Targeted Ablation of Multifocal Atrial Tachycardia

EP Lab Digest. 2023;23(2):1,10-12.

Multifocal atrial tachycardia (MAT) is commonly associated with obstructive sleep apnea (OSA) and chronic pulmonary disease of different etiologies. Incidence of MAT is estimated to be .05%-.32% of hospitalized patients and associated with lung disease in 60% of cases. MAT is found in 20% of patients with acute respiratory failure and in 17% of patients hospitalized with chronic obstructive pulmonary disease.¹

Management of MAT is difficult and generally focused on the management of the underlying pulmonary disease. Medication options are often ineffective (calcium channel blockers) or have relative contraindications because of lung disease and other comorbidities (beta-blockers, amiodarone, Class 1c agents). MAT is also considered not amenable to targeted ablation due to the multifocal nature of the tachycardia, which raises the concern of global involvement of atrial tissue and renders mapping a tedious and challenging process.

We describe successful ablation of incessant MAT in 2 patients—one with severe OSA and a second patient with severe fibrotic interstitial lung disease. Both cases showed multiple foci limited to the right pulmonary veins (PVs) and their vicinity.

Case Presentation #1:

A 51-year-old male with severe OSA treated with continuous positive airway pressure (CPAP) presented with recurrent highly symptomatic supraventricular tachycardia (SVT). On surface electrocardiogram (ECG), the SVT episodes occasionally appeared to be consistent with typical atrial flutter (AFL) (Figure 1A) and incessant runs of MAT with multiple P-wave morphologies (Figure 1B). The arrhythmia did not respond to beta-blocker therapy and was frequently recurrent despite optimal treatment of the sleep apnea with CPAP. His echocardiogram showed normal left ventricular (LV) and right ventricular (RV) function with normal pulmonary artery (PA) pressures.

He was taken to the electrophysiology (EP) laboratory for further investigation. An EP study was performed under monitored anesthesia care. A decapolar catheter was placed into the coronary sinus (CS). A high-density mapping catheter and irrigated contact force ablation catheter were used to create an electroanatomical map of the atria. Intracardiac echocardiography (ICE) was used to guide catheter movement inside the heart. During the EP study, the patient was noted to have frequent runs of MAT that were precipitated by spontaneous apnea episodes under monitored anesthesia. These MAT runs were characterized by atrial beats with different P-wave morphologies, variable cycle length, and slightly different activation patterns on the CS catheter (Figure 2). These MAT runs would occasionally organize to a counterclockwise cavotricuspid isthmus (CTI) dependent (typical) AFL, thus explaining both the clinically noted arrhythmias.

CTI ablation abolished the organized typical AFL episodes. The MAT was targeted next, and based on activation mapping, we noted that the right atrial sites were late compared with activation on the CS electrodes. Activation mapping of the left atrium (LA) through transseptal access showed that all the foci of the MAT were within the ostium of the right superior PV. Electrical activities in the left veins were not early and were passive PV potentials only.

We performed electrical isolation of the right PVs with wide area antral ablation circumferentially around the right superior and inferior PVs. Ablation lesions were delivered with a 4-mm irrigated tip, contact force sensing catheter. Power of 35 watts on the anterior/septal aspect of the right PVs, and 25-30 watts on the posterior wall were applied for each lesion until impedance dropped by 10 Ohms, or until local electrograms disappeared. Esophageal temperature was monitored with a multielectrode thermistor during posterior wall ablation to reduce the risk of esophageal injury. Prior to the ablation, on the anterior aspect of the right PVs, high-amplitude pacing was performed to evaluate the phrenic nerve course while assessing for diaphragmatic capture. The course of the phrenic nerves was marked and avoided during lesion delivery. Circumferential ablation around the right PV was considered complete once bidirectional block of the veins was achieved (Figure 3A). Right PV isolation instantly suppressed the MAT episodes, while frequent runs of dissociated potentials from the right superior PV were still noted (Figure 3B).

The patient remains symptom free 3 years after the ablation without any rate or rhythm control medications. Of note, although all the foci were located in and around the right superior PV, the P waves on the surface ECG and the intracardiac activation patterns were visibly different, likely secondary to different routes of exit from the vein. This, in addition to the irregularity of the rhythm, qualified the rhythm as a MAT.

