Silent Cerebral Thromboembolism with Left Atrial Ablation: A Lurking Danger

A randomized comparison of two direct oral anticoagulants for patients undergoing cardiac ablation with a contemporary warfarin control arm

BACKGROUND

The safety and efficacy of periprocedural use of direct oral anticoagulants (DOACs) for atrial fibrillation (AF) remain unclear. We compared the incidence of asymptomatic cerebral micro-thromboembolism and hemopericardium following AF ablation among patients receiving edoxaban, rivaroxaban, and warfarin and between normal- and low-dose use of edoxaban and rivaroxaban.

METHODS

This prospective randomized study included 170 consecutive AF patients. Patients taking DOACs upon admission to our hospital were randomly assigned to an edoxaban group or to a rivaroxaban group. Warfarin was continued in patients receiving warfarin at admission. All patients underwent AF ablation, and cerebral MRI was performed to evaluate asymptomatic cerebral micro-thromboembolism the day after the procedure.

RESULTS

Sixty-one patients were assigned to edoxaban and 63 to rivaroxaban. Warfarin was continued in 46 patients. Although asymptomatic cerebral micro-thromboembolism was detected in 25 patients (16.3%), there were no significant differences among the groups. Hemopericardium occurred in 2 patients (one each in the rivaroxaban and warfarin groups). The incidence of asymptomatic cerebral micro-thromboembolism was higher in the low-dose group (9 patients, 25.7%) than in the normal-dose group (8 patients, 10.0%) for patients prescribed either edoxaban or rivaroxaban (p < 0.05). The proportion of males (88.0%, 69.5%, p < 0.05), history of prior AF ablation (64.0%, 42.2%, p < 0.05), and hypertension (68.0%, 46.1%, p < 0.05) were significantly higher in patients with cerebral thromboembolism.

CONCLUSIONS

The incidence of asymptomatic cerebral micro-thromboembolism and hemopericardium in AF ablation was similar among patients using edoxaban, rivaroxaban, and warfarin. However, low doses of DOACs may increase the risk of asymptomatic stroke.

Prevention of Coagulum Formation With Simultaneous Charge Delivery in Radiofrequency Ablation: A Canine Model

OBJECTIVES

This study reports on a novel method to prevent coagulum formation by continuously delivering a negative charge to the catheter tip to repel negatively charged fibrinogen molecules during RF ablation.

BACKGROUND

Radiofrequency (RF) ablation for cardiac arrhythmias is associated with a 70% incidence of coagulum formation on the catheter tip during ablation and a 10% incidence of thromboembolic events. Catheter tip thrombus can impede RF energy to the tissue, reducing efficacy and increasing procedure times.

METHODS

A novel circuit was built to deliver a negative, fixed-offset, direct current-based charge using a 9-V battery, placed in parallel with an RF delivery unit during RF ablation. In in vivo canine experiments, standard ablation catheters were advanced into atria and ventricles under fluoroscopic guidance. The presence of thrombus with and without RF delivery was identified with intracardiac echocardiography.

RESULTS

Scanning electron microscopy of the catheter tips showed clot coverage of the catheter tip to be 90% for noncharged catheters compared to 0% (p < 0.01) in negatively charged catheters. Volume of clot formed on the catheter tip decreased with increased amount of charge (140 ± 5.3 arbitrary units with no charge vs. 0 arbitrary units with a 100-μA current delivering negative charge, p < 0.01). Application of a negative charge did not affect the quality of the intracardiac electrogram or induce malignant ventricular arrhythmias.

CONCLUSIONS

Negative-charge delivery to ablation catheter tips and tissue during RF ablation is feasible and safe and can eliminate coagulum formation, potentially reducing thromboembolic complications.

Risk of stroke after catheter ablation versus cardioversion for atrial fibrillation: A propensity-matched study of 24,244 patients

BACKGROUND

Stroke is the major cause of morbidity and mortality related to atrial fibrillation (AF). Catheter ablation for AF is effective in reducing AF burden, but its impact on long-term stroke risk is unknown.

