Non-invasive Neuromodulation of Arrhythmias

Dysfunction of the cardiac autonomic nervous system (CANS) is associated with various cardiac arrhythmias. Subsequently, invasive techniques have successfully targeted the CANS for the treatment of certain arrhythmias, such as sympathetic denervation for ventricular tachycardia storm. Non-invasive strategies capable of modulating the CANS for arrhythmia treatment have begun to gain interest due to their low-risk profile and applicability as an adjuvant therapy. This review provides an evidence-based overview of the currently studied technologies capable of non-invasively modulating CANS for the suppression of atrial fibrillation and ventricular arrhythmias.

Pseudo-vagal Responses Elicited by Cryoballoon Ablation

Pulmonary vein isolation via cryoballoon (CB) ablation is the cornerstone ablation strategy for the treatment of atrial fibrillation (AF). Acute intraprocedural hypotensive and/or bradycardic responses have been reported in patients undergoing CB ablation for AF. However, it remains unclear as to whether these are due to a true vagal response (VR), which can be used to predict long-term outcomes of CB ablation. We analyzed 139 freezes across 17 patients who received CB ablation for paroxysmal AF, measuring vital signs and freeze characteristics. Only one freeze was associated with both hypotension and bradycardia, constituting a true VR. Several freezes were associated with hypotension only that did not respond to atropine administration, suggesting that these responses are not associated with a VR. Hypotensive responses were significantly associated with ice bubble bursts during CB deflation. Unlike the true VR reported in patients undergoing conscious sedation, the presence of acute hypotension shortly after CB deflation cannot be used as a predictor for long-term ablation outcomes.

Impact of low-level electromagnetic fields on the inducibility of atrial fibrillation in the electrophysiology laboratory

Background

Atrial fibrillation (AF) is the most common sustained arrhythmia in adults. Research suggests that autonomic nervous (ANS) system dysfunction contributes to AF pathophysiology. Animal studies have shown that low-level electromagnetic fields (LL-EMF) are potentially capable of AF suppression. This study evaluated the safety and efficacy of LL-EMF in suppressing AF in humans.

Objective

To investigate the impact of LL-EMF on AF inducibility in humans.

Methods

Patients presenting for ablation of paroxysmal AF were randomized to a sham protocol or LL-EMF (3.2 × 10^-8 G at 0.89 Hz) applied via a Helmholtz coil around the head. AF was induced via atrial pacing, and was cardioverted if duration was greater than 15 minutes. The protocol was then run for 60 minutes, followed by reinduction of AF. The primary endpoint was the duration of pacing-induced AF after protocol completion compared between groups.

Results

Eighteen patients completed the study protocol (n = 10 sham, n = 8 LL-EMF). Pacing-induced AF duration in the LL-EMF group was 11.0 ± 3.43 minutes shorter than control after protocol completion (CI 3.72–18.28 minutes, P = .03). A smaller proportion of LL-EMF patients experienced spontaneous firing initiating an AF episode (0/7 vs 5/6, P = .0047). A significantly greater proportion of patients in the control group required direct current cardioversion after 1 hour (0.78 vs 0.13, P = .02).

Conclusion

In patients with paroxysmal AF, LL-EMF stimulation results in shorter episodes of pacing-induced AF and a reduced likelihood of spontaneous firing initiating an episode of AF.

Successful Catheter Ablation of Two Macro-reentrant Atrial Tachycardias in a Patient with Congenitally Corrected Transposition of the Great Arteries: A Case Report

Adults with congenital heart disease represent a complex and growing patient population. By virtue of their variant anatomy and the complex surgical repair often required in infancy, these patients are at risk of developing unique atrial and ventricular arrhythmias throughout their lifetimes. Electrophysiologists involved in the care of these patients should have a detailed understanding of their underlying anatomy and any prior surgical procedures to guide procedural planning and should have knowledge of the range of possible arrhythmia mechanisms that may differ from patients without structural heart disease. Despite this complexity, standard mapping techniques and electrophysiologic maneuvers may still be used to elucidate arrhythmia mechanisms, map tachycardia circuits, and guide catheter ablation. We report a case of two different macroreentrant right atrial tachycardias that were successfully ablated in a patient with congenitally-corrected transposition of the great arteries.

Effects of 60-Hertz notch filtering on local abnormal ventricular activities

BACKGROUND

It is known that electrical signals can be affected by notch filtering.

OBJECTIVE

We sought to investigate the effect of 60-Hz notch filtering on local abnormal ventricular activities (LAVA) in patients undergoing ventricular tachycardia ablation.

METHODS

To ensure catheter stability, only patients undergoing ablation using Stereotaxis mapping catheters were enrolled. Catheter stability was judged by the display on the electroanatomic map and the morphology of the bipolar and unipolar electrograms of the ablation catheter. At sites recording stable LAVA, 60-Hz notch filtering was applied. The duration, amplitude, and morphology of LAVA were compared before and after filtering. The area under LAVA was used to analyze the amplitude of continuous LAVA.

