Atrial fibrillation: Atrioventricular node ablation

INTRODUCTION — In patients with atrial fibrillation (AF), the ventricular rate is determined in large part by the conduction properties of the atrioventricular (AV) node. In the typical patient with untreated AF, the ventricular rate can reach 150 beats per minute or higher. There are three important reasons to prevent a rapid ventricular response in patients with AF:

●Avoidance of hemodynamic instability. (See "Hemodynamic consequences of atrial fibrillation and cardioversion to sinus rhythm".)

●Avoidance of bothersome symptoms. (See "Atrial fibrillation: Overview and management of new-onset atrial fibrillation", section on 'History and physical examination'.)

●Avoidance of a tachycardia-mediated cardiomyopathy. (See "Arrhythmia-induced cardiomyopathy".)

A rapid ventricular response can be prevented either by restoring sinus rhythm (ie, rhythm control) or by using therapies that reduce the ventricular response (ie, rate control) to AF. When rate control is chosen, it can usually be accomplished with pharmacologic therapy. However, some AF patients will respond poorly to or be intolerant of rate control medications. Options for such patients include reconsideration of a rhythm control strategy or nonpharmacologic methods to control the ventricular rate. (See "Atrial fibrillation: Overview and management of new-onset atrial fibrillation" and "Management of atrial fibrillation: Rhythm control versus rate control".)

The use of AV node ablation to achieve rate control in AF will be reviewed here. Pharmacologic therapies for rate control in AF are discussed separately. (See "Control of ventricular rate in patients with atrial fibrillation who do not have heart failure: Pharmacologic therapy".)

GENERAL PRINCIPLES — Choosing the appropriate rate control therapy for a patient with AF is guided by an understanding of the determinants of the ventricular rate and an assessment of the adequacy of rate control. The discussions of rate control and the determinants of ventricular rate in patients with AF are found elsewhere. (See "Control of ventricular rate in patients with atrial fibrillation who do not have heart failure: Pharmacologic therapy".)

There are several strategies for assessing the adequacy of rate control efforts. With any strategy, rate control should be assessed both at rest and with exertion. Rate control goals are discussed separately. (See "Control of ventricular rate in patients with atrial fibrillation who do not have heart failure: Pharmacologic therapy", section on 'Evaluation and goal ventricular rate'.)

INDICATIONS — AV node ablation is an option for rate control in AF patients who have failed medical therapy for rhythm control, have failed or are not candidates for catheter ablation for rhythm control, and have failed aggressive attempts at pharmacological rate control. Many of these patients are labeled as having permanent AF, which is the term used to identify individuals with persistent AF where a joint decision by the patient and clinician has been made to no longer pursue a rhythm control strategy.

Patients who are candidates for AV node ablation should be highly symptomatic, hemodynamically intolerant of AF, or have cardiomyopathy that is thought to be at least some part tachycardia induced. In general, the procedure is most commonly performed in elderly patients, many of whom have a preexisting pacemaker or implantable cardioverter-defibrillator (ICD) (table 1). Other patients include those who are not candidates for rhythm control with catheter ablation or drug therapy, those with refractory AF with tachycardia-induced cardiomyopathy, or those with a preexisting pacemaker.

Careful thought needs to be given to other treatment options, including curative attempts with catheter ablation before proceeding to AV node ablation in patients in whom medical therapy has failed to control the ventricular rate. The specific clinical scenario will dictate the appropriateness of AV node ablation vis-a-vis other treatment options. In younger patients, all treatment options should be considered/exhausted before proceeding to AV node ablation. AV node ablation may be more appropriate in older patients, particularly those with preexisting pacing devices, and in those in whom curative attempts at AF ablation are unlikely to be successful (eg, very longstanding/permanent AF, marked left atrial dilatation, etc).

Prior to performing AV node ablation, the patient needs to be informed about the invasive nature of the procedure, the requirement for lifelong permanent pacemaker therapy, and the long-term risk of a pacing-induced cardiomyopathy when RV apical pacing is used.

