Radiofrequency modification of atrioventricular conduction by selective ablation of the low posterior septal right atrium in a patient with atrial fibrillation and a rapid ventricular response

A review on atrioventricular junction ablation and pacing for heart rate control of atrial fibrillation

Atrioventricular junction ablation with permanent pacemaker implantation is a highly effective treatment approach in patients with atrial fibrillation and high ventricular rates resistant to other treatment modalities, especially in the elderly or those with severe comorbidities. Compared with pharmacological therapy alone, the so-called “ablate and pace” approach offers the potential for more robust control of ventricular rate. Atrioventricular junction ablation and pacing strategy is associated with improvement in symptoms, quality of life, and exercise capacity. Given the close relationship between atrial fibrillation and heart failure, there is a particular benefit of such a rate control in patients with atrial fibrillation and reduced systolic function. There is increasing evidence that cardiac resynchronization therapy devices may be beneficial in selected populations after atrioventricular junction ablation. The present review article focuses on the current recommendations for atrioventricular junction ablation and pacing for heart rate control in patients with atrial fibrillation. The technique, the optimal implantation time, and the proper device selection after atrioventricular junction ablation are also discussed.

Ventricular rate control during atrial fibrillation and AV node modifications: past, present, and future

Atrial fibrillation (AF) is the most common arrhythmia. Currently there are two broad strategic treatment options for AF: rhythm control and rate control. For rhythm control, the treatment is directed toward restoring and maintaining the sinus rhythm. For rate control, the intention is to slow ventricular rate while allowing AF to continue. In both cases anticoagulation therapy is recommended. The results of currently available clinical trials demonstrated clearly that rate control is not inferior to rhythm control. Thus, rate control is an acceptable primary therapy for many AF patients. The rate control can be achieved essentially by depressing or modifying the filtering properties of the atrioventricular (AV) node. This can be attained by medications that depress the impulse transmission within the AV node, by anatomic modification of the AV communications, as well as by autonomic manipulations that produce AV node negative dromotropic effect. We are reviewing current clinical and newer experimental modalities aimed at enhancing the lifesaving function of this remarkable nodal structure.

A perspective on rate control in the treatment of atrial fibrillation

Until recently, the standard approach to therapy of atrial fibrillation (AF) in most cases was restoration and maintenance of sinus rhythm (rhythm control). Although difficult to accomplish, and associated with potential serious adverse effects of antiarrhythmic agents, this therapeutic approach was influenced by the belief that rhythm control was associated with better survival, fewer symptoms, better exercise tolerance, lower risk of stroke, better quality of life, and absence of need for long-term anticoagulation. However, four clinical trials comparing rate control with rhythm control have failed to demonstrate these advantages, indicating that rate control should be considered a legitimate primary therapeutic option, particularly in patients at risk for stroke. Pursuit of rate or rhythm control should be decided on a case-by-case basis.

His electrogram alternans reveal dual atrioventricular nodal pathway conduction during atrial fibrillation: the role of slow-pathway modification

BACKGROUND

Traditional tools to study dual-pathway atrioventricular nodal (AVN) electrophysiology are not applicable in subjects with permanent atrial fibrillation (AF). The presence of fast-pathway (FP) and slow-pathway (SP) wavefronts and their possible modification remain uncertain in this condition. We demonstrated previously that His electrogram (HE) alternans can determine whether the FP or the SP reaches the His bundle on a beat-by-beat basis. We have now applied this novel index to monitor dual-pathway conduction and the effects of SP modification during AF.

METHODS AND RESULTS

In 12 rabbit AVN preparations, HE alternans were confirmed during a standard A(1)A(2) pacing protocol. During AF, in 9 of the 12 hearts, HE alternans indicated the presence of dual pathways. Successful SP modification guided by the HE alternans eliminated the SP, resulting in a predominantly FP conduction during AF in all hearts. This increased the average His-His interval (204+/-14 versus 276+/-51 ms, P<0.001). Morphological studies revealed that SP modification damaged only the posterior extension of the AVN.

CONCLUSIONS

We have demonstrated for the first time in rabbits that HE alternans permit "visualization" of dual-pathway electrophysiology and confirmed the presence of both FP and SP wavefronts during AF. This novel index has been used in a selective SP ablation that resulted in a significant slowing of the ventricular rate. HE alternans provide a new insight into the mechanisms of AVN conduction and could guide AVN modification for ventricular rate control in AF clinically.

Safety and feasibility of a novel rate-smoothed ventricular pacing algorithm for atrial fibrillation

OBJECTIVES

This study was conducted to establish the safety and performance of a new rate-smoothing pacing algorithm for patients with atrial fibrillation (AF).

BACKGROUND

Irregularity of the ventricular response is a hallmark of AF. This irregularity may contribute to symptoms and hemodynamic compromise in patients with AF. Interventions designed to reduce irregularity have not previously been evaluated in a long-term, clinical setting.

METHODS

We designed a prospective, double-blind study with randomized crossover. Patients with either paroxysmal or chronic AF whose conditions were medically refractory and who were referred for an atrioventricular node ablation procedure all underwent pacemaker implantation. Subjects were then randomly assigned to either DDD mode with the rate-smoothing algorithm (RSA) on, or to OOO mode. After 2 months they were crossed over to the other arm.

