Advertisement
Advertisement
July/August 2010
Balloon Aortic Valvuloplasty in the TAVI Era
A review of current technique and uses in stand-alone, bridging, and predilation settings.
By Wes R. Pedersen, MD, FACC, FSCAI; Irvin F. Goldenberg, MD, FACC, FSCAI; and Ted E. Feldman, MD, FESC, FACC, FSCAI
Balloon aortic valvuloplasty (BAV) as a treatment for severe aortic stenosis (AS), a common disease of the elderly, was introduced by Dr. Cribier in 1985.1 The initial experience demonstrated the technical feasibility, acceptable safety, and a fairly consistent, modest improvement in valve areas. In spite of only modest valve area improvement, patients experienced significant symptomatic benefit. The result led to a prematurely enthusiastic embrace by interventional cardiologists. However, the rapid recognition of extremely high restenosis rates within a year of the procedure quickly tempered enthusiasm. A subsequent large series showed high restenosis rates and a failure to improve survival despite its palliative benefits.2-4 Echocardiographic restenosis rates of 40% to 80% at 6 to 9 months, as well as rates consistently > 80% at 1 year, were reported. One-year mortalities have generally ranged from 25% to 45%. However, the clinical lag in recurrence of baseline symptoms extends 6 to 12 months beyond hemodynamic restenosis. Therefore, a quality-of-life (QOL) benefit after BAV will usually last 1 to 2 years in these elderly patients, who are generally less concerned about longevity.
The treatment of choice for severe, symptomatic AS has remained surgical aortic valve replacement (AVR). However, with the rapidly expanding population of patients in their 80s and 90s, who often carry the burden of significant comorbidities, a resurgence of palliative valvuloplasty has taken place during the past decade. Reported series in octogenarians and nonagenarians have shown its relative safety, with procedural mortalities in the range of 2%.5,6 Elderly patients with high surgical risk or Society of Thoracic Surgeons (STS) scores of > 10% and the probability of prolonged postoperative recovery generally find the risk:benefit ratio of aortic valvuloplasty quite favorable. Furthermore, from the patient's perspective, a strategy of serial BAV has resulted in more protracted periods of QOL enhancement.
The arrival of transcatheter aortic valve implantation (TAVI) is timely, particularly given the increase in life expectancy and the need for a more durable alternative to BAV in poor surgical candidates. The prevalence of AS in patients older than 75 years is reported to be 4.6%.7 The first-in-man implantation was successfully performed in 2002 by Cribier et al.8 Progressive technological improvements in both of the stented valve implants and delivery systems, along with operator experience, have resulted in a logarithmic growth in TAVI since CE Mark approval was obtained in Europe. Two valves have emerged early and include the Sapien balloon-expandable stent valve (Edwards Lifesciences, Irvine, CA) and the self-expanding CoreValve device (Medtronic, Inc., Minneapolis, MN). Implant success
rates are now reported to be > 90%, procedural mortality is down to 2%, and 30-day mortality rates are < 10% in appropriately selected patients.9,10 Acute hemodynamics after implantation yield mean gradients of < 10 mm Hg and aortic valve areas > 1.5 cm2. Limited midterm follow-up has not shown any valve failures.11
BAV is an essential procedural step during TAVI to predilate the stenosed leaflets for easier transcatheter delivery. Additionally, BAV during predilation can be used for valvesizing strategies. BAV will undoubtedly be used not only as a bridge to surgical AVR, but to TAVI as well. Even at centers in which TAVI has become an established practice, significant proportions of patients are deemed to be unsuitable for TAVI and are treated with BAV.12
PATIENT SELECTION
Current indications for BAV based on American College
of Cardiology/American Heart Association guidelines13 will
soon evolve. The substantial increase in BAV volumes during
the past 5 to 10 years, reflecting less stringent patient
selection, has come about for two primary reasons. The
first is based on a realization that a substantial population
of comorbid and elderly patients who are poor candidates
for surgical AVR derive a significant palliative benefit. It has
been shown in multiple published experiences that New
York Heart Association (NYHA) class can be significantly
improved.6,14-16 The demonstrated safety in serial BAVs for
patients with recurrent restenosis extends the opportunity
for achieving longer periods of enhanced QOL even further.