PROCEDURE — AV node ablation usually produces complete AV block and often leaves the patient with a slow junctional or idioventricular escape rhythm. Consequently, patients require implantation of a permanent pacing device to adequately control the ventricular rate (waveform 1A-B). If a preexisting pacemaker or ICD is not already in place, a permanent pacemaker or ICD is implanted prior to AV node ablation. This is usually carried out immediately prior to the AV node ablation, but in some cases the device may be implanted in advance of the ablation procedure. Traditional leaded devices are implanted in the subclavicular region; a leadless pacemaker may be implanted directly in the right ventricle. (See 'Device selection' below and "Permanent cardiac pacing: Overview of devices and indications", section on 'General considerations'.)

If a functional pacemaker or ICD is in place and no system revision is planned, the femoral vein is generally used for access for ablation of the AV node. An ablation catheter is advanced to the AV junction where a bundle of His potential can be recorded. Radiofrequency ablation of the AV node/bundle of His is performed. Ablation lesions should be delivered at a site proximal in the AV conduction system where a large atrial electrogram is also recorded to increase the likelihood of a junctional escape rhythm after creation of AV bock to avoid pacemaker dependency. With a successful lesion, there is usually an accelerated junctional rhythm and then heart block. If initial ablation is ineffective, or if conduction recurs, a larger lesion can be created with either a larger tip or saline-irrigated catheter.(See "Overview of catheter ablation of cardiac arrhythmias".)

On rare occasions, AV node ablation cannot be accomplished via the right heart. In these cases, establishing femoral arterial access allows passage of an ablation catheter retrograde across the AV node. A bundle of His potential can be recorded just below the aortic valve, in the septal aspect of the left ventricular (LV) outflow tract. Alternatively, ablation by way of the left heart can be accomplished using a patent foramen ovale or transseptal puncture. If left heart access is necessary, systemic anticoagulation with intravenous heparin is generally administered while the left heart is instrumented.

If a leadless pacemaker is placed, the same femoral venous sheath can then be used to advance the ablation catheter (see "Permanent cardiac pacing: Overview of devices and indications", section on 'Leadless systems'). Care must be taken to make sure that newly placed leads or a leadless pacemaker are not dislodged by the ablation catheter. In rare cases, when right heart ablation of the AV node is ineffective and a new leaded pacing system has just been placed, it may be reasonable to defer the left heart AV node ablation for days/weeks to obviate the need for intravenous heparin with the attendant risks of bleeding.

Device selection — Following AV node ablation (see 'Procedure' above), most patients are pacemaker dependent. Therefore a device with pacemaker capability must be in place prior to the ablation procedure. The choice of which type of pacing device is implanted depends on the patient's clinical profile.

Single-chamber ventricular pacemaker — In patients with persistent AF, a single-chamber (right) ventricular pacemaker is often adequate. After AV node ablation, the patient's ventricular rate will not naturally respond to increased demand; therefore, a device with rate-adaptive capabilities is used (ie, VVIR pacing). All contemporary pacemakers have rate-adaptive capabilities. (See "Modes of cardiac pacing: Nomenclature and selection", section on 'Rate responsiveness'.)

Leadless RV pacing (see "Permanent cardiac pacing: Overview of devices and indications", section on 'Leadless systems') has also been used in association with AV node ablation [1].

Dual-chamber pacemaker — In patients with paroxysmal AF, dual-chamber pacemakers are preferred to single-chamber devices because they maintain AV synchrony during periods of sinus rhythm (eg, DDDR pacing). (See "Modes of cardiac pacing: Nomenclature and selection", section on 'Dual-chamber pacing'.)

In order to prevent rapid ventricular pacing during episodes of AF, patients with dual-chamber pacemakers following AV node ablation should have devices with automatic mode-switching capabilities. All contemporary pacemakers have this ability. (See "Modes of cardiac pacing: Nomenclature and selection", section on 'Mode switching'.)

In patients with paroxysmal AF, two randomized trials demonstrated that dual-chamber pacemakers with mode-switching capabilities improve symptoms and quality of life compared with single- or dual-chamber pacemakers without mode-switching capabilities [2,3].

Many patients who undergo AV node ablation with pacemaker implantation for paroxysmal AF eventually progress to persistent AF [4]. Although dual-chamber pacing has not been shown to prevent this progression [5], we favor dual-chamber pacing in patients with paroxysmal AF because of the clinical benefits of physiologic pacing. (See "The role of pacemakers in the prevention of atrial fibrillation".)