RESULTS

Fourteen patients (9 with paroxysmal AF and 5 with chronic AF) were enrolled. There were no significant differences between the group randomly assigned to RSA first versus the group assigned to OOO first. The mean left ventricular ejection fraction with the RSA was not significantly different than it was in OOO mode (45.1 +/- 18.6 vs 51.9 +/- 12.3; P =.11), although some individuals with uncontrolled ventricular rates did have a large decrease in ejection fraction with rate smoothing. One developed overt heart failure. One quality-of-life instrument detected a significant improvement in the "physical limitations" domain with the rate-smoothing mode. Eleven of 14 patients preferred the RSA ON arm, and 6 of those 11 elected to defer the ablation procedure.

CONCLUSIONS

Long-term rate-smoothed pacing is feasible. Because of concerns about pacing-induced heart failure in some patients with rapid ventricular rates, rate-smoothed pacing should be reserved for those who remain symptomatic despite adequate control of the ventricular rate. The RSA may help to reduce symptoms in patients with medically refractory AF; more study is required to define its efficacy in reducing symptoms and morbidity in this population.

Multiple AV nodal pathways with multiple peaks in the RR interval histogram of the Holter monitoring ECG during atrial fibrillation

Two or more peaks on the 24-hour electrocardiogram (ECG) RR interval histogram of patients with atrial fibrillation suggests the presence multiple AV nodal pathways. The prevalence of multiple AV nodal pathways in this population is unknown. The study included 250 patients with permanent atrial fibrillation during 24-hour ECG. The number of peaks on the RR interval histogram was measured in each patient. A single peak was present in 153 patients (61%), 80 patients (32%) had two peaks, 13 patients (5%) had three, and 4 patients (2%) had four peaks. Among the 97 patients (39%) with > 1 AV nodal pathway, the estimated mean heart rate reduction by hypothetical ablation of all supernumerary AV nodal pathways with short refractory periods was 16 beats/min, from 82 to 65 beats/min. Among the overall population, 16 patients (6%) with > 1 AV nodal pathway had a mean heart rate > 100 beats/min. In this subgroup, modulation of AV node conduction by hypothetical ablation of all supernumerary AV nodal pathways with short refractory periods yielded an estimated reduction in mean heart rate of 26 +/- 15 beats/min, from 110 +/- 9 beats/min to 84 +/- 14 beats/min (P < 0.01), a 23% decrease. The presence of > 1 AV nodal pathway was suspected in 39% of all patients with permanent atrial fibrillation. The hypothetical ablation of all supernumerary AV nodal pathways with short refractory periods resulted in a clinically significant reduction in heart rate in 6% of patients in this population.

A randomized, prospective comparison of anterior and posterior approaches to atrioventricular junction modification of medically refractory atrial fibrillation

To compare the safety and efficacy of anterior versus posterior approach for atrioventricular (AV) junction modification, 40 patients with medically refractory paroxysmal (PAF) or chronic atrial fibrillation (AF) were randomly assigned to receive AV junction modification with an anterior or posterior approach. If the ablation session had taken more than 1 hour without success, the alternative ablation approach was attempted. Among the 18 patients assigned to receive the anterior approach, 14 (78%) had a primary success. One (5%) patient had complete AV block after ablation. Three patients crossed over to the posterior approach and had a successful outcome. Fourteen (64%) of 22 patients initially treated with the posterior approach had primary success. One (4%) patient developed complete AV block. Seven patients crossed over to the anterior approach and had a successful outcome. The primary success rate (14/18 vs 14/22, P = NS), incidence of transient AV block (3/18 vs 3/22, P = NS), and complete AV block (1/18 vs 1/22, P = NS) were similar between the anterior approach and posterior approach. The major differences between the two groups showed more radiofrequency pulses (10 +/- 4 vs 6 +/- 3 pulses, P < 0.01), longer procedure duration (50 +/- 24 vs 28 +/- 18 minutes, P < 0.01), and longer fluoroscopy exposure time (28 +/- 17 vs 16 +/- 8 minutes, P < 0.01) in the patients who had primary success with the posterior approach. In conclusion, this study demonstrated that (1) the two techniques had similar efficacies; (2) if one approach was ineffective, switching to the other approach might be safe; (3) combining these two approaches resulted in overall improvement in the success rate of this procedure, and (4) the posterior approach needed more radiofrequency pulses, longer procedural time, and longer fluoroscopy exposure time.

A noninvasive method for the detection of dual atrioventricular node physiology in chronic atrial fibrillation

Considering the electrophysiologic study as a reference, the RR interval distribution analysis is a sensitive (88%) and specific (80%) noninvasive method for detecting dual atrioventricular (AV) node physiology. This method may prove useful in selecting patients with atrial fibrillation who are considered appropriate candidates for radiofrequency modification of AV nodal conduction as opposed to AV nodal ablation.