RESULTS

A total of 110 LAVA potentials recorded from 13 patients were analyzed. Notch filtering significantly affected the LAVA morphology and reduced their amplitude (the sum of the absolute value of the largest positive and negative voltages before filtering: 0.267 mV [0.191-0.395 mV]; after filtering: 0.172 mV [0.112-0.266 mV]; P < .001). At least 2 high-frequency components were introduced into the LAVA by filtering at 33 sites. The area under continuous LAVA was reduced by 28% from 24.64 cm² (16.20-33.45 cm²) to 17.53 cm² (10.52-23.82 cm²) (P < .001). The duration of continuous LAVA was reduced by 12% from 79.2 ms (55.0-93.0 ms) to 69.5 ms (53.0-88.5 ms) (P < .001).

CONCLUSION

Notch filtering can distort LAVA by reducing their amplitude, changing their morphology, and shortening their duration, leading to potential false positives and negatives. Mitigating the 60-Hz noise should focus on eliminating the source of noise, not applying notch filtering.

Left Atrial Size May Predict Blood Pressure Improvement After Ganglionated Plexi Ablation in Addition to Pulmonary Vein Isolation

Background

Hypertension (HTN) and atrial fibrillation (AF) commonly co-exist. An improvement in control of HTN in a subset of patients undergoing AF ablation was previously demonstrated by our group. In the present study, we aimed to assess whether left atrial (LA) size based on transthoracic echocardiography may predict the patients who demonstratebetter HTN improvement after ganglionated plexus ablation (GPA) in addition to pulmonary vein isolation (PVI).

Methods

This was a retrospective chart review of patients with AF and HTN who underwent GPA+PVI. Patients were divided into 2 groupsbased on LA size: Patients with normal LA size and patients with LA enlargement. Systolic blood pressure (SBP) levelswere compared at baseline, and 3, 6, and 12 months post-ablation. The primary endpoints of the study weremean systolic blood pressure change compared between groups from baseline to 12-months, as well as the absolute difference in systolic blood pressure at 12 months follow-up.Medical therapy for HTN was also assessed before the procedure, and at 12 months post-procedure.

Results

53 patients (37 with LA enlargement, 16 with normal LA size) met inclusion criteria. At 12 months follow-up, SBP was 136.46 ± 22.38 mmHg in patients with LA enlargementand 118.25 ± 9.81 mmHg in patients with normal LA size (estimated difference of 19.04 ± 6.98 mmHg, p = 0.01). Patients with normal LA size were on significantly fewer anti-hypertensive agents at 12 months (2.33 ± 1.49 vs. 1.44 ± 1.21, p < 0.05).

Conclusions

In patients undergoing PVI+GP ablation, normal LA size may predict HTN improvement at 12 months post-procedure. Normal LA size may identify hypertensive AF patients for whom autonomic modulation could be an effective therapy.

New approaches for treating atrial fibrillation: Focus on autonomic modulation

Atrial fibrillation (AF) is a rapidly growing clinical problem in routine practice, both for cardiologists as well as general practitioners. Current therapies aimed at the management of AF include anti-arrhythmic drug therapy and catheter ablation. These therapies have a number of limitations and risks, and have disappointing long-term efficacy in maintaining sinus rhythm and improving hard clinical outcomes. Because of this, there is growing interest in pursuing alternative management strategies in patients with AF. This review seeks to highlight emerging AF therapies, with a specific focus on several modalities aimed at modulation of the autonomic nervous system. These therapies have shown promise in early pre-clinical and clinical trials, and represent exciting alternatives to standard AF treatment.

Newer algorithms in bradycardia management

Permanent cardiac pacemakers (PPM) are effective in the treatment of bradycardia in a growing number of clinical scenarios. An appreciation of the capacity of PPMs to result in negative hemodynamic and proarrhythmic effects has grown alongside clinical experience with permanent pacing. Such experience has necessitated the development of algorithms aimed at optimizing device functionality across a broad spectrum of physiologic and pathologic conditions. This review highlights recent device-based algorithms used in automated threshold testing, reduction of right ventricular pacing, prevention and treatment of pacemaker-mediated tachycardia, mode switching for atrial tachyarrhythmias, rate-modulated pacing, and advances in arrhythmia storage and remote monitoring.

Current trends in supraventricular tachycardia management

BACKGROUND

Supraventricular tachycardia (SVT) is a general term describing a group of arrhythmias whose mechanism involves or is above the atrioventricular node. The mechanisms of most forms of SVT have been elucidated, and pharmacologic and invasive therapies have evolved simultaneously.

METHODS

We provide a brief overview of the mechanisms, classifications, and electrocardiographic characteristics of different SVTs and describe current trends in noninvasive and invasive therapies.

RESULTS

The term SVT encompasses a heterogeneous group of arrhythmias with different electrophysiologic characteristics. Knowledge of the mechanism of each SVT is important in determining management at the bedside and in the electrophysiology laboratory.

CONCLUSION

In the acute setting, vagal maneuvers and pharmacologic therapy can be effective in arrhythmia termination. Catheter-based radiofrequency ablation has revolutionized therapy for many SVTs, and newer techniques have significantly improved ablation efficacy and reduced periprocedural complications and procedure times. Cryoablation is currently being investigated as an alternative form of energy delivery, although the long-term effectiveness of this procedure currently limits its use for many SVTs.