With an increase in the aging population in the United States, the prevalence of degenerative valvular diseases such as aortic stenosis has continued to rise. Some studies estimate an incidence of 3.4% of aortic stenosis in Western nations.¹ Historically, the assessment of an individual with severe aortic stenosis necessitating treatment involved an evaluation of the individual's risk-benefit analysis, combining the STS risk estimate, frailty score, presence of major organ system compromise, severity of disease, and procedure-specific impediments. These factors have been used to weigh the benefits and risks of surgical versus medical treatment, with surgical aortic valve replacement (SAVR) being the mainstay of treatment for those patients with severe aortic stenosis and low to moderate risk for surgery. There were few options for treatment in patients who were not ideal surgical candidates. However, in recent years an evolving non-invasive approach known as transcatheter aortic valve replacement (TAVR) has advanced to the forefront of treatment, starting with patients deemed too high risk for surgery. With promising results from trials like the Placement of AoRTic TraNscathetER (PARTNER) trial, the minimally invasive approach of TAVR is now accepted as standard of care for candidates in high risk and intermediate surgical risk subgroups in treatment of severe aortic stenosis.^2,3 Our experience with conduction abnormalities in surgery has prepared us for the same following TAVR,⁴ but the incidence of complete heart block and pacemaker implantation has been higher than expected, with rates of implantation up to 25% being reported.⁵ With recent reports suggesting permanent pacemaker implantation not only increases length of ICU and hospital stay post procedure, but also can increase overall mortality and exacerbation of heart failure, the role of pacemaker placement in TAVR is being more closely examined.⁶ The question about the role of pacemaker placement, the timing of placement, and prognosis of patients who require pacing remains a controversial matter at this time.

The relationship between conduction disease and calcific aortic valve disease was first described by Yater and Cornell in 1935.⁷ Following, a study in 1979 detailing left ventricular outflow tract (LVOT) calcification in these patients noted a high correlation between septal calcification and conduction abnormalities.⁸ While the incidence of pacemaker implantation was not included in that study, evidence of new left and right bundle block progressing to complete heart block was noted as being related to LVOT calcification in these patients. The issue at stake is the anatomy of the aortic valve and outflow tract complex and its proximity to the conduction system.⁹ Kawashima et al. described this further,¹⁰ reporting that the atrioventricular bundle and left bundle branch are located more anteriorly, distally, and cranially to the aortic valve complex than previously thought, resulting in increased frequency of conduction system injury post TAVR when compared to SAVR.

With this in mind, when considering heart block in the TAVR patient, the practitioner is left with the following questions:

1. What are the conduction abnormalities that absolutely require the placement of a device?
2. Are there technical procedural steps that can be undertaken to decrease the risk of complete heart block post TAVR?
3. When is it reasonable to place a pacing device? When is the injury to the conduction system considered irreversible?
4. What effect does placement of a device have on prognosis post-TAVR, and mortality or cardiac morbidity?

In considering these questions, what do we know? Landmark studies agree that complete heart block noted in the periprocedural period is an indication for permanent pacemaker (PPM) implantation,^11,12 with most studies recommending an at least 24hr, and up to 48hr, wait prior to device implant to determine reversibility. Patient factors that have been deemed high risk have included patients with pre-existing 1° AV block, right bundle branch block (RBBB), and left hemi-block. Depth of prosthesis placement has been considered significant in some cases, as well as the type of valve used.¹³ The latter may change on further analysis, with new iterations of the Edwards Sapien valve more closely mimicking the cardiac footprint of the Medtronic Corevalve. Whether these factors are additive or strongly suggestive of PPM implant on their own is unclear. Addressing the patient with complete heart block noted during valve deployment but no evidence of conduction disease prior to the procedure and complete reversal of valve block is still somewhat controversial, as is evaluating new instances of 1° AV block or left bundle branch block (LBBB) related to TAVR procedure. The timing of pacemaker implant (if indicated initially) is also unclear at this time. Moreover, the fate of the patient with markers of severe conduction disease prior to TAVR and transient complete heart block (CHB) during the procedure who has recovered post procedure is equally confusing. Is that patient still indicated for a pacemaker placement? Present ACC/HRS guidelines encourage that these decisions be left to the discretion of the physician.¹⁴ The European Society of Cardiology (ESC) has come out with a stronger recommendation, that permanent pacemaker implants be considered only in cases with complete or high-grade AV block (Class I recommendation),¹⁵ but even in that instance, timing or duration of block is not addressed.

