Abstract
- 1.
The presence of a prosthetic tricuspid valve is a relative but not absolute contraindication to endocardial pacing.
- 2.
Epicardial pacing is a good option but does involve more surgery.
- 3.
Innovative endocardial approaches, such as the leadless pacemaker, can be considered depending on the indication to pace.
- 4.
Hybrid procedures (part endocardial and part epicardial) and newer leads (lumenless leads) can be used in some patients.
Keywords
Atrioventricular block, Coronary sinus, Ebstein’s anomaly, Hybrid procedure, Pacemaker, Tricuspid valve
Case Report
A 61-year-old man with a history of Ebstein anomaly underwent valve repair with concomitant intraoperative ablation of an accessory pathway and right atrial maze procedure in 1997 at age 41.
This was followed by tricuspid valve replacement in 2001 with a 35-mm Carpentier-Edwards bioprosthesis.
Owing to recurrent symptomatic paroxysmal atrial fibrillation, he then underwent a successful pulmonary vein isolation (PVI) procedure in 2004. The electrophysiologic study performed at that time revealed severe sinus node dysfunction with intact atrioventricular (AV) conduction; however, he was asymptomatic. It was also noted that the tricuspid valve prosthesis was implanted proximal to the coronary sinus.
The patient now presents with frequent severe near-syncopal episodes with evidence of sinoatrial exit block and episodes of high-grade AV block on ambulatory monitoring ( Fig. 5.1 ). Given the symptomatic conduction system disease, permanent pacemaker implantation was recommended.
The patient is an overweight gentleman with a body mass index of 27. He has no hypertension and his resting heart rate is 52 beats per minute. On examination, he has normal carotid and jugular venous findings. The cardiac examination reveals a moderate right ventricular (RV) heave with a regular heart rate and no murmurs.
His electrocardiogram (ECG) reveals a sinus bradycardia with ventricular rate of 45 beats per minute and a right bundle branch block with a QRS duration of 156 ms, with a PR interval of 136 ms ( Fig. 5.1 ). The chest radiograph is in shown in Fig. 5.2 . The transthoracic echo identifies normal left ventricular (LV) size and function with no regional wall abnormalities. The RV is moderately enlarged with moderate systolic dysfunction; the mean gradient across the tricuspid valve prosthesis was 3 mmHg at a heart rate of 42 beats per minute with trace tricuspid regurgitation.
Although permanent pacemaker implantation has been recommended, the type of pacemaker/pacing system has not been decided upon. For many patients with multiple prior sternotomies and a bioprosthetic tricuspid valve, it has been a preference to avoid placing a pacemaker lead through the bioprosthetic leaflets so as to preserve valve function.
Questions
- 1.
Should he have implantation of a transvenous or an epicardial pacemaker?
- 2.
Could this be intra-atrial block that masquerades as a block at the AV nodal level?
Consultant Opinion #1
- Narayanswami Sreeram, MD
- Daniel Steven, MD
The patient presents with symptomatic bradyarrhythmia. The ECG and Holter traces confirm episodes of sinoatrial exit block and high-grade AV block. In association with the frequent episodes of near syncope, the indication for implantation of a permanent pacemaker seems given.
Progressive conduction system disease is part of the disease process in a variety of structural heart lesions, including Ebstein anomaly, and may be inherent to the disease or acquired as a result of multiple surgical procedures. Our patient has undergone previous surgery for tricuspid valve regurgitation and a surgical right atrial maze procedure. The commonest indications for permanent pacing in adults with structural heart disease are sinus node dysfunction and AV block acquired outside the acute surgical setting. Our patient appears to have developed both these pathologic conditions. It is possible that the intra-atrial block, resulting in part from the previous right atrial maze procedure, may be masquerading as an episodic AV block as seen on the Holter recording. This, however, should not influence the choice of permanent pacemaker but necessitates implantation of a ventricular lead.