A leadless RV pacemaker capable of sensing atrial mechanical systole and providing AV synchrony has been approved by the U S Food and Drug administration. At this point, leadless RV pacing is not able to pace the atrium, so it would not be an optimal choice in a patient with sinus node dysfunction and paroxysmal AF who is to undergo AV node ablation. (See "Permanent cardiac pacing: Overview of devices and indications", section on 'Leadless systems'.)

Cardiac resynchronization therapy — The majority of well-selected patients improve hemodynamically following AV junction ablation and standard right ventricle (RV) pacing. However, RV pacing causes the RV to contract before the LV (interventricular dyssynchrony), which may impair LV systolic function, reduce functional status, and increase mortality. In patients with significant dyssynchrony due to intrinsic conduction disease or pacing, cardiac resynchronization therapy (CRT) can improve ventricular synchrony. Use of CRT in patients with AF with or without AV node ablation is presented separately. (See "Cardiac resynchronization therapy in atrial fibrillation".)

There is a trend toward using CRT in many patients who undergo AV node ablation. If the implant and ablation are to be done concurrently, we use CRT with an atrial lead if the AF is paroxysmal and no atrial lead if persistent/permanent. In addition to providing CRT, two ventricular leads mitigate the unlikely but potentially disastrous effects of RV lead dislodgment and loss of RV capture. If transient pacing inhibition due to RV lead malfunction is noted, the sensing vector can sometimes be reprogrammed to an LV vector, which may mitigate the need for urgent lead revision. If, however, in the unlikely event that RV lead dislodgement or fracture results in continuous oversensing and inhibition of pacing, the additional LV pacing lead will not prevent asystole. If the patient has a preexisting non-CRT device and is undergoing AV node ablation, we will usually see how the patient responds to unopposed RV pacing, particularly if LV function is preserved. If LV function is significantly depressed and/or systolic heart failure has already been an issue, we may upgrade the patient to a CRT pacing or defibrillator system (as appropriate) at the time of AV node ablation. The main "downsides" to concurrent device upgrade are the associated procedural risks, most notably the risk of infection in a patient who will be pacemaker dependent. Adding a device upgrade procedure to an AV ablation increases procedure time considerably, so in patients who are very tenuous hemodynamically due to rapid ventricular rates and/or rate controlling, it may be reasonable to initially perform AV node ablation alone, and then upgrade the device if the patient does not improve.

The relative efficacy of CRT with AV node ablation for rate control and pulmonary vein isolation for rhythm control in patients with HF is discussed separately. (See "The management of atrial fibrillation in patients with heart failure", section on 'Atrioventricular node ablation with pacing' and "The management of atrial fibrillation in patients with heart failure", section on 'Catheter ablation'.)

Implantable cardioverter-defibrillators — All of the aforementioned pacing modalities (eg, single chamber, dual chamber, and CRT) and functions (eg, rate adaptive pacing and mode switching) are available on contemporary ICDs. Thus, patients with an ICD who require an AV node ablation procedure can sometimes be managed without changing the device. As most of these patients have significant LV dysfunction and systolic heart failure (given the indications for prophylactic ICD implantation), consideration should be given to upgrading to a CRT-D system with an atrial lead, if appropriate, at the time of AV node ablation. (See "Implantable cardioverter-defibrillators: Overview of indications, components, and functions".)

Physiological pacing — CRT (or biventricular pacing) is a strategy to avoid the dyssynchrony associated with standard RV apical pacing in patients who become pacemaker dependent after AV node ablation (see 'Cardiac resynchronization therapy' above). A potential alternative to CRT is the positioning of a pacing lead near the His bundle (image 1) or deep in the ventricular septum near the area of the left bundle branch.

A pacing lead near the His bundle will activate the native conduction system, resulting in less dyssynchrony and a more normal QRS complex. It is technically difficult to place a conventional pacing lead in a position that results in capture of the His bundle at a reasonable pacing output because the His bundle is insulated from the endocardium. Newer, small caliber, screw-in pacing leads that are delivered using a guiding sheath rather than a stylet may improve the ability to accomplish permanent His bundle capture [6].