Catheter-ablative techniques for the treatment of atrial fibrillation

Atrial fibrillation is the most commonly encountered arrhythmia in clinical practice and is associated with significant morbidity and mortality. Pharmacologic therapy, although useful for rate control, has proven much less effective in the long term maintenance of sinus rhythm. The utility of implantable atrial defibrillators or pacing to prevent atrial fibrillation remains largely untested. This article describes four catheter-based therapies for atrial fibrillation: His ablation, atrioventricular nodal modification, the Maze procedure, and the ablation of pulmonary vein foci which initiate the arrhythmia. Whereas the first two procedures are largely palliative and recommended for patients with symptomatic, drug-refractory atrial fibrillation, the latter two offer the potential for a curative intervention.

Acute testing of the rate-smoothed pacing algorithm for ventricular rate stabilization

We evaluated the capability of a new pacemaker-based rate-smoothing algorithm (RSA) to reduce the irregular ventricular response of AF. RSA prevents sudden decreases in rate using a modified physiological band and flywheel feature. Twelve patients (51 +/- 21 years) with hemodynamically tolerated AF of 4 months to 20 years duration were studied. Atrial and ventricular leads were connected to the external pacemaker device in the electrophysiology laboratory. Consecutive RR intervals during AF were measured at baseline and after ventricular pacing with RSA ON. Ventricular pacing with the rate smoothing algorithm reduced maximum RR intervals (1,207 +/- 299 vs 855 +/- 148 ms, P = 0.0005), with no significant change in the minimum RR interval (401 +/- 55 vs 393 +/- 74 ms, P = 0.292). A small shortening of the mean RR interval (634 +/- 153 vs 594 +/- 135 ms, P = 0.007) was seen with no change in the median RR interval (609 +/- 153 vs 595 +/- 143 ms, P = 0.388). There was a 43% reduction in RR standard deviation (145 +/- 52 vs 82 +/- 28, P = 0.0005), 49% reduction in mean absolute RR interval difference (MAD) (152 +/- 64 vs 77 +/- 34, P = 0.0005) and MAD/mean RR ratio (0.23 +/- 0.05 vs 0.13 +/- 0.04, P = 0.0005). We conclude that rate-smoothed pacing effectively reduces RR variability of AF in the acute setting.

Radiofrequency modification of the atrioventricular node in patients with chronic atrial fibrillation: comparison between anterior and posterior approaches

INTRODUCTION

We compared, in a prospective and randomized fashion with a cross-over design, the anterior and posterior approaches to radiofrequency (RF) modification of the AV node in patients with chronic atrial fibrillation.

METHODS AND RESULTS

Thirty-three patients were randomized to receive first an anterior (group I) or posterior (group II) approach for RF modification of AV nodal conduction. Patients who did not fill the endpoint ventricular rate (< 90 beats/min) were crossed over to the alternative approach. After the anterior approach in group I patients, mean ventricular rate was significantly lower than in group II patients after the posterior approach (79.6 +/- 18.8 beats/min vs 110.8 +/- 16.2 beats/min, P < 0.001). In group I, 14 (82%) of 17 patients fulfilled the endpoint, 1 (6%) had complete AV block, and 2 (12%) were crossed over to the posterior approach fulfilling the endpoint. In group II, 4 (25%) of 16 patients fulfilled the endpoint. No transient or permanent high-degree AV block was observed. Among the 12 patients who were crossed over to the anterior approach, 8 fulfilled the endpoint, whereas 4 had permanent high-degree AV block. RF ablation carried out only in the anterior region was safer than a stepwise approach (6% vs 33% incidence of AV block), even though the difference did not reach statistical significance (P = 0.09).

CONCLUSION

Posterior AV nodal modification is less effective but safer than anterior AV nodal modification. However, to reduce the incidence of AV block, the anterior approach is preferable to a stepwise approach from the posterior to the anterior zone.

Radiofrequency catheter ablation for atrial fibrillation

Until recently, catheter-based radiofrequency ablation for atrial fibrillation was limited to palliative approaches of either atrioventricular node ablation or modification. It is now recognized that at least a proportion of patients with paroxysmal atrial fibrillation may be suitable for curative ablation of an underlying single arrhythmogenic focus. With the intense interest in this area, a catheter-based cure involving endocardial linear lesion creation for patients with chronic or paroxysmal atrial fibrillation may not be far in the future.

Long-term follow-up after radiofrequency modification of the atrioventricular node in patients with atrial fibrillation

OBJECTIVES

The purpose of this study was to describe the long-term follow-up results in 62 patients with atrial fibrillation and an uncontrolled ventricular rate, who underwent radiofrequency modification of the atrioventricular (AV) node.

BACKGROUND

Previous studies in small numbers of patients have suggested that radiofrequency modification may be effective in controlling the ventricular rate in patients with atrial fibrillation, but long-term follow-up data have been lacking.

METHODS

The subjects of this study were 62 consecutive patients (mean age +/- SD 65 +/- 14 years; 43 with structural heart disease) who underwent an attempt at radiofrequency modification of the AV node because of symptomatic, drug-refractory atrial fibrillation with an uncontrolled ventricular rate. The atrial fibrillation was chronic in 46 patients and paroxysmal in 16. Radiofrequency energy was applied to the posteroseptal or mid-septal right atrium to lower the ventricular rate in atrial fibrillation to 120 to 130 beats/min during an infusion of 4 micrograms/min of isoproterenol.