The choice of optimal technique and the route for permanent pacing in this patient are complicated by three factors: Ebstein anomaly with a history of surgery and evidence of persistent RV dysfunction, a bioprosthetic tricuspid valve, and its implanted location upstream from the coronary sinus. Patients with operated structural heart disease and residual hemodynamic sequelae benefit from retaining AV synchrony, necessitating the consideration of a dual chamber pacing system in this patient. In general, it is preferable not to have a permanent pacing lead passing through the prosthetic valve in order to prevent the development of unacceptable tricuspid valve insufficiency (which was likely the primary indication for bioprosthetic tricuspid valve implantation in this patient). This is particularly important in the setting of Ebstein anomaly, where RV function is likely to remain compromised, regardless of previous surgical repair. A possible option in the setting of replacement of the tricuspid valve in a patient with a preexisting endocardial ventricular pacing lead would have been to allow the lead to be placed exterior to the sewing ring of the valve, but this was not a consideration here, as the patient did not have symptomatic bradyarrhythmia or a preexisting endocardial pacing lead at the time of valve surgery.
In the recent years, there has been considerable controversy regarding the optimal ventricular pacing site. Several large studies in adults and children have established that chronic RV pacing is associated with LV dyssynchrony, dysfunction, and structural alterations in the LV that may be progressive. Although this is probably of particular importance to children, who will require lifelong pacing over several decades, several studies have established that a relevant proportion of patients with Ebstein anomaly have preexisting structural and functional abnormalities affecting the LV. Structural alterations include LV noncompaction, mitral valve prolapse, and LV fibrosis. Both systolic and diastolic dysfunction of the LV have been reported in Ebstein anomaly, and some of these functional alterations persist and may progress despite surgical procedures in the right side of the heart. The ideal pacing technique would therefore be dual chamber pacing with a right atrial and a LV lead. In this patient, access to the coronary sinus, and therefore the possibility of transvenous LV pacing, is precluded by the location of the tricuspid valve bioprosthesis. Permanent pacing would therefore have to be accomplished by the use of an epicardial LV lead, accepting the fact that epicardial systems are less durable and have a shorter lifespan than transvenous systems. The choice of location for the atrial lead also needs to be carefully considered. Owing to the previous surgical procedures (right atrial maze and tricuspid valve replacement), there is a considerable risk that poor atrial thresholds may be obtained from epicardial atrial sites caused by scar tissue from prior surgery. It may be necessary therefore to implant an endocardial atrial lead in combination with the epicardial LV pacing lead.
Permanent pacing in adults with structural heart disease also presents unique problems, both procedure related and at follow-up. Surgical access is likely to be more complicated, and the incidence of acute complications such as bleeding, pocket infection, and pneumothorax is higher. Failed or difficult lead placement is common in this setting, with increasing difficulty being associated with a higher number of prior surgical procedures. Such procedural difficulties and failures occur more frequently in Ebstein anomaly than in other structural lesions. Late complications such as early battery depletion, pacemaker migration, and erosion are also more frequently observed in the setting of permanent epicardial pacing in this patient population.
Lead failures, defined as a failure to reliably capture or sense the ventricle or atrium, and lead dislodgement or fracture are commonly encountered with epicardial ventricular leads. The presence of Ebstein anomaly has been noted to be an independent risk factor for lead failure in one study, regardless of epicardial or endocardial location and whether the lead was implanted in the RV or LV. It has been suggested that this may be a unique feature of this anomaly and may be the result of an inherent tendency to fibrosis around the lead tip at the site of implantation.
In summary, the rather unique postsurgical anatomy of this patient necessitates the choice of a suboptimal dual chamber pacing system, with an anticipated higher rate of acute and follow-up complications. A final consideration would be the transvenous implantation of a leadless single chamber pacemaker. There are few reports on the use of such a system in adults with complex structural heart disease and little follow-up data on their performance in this patient population. There is a small risk of cardiac perforation, and this may be relevant in the setting of Ebstein anomaly and a thinned-out RV. Considering that the patient is still relatively young and fit, this would not be the procedure of choice but may be considered in the future.