OBJECTIVE

We sought to evaluate the periprocedural and long-term stroke risk after catheter ablation or cardioversion for AF.

METHODS

This retrospective, propensity-matched study using a national administrative claims database identified patients with AF who underwent catheter ablation and a comparison group (matched on age, sex, year of treatment, CHA2DS2-Vasc score, and Charlson index) who underwent cardioversion between 2005 and 2012. The primary end points were (1) time to first ischemic or hemorrhagic stroke or transient ischemic attack (TIA) and (2) time to first ischemic or hemorrhagic stroke excluding TIA. We compared periprocedural incident stroke (within 30 days of ablation or cardioversion) as well as total strokes between the 2 groups.

RESULTS

A total of 24,244 patients (12,122 patients undergoing ablation and 12,122 patients undergoing cardioversion) were included in the analysis. Incident periprocedural stroke or TIA occurred in 0.5% of the ablation group and 0.3% of the cardioversion group (P = .04). There was a significant initial risk of stroke/TIA with ablation within the first 30 days (rate ratio 1.53; P = .05). After 30 days, this risk was significantly lower in the ablation group (rate ratio 0.78; P = .03).

CONCLUSION

In patients with AF, there is a small periprocedural stroke risk with ablation in comparison to cardioversion. However, over longer-term follow-up, ablation is associated with a slightly lower rate of stroke.

Illustrated Atlas of Post-AF Ablation Cerebral Abnormalities

Atrial fibrillation (AF) is one of the most common cardiac arrhythmias and relates to high morbidity and mortality due to thromboembolic events, especially ischemic stroke. During the last 15 years, transcatheter ablation has emerged as an effective therapeutic option to treat AF but carries a risk of possible complications. The occurrence of cerebrovascular accidents, both symptomatic and silent, is one of the most frequent and severe. Transcatheter AF ablation entails a relevant risk of silent cerebral ischemia detected by means of magnetic resonance imaging, and many efforts have been directed to improve the safety of this procedure.

The Phrenic Nerve And Atrial Fibrillation Ablation Procedures

Radiofrequency ablation is increasingly used as an option to optimally manage patients with symptomatic atrial fibrillation. Presently, ablationists strive to improve success rates, particularly with persistent atrial fibrillation, while simultaneously attempting to reduce complications. A well-recognized complication with atrial fibrillation ablation is injury to the phrenic nerve giving rise to diaphragmatic paresis and patient discomfort.Phrenic nerve damage may occur when performing common components of atrial fibrillation ablation including pulmonary and superior vena caval isolation. The challenge for ablationists is to successfully target the arrhythmogenic substrate while avoiding this complication. In order to do this, a thorough knowledge of phrenic nerve anatomy, points in the ablation procedure where nerve damage is more likely, and an understanding of the presently utilized techniques to avoid this complication is required. In addition, when this complication does arise, prompt recognition of its occurrence, knowledge of the natural history, and available methods for management are needed.In this review, we discuss the underlying anatomic principles, techniques of avoiding phrenic nerve damage, and presently available methods of diagnosing and managing this complication.

Innovation focus: the patient with arrhythmia

Great strides have been made over the last two decades in the management of patients with rhythm disorders. Despite this, however, the remaining critical problems of stroke related to atrial fibrillation or as a result of radiofrequency ablation require innovative solutions to fully realize the potential of these recent advances. Similarly, implanted cardiac devices have revolutionized the care of patients with bradyrhythmias and tachyarrhythmias. Dyssynchronus ventricular pacing associated with present devices; however, results in heart failure, tricuspid regurgitation, and inappropriate device therapy once again create a demand for creative solutions. While not technically an arrhythmia, epilepsy management today is riddled with many of the problems that plagued cardiac arrhythmia management previously, and thus an appreciation of the similarities in requirement for investigative solutions may yield groundbreaking solutions. In this paper, we describe some novel methods to reduce complications associated with rhythm disorders and their treatment and apply the lessons learned from cardiovascular arrhythmia management to the brain. These include: a method to reduce coagulum formation and thus subsequent thromboembolism with indwelling catheters specifically during radiofrequency ablation procedures; a technique to ligate the left atrial appendage through percutaneous subxiphoid pericardial access; development and testing of a novel intramyocardial pace-sense lead, particularly used in a unique anatomic location (the atrioventricular septum) to allow pacing the ventricles in a relatively synchronous manner without crossing the tricuspid valve or entering the coronary sinus; finally, novel modifications of the cardiovascular mapping and ablation techniques used for the management of the central nervous system disorders primarily via the venous drainage of the brain. Innovative and potential solutions to treat the patient with arrhythmia are presented.