RESULTS

Short-term control of the ventricular rate was successfully achieved without the induction of pathologic AV block in 50 (81%) of 62 patients. Inadvertent high degree AV block occurred in 10 (16%) of 62 patients, with the AV block occurring at the time of the procedure in 6 patients and 36 to 72 h after the procedure in 4. During 19 +/- 8 months of follow-up (range 4 to 33), 5 (10%) of 50 patients had a symptomatic recurrence of an uncontrolled rate during atrial fibrillation. Overall, adequate rate control at rest and during exertion, without pathologic AV block, was achieved long term in 45 (73%) of 62 patients. Among 37 patients with a successful outcome, left ventricular ejection fraction increased from (mean +/- SD) 0.44 +/- 0.14 to 0.51 +/- 0.10 one year later (p < 0.001). Complications other than AV block included polymorphic ventricular tachycardia 10 to 24 h after the procedure in two patients who had a predisposing factor for ventricular tachycardia and sudden death 1 to 5 months after the procedure in two patients with idiopathic dilated cardiomyopathy, one of whom had a pacemaker for AV block.

CONCLUSIONS

In approximately 70% of properly selected patients with atrial fibrillation and an uncontrolled ventricular rate, radiofrequency modification of the AV node results in excellent long-term control of the ventricular rate at rest and during exertion.

Mechanism of ventricular rate control after radiofrequency modification of atrioventricular conduction in patients with atrial fibrillation

BACKGROUND

Modification of atrioventricular (AV) conduction during atrial fibrillation (AF) may be achieved by radiofrequency ablation in the posteroseptal region of the tricuspid annulus. We tested the hypothesis that elimination of the posterior atrionodal input rather than direct damage to the compact AV node accounts for the decrease in ventricular rate after AV nodal modification.

METHODS AND RESULTS

Twenty-four patients with the typical form of AV nodal reentrant tachycardia (AVNRT) underwent selective radiofrequency ablation of the slow AV nodal pathway in the posteroseptal tricuspid annulus. AF was induced before ablation (phase 1), 30 minutes after ablation (phase 2), and during follow-up 24 hours after ablation (phase 3), both with and without concurrent infusion of isoproterenol (4 micrograms/min). Successful elimination of AVNRT was achieved in all patients. During phase 3, 11 patients (46%) had residual dual pathway physiology. AV nodal Wenckebach cycle length (AVNW-CL) increased progressively during each phase of the protocol (356 +/- 72 versus 371 +/- 78 ms versus 432 +/- 104 ms, P < .0001), as did the effective refractory period of the AV node (279 +/- 60 versus 304 +/- 67 ms versus 372 +/- 56 ms, P < .0001). Minimal, mean, and maximal RR intervals during AF progressively increased immediately after ablation and 24 hours later (485 +/- 88 versus 533 +/- 116 ms versus 637 +/- 142 ms for mean RR, P < .0001). The changes in AVNW-CL, AV nodal effective refractory period, and ventricular response during AF were independent of residual dual pathway physiology after ablation. Similar observations were observed during isoproterenol infusion.

CONCLUSIONS

Modification of AV nodal conduction during AF by radiofrequency ablation in the posteroseptal tricuspid annulus is independent of the presence or absence of a residual slow AV nodal pathway. On the basis of these observations, the mechanism of AV nodal modification is consistent with elimination of the posterior atrionodal input.

Electrophysiological mechanisms in successful radiofrequency catheter modification of atrioventricular junction for patients with medically refractory paroxysmal atrial fibrillation

BACKGROUND

Mechanisms and changes of electrophysiological (EP) characteristics in successful radiofrequency (RF) modification of right midseptal and posteroseptal areas for controlling rapid ventricular response to atrial fibrillation (Af) are not clear.

METHODS AND RESULTS

We studied 50 patients with medically refractory paroxysmal Af. Group 1 consisted of 40 patients without dual atrioventricular (AV) node physiology with modification sites located in the mid/posteroseptal area. Of the 40 patients, 36 had successful modification (follow-up of 14 +/- 8 months), and 3 had AV block. Late follow-up electrophysiological study (98 +/- 10 days) showed pattern 1 (67%) with prolongation of AV node effective refractory period (ERP, > or =40 milliseconds) and Wenckebach block cycle length (WBCL, > or =40 milliseconds); pattern 2 (22%) with prolongation of AH interval (> or =20 milliseconds), ERP, and WBCL; and pattern 3 (11%) without any change in AV node conduction parameter. Change in ventricular rate negatively correlated with change of WBCL in patterns 1 (r=-.691, P=.019) and 2 (r=-.90, P=.01). Group 2 consisted of 10 patients with dual AV node pathway; elimination of slow pathway property was performed. Late follow-up electrophysiological study (92+/-7 days) showed that change in ventricular rate negatively correlated with change in AV node ERP (r=-.926, P=.0001) and WBCL (r=-.969, P=.0001). Four patients without significant modification effect had success after RF energy was delivered to higher levels (follow-up, 15+/-7 months).