With regard to new LBBB, recent studies have revealed an association between new LBBB and increased mortality and heart failure hospitalization.^16,17 These echo findings seen in SAVR, where worsened outcomes were seen with patients with new LBBB, but mostly in the context of a left axis deviation or decreased pre-procedure left ventricular function.¹⁸ There have been reports of increased incidence of complete heart block in patients with new persistent LBBB following TAVR, but this has not been a consistent result on review of the literature.

In our opinion, the first step in solving this dilemma is proper patient selection for evaluation. Patients with pre-existing conduction abnormalities (mostly PR prolongation > 200ms, RBBB, presence of bifascicular block, and LBBB to a lesser extent) continue to be at risk for further AV node injury following TAVR. Also, the choice of valve (Medtronic CoreValve more so than the Edwards valve), depth of valve placement and use of the transfemoral (as opposed to the transapical or transaortic) approach for valve placement can be considered when placing a valve in a patient with preexisting conduction disease as placing that patient at higher risk for CHB post TAVR. CHB occurring during the procedure (mostly during deployment of the valve) suggests an increased risk of AV block to follow, especially when considered in patients with pre-existing conduction abnormalities, and we would suggest either placement of a pacemaker in a patient with these abnormalities, and prior syncope (regardless of reversibility of the insult). On the other hand, placement of an ambulatory monitor or implantable loop recorder implant might be indicated in a high risk patient if CHB noted in the procedure is transient and AV conduction has recovered prior to leaving the cath lab.

Special care should be undertaken in patients with prior evidence of LV systolic dysfunction. Correction of LV function post valve placement is unlikely, and further conduction abnormality as a result of TAVR might put the patient at increased mortality and morbidity risk. New LBBB in these patients should be addressed promptly with placement of a biventricular device. Since reports have been made that up to 30% of these patients report recovery of the conduction in the first 30 days post procedure, the decision on placement of a device can be made at that time.¹⁷

In order to improve ambulation post procedure, as well as decrease risk for thromboembolism and decrease length of stay in our institution, we have recommended implantation of a temporary permanent pacemaker through the right internal jugular vein (a screw-in lead with an externalized pacemaker generator) when indicated instead of leaving a temporary transvenous pacemaker in place. This has the added benefit of quantifying pacemaker pacing dependence post implant more accurately, a factor to be considered when deciding on PPM implantation post TAVR. Pacemakers are usually programmed to VVI 50ppm to better detect native conduction system recovery, and decrease unnecessary pacing post procedure. More information on infrahisian disease in patients with significant LBBB (especially when in combination with new 1° AV block) can be determined by an EP study to help identify patients who are at increased risk for sudden AV conduction failure post TAVR.

A review of the literature leaves more questions than answers. Timing of pacemaker placement is definitely an issue that needs to be addressed, with identification of the patient with new conduction abnormalities post TAVR that requires device placement a close second. A study being undertaken at the Centre de Recherche de l'Institut Universitaire de Cardiologie et de Pneumologie de Quebec, evaluating time and rate of incidence of CHB or high-degree heart block 1 year following TAVR (the MARE study) with results expected in 2018,¹⁹ might shed some light on the questions posed. As we wait, the results of recent publications can be used to guide management until such a time when formal guidelines can be established in this area.

