Electrical stimulation to identify neural elements on the heart: their role in atrial fibrillation

Atrial fibrillation begets atrial fibrillation: autonomic mechanism for atrial electrical remodeling induced by short-term rapid atrial pacing

BACKGROUND

The mechanism(s) for acute changes in electrophysiological properties of the atria during rapid pacing induced atrial fibrillation (AF) is not completely understood. We sought to evaluate the contribution of the intrinsic cardiac autonomic nervous system in acute atrial electrical remodeling and AF induced by 6-hour rapid atrial pacing.

METHODS AND RESULTS

Continuous rapid pacing (1200 bpm, 2x threshold [TH]) was performed at the left atrial appendage. Group 1 (n=7) underwent 6-hour pacing immediately followed by ganglionated plexi (GP) ablation; group 2 (n=7) underwent GP ablation immediately followed by 6-hour pacing; and group 3 (n=4) underwent administration of autonomic blockers, atropine (1 mg/kg), and propranolol (0.6 mg/kg) immediately followed by 6-hour pacing. The effective refractory period (ERP) and window of vulnerability (WOV, in milliseconds), ie, the difference between the longest and the shortest coupling interval of the premature stimulus that induced AF, were measured at 2xTH and 10xTH at the left atrium, right atrium, and pulmonary veins every hour before and after GP ablation or autonomic blockade. In group 1, ERP was markedly shortened in the first 2 hours and then stabilized both at 2xTH and 10xTH; however, WOV was progressively widened throughout the 6-hour period. After GP ablation, ERP was significantly longer than before ablation and AF could not be induced (WOV=0) at either 2xTH or 10xTH. In groups 2 and 3, rapid atrial pacing failed to shorten the ERP. AF could not be induced in 6 of 7 dogs in group 2 and all 4 dogs in group 3 during the 6-hour pacing period.

CONCLUSIONS

The intrinsic cardiac autonomic nervous system plays a crucial role in the acute stages of atrial electrical remodeling induced by rapid atrial pacing.

Catheter Ablation of Left Atrial Ganglionated Plexi for Atrial Fibrillation

Radiofrequency ablation of pulmonary vein ostia does not provide complete and long-term elimination of atrial fibrillation. Combining this procedure with local radiofrequency application on sites with strong vagal reflexes results in partial parasympathetic denervation and increases the antiarrhythmic effect. A novel catheter-ablation technique to modify ganglionated plexi in the left atrium was assessed in 58 patients (mean age, 52.1 ± 1.9 years, 67% male) with drug-refractory atrial fibrillation, which was chronic in 21 (36%; mean duration, 14.3 ± 2.9 months; range, 5–39 months). The mean left atrial volume was 93.1 ± 6.1 mL. The patients underwent ablation of 4 areas of ganglionated plexi in the left atrium, with no circumferential ablation of the pulmonary veins; atrial fibrillation ceased immediately in 94.1% of them. Transient vagal bradycardia was seen in 93% of patients. For 7.2 ± 0.4 months after the procedure, 86.2% of them were free from arrhythmias, and no antiarrhythmic drugs were administered. Ganglionated plexi ablation is an efficient treatment for atrial fibrillation.

Routine ganglionic plexi ablation during Maze procedure improves hospital and early follow-up results of mitral surgery

OBJECTIVE

Ganglionic plexi are claimed to be potentially responsible for atrial fibrillation. We evaluated whether ganglionic plexi isolation improves the results of the Maze procedure during mitral valve surgery.

METHODS

A total of 75 patients with atrial fibrillation underwent radiofrequency ablation during mitral valve surgery without (group A) or with (group B) ganglionic plexi ablation with bipolar radiofrequency plus fat pad resection along the Waterston groove, left pulmonary veins, and Marshall's ligament. Ganglionic plexi were intraoperatively mapped, and fat pad specimens were sectioned and analyzed. Hospital and follow-up results were recorded. Amiodarone was discontinued at the sixth month.