The value of this approach was evaluated in a prospective single-center trial of 52 patients with heart failure and refractory AF who underwent attempted AV node ablation and permanent His bundle pacing; backup RV or LV leads were placed as well [7].

●During His bundle pacing, the average QRS duration was 105 msec, compared with 107 msec at baseline.

●The mean New York Heart Association functional class improved from baseline 2.9 in patients with heart failure with reduced ejection fraction to 1.4 with His bundle pacing, and from baseline 2.7 in patients with heart failure with preserved ejection fraction to 1.4.

●LV end-diastolic dimension, LV ejection fraction (LVEF), and mitral regurgitation all improved with His bundle pacing compared with baseline.

Successful His bundle pacing is technically difficult to accomplish. In addition, lead dislodgement may be more likely compared with conventional pacing sites. Pacing thresholds may also be higher with His bundle pacing, leading to shorter generator longevity. Lead dislodgement would have serious complications in this setting due to complete heart block after ablation of the AV node.

Another alternative to CRT is left bundle branch area pacing. Pacing the left bundle branch has been shown to avoid some of the limitations of His-bundle pacing such as high pacing thresholds and atrial oversensing, and has been used in patients undergoing AV node ablation. This is accomplished by placing an active fixation, sheath-delivered, pacing lead deep into the RV septum to capture the left bundle branch, giving rise to a relatively narrow QRS complex to minimize pacing-induced ventricular dyssynchrony. An image shows the position of the tip of a left bundle branch pacing lead in the RV septum during administration of contrast through the delivery sheath at the time of implant. (See "Permanent cardiac pacing: Overview of devices and indications".)

Further studies in larger populations are necessary to clarify both the clinical benefits and safety of these physiological pacing approaches in patients undergoing AV node ablation. In addition, given the risks of lead dislodgement, the safety and efficacy of His bundle pacing should be compared against biventricular pacing. At this point, a backup RV lead is generally placed when His bundle pacing is employed, particularly in pacemaker-dependent patients.

Ventricular rate regularization — Ventricular rate regularization (or ventricular rate stabilization) is a pacemaker mode that can attenuate the rate and irregularity of the ventricular response during AF [8]. The ventricle is paced at a variable rate at or near the mean native rate. This causes concealed retrograde conduction into the AV node, which makes it refractory to subsequent anterograde impulses from the atria. This tends to reduce the number of short RR intervals, which may improve symptoms by making the ventricular rate more regular during AF and sometimes slower. A potential advantage of this approach is that no catheter ablation of the AV junction is performed. However, this technique may be less effective at controlling AF during physical activity than at rest.

EFFICACY — AV node ablation is highly effective, as demonstrated by the following reports:

●AV node ablation was acutely successful in 97.4 percent of 646 patients, although 3.5 percent had recurrence of AV conduction during follow-up [9].

●In a report from the prospective Ablate and Pace trial, the procedure was successful in all but 1 of 156 patients who underwent radiofrequency ablation of the AV node [10]. Persistent complete heart block was present in 96 percent; 33 percent of patients had no escape rhythm, while 35 percent had an escape rhythm with an escape rate <40 beats per minute.

OUTCOMES — Symptoms and quality of life are significantly improved in patients with poorly controlled AF who undergo AV node ablation and permanent pacemaker implantation [11-15]. In a series of 107 such patients, ablative treatment was associated with significant reductions in [11]:

●Physician visits (5 versus 10 prior to ablation)

●Hospital admissions (0.17 versus 2.8 prior to ablation)

●Episodes of heart failure (8 versus 18 prior to ablation)

●Antiarrhythmic drug trials

Further support for the benefits of this approach come from a meta-analysis of 21 studies, involving 1181 patients [12]. This report noted significant improvement in all 19 outcome measures evaluated, including quality of life, ventricular function, exercise duration, and health care use [12]. While such benefits are often due to improved LV systolic function, improvement in some patients occurs independent of changes in LVEF and probably results from the slower and more regular heart rate [13,14].