References

1. Osnabrugge RL, Mylotte D, Head SJ, et al. Aortic stenosis in the elderly: disease prevalence and number of candidates for transcatheter aortic valve replacement: a meta-analysis and modeling study. J Am Coll Cardiol 2013;62:1002-12.
2. Svensson LG, Tuzcu M, Kapadia S, et al. A comprehensive review of the PARTNER trial. J Thorac Cardiovasc Surg 2013;145:S11-6.
3. Leon MB, Smith CR, Mack MJ, et al. Transcatheter or surgical aortic-valve replacement in intermediate-risk patients. N Engl J Med 2016;374:1609-20.
4. Kim MH, Deeb GM, Eagle KA, et al. Complete atrioventricular block after valvular heart surgery and the timing of pacemaker implantation. Am J Cardiol 2001;87:649-51.
5. Maan A, Refaat MM, Heist EK, et al. Incidence and predictors of pacemaker implantation in patients undergoing transcatheter aortic valve replacement. Pacing Clin Electrophysiol 2015;38:878-86.
6. Fadahunsi OO, Olowoyeye A, Ukaigwe A, et al. Incidence, predictors, and outcomes of permanent pacemaker implantation following transcatheter aortic valve replacement: analysis from the U.S. Society of Thoracic Surgeons/American College of Cardiology TVT Registry. JACC Cardiovasc Interv 2016;9:2189-99.
7. Yater WM, Cornell VH. Heart block due to calcareous lesions of the bundle of His: review and report of a case with detailed histopathologic study. Ann Intern Med 1935;8:777-89.
8. Thompson R, Mitchell A, Ahmed M, Towers M, Yacoub M. Conduction defects in aortic valve disease. Am Heart J 1979;98:3-10.
9. Piazza N, de Jaegere P, Schultz C, Becker AE, Serruys PW, Anderson RH. Anatomy of the aortic valvar complex and its implications for transcatheter implantation of the aortic valve. Circ Cardiovasc Interv 2008;1:74-81.
10. Kawashima T, Sato F. Visualizing anatomical evidences on atrioventricular conduction system for TAVI. Int J Cardiol 2014;74:1-6.
11. Hoffmann R, Herpertz R, Lotfipour S, et al. Impact of a new conduction defect after transcatheter aortic valve implantation on left ventricular function. JACC Cardiovasc Interv 2012;5:1257-63.
12. Nazif TM, Dizon JM, Hahn RT, et al. Predictors and clinical outcomes of permanent pacemaker implantation after transcatheter aortic valve replacement: the PARTNER (Placement of AoRtic TraNscathetER Valves) trial and registry. JACC Cardiovasc Interv 2015;8:60-9.
13. Siontis GC, Juni P, Pilgrim T, et al. Predictors of permanent pacemaker implantation in patients with severe aortic stenosis undergoing TAVR: a meta-analysis. J Am Coll Cardio 2014;64:129-40.
14. Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices) developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. J Am Coll Cardiol 2008;51:e1-62.
15. Brignole M, Auricchio A, Baron-Esquivias G, et al. 2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the Task Force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA). Eur Heart J 2013;34:2281-329.
16. Houthuizen P, Van Garsse LA, Poels TT, et al. Left bundle-branch block induced by transcatheter aortic valve implantation increases risk of death. Circulation 2012;126:720-8.
17. Urena M, Webb JG, Cheema A, et al. Impact of new-onset persistent left bundle branch block on late clinical outcomes in patients undergoing transcatheter aortic valve implantation with balloon-expandable valve. JACC Cardiovasc Interv 2014;7:128-36.
18. El-Khally Z, Thibault B, Staniloae C, et al. Prognostic significance of newly acquired bundle branch block after aortic valve replacement. Am J Cardiol 2004;94:1008-11.
19. https://clinicaltrials.gov/ct2/show/NCT02153307

Keywords: Aortic Valve, Aortic Valve Stenosis, Arrhythmias, Cardiac, Atrioventricular Block, Atrioventricular Node, Heart Conduction System, Heart Defects, Congenital, Heart Failure, Heart Valve Diseases, Jugular Veins, Risk Assessment, Syncope, Thromboembolism, Transcatheter Aortic Valve Replacement, Ventricular Function, Left

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