Although unproven, some authors have suggested a survival
benefit as well.12,14 Second, the option for TAVI in
these poor-surgical-risk groups has had an explosive impact
on the use of BAV. BAV is not only essential for predilation
but has now been reported to successfully bridge patients
to TAVI.16,17 Patient groups that were initially too unstable
in one series underwent successful TAVI after a mean interim
period of 59 ± 57 days.16 The precise role of BAV in this
regard will obviously require a broader experience.
In the pre-TAVI era, we had published our indications for stand-alone BAV18 and have subsequently modified them (see Severe, Symptomatic AS Patients in Whom Balloon Aortic Valvuloplasty Should Be Considered sidebar). We did not include patients undergoing predilation for TAVI on this list.
MECHANISMS OF ACTION
The effects of BAV on stenosed aortic valves are poorly
understood, but several mechanisms appear likely.19
Primarily, balloon-induced fracturing of calcified nodules
creates hinge points,20 which along with the creation of
cleavage planes in collagenous stroma, results in improved
leaflet flexibility and valve opening. Separation of fused
leaflets is uncommon given its infrequent occurrence in this
patient population with calcific aortic stenosis. Enhanced
compliance or stretching of the adjacent annulus and calcified
aortic root has also been suggested.18
TECHNIQUE
There are two balloon aortic valvuloplasty techniques
(Figure 1), both of which are well described in the literature.
21,22 The retrograde technique is the simplest and the
one most commonly used. The antegrade technique, which
we will not discuss in detail in this article, is carried out percutaneously
from the femoral vein or surgically from the
transapical approach.
Antegrade Approach
The transfemoral antegrade approach requires transseptal
access to the left heart and a transcirculatory wire loop
for balloon delivery, which is technically demanding. The
predominant advantage remains its ability to avoid placement
of a large sheath introducer in diseased peripheral
arteries and thus avoiding the more common bleeding and
ischemic complications seen with retrograde arterial access.
Nonrandomized studies have shown a more effective valve
opening with the antegrade approach when used in conjunction
with the Inoue balloon. It is suggested that the
bulbous distal balloon segment is able to hyperextend the
valve leaflets more broadly into the aortic root sinuses of
Valsalva. One series reported a 20% greater valve area for
patients undergoing antegrade BAV with an Inoue balloon
compared to a retrograde approach using standard aortic
balloons.21
Retrograde Approach
This technique is generally carried out from the transfemoral
artery approach. Good technique in ensuring common
femoral access via anterior wall puncture is critical for
minimizing procedural and postprocedural complications.
A test contrast injection with the initial arterial puncture
can ensure correct positioning before placing larger sheaths.
Percutaneous preclosure sutures can be deployed after the
initial placement of a 6-F sheath. One method uses two 6-F
ProGlide devices (Abbott Vascular, Santa Clara, CA) placed
sequentially at 90° angles for suture deployment, after
which, a larger sheath is exchanged for the initial 6-F sheath.
Alternatively, a single 10-F Prostar device (Abbott Vascular)
can be used. A 10- to 12-F sheath is then placed, depending
on the balloon that is selected. Intravenous heparin is
administered to achieve an activated clotting time of 250 to
300 seconds. All patients should be pretreated with 325 mg
of aspirin. Coronary angiography and bilateral heart
catheterization is then carried out, and baseline hemodynamics
are recorded.
The aortic valve is crossed with an Amplatz left 1 or 2 diagnostic catheter (Boston Scientific Corporation, Natick, MA). In a left anterior oblique projection, a brief cine run for two to three cardiac cycles should be captured to evaluate the location of systolic leaflet separation. Positioning the delivery catheter within the systolic jet, which is confirmed by catheter tip vibration, can reduce the time required to successfully cross the valve. A straight-tipped wire is used to probe the valve and access the left ventricle. Switching to a right anterior oblique (RAO) projection is helpful for exchanging a dual-lumen pigtail catheter or other diagnostic catheter over an exchange-length wire, after which, peak and mean systolic valve gradients are measured.