RESULTS

Active ganglionic plexi were mainly located in the upper parts of fat pads. Active specimens demonstrated more ganglionic plexi than inactive specimens (P <or= .015 at different levels) but did not correlate with atrial fibrillation recurrence (P = not significant). Atrial fibrillation was higher in group A at aortic declamping (P = .03) and discharge (P = .03). Early events were comparable (P = .565). At 16.7 +/- 0.95 (standard error) months, the cumulative freedom from atrial fibrillation, atrial flutter, and atrial tachycardia with antiarrhythmic therapy was 63.2% +/- 7.3% and proved higher in group B (83.9% +/- 7.9% vs group A 52.8% +/- 8.7%; P = .035). However, after the sixth month, at 12.8 +/- 0.80 months, freedom from atrial fibrillation, atrial flutter, and atrial tachycardia without antiarrhythmic therapy was 72.5% +/- 7.7% and proved higher in group B (92.9% +/- 6.9% vs 62.5% +/- 9.4%; P = .023). A higher proportion of patients in group B showed normalized E/A ratio (61.3% vs group A 36.4%; P = .029). No differences were detected in follow-up freedom from congestive heart failure (group A: 83.4% +/- 7.0% vs group B: 93.5% +/- 4.4%; P = .978) and hospital readmission (group A: 84.2% +/- 5.9% vs group B: 92.6% +/- 5.1%; P = .376).

CONCLUSION

Ganglionic plexi isolation can improve hospital and follow-up results during mitral valve surgery and possibly ameliorate echocardiographic recovery of atrial function during follow-up.

The electrical substrate of vagal atrial fibrillation as assessed by the signal-averaged electrocardiogram of the P wave

BACKGROUND

The autonomic nervous system is thought to be involved in the initiation of atrial fibrillation (AF). However, there is a distinct entity of vagal AF characterized by episodes occurring at rest, postprandially, or during sleep. The purpose of this study was to compare intraatrial conduction in patients with vagally mediated AF to those with nonvagal AF, using the signal-averaged electrocardiogram (SAECG) of P wave.

METHODS

SAECG of P wave was performed in 58 patients with AF using the Marquette Medical System, and the mean filtered P-wave duration (SAPW) was measured. Nine patients were categorized as having pure vagal AF (Group I), and 42 patients as having nonvagal AF (Group II); the remaining seven patients were excluded from analysis because of incomplete data.

RESULTS

The patients in Group I were significantly younger and more likely to have paroxysmal lone AF, as compared to those in Group II. There was no significant difference in left atrial size and left ventricular function in the two groups. The mean SAPW was significantly shorter in Group I when compared to Group II (118 +/- 5 ms vs 149 +/- 39 ms, P < 0.001). Whereas all patients in Group I had a normal SAPW, 79% of patients in Group II had an abnormal SAPW (P < 0.001). A normal SAPW was significantly predictive of vagal AF independent of other co-variables.

CONCLUSIONS

(1) Patients with vagal AF are younger, and invariably have paroxysmal lone AF. (2) SAPW is normal and significantly shorter in vagal AF when compared to patients with nonvagal AF. (3) This suggests that those in the vagal AF population have normal intraatrial conduction, which has implications for AF ablation in these patients.

The role of autonomic denervation during catheter ablation of atrial fibrillation

PURPOSE OF REVIEW

To analyse recent experimental and clinical studies and show that all the pathological events occurring in the myocardium during atrial fibrillation are caused by changes in the autonomic nervous system. The current methods of radiofrequency ablation focus on damaging healthy myocardial tissue involved in the dysregulation caused by autonomic nervous system hyperactivity. Radiofrequency ablation should instead be targeted at compromised nerves and autonomic ganglia (ganglionated plexi).

RECENT FINDINGS

Experimental data show that electrical stimulation of the autonomic nervous system may facilitate the induction of atrial fibrillation. The active role of pulmonary veins in atrial fibrillation results from the high density of adrenergic and cholinergic nerves around pulmonary veins. The areas most suitable for autonomic nervous system modification procedures are located in the immediate vicinity of the pulmonary vein-left atrial junction. The first clinical results of radiofrequency ablation of ganglionated plexi resulting in autonomic denervation are encouraging, and show this as a promising approach. There remain many debatable points; the most important of which is the best approach for locating clusters of ganglionated plexi.

SUMMARY

Recent experimental and clinical findings have provided new insights into the causes of atrial fibrillation and allowed a re-evaluation of its treatment.

Antifibrillatory actions of cisatracurium: an atrial specific M2 receptor antagonist

INTRODUCTION

Muscarinic receptor antagonists are proposed to prevent atrial fibrillation (AF), but also facilitate AV conduction, limiting clinical usefulness.

METHODS

Cisatracurium, a neuromuscular blocker, was administered to anesthetized dogs (0.05-0.8 mg/kg IV) and was administered to superfused pulmonary vein (PV) tissues in vitro.