CONCLUSIONS

RF modification of right mid/posteroseptal area is feasible in 92% of patients with paroxysmal Af. Mechanisms of successful modification might be elimination of posterior input and/or partial injury of the compact node. Furthermore, simple elimination of slow pathway might be inadequate for control of ventricular rate in patients with little difference in conduction properties between fast and slow pathways.

Effect of sequential radiofrequency ablation lesions at fast and slow atrioventricular nodal pathway positions in patients with paroxysmal atrial fibrillation

OBJECTIVE

To examine the hypothesis that the anatomic equivalents of the fast and slow pathways identified in patients with atrioventricular (AV) nodal tachycardia may be universal and represent the principal sites of atrial input into the normal compact AV node.

METHODS

15 patients undergoing complete AV junction ablation for paroxysmal atrial fibrillation were studied. Radiofrequency energy was delivered first in the anterior "fast pathway" position so as to prolong the atrium to bundle of His (AH) interval by over 50% of baseline (protocol 1) and then to the "slow pathway" position using the anatomical technique (protocol 2).

RESULTS

Ablation protocol 1 resulted in prolongation of AH interval in all patients. Subsequent lesions at the level of the coronary sinus produced complete heart block in four patients, and in five caused a further increase in AH interval above that produced by protocol 1. Four of these latter patients developed complete block after delivery of RF energy slightly anterior to the level of the coronary sinus os, as did three further patients in whom ablation at the level of the coronary sinus had no effect. In four patients complete heart block could not be achieved by protocol 2.

CONCLUSIONS

A discrete anterior "fast" pathway and a posterior "slow" pathway or network of posterior pathways form the principal inputs to the compact AV node in most patients with atrial fibrillation. The absence of dual AV nodal physiology in the majority of these patients may be related to the functional properties of the individual components of this posterior network.

Effect of slow pathway ablation on ventricular rate during atrial fibrillation. Dependence on electrophysiological properties of the fast pathway

BACKGROUND

Catheter ablation of the posteroseptal right atrium has been proposed for control of ventricular rate in patients with tachycardic atrial fibrillation (AF). However, the exact mechanism of rate control is unclear. Because the ablation site corresponds to the location of the slow pathway in patients with AV nodal reentry tachycardia (AVNRT), we investigated whether selective ablation of this posterior AV nodal input can provide a sufficient reduction in heart rate during AF.

METHODS AND RESULTS

In 30 patients with AVNRT, conduction properties of the AV nodal pathways were determined before and after slow pathway ablation. AF was induced by burst pacing at baseline and after ablation, and the mean ventricular cycle length was determined. After slow pathway ablation, the mean ventricular cycle length during AF increased (449 +/- 98 versus 515 +/- 129 milliseconds, P < .01). At baseline, the mean ventricular cycle length correlated with the Wenckebach cycle length of both the slow (r = .90) and fast (r = .86) pathways. After ablation, the mean ventricular cycle length was extremely well determined by the Wenckebach cycle length of the fast pathway (r = .94). However, the slope of the regression line was significantly steeper compared with baseline (1.50 versus 0.77, P < .0001), illustrating that the reduction in ventricular rate was not as evident if the fast pathway had a short Wenckebach cycle length.

CONCLUSIONS

Selective elimination of the slow pathway reduces ventricular rate during AF. However, in patients with a short Wenckebach cycle length of the anterior AV nodal input that causes tachycardic AF, this effect may be insufficient to provide adequate control of ventricular rate.

Slowing of the ventricular rate during atrial fibrillation by ablation of the slow pathway of AV nodal reentrant tachycardia

INTRODUCTION

The mechanisms whereby radiofrequency catheter modification of AV nodal conduction slows the ventricular response are not well defined. Whether a successful modification procedure can be achieved by ablating posterior inputs to the AV node or by partial ablation of the compact AV node is unclear. We hypothesized that ablation of the well-defined slow pathway in patients with AV nodal reentrant tachycardia would slow the ventricular response during atrial fibrillation.

METHODS AND RESULTS

In 34 patients with dual AV physiology and inducible AV nodal reentrant tachycardia, atrial fibrillation was induced at baseline and immediately after successful slow pathway ablation and at 1-week follow-up. The minimal, maximal, and mean RR intervals during atrial fibrillation increased from 353 +/- 76, 500 +/- 121, and 405 +/- 91 msec to 429 +/- 84 (P < 0.01), 673 +/- 161 (P < 0.01), and 535 +/- 98 msec (P < 0.01), respectively. These effects remained stable during follow-up at 1 week. The AV block cycle length increased from 343 +/- 68 msec to 375 +/- 60 msec (P < 0.05) immediately and to 400 +/- 56 msec (P < 0.01) at 1-week follow-up. The effective refractory period of the AV node prolonged from 282 +/- 83 msec to 312 +/- 89 msec and to 318 +/- 81 msec after 1 week (P < 0.05), respectively.