Consultant Opinion #2
- Henry Chubb, MBBS, PhD
- Eric Rosenthal, MD FRCP
Introduction
In general, the need for device implantation or renewal in patients with adult congenital heart disease (ACHD) should not be considered as a “stand-alone device procedure.” It should prompt a multidisciplinary meeting with ACHD surgeons, cardiologists, and electrophysiologists to consider the impact of the device in the specific anatomy and in respect of potential concomitant or future catheter interventions or cardiac surgery. Although updating the imaging is always important, some pacemaker systems will render the patient ineligible for magnetic resonance imaging (MRI) scanning in the future and so the opportunity to perform a cardiac MRI should be considered before device implantation. Currently, epicardial leads and most coronary sinus (LV) leads are not MRI compatible.
This patient has had a good result from his bioprosthesis and antitachycardia surgery. He now presents with evidence of both sinoatrial disease and atrioventricular disease manifesting in near syncope. He has had a previous sternotomy for a valve repair, and the type of pacing system needs to be considered. It would appear that no other procedures are considered to be imminent, and the choice of system is predominantly affected first by the presence of a bioprosthetic tricuspid valve that is functioning well and second by previous sternotomy.
Permanent Pacing Implantation Methods
Although a single chamber ventricular pacemaker may be enough to prevent syncopal pauses, a dual chamber system will enable reliable atrioventricular synchrony and be more effective if his sinoatrial disease progresses as it is likely to do. There is the small possibility that a single lead atrial system would suffice (see response to question 2) but this is unlikely. The main concern is regarding the placement of the ventricular lead, which include several options.
Transvenous Ventricular Pacing
Coronary sinus pacing
The coronary sinus would be the first choice in patients with a prosthetic tricuspid valve so as to avoid any valve leaflet dysfunction and not interfere with subsequent surgical or percutaneous replacement. An additional benefit would be reduction in LV dysfunction in patients who needed continuous ventricular pacing; this is not the case for our patient but the pacing burden may increase with time.
For this patient, it has been documented that the coronary sinus is not available, but this option should nonetheless be explored before dismissal—referral to the PVI procedural note from 2004 is not sufficient, as access may have been attempted only with larger or nonsteerable catheters. The original operation note should be consulted, and further imaging (e.g., computed tomography [CT]) should be considered in the event of any doubt. In addition, a left-sided superior vena cava to coronary sinus has been described in patients with Ebstein anomaly, and this should also be excluded because its presence would allow ventricular pacing without crossing the tricuspid valve prosthesis. Angiography in the coronary sinus may identify coronary veins draining directly to the right atrium. Manipulating a guide wire through the coronary sinus and into the right atrium would allow the wire to be snared in the right atrium and exteriorized to place a coronary sinus lead over the guide wire circuit (with or without coronary venoplasty) into the coronary venous system, which would allow ventricular pacing without crossing the tricuspid valve. Such connections are unlikely to be seen with CT scanning.
Transvalvular pacing
The placement of a pacing lead across a valve prosthesis is not ideal, but in some cases, it is unavoidable. The long-term impact of the presence of pacing lead upon valve function has not been well described but can only be detrimental. McCarthy and colleagues identified the presence of pacing to increase the incidence of severe tricuspid prosthesis regurgitation from 23% to 42% of subjects at 5 years, but the type, positioning, and timing of the ventricular pacing leads were not detailed. Cooper and colleagues described in more detail the placement of a pacing lead across a tricuspid valve prosthesis (two mechanical and two bioprosthetic), and this was well tolerated by patients with bioprosthetic valves, albeit with short follow-up. If transvalvular pacing is necessary, the use of a SelectSecure 4F lead (Medtronic) across the bioprosthesis is likely to minimize any valve dysfunction and allows for easier extraction.
