Aortic Unfolding Complicating Typical Atrial Flutter Ablation in the Elderly: A Case of Anatomic Intrusion Where Seeing is Believing

Introduction

Atrial flutter is a relatively common arrhythmia, with an estimated 200,000 new cases documented in the United States per year.¹ The populations at highest risk for developing atrial flutter include men, individuals with preexisting heart failure or chronic obstructive lung disease, and the elderly.¹ Radiofrequency ablation (RFA) of the cavotricuspid isthmus (CTI) is widely considered a safe and effective treatment for typical CTI-dependent atrial flutter, with an acute success rate of approximately 97%.^2,3 Due to the relative simplicity of creating the CTI line, it is often performed with the use of fluoroscopy guidance alone. There has been a trend towards utilization of three-dimensional (3D) mapping systems, but the use of imaging for evaluation of CTI anatomy is only reserved for challenging cases.²

However, in the elderly, anatomic changes might factor in to add complexity to a relatively straightforward procedure. To our knowledge, this is the first case in which age-associated aortic unfolding led to abortion of a CTI-dependent atrial flutter ablation procedure owing to high perceived risk of AV block.

Case Description 

An 81-year-old Caucasian male with past medical history of hypertension, diabetes, dyslipidemia, and gout presented for elective RFA of CTI-dependent atrial flutter that was diagnosed during a urosepsis hospitalization five months prior. He had a past urologic history of benign prostatic hyperplasia requiring use of an indwelling Foley catheter, and nephrolithiasis with placement of indwelling bilateral ureteral stents. He was initiated on apixaban to reduce thromboembolic risk for atrial flutter. Of note, his baseline EKG demonstrated first-degree AV block and left bundle branch block (Figure 1). He denied prior history of near-syncope or syncope. A transthoracic echocardiogram in 2018 showed preserved ejection fraction with mild calcification of the aortic leaflets. Prior to his ablation procedure, there was no imaging evidence to suggest aortic unfolding. Recent chest x-rays during his hospitalization for urosepsis did not demonstrate a widened cardiomediastinal silhouette. Additionally, there were no prior CT chest or MRI data. 

Under fluoroscopic guidance, a multipolar catheter was positioned in the coronary sinus. Intracardiac echocardiography (ICE) was then employed for visualization of the CTI. Mapping of the tricuspid annulus was performed using a TactiCath Quartz Contact Force Ablation Catheter (Abbott) and a reprocessed 6 French Dynamic XT Decapolar Catheter (Boston Scientific) under the guidance of an EnSite NavX mapping system (Abbott). ICE images revealed that the aortic valve was compressing the CTI region with cardiac motion (Video 1, Figure 2), most likely due to aortic unfolding. When placed on the CTI line, the mapping catheter would register His signals as a result of intermittent proximity to the septal region (Figure 3). Since the HV interval was already prolonged at 86 ms, it was feared that ablation of the lateral CTI region could risk further damage to the His bundle, leading to complete heart block. Given this clinical concern, we elected to abort the procedure and focus on medical management of his arrhythmia. Of note, the placement of a pacemaker in this patient would have been particularly dangerous due to the high risk of device infection from his history of urosepsis. 

Discussion

The average age of patients requiring invasive procedures is on the rise. Therefore, current techniques need to be adapted to determine unforeseen complications that can arise with procedures in the elderly.⁴ A relatively simple procedure such as atrial flutter ablation would similarly require additional consideration. The advent of ICE has revolutionized the safety of invasive EP procedures by permitting real-time visualization of catheter contact and critical anatomical structures. Select studies have demonstrated the use of ICE for catheter ablations both singularly and in combination with 3D electroanatomical mapping (EAM).^5,6 Herman et al showed that use of ICE alone for CTI-dependent atrial flutter ablations was associated with less fluoroscopy time and improved ability to achieve bidirectional block.⁵ Haegeli et al demonstrated that it is feasible to solely use ICE and EAM with zero or near-zero fluoroscopy for a variety of catheter ablations.⁶

Aortic unfolding is a notable example of an important anatomical change that can affect the safety and efficacy of procedures in the elderly. Aortic unfolding is positively correlated with age, associated with aortic calcification, and occurs as a result of aortic degeneration and hypertension.⁷ It is normally diagnosed by noting a widened mediastinum on a chest radiograph, which reflects proximal aortic dilation, aortic arch widening, and decreased curvature.⁷ In our patient, there was likely mild aortic unfolding that did not significantly alter the cardiomediastinal silhouette on chest x-ray, and therefore, did not raise suspicion for concerning aortic changes prior to the procedure. However, the proximal aortic widening was easily observed intraprocedurally using ICE (Video 1, Figure 2), which alerted us to the potential for complications during ablation due to anatomic intrusion. The non-coronary aortic cusp is adjacent to the nodal conduction system, which passes through the membranous septum.⁸ Aortic root dilatation and lengthening can therefore compress the paraseptal region and bring it closer to the lateral tricuspid annulus. This could set the stage for an iatrogenic block while ablating over the CTI region, as was anticipated in our case. Iatrogenic blocks should also be considered during slow pathway modifications for AV nodal reentrant tachycardia (AVNRT), right posteroseptal accessory pathways, or atrial tachycardia ablation in the posteroseptal region. In a prior study that examined the impact of aortic unfolding on AVNRT, aortic unfolding led to a smaller Koch’s triangle by mechanical compression, which in turn heightened the risk of AV block as the slow and fast pathway signals were now closer in space and easier to ablate concurrently.⁹ A similar process could explain why this patient’s His signals were being registered simultaneously over his lateral CTI region, leaving him vulnerable to a conduction block if the lateral CTI region was ablated. 

Summary

It is important to be cognizant of how advanced age- and cardiovascular disease-related changes can impact cardiac anatomy. Vigilant procedure planning with utilization of available imaging and mapping modalities to better understand the anatomy at hand can reduce the risk of iatrogenic complications during catheter ablation.  

Disclosures: The authors have no conflicts of interest to report regarding the content herein. 

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