RESULTS

Dose-dependent suppression of AF induced by premature atrial stimuli was observed under control conditions (n = 3), right vagus nerve stimulation (n = 7), and anterior right ganglionated plexus stimulation (n = 3). AF was prevented (P < 0.0001) concurrent with suppression of the decreased atrial MAP duration/ERP accompanying vagus nerve stimulation without altering AH intervals or sinus cycle length. Although atropine (0.001-0.016 mg/kg, n = 4) suppressed AF (P < 0.04) in association with suppression of atrial MAP shortening induced by vagus nerve stimulation, atropine also prevented sinus cycle length and AH interval prolongation with vagus nerve stimulation, and decreased AV effective and functional refractory periods. In vitro, both cisatracurium and atropine prevented (1) action potential shortening produced by acetylcholine administration and (2) action potential shortening and arrhythmia triggering within PV sleeves produced by local autonomic nerve stimulation, atropine producing competitive inhibition, and cisatracurium producing noncompetitive M(2) muscarinic receptor blockade.

CONCLUSIONS

Cisatracurium demonstrates a dose-dependent (1) suppression of AF and atrial action potential shortening accompanying vagus nerve stimulation without facilitating sinus or atrioventricular nodal function and (2) noncompetitive blockade of action potential shortening and triggered firing induced in isolated PVs by local autonomic nerve stimulation. The data are consistent with allosteric binding of cisatracurium to the M(2) muscarinic receptor in canine atrium.

Gastric Hypomotility Following Epicardial Vagal Denervation Ablation to Treat Atrial Fibrillation

We report a case of a 55-year-old man with vagal paroxysmal atrial fibrillation (AF) who was submitted to selective epicardial and endocardial atrial vagal denervation with the objective of treating AF. Radiofrequency pulses were applied on epicardial and endocardial surface of the left atrium close to right pulmonary veins (PVs) and also on epicardial surface close to left inferior PV. Following the procedure, patient presented with symptoms of gastroparesis, which was documented on CT scan and gastric emptying scintigraphy. Symptoms were transient and the patient recovered completely.

Noninvasive assessment of atrial substrate change after wide area circumferential ablation: a comparison with segmental pulmonary vein isolation

BACKGROUND

The wide area circumferential ablation (WACA) approach to atrial fibrillation is thought to result in 'substrate modification' perhaps related to autonomic denervation. We examined this prospectively by comparing WACA and segmental pulmonary vein isolation (PVI) using noninvasive surrogate markers.

METHODS

Heart rate variability (HRV) and signal averaged P wave (SAPW) data were derived from high-resolution (HR) recordings ('SpiderView' ELA Medical) made in sinus rhythm immediately before and 24 hours after ablation.

RESULTS

Forty patients recruited (20 WACA; 20 PVI); cohorts were comparable. WACA caused marked SAPW change: P wave duration (PWD) (149[4.6] ms to 160[5.9] ms; P = 0.003), root mean square (RMS) (4.4[0.4]microV to 2.8[0.4]; P = 0.001) and energy content (30-150 Hz; 20.4 [3.6]microV(2)/s to 13.7[2.4]; P = 0.001). No significant change was seen after PVI. Heart rate increased after WACA and PVI (61.4 to 73.5 [P = 0.001]; 69.5 to 75.0 [P = 0.07], respectively). HRV was significantly influenced after WACA: low frequency power (LF) 5.7(0.4) to 3.6(0.4); P = 0.001), high-frequency power (HF) 4.6(0.4)-3.4(0.3); P = 0.024, and after PVI: LF 5.4(0.3) to 4.3(0.3); P = 0.024. HF: 4.4(0.4) to 3.0(0.4); P = 0.018).

CONCLUSIONS

HR recordings exhibit change in HRV after WACA and PVI. Marked change in both HRV and SAPW is observed after WACA. SAPW variables provide a measure of atrial substrate change after WACA unrelated to autonomic denervation.

Pulmonary vein region ablation in experimental vagal atrial fibrillation: role of pulmonary veins versus autonomic ganglia

BACKGROUND

Pulmonary vein (PV) -encircling radiofrequency ablation frequently is effective in vagal atrial fibrillation (AF), and there is evidence that PVs may be particularly prone to cholinergically induced arrhythmia mechanisms. However, PV ablation procedures also can affect intracardiac autonomic ganglia. The present study examined the relative role of PVs versus peri-PV autonomic ganglia in an experimental vagal AF model.

METHODS AND RESULTS

Cholinergic AF was studied under carbachol infusion in coronary perfused canine left atrial PV preparations in vitro and with cervical vagal stimulation in vivo. Carbachol caused dose-dependent AF promotion in vitro, which was not affected by excision of all PVs. Sustained AF could be induced easily in all dogs during vagal nerve stimulation in vivo both before and after isolation of all PVs with encircling lesions created by a bipolar radiofrequency ablation clamp device. PV elimination had no effect on atrial effective refractory period or its responses to cholinergic stimulation. Autonomic ganglia were identified by bradycardic and/or tachycardic responses to high-frequency subthreshold local stimulation. Ablation of the autonomic ganglia overlying all PV ostia suppressed the effective refractory period-abbreviating and AF-promoting effects of cervical vagal stimulation, whereas ablation of only left- or right-sided PV ostial ganglia failed to suppress AF. Dominant-frequency analysis suggested that the success of ablation in suppressing vagal AF depended on the elimination of high-frequency driver regions.

