials. In some of our cases, the amplitude of the disassociated pulmonary vein potentials exceeds the amplitude of the corresponding left atrial potentials, suggesting that large amounts of potentially arrhythmogenic myocardium are being isolated. This we attribute, again, to the very ostial and antral locations of our ablation delivery. Following isolation of all four veins, we test for sustainability of atrial fibrillation by inducing PAF with rapid atrial pacing. In the patient s case illustrated here, PAF was non-sustainable post-ablation, and this patient has been free of atrial fibrillation and off anti-arrhythmic medical therapy for the past four months following the ablation procedure.

Results

The larger tipped ablation catheter has shortened our average atrial fibrillation ablation case times to 82 minutes (from 134 minutes with 4 mm tipped catheters), with the number of RF deliveries per case now averaging 21. Efficacy for cure of fibrillation appears to be enhanced. We have only had access to 10 mm tipped catheters for veno-atrial isolation since November 2003. Thus, our data is still preliminary but includes two groups of patients: those that underwent circumferential, electroanatomically-based LA ablations with an 8 mm tipped electroanatomical mapping/ablation catheter (Biosense Webster, Inc., Diamond Bar, California), and those who underwent antral/ostial isolations with a 10 mm tipped ablation catheter. We have performed ostial/antral isolations with 10 mm tipped catheters in 23 patients and circumferential electroanatomically mapped LA ablations in 22 patients. Seventeen patients in the 10 mm group have achieved definite cure (74%), with nine patients in the electroanatomically mapped LA ablation group achieving definite cure (41%). Atrial reentrant tachycardias have occurred in eight of the 22 electroanatomically mapped LA ablation patients (36%). No symptomatic pulmonary vein stenosis was seen in the 10 mm ostial ablation group. One patient in the electroanatomically mapped LA ablation group demonstrated transient dyspnea with a spiral CT scan showing 60-70% stenosis of the left lower pulmonary vein. Follow-up on these two patient groups, however, is still early. It is well established that in the first two to three months post-ablation for atrial fibrillation (irrespective of technique), a variety of atrial arrhythmias can occur, including recurrent PAF, many of which ultimately resolve with more prolonged follow-up. Thus, the long-term cure rate in both the ostial/antral ablation group and the electroanatomically mapped group will likely continue to increase above the initial 74% and 41% respective cure rates seen to date.

Conclusion

The availability of ablation catheters with a 10 mm tip length has facilitated the ease of ostial veno-atrial isolations. Case times and number of RF deliveries are also shortened compared to ablation catheters with conventional length tips. Longer catheter tip sizes also allow more energy delivery into the veno-atrial antral region, thus potentially enhancing ultimate efficacy of these ablations. Preliminary data from our patients shows early efficacy, at least comparable to electroanatomically mapped circumferential ablations, without the pro-arrhythmia seen in circumferential ablation patients. Differences in ultimate cure rates between these two techniques, however, will require enrollment of additional patients and longer term follow-up data.