CONCLUSION

This study shows a decrease in ventricular response to pacing-induced atrial fibrillation after ablation of the slow pathway in patients with AV nodal reentrant tachycardia. Since the AV nodal conduction properties could be defined, this study supports the hypothesis that the main mechanism of AV nodal modification in chronic atrial fibrillation is caused by ablation of posterior inputs to the AV node.

Radiofrequency catheter ablation versus modification of the AV node for control of rapid ventricular response in atrial fibrillation

Atrial fibrillation is a common arrhythmia, which is frequently difficult to control. Symptoms and ventricular dysfunction may be caused by a rapid ventricular response to atrial fibrillation. Radiofrequency catheter ablation techniques for ventricular rate control have been developed, including AV node modification and AV node ablation with pacemaker implantation. For both AV node modification and ablation, radiofrequency energy is applied via a 4-mm tipped electrode catheter. For AV node ablation radiofrequency energy is applied near the compact AV node or His bundle via the right atrium, or occasionally at the His bundle via the left ventricle. For AV node modification radiofrequency energy is applied in the low middle or posterior septal right atrium near the tricuspid valve annulus. Both techniques can effectively control ventricular response to atrial fibrillation and the associated symptoms, although AV node modification is effective in only about 70% of patients compared to AV node ablation, which is effective in nearly 100%. In patients responding to AV node modification, maximal and mean ventricular response to atrial fibrillation is reduced by 25% to 35% chronically. Inadvertent AV block may occur during attempted AV node modification. It seems appropriate to attempt AV node modification prior to AV node ablation in patients with refractory atrial fibrillation and rapid ventricular response, in order to avoid the need for permanent pacemaker implantation. Although unproven, studies suggest that the mechanism by which AV node modification achieves ventricular rate control may be slow-pathway ablation in the low posterior septal right atrium.

Characterization of atrioventricular nodal behavior and ventricular response during atrial fibrillation before and after a selective slow-pathway ablation

BACKGROUND

The presence of atrioventricular nodal dual-pathway physiology in patients with atrioventricular nodal reentrant tachycardia (AVNRT) provides an opportunity to characterize the effect of a selective slow-pathway ablation on the ventricular rate during atrial fibrillation (AF). This may have important clinical implications for the nonpharmacological management of AF with a rapid ventricular rate.

METHODS AND RESULTS

Selective radiofrequency catheter ablation of the atrioventricular nodal slow pathway was performed with a stepwise approach in patients with documented sustained AVNRT. The AV nodal conduction properties and refractoriness and the ventricular rate during induced AF were assessed at baseline and under autonomic blockade before and after a selective slow-pathway ablation in 18 patients (mean age, 34 +/- 8 years). Sustained AVNRT was induced with a mean cycle length of 339 +/- 58 ms. A slow-pathway ablation was successfully achieved with 5 +/- 4 applications of radiofrequency energy. The shortest cycle length of 1:1 AV conduction and the AV nodal effective refractory period significantly prolonged after ablation (367 +/- 53 versus 403 +/- 55 ms, P < .0001, and 258 +/- 55 versus 292 +/- 74 ms, P < .05, respectively). Selective slow-pathway ablation significantly prolonged the mean (526 +/- 93 versus 612 +/- 107 ms, P < .0001), the shortest (378 +/- 59 versus 423 +/- 73 ms, P < .0001), and the longest (826 +/- 150 versus 969 +/- 226 ms, P < .01) cycle lengths of the ventricular response to AF. Significant slowing of the ventricular rate during AF occurred in 13 patients (72%), including all eight patients in whom AV nodal dual-pathway physiology was abolished. Five patients did not have a significant change in the ventricular rate during AF; a persistent dual AV nodal pathway physiology was demonstrable in four of these patients. Loss of dual-pathway physiology after ablation had a sensitivity of 77%, specificity of 80%, and positive predictive value of 91% for slowing the ventricular rate during AF.

CONCLUSIONS

In patients undergoing a slow-pathway ablation for control of AVNRT, selective slow-pathway ablation may cause a significant decrease in the ventricular rate during AF. These effects are primarily due to the prolongation of AV nodal conduction properties and refractory period of the residual AV nodal transmission system. These findings may have important therapeutic implications for the nonpharmacological treatment of AF, particularly in patients with underlying dual AV nodal physiology.

Catheter ablation for the treatment of atrial tachycardia

Radiofrequency (RF) catheter ablation has revolutionized the treatment of supraventricular tachycardia, particularly those caused by atrioventricular nodal reentry and Wolff-Parkinson-White syndrome. Recently, RF catheter ablation has also been used to treat atrial flutter (AFL), focal automatic atrial tachycardia, and intra-atrial reentrant tachycardia. Typical AFL is caused by reentry in the right atrium, with an area of slow conduction in the isthmus between the inferior vena cava and tricuspid valve annulus. Ablation of exit sites from the isthmus near the coronary sinus ostium, or the isthmus itself, may cure AFL in the majority of patients. Intra-atrial reentrant tachycardia also has an area of slow conduction where application of RF energy is curative in most patients. In this arrhythmia, which is particularly common after congenital heart disease surgery, the reentrant circuit may occur in the right or left atrium. Focal automatic atrial tachycardia is probably caused by abnormal automaticity and, although it may arise from the right or left atrium, is easily ablated in most patients. Thus, RF catheter ablation is a highly effective alternative to pharmacologic therapy for treating atrial tachycardia, and it is likely to be increasingly used as curative therapy in the future.