CONCLUSIONS

Intact PVs are not needed for maintenance of experimental cholinergic AF. Ablation of the autonomic ganglia at the base of the PVs suppresses vagal responses and may contribute to the effectiveness of PV-directed ablation procedures in vagal AF.

How Does Successful Off-Pump Pulmonary Vein Isolation for Paroxysmal Atrial Fibrillation Influence Heart Rate Variability and Autonomic Activity?

Objective

Surgical pulmonary vein isolation (PVI) for paroxysmal atrial fibrillation (PAF) blocks trigger stimulation from PVs and partially disconnects the atria from sympathetic and parasympathetic neural stimulation. This study describes long-term changes in heart rate variability (HRV) and autonomic activity (AA) after successful bipolar radiofrequency PVI.

Methods

Twenty-seven patients who underwent coronary artery bypass grafting and successful (defined as stable sinus rhythm for 1 year) off-pump bipolar radiofrequency PVI for PAF were prospectively followed 3, 6, and 12 months after surgery including 24 hours Holter electrocardiogram. The following HRV and AA parameters were calculated: mean NN-interval, SD of NN-intervals, SD of averaged NN-intervals, root mean square of successive differences, low frequency (LF) power (0.04–0.15 Hz; a parameter specific for sympathetic activity), high frequency (HF) power (0.15–0.4 Hz; a parameter specific for parasympathetic activity), and the LF:HF ratio.

Results

Preoperatively, high HRV and AA parameters were recorded. In 3-, 6-, and 12-month time, a progressive reduction of HRV and AA was observed, reaching significance after 12 months. Respective rates before surgery and 12 months after it were: for SD of averaged NN-intervals (122.4 ± 113; 80.5 ± 42 milliseconds; P = 0.046), for root mean square of successive differences (79.2 ± 93; 45 ± 20 milliseconds; P = 0.04). The LF:HF ratios were 1.22 and 0.73 before and 12 months after surgery, respectively. The statistically significant continuous reduction in LF:HF ratio (P = 0.02) is suggestive of a progressive parasympathetic dominance 12 months after surgery.

Conclusions

Successful PVI for PAF results in HRV and sympathetic activity reduction with preoperative sympathetic dominance and oncoming vagal dominance after 1 year from surgery. Despite preoperative sympathetic dominance, successful PVI for PAF results in HRV and a reduction in sympathetic activity with emerging parasympathetic dominance 12 months after surgery.

Frequency gradients during two different forms of fibrillation in the canine atria

BACKGROUND

Atrial fibrillation (AF) is thought to be sustained by multiple reentrant wavelets or firing foci.

OBJECTIVE

The aim of this study was to compare the spectral domain characteristics in the left atrium (LA) and right atrium (RA) in two different models of AF.

METHODS

Rectangular 8 x 14 electrode arrays were placed on the LA and RA of 14 anesthetized dogs. AF episodes were induced with burst pacing and aconitine in each dog. For each model, AF was induced from the RA in six dogs and from the LA in six dogs. Dominant frequencies (DFs) were obtained using the fast Fourier transform of the unipolar recordings obtained from each electrode of the array. Standard deviation (SD) was used to compute the frequency dispersion within an atrium. Regularity of the signal was quantified using an organization index (OI).

RESULTS

DFs were largest in the atrium where aconitine was applied. Aconitine AF had larger gradients than burst-pacing AF (5.0 +/- 4.5 vs. 0.9 +/- 1.0 Hz: P <.006). Aconitine AF when compared with burst-pacing AF had greater absolute LA-RA differences in the SD of DFs (2.3 +/- 1.9 vs. 0.2 +/- 0.2 Hz; P <.001) and in OI (0.11 +/- 0.07 vs. 0.06 +/- 0.07; P <.07).

CONCLUSIONS

Differences in frequency gradients and organization were observed during AF induced by burst pacing and aconitine. This suggests that different mechanisms of AF are possible and may be identified with frequency domain analysis.