Electrotonic remodeling following myocardial infarction in dogs susceptible and resistant to sudden cardiac death

Passive electrical remodeling following myocardial infarction (MI) is well established. These changes can alter electrotonic loading and trigger the remodeling of repolarization currents, a potential mechanism for ventricular fibrillation (VF). However, little is known about the role of passive electrical markers as tools to identify VF susceptibility post-MI. This study investigated electrotonic remodeling in the post-MI ventricle, as measured by myocardial electrical impedance (MEI), in animals prone to and resistant to VF. MI was induced in dogs by a two-stage left anterior descending (LAD) coronary artery ligation. Before infarction, MEI electrodes were placed in remote (left circumflex, LCX) and infarcted (LAD) myocardium. MEI was measured in awake animals 1, 2, 7, and 21 days post-MI. Subsequently, VF susceptibility was tested by a 2-min LCX occlusion during exercise; 12 animals developed VF (susceptible, S) and 12 did not (resistant, R). The healing infarct had lower MEI than the normal myocardium. This difference was stable by day 2 post-MI (287 +/- 32 Omega vs. 425 +/- 62 Omega, P < 0.05). Significant differences were observed between resistant and susceptible animals 7 days post-MI; susceptible dogs had a wider electrotonic gradient between remote and infarcted myocardium (R: 89 +/- 60 Omega vs. S: 180 +/- 37 Omega). This difference increased over time in susceptible animals (252 +/- 53 Omega at 21 days) due to post-MI impedance changes on the remote myocardium. These data suggest that early electrotonic changes post-MI could be used to assess later arrhythmia susceptibility. In addition, passive-electrical changes could be a mechanism driving active-electrical remodeling post-MI, thereby facilitating the induction of arrhythmias.

Contributions of sustained INa and IKv43 to transmural heterogeneity of early repolarization and arrhythmogenesis in canine left ventricular myocytes

The roles of sustained components of I(Na) and I(Kv43) in shaping the action potentials (AP) of myocytes isolated from the canine left ventricle (LV) have not been studied in detail. Here we investigate the hypothesis that these two currents can contribute substantially to heterogeneity of early repolarization and arrhythmic risk. Quantitative data from voltage-clamp and expression profiling experiments were used to complete meaningful modifications to an existing "local control" model of canine midmyocardial myocyte excitation-contraction coupling for epicardial and endocardial cells. We include 1) heterogeneous I(Kv43), I(Ks), and I(SERCA) density; 2) modulation of I(Kv43) by Kv channel interacting protein type 2 (KChIP2) channel subunits; 3) a possible Ca(2+)-dependent open-state inactivation of I(Kv43); and 4) a sustained component of the inward Na(+) current, I(NaL). The resulting simulations illustrate ways in which KChIP2- and Ca(2+)-dependent control of I(Kv43) can result in a sustained outward current that can neutralize I(NaL) in a rate- and myocyte subtype-dependent manner. Both these currents appear to play significant roles in modulating AP duration and rate dependence in midmyocardial myocytes. Furthermore, an increased ratio of I(Kv43) to I(NaL) is capable of protecting epicardial myocytes from the early afterdepolarizations resulting from the SCN5A-I1768V mutation-induced increase in I(NaL). Experimentally observed transmural differences in Ca(2+) handling, including greater sarcoplasmic reticulum Ca(2+) content and faster Ca(2+) transient decay rates on the epicardium, were recapitulated in our simulations. By design, these models allow upward integration into organ models or may be used as a basis for further investigations into cellular heterogeneities.