Modulation of atrioventricular conduction by ablation of the "slow" atrioventricular node pathway in patients with drug-refractory atrial fibrillation or flutter

OBJECTIVES

We hypothesized that modulation of atrioventricular (AV) node conduction, allowing a reduction in ventricular rate during atrial fibrillation or flutter without affecting AV conduction during sinus rhythm, might be achieved through ablation of the "slow" AV node pathway.

BACKGROUND

In patients with atrial fibrillation or flutter not amenable to a direct atrial approach, ablation of the His bundle is performed to induce complete AV block. This procedure causes pacemaker dependence.

METHODS

Fourteen patients with drug-refractory paroxysmal atrial flutter or fibrillation underwent ablation of the slow AV node pathway. Radiofrequency current was delivered in six patients during sinus rhythm, in six during atrial flutter and in two during atrial fibrillation.

RESULTS

The anterograde effective refractory period of the AV node was prolonged from 270 +/- 50 (mean +/- SD) to 390 +/- 87 ms (p = 0.005) and the Wenckebach cycle from 346 +/- 33 to 458 +/- 75 ms (p = 0.004) in six patients during sinus rhythm. Mean AV ratio increased from 1.6 +/- 0.5 to 3.0 +/- 0.6 (p = 0.02) in six patients with atrial flutter. Mean ventricular rate decreased from 157 +/- 38 to 67 +/- 10 beats/min in two patients with atrial fibrillation. Complete AV block was induced in two patients (transient in one, permanent in one). During a follow-up period of 5.8 +/- 3.5 months, 11 patients experienced a recurrence of atrial fibrillation at 60 to 95 beats/min. No patient had progression to any degree of AV block.

CONCLUSIONS

Ablation of the slow AV node pathway allows reduction of ventricular rate during atrial fibrillation or flutter while maintaining intact AV conduction during sinus rhythm. Modulation of AV node conduction is effective in most patients as an alternative to His bundle ablation for control of ventricular rate in paroxysmal atrial fibrillation or flutter.

Radiofrequency catheter ablation and modulation of atrioventricular conduction in patients with atrial fibrillation

We attempted radiofrequency ablation of the AV junction with a sequential right- and left-sided approach in 78 patients affected by severely symptomatic, drug refractory atrial fibrillation. Stable third-degree AV block was obtained in 99% of cases and, after 3 months, persisted in 92% of cases. Single session, stepwise, radiofrequency modulation of the AV node was attempted in 13 patients with paroxysmal atrial fibrillation. During sinus rhythm, ablation of the slow and fast AV node pathways was performed in order to increase the nodal refractory period or to slow conduction. Clinically successful modulation of AV conduction was achieved in 15% of cases and persisted during a 3-month follow-up. In conclusion, AV junction ablation is a well-established means of treating atrial fibrillation, but implies the implant of a permanent pacemaker. AV node modulation avoids the pacemaker implant, but is efficacious only in a minority of patients. Thus, in patients affected by paroxysmal atrial fibrillation, AV modulation should be attempted first; if this is ineffective, AV ablation can be performed during the same session.

Control of rapid ventricular response by radiofrequency catheter modification of the atrioventricular node in patients with medically refractory atrial fibrillation

BACKGROUND

Pharmacological control of rapid ventricular response to atrial fibrillation may be difficult in some patients. Alternative treatments, including curative surgery or atrioventricular (AV) node ablation with pacemaker implantation, have significant potential morbidity. In view of evidence that dual AV nodal physiology may exist in a significant percentage of the population, even in those without AV nodal reentrant tachycardia, we postulated that control of ventricular response might be achieved by radiofrequency (RF) catheter ablation in the region of the AV nodal slow pathway with its short refractory period.

METHODS AND RESULTS

Ten patients underwent attempted AV node modification using a 4-mm-tipped electrode catheter positioned in the middle or posterior septum, between the His bundle and coronary sinus ostium on the tricuspid valve annulus. RF energy was applied at 16 to 30 W for up to 60 seconds, until average ventricular response fell below 100 beats per minute. Reduction of maximal ventricular response below 120 beats per minute was confirmed with atropine 1 mg IV. If required, additional ablations were performed progressively more posteriorly up to the coronary sinus ostium. Patients with successful AV node modification were discharged off AV node-blocking drugs and followed in the clinic at regular intervals. Twenty-four-hour ambulatory ECG recordings and/or treadmill stress tests were obtained before and after ablation for statistical comparison of maximum ventricular rate. Resting average ventricular rate was determined during electrophysiology study before and after ablation. In 7 of 10 patients (70%), maximum ventricular rate was reduced from a mean of 164 +/- 12 to 123 +/- 16 beats per minute (P < .01) and average ventricular rate from a mean of 128 +/- 11 to 83 +/- 10 beats per minute after ablation. Mean minimum ventricular rate was 54 +/- 11 beats per minute after ablation. These 7 patients have remained symptom free from rapid ventricular response for a mean of 14 +/- 8 months (range, 1 to 22). Three remain off all AV node-blocking drugs, 3 remain on digoxin alone, which was previously ineffective, and 1 remains on a beta-blocker for angina. In the 3 patients who did not respond to AV node modification, complete AV node ablation and permanent pacemaker implantation was performed in 2 and DC cardioversion after amiodarone loading was performed in 1.