Evidence-based approach to ablating atrial fibrillation

Catheter ablation of atrial fibrillation (AF) has made considerable advances over the past decade. Although pulmonary vein (PV) isolation has proven to be a reliable curative treatment, especially for paroxysmal AF, it still has several issues to resolve. Because the AF mechanisms are complex and multifactorial, especially in persistent or permanent AF, they cannot be eliminated altogether by PV isolation alone. Beyond PV isolation, several other techniques have shown promise in improving the long-term success. Several recent reports comparing the superiority between AF ablation and antiarrhythmic drug therapy have shown early evidence suggesting that AF ablation warrants consideration as a first-line therapy in selected patients.

Magnetic resonance imaging and radiofrequency ablations

Cardiac MRI has evolved one of the major imaging technologies in cardiology. Increasingly MRI has also been used for electrophysiological applications. Anatomically based procedures such as the circumferential pulmonary vein ablation emphasized the importance of including the individual's cardiac anatomy in a tailored ablation approach. Today, many centers routinely perform pre-ablation imaging to identify left atrial anatomy. Three-dimensional reconstructions based on MRI are frequently integrated in clinical mapping systems to provide cardiac anatomy during the ablation procedure. Similarly, MRI is a clinically very valuable tool in assessing potential ablation complications such as pulmonary vein stenosis. New innovative use of MRI is likely to occur in three areas over the next several years. During ventricular tachycardia ablations volume rendering/fusion imaging will enable a detailed three-dimensional substrate evaluation and provide supplementary scar characterization using a combination of different imaging approaches. With the ongoing technical improvements real-time MRI will likely emerge as a stand-alone clinical modality to directly guide catheter ablation procedures. The advent of stronger field strength MRI, faster imaging protocols, and improved gating techniques will allow accurate peri- and post-procedural visualization of ablation lesions. These developments should result in shorter procedure times and decreased complications rates. Ultimately, they will enable the development of novel ablation strategies and expand the current indications for electrophysiological ablations.

Stepwise linear approach to catheter ablation of atrial fibrillation

BACKGROUND

This study attempted to convert atrial fibrillation (AF) to sinus rhythm using a stepwise linear catheter ablation approach.

METHODS

One hundred and ninety-six patients (43 with persistent AF) were enrolled in the study. A multiple electrode array was used for anatomical navigation and activation mapping. Continuously incremental stimulation was used to induce AF if spontaneous AF was not present. Stepwise linear ablation was applied until AF was converted to sinus rhythm or atypical atrial flutter (AAFL) or atrial tachycardia (AT). The stepwise approach initially utilized a figure-7 lesion line between the right and left superior pulmonary vein on the roof of the left atrium and then extended along the ridge between the left appendage and the left pulmonary veins until the mitral valve annulus, as the primary lesions. If AF still persisted, high-frequency potentials in the inferior left atrium, coronary sinus, or right atrium were targeted. Noninducibility of AF was used as the end point.

RESULTS

AF was converted to sinus rhythm in 81.6% of patients (90.8% of paroxysmal and 51.1% of persistent AF, P<.01). The remainders of patients were converted to AAFL or AT. AF was terminated after ablation in right atrium in 7 patients. During an 18.2+/-7.3 month follow-up, 88.3% of patients were free of atrial tachyarrhythmias without medication, 9.7% of patients had refractory AAFL/AT, and only 2.1% of patients had paroxysmal AF.

CONCLUSION

Stepwise linear ablation is effective in converting AF to sinus rhythm and the figure-7 lesion line should be the basic lesion. Right atrium ablation is necessary in some patients.

Can atrial vagal denervation influence ventricular function in a failing heart?

Atrial fibrillation (AF) and congestive heart failure (CHF) often coexist (AF-CHF), and each adversely affects the other with respect to management and prognosis. Therapy with antiarrhythmic drugs to maintain sinus rhythm was disappointing. Ablation is more successful than antiarrhythmic drug therapy for the prevention of AF with few complications, although in patients with AF-CHF it is noted. Ablating autonomic nerves and ganglia on the large vessels and the heart can result in AF suppression with little damage to healthy myocardium. Our study in patients with AF-CHF found that cardiac function aggravation was more frequent in patients with AF recurrence than that of those who successfully maintain sinus rhythm. The autonomic nervous system is a fine network spreading throughout the myocytes; hence the elimination of atrial vagal with radiofrequency catheter ablation can influence the innervation in sinus and AV nodes even in the ventricular region. Thus we propose that atrial vagal denervation may result in paratherapeutic sympathovagal imbalance in the ventricular region, which has a negative effect in a failing heart, although it is neutralized by the benefit accrued from sinus rhythm after successful ablation.