Future considerations would include the eventuality that further valve replacement may be required. Intraoperative removal of the transvenous lead should be achievable, and permanent epicardial leads should be placed if a good epicardial site is identified. If not, temporary epicardial pacing would be required, with later placement of a new transvenous system (ideally via coronary sinus at that stage). If a percutaneous valve-in-valve is possible, then the SelectSecure lead will need extracting so as not to be trapped between the two valves followed by placement of a new system at the same sitting, or later if the patient is not pacemaker dependent at that time.
If the decision is made to place a transvalvular lead, the lead should be targeted to the true septum or His bundle below the bioprosthesis or RV apex in order to minimize any LV dysfunction. The RV is not dysfunctional, so dual site ventricular pacing or free wall RV pacing is not required to resynchronize the RV.
His bundle pacing
Pacing of the compact AV node or the bundle of His in the right atrium has been well described, screwing the lead into the membranous septum. This would avoid both crossing the bioprosthesis and ventricular dyssynchrony. There have been no published reports on the use of His bundle pacing in patients with tricuspid valve bioprosthesis, but the theory is attractive if a suitable location could be found. Prior or simultaneous electroanatomic mapping may be useful in searching for appropriate sites in the immediate vicinity of the valve.
Leadless Pacemaker
The long-term data regarding leadless pacemakers is limited but could provide a relative simple pacing solution. Two leadless pacemakers are currently available: the Nanostim LP (St. Jude Medical) and the Micra transcatheter pacing system (Medtronic). The Nanostim is 42 mm in length with maximum diameter 6 mm and delivered via 18F sheath, whereas the Micra is 26 mm in length with maximum diameter 6.7 mm and delivered via a 23F internal diameter (27F external diameter) steerable catheter. Both these pacemakers are currently limited to single chamber functionality only (VVIR), and the main concerns regard those of cardiac perforation and vascular access. In a patient with Ebstein anomaly, and potentially thin RV wall, careful evaluation before implantation is required and CT may represent the best imaging modality for delineation of wall thickness. Positioning in the apical septum is likely to be required for a Nanostim device; however, there may be difficulty in finding sufficient trabeculation within the RV to anchor the passive tines of the Micra.
In the longer term, the battery lifespan of the leadless pacing device remains to be determined, but has been estimated at 10–15 years. For this patient, it would be anticipated that the pacing burden could be kept low unless there is further deterioration in the conduction system and this would also minimize the impact of the anticipated pacing dyssynchrony. However, the device should be implanted with the expectation that it will not be retrievable following endothelialization.
Epicardial Ventricular Pacing
While possible with all anatomies, previous surgical scarring may make it difficult to find a suitable site that gives low thresholds and does not cause ventricular dyssynchrony. Extensive scarring is likely to preclude the use of minimally invasive surgical techniques. Historic concerns regarding lead longevity and high thresholds have been largely overcome with the use of bipolar steroid-eluting leads. However repeated sternotomies render epicardial placement of pacing leads less attractive, and, in general, this approach would be reserved for obligatory sternotomy for additional intracardiac procedures. Multidisciplinary discussion among the surgeon, implanting physician, and imaging teams would be important to delineate the relative risk of epicardial versus endocardial approaches for the placement of the ventricular lead.
Intra-Atrial Block Versus Atrioventricular Nodal Level Block
Could he have only sinus node disease with intra-atrial delayed or blocked conduction due to the right atrial maze? Would a site in the right atrium allow atrial pacing that conducts normally to the AV node?
The P-wave morphology on the 12-lead ECG is within normal limits for sinus nodal origin (positive in II, III, and aVF; positive then negative in V1 ) and, furthermore, is not prolonged. Significant lengthening of the P wave would be anticipated in the case of severe intra-atrial block at rest. The ambulatory monitoring ( Fig. 5.3 , 4 p.m.) demonstrates P waves marching through with a similar morphology and rate to baseline; it is unlikely that atrial conduction disease will have developed to an extent sufficient to cause intermittent intra-atrial block in the absence of P-wave morphology alteration.
