Corresponding author:
Jeffrey J. Goldberger, M.D.
University of Miami Miller School of Medicine
Cardiovascular Division
1120 NW 14th St.
Miami, FL 33136
Telephone: (305) 243-8092
Fax: (305) 243-1731
E-mail:
j-goldberger@miami.edu
Aortic stenosis (AS) is the most common valve disease worldwide, with
degenerative (calcific) AS being the most common etiology in western
countries. Patients experience a high morbidity and mortality without
intervention to correct the mechanical obstruction to cardiac
output1. Since 1960, when Dwight Harken performed the
first in-situ aortic valve replacement with a ball-in-cage mechanical
valve, cardiothoracic surgeons have been dramatically improving
patients’ lives2. The implications of how we treat
this condition will become amplified by an aging US population and an
increased incidence of AS with age. 3 At its
inception, surgical aortic valve replacement was recognized to have
trade-offs including injury to the native atrioventricular(AV)
conduction system4. The AV conduction system of the
heart resides in such close anatomic proximity to the aortic valve that
injury is often encountered. As surgical techniques improved, the rate
of significant post-operative heart block that requires permanent
pacemaker implantation (PPMI) decreased and now hovers between
3.3-6.9%. 5-7
In the last two decades, patients deemed poor surgical candidates were
offered an opportunity of similar improvements in mortality and quality
of life when trans-catheter techniques for valve replacement were
developed. The low morbidity and mortality associated with these
techniques have driven the medical community to consider these therapies
for moderate and even low risk surgical cases.7 As the
number of patients who receive this life-saving therapy increases, so
too will its most common complication occur.
Between 10-25% of patients that receive transcatheter aortic valve
replacement (TAVR) undergo PPMI. Understanding the pre-operative and
intra-operative case characteristics that are associated with PPMI is so
popular that Wang et al. was able to pool a total of 97,294 patients in
67 retrospective and prospective studies that examine this subject. In
this meta-analysis they concluded that pre-existing cardiac conduction
abnormality and trans-femoral pathway selection were significantly
associated with PPMI. Pre-existing left bundle branch block,
patient-prosthesis mismatch, and implantation depth were not.8
While the information provided in this meta-analysis is valuable, the
main question confronting the clinician managing a patient following
TAVR is whether the patient needs to have a PPMI. In the patient with
persistent complete or high-grade AV block, the clinical decision is
easy. Similarly, in those without pre-existing conduction system disease
and in those with no change in their pre-existing conduction system
disease post-TAVR, there is consensus that pacing is not required. The
challenge and management disparity lie among those with transient severe
conduction abnormalities and those with significant changes in native
conduction, including significant PR interval prolongation and those
with new left bundle branch block. Anatomically, there may be
considerable variation in the location of the AV conduction system and
left bundle in the proximity to the aortic valve9.
Unfortunately, this major anatomic determinant of the risk of AV block
cannot be assessed or imaged prior to the procedure. The surface ECG
provides important clues. While striking changes in the QRS complex, ie
the development of left bundle branch block, are routinely recognized
and addressed, subtler changes in the PR interval may be overlooked. The
PR interval has 3 components – intratrial conduction time from the
sinus node to the AV node, AV nodal conduction time, and His-Purkinje
system conduction time. A 50 ms increase in the PR interval from 140 to
190 ms, for example, might still be considered normal when reviewed in
isolation, but a 50 ms increase in His-Purkinje system conduction time
could be a harbinger of risk for complete AV block. Interestingly, the
meta-analysis reported an enhanced risk for PPMI in patients with first
degree AV block but not those with second degree AV block. A physiologic
explanation is that in patients with first degree AV block much of this
delay may be in the His-Purkinje system, while in those with second
degree AV block (if it is Wenckebach) this is a manifestation of AV
nodal delay and not considered pathologic. It is therefore critical to
evaluate serial changes in conduction post-TAVR and follow expert panel
guidance on management10. Electrophysiologic testing
is sometimes necessary to assess the integrity of the conduction system
and to decide whether a pacemaker is required (see
figure)11. Continued assessment is sometimes
necessary, as there is a possibility that late sudden cardiac deaths may
be due to heart block. It is clear that the post-procedure course and
findings are the critical factors that will determine the need for PPMI
for the individual patient.
Other important issues arise regarding PPMI post-TAVR. First, once a
PPMI is indicated, what kind of cardiac implanted electronic device
(CIED) is appropriate? PPMI implantation is associated with elevated
re-hospitalization and mortality risk. 12 The cause of
this observation is unclear, but one could postulate that device related
complications including infection could play a role13. In general, 2% of patients implanted with CIED
develop a device related infection at 5 years14.
Intravascular infection associated with a valve prosthesis carries with
it a high mortality. Patients with prosthetic valve endocarditis
experience a mean hospital stay of 28-33 days and an in-hospital
mortality of 22-27%.15 Without pre-existing
ventricular dysfunction and sinus node dysfunction, a VDI leadless
pacemaker may be sufficient to maintain AV synchrony and reduce risk of
CIED related infection. For those with second degree AV block or high
degree AV block post TAVR, RV pacing requirements may be low and
decrease over time. Thus, a VVI leadless pacemaker may also be
sufficient.
Conversely, reduction in infection risk by implanting a leadless
pacemaker may be offset by the potentially deleterious effects of right
ventricular pacing on ventricular systolic function.16Similarly, left bundle branch block may also be associated with
development of left ventricular systolic dysfunction. Initially, the
development of left bundle branch block was not considered to affect
morbidity and mortality post TAVR. However, recent data suggest that
mortality is worse with new-onset LBBB post TAVR.17The impacts of cardiac dyssynchrony, via right ventricular pacing or
LBBB, on long-term post-TAVR outcomes is unclear. Also unclear, is
whether or not early physiologic pacing would benefit this group of
patients. In the setting of LBBB and preserved left ventricular ejection
fraction, cardiac resynchronization therapy (CRT) has not been shown to
have meaningful improvement in outcomes.18 The timing
of CRT implantation for those with LBBB and systolic dysfunction
post-TAVR also requires further investigation, since the effects of
cardiac dyssynchrony are likely to be higher in this group.
On the horizon, leadless absorbable temporary pacing is an emerging
technology that could change the way we approach risk stratification of
post-TAVR patients to further limit morbidity associated with
pacing.19 Most cardiac conduction abnormalities
improve or present within 48 hours, but some patients resolve their
cardiac conduction or present with high degree AV block beyond this
period20,21. For patients requiring percutaneous
trans-venous temporary pacing in the perioperative period, observation
in the ICU with temporary pacing in a geriatric population comes with
its own hazard, namely, hospital-associated functional
decline.22 Pre-operative frailty in this patient
populace also influences this outcome. Even a pectoral wound and the
shoulder restrictions required to prevent lead dislodgment can conflict
with the moderate assistance measures to allow mobility. Leadless
absorbable temporary pacing could allow a longer observation period to
decide whether PPMI is necessary enabling early hospital discharge and
early mobilization.
In conclusion, while pre-procedure risk factors for PPMI following TAVR
as outlined in this meta-analysis are important for determining
procedural approaches, including choice of valve, and the risk for PPMI,
many questions about the rhythm management of these patients remain
unanswered and will require continual re-evaluation as TAVR technology
continues to evolve.