Recent insights into the pathophysiology of atrial fibrillation

Although the problem of atrial fibrillation is now widely appreciated, the fundamental mechanisms that lead to arrhythmia onset and persistence have been difficult to elucidate. As a result, available pharmacologic therapies have focused more on modifying ion channel activity than on the underlying mechanisms. Recent studies suggest an important role for alterations in autonomic regulation, neurohormonal activation, and a systemic inflammatory state in the genesis and persistence of atrial fibrillation. The relative contributions of these distinct pathways to atrial fibrillation likely vary from patient to patient, and within a patient, as a function of age. Tailored therapies, together with patient-specific ablative interventions, may increase the success with which atrial fibrillation is treated and minimize the occurrence of life-threatening thromboembolic complications.

Ganglionated plexi modulate extrinsic cardiac autonomic nerve input: effects on sinus rate, atrioventricular conduction, refractoriness, and inducibility of atrial fibrillation

OBJECTIVES

This study sought to systematically investigate the interactions between the extrinsic and intrinsic cardiac autonomic nervous system (ANS) in modulating electrophysiological properties and atrial fibrillation (AF) initiation.

BACKGROUND

Systematic ganglionated plexi (GP) ablation to evaluate the extrinsic and intrinsic cardiac ANS relationship has not been detailed.

METHODS

The following GP were exposed in 28 dogs: anterior right GP (ARGP) near the sinoatrial node, inferior right ganglionated plexi (IRGP) at the junction of the inferior vena cava and atria, and superior left ganglionated plexi (SLGP) near the junction of left superior pulmonary vein and left pulmonary artery. With unilateral vagosympathetic trunk stimulation (0.6 to 8.0 V, 20 Hz, 0.1 ms in duration), sinus rate (SR), and ventricular rate (VR) during AF were compared before and after sequential ablation of SLGP, ARGP, and IRGP.

RESULTS

The SLGP ablation significantly attenuated the SR and VR slowing responses with right or left vagosympathetic trunk stimulation. Subsequent ARGP ablation produced additional effects on SR slowing but not VR slowing. After SLGP + ARGP ablation, IRGP ablation eliminated VR slowing but did not further attenuate SR slowing with vagosympathetic trunk stimulation. Unilateral right and left vagosympathetic trunk stimulation shortened the effective refractory period and increased AF inducibility of atrium and pulmonary vein near the ARGP and SLGP, respectively. The ARGP ablation eliminated ERP shortening and AF inducibility with right vagosympathetic trunk stimulation, whereas SLGP ablation eliminated ERP shortening but not AF inducibility with left vagosympathetic trunk stimulation.

CONCLUSIONS

The GP function as the "integration centers" that modulate the autonomic interactions between the extrinsic and intrinsic cardiac ANS. This interaction is substantially more intricate than previously thought.

Tako-tsubo Cardiomyopathy Complicating Left Atrial Radiofrequency Ablation

Two female patients undergoing left atrial radiofrequency catheter ablation developed Tako-tsubo cardiomyopathy. This reversible form of left ventricular dysfunction is known to occur under conditions associated with marked sympathetic nervous activation. Radiofrequency catheter ablation in the left atrium can damage autonomic ganglionated plexi, leading to vagal withdrawal, thus resulting in enhanced sympathetic tone. Tako-tsubo cardiomyopathy has not been previously described following radiofrequency catheter ablation.

View-Synchronized Robotic Image-Guided Therapy for Atrial Fibrillation Ablation

Background— A robotic catheter navigation system has been developed that provides a significant degree of freedom of catheter movement. This study examines the feasibility of synchronizing this robotic navigation system with electroanatomic mapping and 3-dimensional computed tomography imaging to perform view-synchronized left atrial (LA) ablation.

Methods and Results— This study consisted of a porcine experimental validation phase (9 animals) and a clinical feasibility phase (9 atrial fibrillation patients). Preprocedural computed tomography images were reconstructed to provide 3-dimensional surface models of the LA pulmonary veins and aorta. Aortic electroanatomic mapping was performed manually, followed by registration with the corresponding computed tomography aorta image using custom software. The mapping catheter was remotely manipulated with the robotic navigation system within the registered computed tomography image of the LA pulmonary veins. The point-to-surface error between the LA electroanatomic mapping data and the computed tomography image was 2.1±0.7 and 1.6±0.1 mm in the preclinical and clinical studies, respectively. The catheter was remotely navigated into all pulmonary veins, the LA appendage, and circumferentially along the mitral valve annulus. In 7 of 9 animals, circumferential radiofrequency ablation lesions were applied periostially to ablate 11 pulmonary veins. In patients, all of the pulmonary veins were remotely electrically isolated in an extraostial fashion. Adjunctive ablation included superior vena cava isolation in 6 patients, cavotricuspid isthmus ablation in 5 patients, and ablation of sites of complex fractionated activity and atypical LA flutters in 3 patients.