Case Presentation #2:

A 39-year-old male with advanced pulmonary fibrosis secondary to scleroderma and listed for lung transplantation presented with severe debilitating tachycardia episodes. Ambulatory monitoring showed these were associated with symptomatic MAT episodes at rest and with minimal activities of daily living (Figure 4). He was tried on flecainide, which did not provide much relief. Amiodarone and beta-blockers were not considered given his severe pulmonary fibrosis. His echocardiogram showed normal LV and RV function with mildly elevated PA pressures (estimated to be 34-39 mm Hg systolic pressure).

He was brought to the EP lab, where an EP study was performed under monitored anesthesia care. A decapolar catheter was placed into the CS, and a high-density mapping catheter and irrigated contact force ablation catheter were used to create an electroanatomical map of the atria. ICE was again used to guide catheter movement inside the heart. The patient was in sinus rhythm when he presented to the EP lab. Isoproterenol was started to induce the tachycardia. Multiple short episodes of AT with varying P-wave morphologies and cycle lengths were noted, consistent with MAT. Activation mapping of the right atrium did not reveal any sites sufficiently early compared to the CS electrodes. The LA was accessed through transseptal puncture. Most of the tachycardia foci initiated from the right upper PV and we performed a wide antral circumferential ablation of the right PVs. Our ablation technique was similar to that described in case #1. This included a 4-mm irrigated contact force catheter, similar power settings, and similar techniques to mitigate risk of injury to the esophagus and phrenic nerve. Circumferential ablation around the right PVs was considered complete once bidirectional block of the veins was achieved. Significant dissociated firing was noted in the right PV following electrical isolation. Repeat induction induced a focal AT originating from the LA roof just in front of the right PVs. We performed focal ablation at this location and a complete suppression of AT episodes was noted immediate postprocedure.

The patient did not experience further AT and subsequently underwent a successful double-lung transplant 3 months later. He experienced atrial fibrillation (AF) in the immediate postoperative period, which appeared to be secondary to postsurgical stress; and this was successfully treated with flecainide and diltiazem. His rhythm subsequently normalized and no tachycardia was noted at 15 months posttransplant.

Discussion

MAT is an irregular supraventricular tachycardia characterized by the presence of an atrial rhythm with 3 or more P-wave morphologies, indicating multiple ectopic foci within the atria. This condition is typically seen in older patients with a variety of underlying conditions, the most common of which is chronic pulmonary disease. The pathophysiology of the electrophysiologic abnormality is not well understood, but is thought to be related to abnormal automaticity and triggered activity including early and delayed afterdepolarization. For the majority of patients, no treatment is required beyond treatment of the underlying conditions.² However, some patients may be symptomatic and refractory to medication and treatment of underlying illness.

In cases of uncontrolled MAT, atrioventricular (AV) node ablation and pacemaker implantation had been described as a viable strategy.^3,4 However, targeted MAT ablation was generally not considered feasible. With significant advances in electroanatomical mapping and ablation techniques, rare cases of mapping and ablation of MAT have been reported.^5-7 However, the evidence of efficacy of this strategy is still scarce. We hereby report 2 cases of MAT that were successfully mapped and ablated without resorting to AV nodal ablation and pacing.

Interestingly, similar to our described cases, the foci of MAT ablation in previously reported cases were all found in the right PVs^5,6 or in the vicinity of the right PVs.⁷ Larger studies are required to investigate whether MAT has a selective predilection to right PVs as opposed to AF, which does not have a selective predilection for PVs on either side.⁸ Given that the right lung has a higher pulmonary circulation than the left lung, the pulmonary venous flow from the right side is significantly higher. Therefore, it is conceivable that the right PVs might experience comparatively higher stretch and stress, especially in the context of pulmonary hypertension, which could possibly explain the higher predilection for arrhythmias compared to left-sided veins. However, at this time, such an explanation is purely hypothetical and would require in-depth hemodynamic measurements of bilateral PVs, which were not performed in these cases. Of note, our patient in case #1 did not have a significantly elevated PA pressure at rest, but severe intermittent hypoxemia and hypercapnia could be his likely triggers of arrhythmia through vasoconstriction, autonomic dysfunction, or direct electrophysiological changes in the atrium.⁹

We acknowledge that our observation is in only 2 patients, and that the second patient remained free of AT for just 3 months prior to lung transplantation and has been followed for another 15 months post lung transplant to date. Further EP studies are warranted to determine the intracardiac mechanism of MAT and efficacy of targeted ablation in a larger cohort of patients with severe pulmonary disease, and longer follow-up data is needed to evaluate if these favorable outcomes are sustained.

Conclusion

MAT associated with severe pulmonary disease may be amenable to targeted ablation with long-term success in selective cases. 

Disclosures: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. They have no conflicts of interest to report regarding the content herein.

References

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