A bipolar pacing lead is then advanced into the right ventricle, and stable capture thresholds are documented. A brief pacing run should be carried out at 180 to 220 beats per minute, ensuring one-to-one capture and verifying that the systolic blood pressure decreases below 60 mm Hg. Lower heart rates are usually inadequate for limiting systolic flow and thus are less likely to maintain a stable balloon position during inflation. Not uncommonly, 2:1 exit block may occur when attempting to pace at rates of 200 beats per minute or greater. Pacing at 180 beats per minute may achieve 1:1 capture, and if the decrease in blood pressure is not sufficient, the rate can be rapidly increased to 200 beats per minute with preservation of 1:1 capture before initiating balloon inflation (Figure 2).
A 0.035-inch, extra-stiff guidewire with a soft tip is placed in the left ventricle. The distal, softer wire tip is first shaped into a broad loop and draped across the anterior left ventricular wall and apex through the diagnostic catheter under fluoroscopy in an RAO projection (Figure 3).
Preserving this wire position is crucial in preventing left ventricle (LV) perforation during subsequent balloon inflations. The diagnostic catheter and sheath are then removed while preserving wire position in the LV. Balloon sizing is generally more aggressive in stand-alone BAV, choosing balloon diameters at the beginning that will achieve a 0.9:1 or 1:1 balloon-to-annulus ratio. A contrast-diluted 1:9 ratio for balloon inflation is used to minimize viscosity and thus inflation and deflation times. Most balloons take 25 to 30 mL of volume to fill and can be delivered with a 30- or 60-mL plastic syringe. A 10-mL side syringe can be placed with a stopcock to allow further full inflation of the balloon. After positioning the uninflated balloon markers across the valve, rapid ventricular pacing is initiated, and balloon inflation is carried out as briskly as possible, making balloon catheter adjustments to preserve stable balloon position throughout inflation. Generally, no more than two to three inflations with each balloon size are carried out before upsizing if needed. It is crucial to allow systemic blood pressures to return to baseline before proceeding to the next inflation. Intravenous phenylephrine in 100- to 200-µg boluses can be used for significant delays in blood pressure recovery.
The diagnostic catheter is then exchanged for the balloon, and valve gradients are remeasured. Although not always achievable, our target is to achieve a 50% reduction in mean gradient. If needed, 1-mm increments in balloon diameter sizes can be used for judicious use in carrying out further inflations. It is important to remember that valve gradients can be reduced not only secondary to improved valve opening but can result from a transient reduction in stroke volume. Thus, repeat cardiac output measurements should be obtained to confirm an adequate increase in valve area. At this point, the catheters are removed, and suture closure is carried out with a guidewire in place. When hemostasis appears to be good, the guidewire is removed. Protamine can be administered for heparin reversal at this point if desired. Patients are then maintained on 3 to 4 hours of bed rest.
Procedural Outcomes
Reported postprocedural improvements in valve area are
variable and have predominately ranged from 0.3 to 0.4
cm2.4,14-16,20,21,26-28 Factors that appear to influence results
include the nature of underlying valve pathology, severity of
preoperative stenosis and calcification, and levels of aggressiveness
in balloon sizing. Criteria for successful BAV have, in
general, included a 30% increase in aortic valve area (AVA).
However, we should not lose sight of the most relevant
measure of success in palliative procedures, which are QOL
measures such as NYHA function class and hospital readmissions,
both of which are improved with BAV. Patients
undergoing BAV are usually NYHA functional class III to IV
at baseline, the majority of whom experience improvement
to class I to II.6,16,17,24 The most important predictor of eventfree
survival after BAV has been left ventricular function at baseline.29 BAV may be repeated when symptoms recur, as
long as aortic insufficiency is not greater than mild to moderate.