Conclusions— This study demonstrates the safety and feasibility of an emerging paradigm for atrial fibrillation ablation involving the confluence of 3 technologies: 3-dimensional imaging, electroanatomic mapping, and remote robotic navigation.

Vagal responses induced by endocardial left atrial autonomic ganglion stimulation before and after pulmonary vein antrum isolation for atrial fibrillation

BACKGROUND

Elimination of vagal inputs into the left atrium (LA) may be necessary for successful catheter ablation of atrial fibrillation (AF). These vagal inputs are clustered in autonomic ganglia (AG) that are close to the pulmonary vein antrum (PVA) borders, but whether standard intracardiac echocardiography (ICE)-guided PVA isolation (PVAI) affects these inputs is unknown.

OBJECTIVE

The purpose of this study was to assess whether standard ICE-guided PVAI affects vagal responses induced by endocardial AG stimulation in the LA.

METHODS

Twenty consecutive patients undergoing first-time PVAI (group 1) and 20 consecutive patients undergoing repeat PVAI for AF recurrence (group 2) were enrolled in the study. Before ablation, electrical stimulation (20 Hz, pulse duration 10 ms, voltage range 12-20 V) was performed through an 8-mm-tip ablation catheter. Based on prior data, regions around all four PVA borders were carefully mapped and stimulated to localize AG inputs. A positive stimulated vagal response was defined as atrioventricular (AV) block, asystole, or increase in mean RR interval by >50%. Locations of positive vagal responses were recorded wth biplane fluoroscopy and CARTO. All patients then underwent standard ICE-guided PVAI by an operator blinded to the locations of vagal responses. Stimulation of the AG locations was then repeated postablation.

RESULTS

Patients (age 54 +/- 11 years, 30% female, ejection fraction 54% +/- 7%) had a history of paroxysmal (75%) and persistent (25%) AF. In group 1, vagal responses were induced in all 20 patients around a mean of 3.8 +/- 0.4 PVAs per patient. The most common response was asystole (53%), mean RR slowing >50% (28%), and AV block (20%). Postablation, vagal responses could no longer be induced in all 20 patients. A diminished response was induced (RR slowing <50%) in 2/20 patients around one PVA each. In group 2, vagal responses were not induced in any of the 20 repeat patients. Stimulation capture postablation was confirmed because transient, nonsustained (<30 seconds) AF or atrial flutter was induced in all 40 patients with stimulation, whether vagal responses were induced or not.

CONCLUSIONS

Standard ICE-guided PVAI eliminates vagal responses induced by AG stimulation. Responses are not seen in patients presenting for repeat PVAI, despite clinical recurrence of AF.

Intraoperative epicardial electrophysiologic mapping and isolation of autonomic ganglionic plexi

BACKGROUND

Autonomic ganglionic plexi (GPs) have been implicated as triggers in lone atrial fibrillation (AF). The purpose of this study was to describe the technique and results of epicardial electrophysiologic mapping and the early effects of GP isolation.

METHODS

Intraoperative epicardial electrophysiologic mapping was performed on 41 consecutive patients during a stand-alone minimally invasive operation for AF. A map labeling anatomic locations was developed to describe the findings. Intraoperative high-frequency stimulation (800/minute, 12 to 16 mA, pulse duration 9.9 ms) was performed using a standard quadripolar catheter placed directly on the epicardium. Locations where stimulation resulted in ventricular slowing with doubling of the electrocardiographic R-R interval were defined as active GPs. These areas were mapped and described. After dry bipolar radiofrequency isolation, the sites were again stimulated to assess isolation.

RESULTS

Forty-one patients (mean age of 60.2 years, 31 males) underwent operation for AF (28 intermittent AF, 13 chronic). Active GPs were identified in all patients (24 bilateral, 17 unilateral). There was a mean of 5.0 GPs on the right and 2.7 on the left. More than 50% of patients had active GPs along the interatrial groove on the right and along the ligament of Marshall. All sites were inactive after radiofrequency isolation. Six-month follow-up is available for 15 patients, with 14 patients free of AF.

CONCLUSIONS

Autonomic GPs can be routinely identified during AF surgery utilizing high-frequency stimulation. The GPs are clustered around the interatrial groove and the ligament of Marshall, and the cardiac response to GP stimulation can be eliminated with bipolar radiofrequency isolation. The addition of GP isolation to bilateral pulmonary vein isolation may increase freedom from AF.