CONCLUSIONS

RF catheter modification of AV node conduction is effective in controlling rapid ventricular response to atrial fibrillation in a significant percentage of medically refractory patients. A possible mechanism of RF modification of AV node conduction is AV nodal slow pathway ablation. Large-scale clinical trials will be needed to determine the overall efficacy and safety of this technique.

Radiofrequency catheter modification of atrioventricular conduction to control the ventricular rate during atrial fibrillation

BACKGROUND

In some patients with atrial fibrillation, the ventricular rate may be difficult to control with medications. We evaluated a radiofrequency catheter technique to modify atrioventricular conduction in atrial fibrillation in order to control the ventricular rate without creating pathologic atrioventricular block.

METHODS

We studied 19 consecutive patients with atrial fibrillation and uncontrolled ventricular rates refractory to drug therapy. They had had atrial fibrillation for a mean (+/- SD) of 5.5 +/- 4.9 years, had had 4.9 +/- 0.9 unsuccessful drug trials, and were 62 +/- 15 years old. Before the procedure, the maximal ventricular rate during exercise was 180 +/- 39 beats per minute. A total of 11 +/- 5 radiofrequency-energy applications were delivered to the posterior septal or midseptal right atrium, near the ostium of the coronary sinus.

RESULTS

Successful control of the ventricular rate without pathologic atrioventricular block was achieved in 14 of the 19 patients (74 percent). Persistent third-degree atrioventricular block requiring a permanent pacemaker occurred inadvertently in four patients (21 percent). Atrioventricular conduction was intentionally ablated in one patient. The 14 patients who had successful modification of conduction had persistent reductions in maximal ventricular rate during exercise (rate at three months, 126 +/- 24 beats per minute; P < 0.01). These patients had resolution of symptoms related to rapid rates during 8 +/- 2 months of follow-up. One patient had a recurrence of a rapid ventricular rate but was again asymptomatic after a second modification procedure. One patient with dilated cardiomyopathy died suddenly, five months after a successful procedure.

CONCLUSIONS

A catheter technique to modify atrioventricular conduction without creating pathologic atrioventricular block is feasible in the majority of patients with symptomatic atrial fibrillation and a rapid ventricular rate refractory to drug therapy.

An approach to therapy of supraventricular tachyarrhythmias: an algorithm versus individualized therapy

Approaches to the treatment of supraventricular arrhythmias, including atrial fibrillation, atrial flutter, atrial tachycardia, atrioventricular (AV) reentrant tachycardia, and AV nodal reentrant tachycardia, continue to evolve. Within the past two decades, many new and effective treatments have become available. These include several new antiarrhythmic agents, ablative therapies, pacing and surgical modalities, and cardioversion/defibrillation techniques. This paper provides an algorithm for the treatment of these supraventricular arrhythmias which includes therapy for the acute episode as well as the prevention of subsequent episodes of the tachyarrhythmia.

Should every patient with atrial fibrillation have the rhythm converted to sinus rhythm?

Atrial fibrillation is the most common atrial tachyarrhythmia. Consideration for the potential conversion of atrial fibrillation and the subsequent maintenance of sinus rhythm may be related to underlying pathology. Typically, extra cardiac factors such as thyroid hyperactivity help to determine initial therapy. Intrinsic cardiac factors may also influence the clinician's decision regarding potential cardioversion and maintenance of sinus rhythm. Some acute events such as pericarditis and the effects of cardiac trauma may resolve and result in spontaneous restoration of sinus rhythm. Other cardiac events such as acute myocardial infarction with or without atrial ischemia, valvular disease, and others may result in the precipitation of atrial fibrillation. The major reasons to consider cardioversion, either medically or electrically, are ventricular rate control, hemodynamic improvement, sense of well being, and the avoidance of embolism. Certain clinical situations (e.g., Wolff-Parkinson-White syndrome) require urgent restoration of sinus rhythm in light of the potential for extremely rapid ventricular rates. It has been suggested that all antiarrhythmic drug administration should be initiated in the hospital setting, but the brief period of drug administration in an inpatient setting does not protect the patient from potential, late-onset proarrhythmic events. Both antiarrhythmic drug therapy and electric cardioversion are useful for restoration of sinus rhythm in both acute and chronic atrial fibrillation. The most important negative aspect of drug conversion of atrial fibrillation may be the potential development of a proarrhythmic drug effect. Although controversial, conversion (medical or electrical) is probably indicated in every patient with the first episode of persistent atrial fibrillation, even if the patient is asymptomatic.(ABSTRACT TRUNCATED AT 250 WORDS)