Many patients have periods of improved QOL for a
year or more after each BAV procedure.12,14
The most relevant procedural complications that need to be reviewed with patients prior to obtaining consent include a procedural mortality rate ranging from 1% to 3%.5,14,24,23 Strokes complicating BAV procedures have consistently ranged from 1% to 2%, and severe aortic insufficiency has ranged from 1% to 2%.15,24,30 The reported incidence of vascular complications related to the percutaneous site depends on how they are defined and include hematoma, need for blood transfusion, and surgical repair. With the introduction of percutaneous closure devices, the need for surgical repair has been reduced from an incidence of 5%14 to < 1% in some case series.24,31M
BAV PREDILATION AND USE IN PATIENT
ASSESSMENT FOR TAVI
BAV in TAVI procedures serves to predilate the valve and
thus enhance transcatheter delivery of the valve implant.
BAV also offers the opportunity to minimize any likelihood
of coronary occlusion, as well as an opportunity for annular
sizing. A separate pigtail catheter is positioned in the aortic
root, and during balloon inflation with full leaflet expansion,
contrast is injected through the pigtail. Both coronaries
should be observed to fill with contrast without aortoosteal
impingement by the flared valve leaflets. If significant
coronary obstruction is documented, TAVI is either aborted,
or coronary access is preserved with a guidewire before TAVI
to permit subsequent stent rescue.
Transesophageal echocardiographic measurement, as well as preoperative cardiac CTA, appear to have limitations in precise annular sizing.32 Although their impact on TAVI outcomes has not been clarified, its relevance for undersizing or oversizing devices seems obvious. Two methods have now been described to aid in more accurate valve size selections.
One method described by Babaliaros et al uses balloon sizing as an adjunct to transesophageal echocardiography for aortic valve annular sizing and device selection.32,33 In brief, a noncompliant balloon is used in tandem with a pressure manometer on an indeflator. On a sterile table, balloons are inflated to achieve 2 atm of intraballoon pressure, and the inflation volume is noted. Calipers are used to determine the balloon diameter achieved. The balloon is then deflated and positioned across the patient's aortic valve, after which it is reinflated with the same volume of dilute contrast. If just 2 atm of pressure are recorded, the balloon diameter is smaller than the annulus. On the other hand, if the intraballoon pressure exceeds 2 atm (ie, additional intraballoon pressure), the annular size has been reached or exceeded by the balloon diameter (Figure 4).
In using this strategy in a reported series of 27 patients, the authors found this technique helpful in selecting the appropriate valve size in 26% of patients.33 There were no complications using this technique.
Dr. Cribier has described a different technique, whereby, if contrast is prevented from regurgitating into the LV with an aortic root injection around an inflated aortic valve balloon of known diameter, more precise confirmation of annular size can be made for valve selection.34 As a broader range of transcatheter valve sizes becomes available, these techniques may have even greater relevance.
CONCLUSION
BAV is experiencing a substantial resurgence. It is now
used not only in aortic valve predilation for TAVI but has
taken on an expanded role with a broader recognition of its
palliative benefits and means for a bridge to TAVI or AVR.
With broader adoption of BAV among less-experienced
interventionists and cardiac surgeons, iterative device developments
will be helpful in making this procedure more controlled
and precise. The opportunity to simultaneously size
the annulus during BAV has been recognized and deserves
further emphasis.
Wes R. Pedersen, MD, FACC, FSCAI, is Director, Transcatheter Valve Program, Interventional Cardiology Department, Minneapolis Heart Institute Foundation, Abbott Northwestern Hospital and Twin Cities Heart Foundation in Minneapolis, Minnesota. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Pedersen may be reached at wesley.pedersen@allina. com.
Irvin F. Goldenberg, MD, FACC, FSCAI, is Codirector, Transcatheter Valve Program, Minneapolis Heart Institute Foundation, Abbott Northwestern Hospital and Twin Cities Heart Foundation in Minneapolis, Minnesota. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein.
Ted E. Feldman, MD, FESC, FACC, FSCAI, is Director of the Cardiac Catheterization Laboratory at Evanston Hospital in Evanston, Illinois. He has disclosed that he receives grant/research funding from Edwards Lifesciences and is a consultant to Edwards Lifesciences and InterValve, Inc. Dr. Feldman may be reached at (847) 570-2250; tfeldman@northshore.org.
Advertisement
Advertisement