Pulmonary vein antrum isolation

Pulmonary vein antrum isolation offers safe and effective treatment of atrial fibrillation by eliminating the potential triggers of this arrhythmia. The pulmonary vein antra encompass, in addition to the pulmonary veins, the left atrial roof and posterior wall and, in the case of the right pulmonary vein antra, a portion of the interatrial septum. Compared with pulmonary vein ostial isolation, this technique offers a higher success rate and a lower complication rate. In patients with nonparoxysmal atrial fibrillation, extension of septal ablation to the region of the mitral annulus is associated with better outcomes. Further adjunctive strategies include ablation in the coronary sinus, atrial side of inferior mitral annulus, superior vena cava, and along the cristae terminalis, targeting complex fragmented electrograms. We usually reserve these adjunctive ablative therapies for patients with persistent or chronic atrial fibrillation and those with unsuccessful prior catheter ablation.

Pulmonary vein encircling ablation alters the atrial electrophysiologic response to autonomic stimulation

OBJECTIVE

Pulmonary vein encircling ablation is often effective in the treatment of atrial fibrillation (AF). The success of the procedure does not depend upon creation of continuous lines of block. Thus mechanisms by which pulmonary vein encircling can cure AF remain unclear. Stimulation of cardiac autonomic ganglia alters atrial refractoriness and potentiates AF. We hypothesized that pulmonary vein encircling alters atrial autonomic function and that these alterations account in part for prevention of AF recurrences following ablation.

METHODS

Atrial effective refractory periods (ERP) and AF inducibility were quantified in ten dogs before and during central autonomic nerve stimulation. Pulmonary vein encircling ablation was then performed and electrophysiologic testing repeated. In two dogs subjected to sham procedures measurements were repeated without performance of ablation. Hearts were examined histologically.

RESULTS

Autonomic nerve stimulation led to decreased atrial refractoriness and increased AF inducibility and duration. Each of these effects were attenuated following pulmonary vein encircling (e.g., mean ERP decreased before (-23.7 +/- 1.8, p < 0.001) but not after ablation (-2.3 +/- 1.9, p = 0.25); AF inducibility increased by 26% before vs. 5% after ablation). No attenuation was seen in the sham operated animals. Histologic analysis following pulmonary vein encircling demonstrated destruction of some but not all autonomic ganglia.

CONCLUSION

Autonomic stimulation shortens atrial refractory periods and potentiates AF. Pulmonary vein encircling ablation partially destroys atrial autonomic inputs, attenuates the refractory period shortening effect of autonomic stimulation and decreases AF inducibility. Destruction of autonomic ganglia may contribute to the anti-fibrillatory effects of pulmonary vein encircling and warrants further investigation.

Pulmonary Vein Isolation for Atrial Fibrillation in Patients With Paroxysmal Atrial Fibrillation and Prolonged Sinus Pause

BACKGROUND

Symptomatic prolonged sinus pauses upon termination of atrial fibrillation (AF) are an indication for pacemaker implantation.

METHODS AND RESULTS

We evaluated the clinical outcomes of 4 patients who showed prolonged sinus pauses (> 2 seconds) upon termination of AF and thus underwent ablation. The ablative procedure included pulmonary vein isolation, superior vena cava isolation, and cavo-tricuspid isthmus ablation. Twenty-four-hour ambulatory electro-cardiogram monitoring was performed before and 1 month after ablation. The maximum sinus pause decreased from 4.5 +/- 2.1 seconds before ablation to 1.7 +/- 0.2 seconds after ablation. Sinus pauses > 2.0 seconds disappeared after ablation in all 4 patients. Minimum heart rate increased from 35.0 +/- 8.1 beats/minute before ablation to 52 +/- 6.7 beats/minute after ablation. The number of heart beats in 24 hours did not change significantly after ablation.

CONCLUSION

Prolonged sinus pauses after paroxysmal AF may result from depressed sinus node function, which can be eliminated by curative ablation of AF.

Catheter Ablation Therapy for Atrial Fibrillation Current Advancements in Strategies

Curing atrial fibrillation (AF) by catheter ablation has significantly improved patient morbidity and mortality. The circumferential pulmonary vein isolation technique is established as the principal procedure, with a high cure rate and acceptable safety, for paroxysmal AF, but new adjunctive ablation strategies targeting the AF substrates and sources for long-standing persistent/chronic AF have been developed. These new techniques include linear ablation, complex fractionated atrial electrogram guided ablation, dominant frequency map-guided ablation, ganglionated plexi ablation and disconnection of the coronary sinus and superior vena cava to ablate the AF substrates and sources. The long-term usefulness of the established technique and these innovative adjunctive approaches for the treatment of AF remains to be investigated.