To date, there is no convincing evidence of a mortality benefit with AV node ablation [12,15,16]:

AV node ablation has also been compared with other nonpharmacologic therapies. In the 2008 PABA-CHF study, in which 81 patients were randomly assigned to AV node ablation with cardiac resynchronization therapy pacing or pulmonary vein isolation, the composite primary endpoint (Minnesota Living with Heart Failure score, 6MW distance, EF) favored the pulmonary vein isolation group [17].

COMPLICATIONS — AV node ablation incurs risks similar to other catheter ablation procedures that require right heart access, though typically only a single venous sheath is required. If a pacemaker or ICD is implanted immediately prior to AV node ablation, the risks of device implantation are also incurred. If simple RV pacing is used, there will be a risk of developing LV dysfunction and/or heart failure. (See "Cardiac implantable electronic devices: Periprocedural complications".)

Specific to patients who undergo AV node ablation and pacing is a very rare but catastrophic risk of ventricular fibrillation (VF) and sudden cardiac death (SCD). In a review of 334 patients who underwent AV node ablation, nine (2.7 percent) experienced SCD [18]. Four events occurred within four days of the procedure, an additional three events occurred within three months, and two occurred late and were thought to be unrelated to the procedure.

Possible causes of post-ablation VF include [18-20]:

●Underlying heart disease

●Activation of the sympathetic nervous system

●Prolongation in action potential duration

●Repolarization abnormalities induced by bradycardia

●Increased dispersion of ventricular refractoriness

The potential for reducing the frequency of early VF with post-ablation pacing at a higher rate was evaluated in a report of 235 patients [21]. The incidence of VF was 6 percent in the first 100 patients in whom the post-ablation chronic pacing rate was ≤70 beats per minute. In the next 135 patients, however, a pacing rate of 90 beats per minute was used for the first three months after the ablation, and there were no episodes of VF.

Pacing at a rate of 90 beats per minute decreases sympathetic activity, which may contribute to the reduction in VF or SCD [19].

Other procedural risks are those related to catheter ablation and pacemaker/ICD implant/upgrade procedures. (See "Overview of catheter ablation of cardiac arrhythmias", section on 'Complications'.)

NEED FOR ANTICOAGULATION — While AV node ablation results in adequate heart rate control, it does not stop the atria from fibrillating. Thus, the risk of thromboembolic events is not affected [22]. As a result, there is a need for long-term anticoagulation similar to that in patients with chronic AF whose heart rate control is achieved pharmacologically. (See "Atrial fibrillation in adults: Use of oral anticoagulants".)

RECOMMENDATIONS OF OTHERS — Our recommendations for patients with AF in whom a rate control strategy has been chosen are in general agreement with those made in major societal guidelines [23-25].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Atrial fibrillation" and "Society guideline links: Arrhythmias in adults".)

SUMMARY AND RECOMMENDATIONS

●Background – Atrioventricular (AV) node ablation is an option for rate control in atrial fibrillation (AF) patients who have failed medical therapy for rhythm control, have failed or are not candidates for catheter ablation for rhythm control, and have failed aggressive attempts at pharmacological rate control.

●Indications – For AF patients with a rapid ventricular response who do not respond to or are intolerant of aggressive attempts at pharmacologic therapy to slow the ventricular rate, and in whom nonpharmacologic approaches, including curative attempts at AF ablation, are not successful or appropriate, we recommend AV node ablation in association with implantation of a permanent pacing device to improve symptoms and quality of life (Grade 1B). (See 'Indications' above.)

●Pacing procedure – For AF patients who undergo AV node ablation, a pacing device is needed to prevent symptomatic bradycardia. A single-chamber ventricular pacemaker with rate-adaptive capability may be appropriate for patients with persistent AF, and a dual-chamber pacemaker with both mode switching and rate-adaptive capabilities may be appropriate for patients with paroxysmal AF. The roles of cardiac resynchronization therapy, physiological pacing, and implantable cardioverter-defibrillator depend on left ventricular function, heart failure symptoms, and history. (See 'Device selection' above.)

●Need for anticoagulation – AV node ablation has no impact on thromboembolic risk; however, most individuals with chronic AF require long-term oral anticoagulation. (See 'Need for anticoagulation' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Leonard Ganz, MD, FHRS, FACC, who contributed to an earlier version of this topic review.