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March 2014 - Issue 3
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117
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Percutaneous Mitral Valve Intervention and
modelling with multi-modality imaging
Robin Chung MPhil MRCP
NIHR Cardiology Academic Clinical Fellow, The Heart Hospital and Great Ormond Street Hospitals University College London, UK
Introduction
Functional mitral regurgitation (MR) is a common finding
occurring in 20% of the general population1 and nearly 40% of
heart failure patients exhibiting at least moderate regurgitation.2
Severity of MR predicts mortality3 and increased morbidity
in ischaemic and non-ischaemic aetiologies4, regardless of
revascularisation techniqueas well as in asymptomatic patients.5
Mitral valve repair, by surgical or interventional techniques, aims
to restore valve competence and electromechanical synchrony
to improve symptoms and survival.
Overview of mitral valve anatomy
The mitral valve apparatus consists of the MV annulus, leaflets,
chordae tendinae, and papillary muscles. The aorto-mitral
fibrous continuity provides an anatomical support to the
anterior mitral leaflet.6 The normal mitral valve annulus (Figure
1) is classically described as a ‘saddle-shaped’ ellipitical
structure where the antero-posterior dimension is less than the
commissural diameter thereby minimising leaflet strain.7 These
normal relations are disturbed by progressive annular dilatation
and papillary muscle dysfunction regardless of aetiology,
resulting in progressive mitral regurgitation, a more spherical
shape, changes in non-planar angle and leaflet tenting8,9.
The coronary sinus (CS) originates posteriorly from the right
atrium, where it is guarded by the thebesian valve. The vein
4. Non-planar
angle
5. MV Annulus Area
AoC
Ao
2 CC-axis
Anterior
Mitral
Valve
Leaflet
1. AP-axis
Posterior
Mitral
Valve
Leaflet
Figure 1: Normal mitral valve and apparatus adapted from 6,8
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Table: Percutaneous MV repair techniques
Classification
Stage
Current status/
safety endpoints
Leaflet
Mitraclip
EVEREST,
EVEREST 2
Mitraflex
pre-clinical
Mobius
Milano II
(trial unsuccessful,
halted)
Percupro space
occupier
Phase I
thrombus formation
Thermacool
Animal models
leaflet ablation
technique causing
scarring/perforation
Coronary Sinus (indirect MV ring annuloplasty)
Carillon
Amadeus
Monarc
Evolution
development halted
Viacor
Ptolmey
development halted
NIH Cerclage
Animal models
ongoing
animal models
asymmetric
cinching of P2 to
posteromedialtrigone
via CS
St Jude device
of Marshall and the incomplete Vieussens valve mark the
external and internal junctions, respectively, where the coronary
sinus continues in the left atrioventricular groove as the great
cardiac vein. The great cardiac vein continues as the anterior
interventricular vein distally, where it runs parallel to the left
anterior descending artery. The coronary sinus is predominantly
related to the posterior left atrial wall, but a proportion of its
course as the GCV is adjacent to the mitral ring annulus. The
CS varies in size; its length ranges from 45 to 63 mm10 and its
diameter is 7 + 1.9 mm11. Thus the proximity of the CS to the
mitral ring makes it an attractive conduit for both pacing and
indirect annuloplasty.
Anatomical and in-vivo imaging studies have documented the
anatomical relations of the left circumflex (LCx) and its marginal
branch arteries to the great cardiac vein/coronary sinus.
Specifically, in normals the incidence of the LCx passing under
the CS ranged from 64 to 96%12,13, 15-17, increasing according to
coronary artery dominance (Right dominant 74%, Left dominant
83%, co-dominant 97%)14. Maselliet al. also reported the
incidence of diagonal or ramus branches of the LAD crossing
under the CS in 16%. In patients with severe MR of ischaemic
aetiology, the LCx crossed under the CS/GCV in 96%14. These
findings have important implications for potential coronary
artery compression due to percutanenous mitral annuloplasty
procedures.
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repair in addition to revascularisation20. However, a substantial
proportion of patients – 49% -- with moderate to severe MR are
rejected for surgical consideration21.
Surgical Approach
Surgical repair commonly based on the ‘Alfieri stitch’ -- socalled edge-to-edge or double-orifice technique -- aims
to reduce central jetregurgitant orifice area with resultant
decrease in MR. This open surgical technique has evolved
since its inception in 1991 when it was performed without ring
annuloplasty,22 but undersize ring annuloplasty is now the
accepted surgical norm23.
Interventional approach
Various interventional techniques have been proposed to
address the problem of significant MR in patients at high
surgical risk. These catheter-based approaches aim to
manipulate components of the mitral valve apparatus to
approximate leaflet coaptation or induce mitral annular,and
subsequently, LV reverse remodelling.
Current percutaneous techniques can be sub-divided according
to the target mitral valve component: leaflet, indirect (coronary
sinus) annuloplasty, direct annular, and LA- and LV-tetheringbased approaches, as detailed in the Table . We will focus on
leaflet and CS techniques as the latter three approaches remain
in nascent first-in-man or animal-model development stages.
Indirect annuloplasty
The Monarc (Edwards Lifesciences, previously Viking) nitinol
CS implant consists of proximal and distal anchors and a
spring-like bridge to displace the posterior annulus towards the
anterior leaflet in order to improve coaptation. Early trials with
the Edwards / Viking device achieved reduction in MR, but were
complicated by device fracture and recurrence and subsequent
halting of the feasibility study24. A subsequent phase I trial of
the redesigned Monarc device involving 72 patients reported
82% implantation success and 18% implantation failure rate
due to CS tortuosity or narrow lumen. Cardiac CT documented
cardiac vein crossing over the obtuse marginal in 55% of
patients; there was angiographic coronary artery compression
in 15 of 72 patients (21%) resulting in 3 acute myocardial
infarctions due to compression. Event-free survival was
reported as 91%, 81%, 72% and 64% at 30 days, 1- , 2-, and 3
years’ follow-up, respectively (Evolution I).25
The frequent incidence of coronary artery anatomy crossing
under the GCV/CS has led to the development of alternative
approaches to indirect mitral annuloplasty. The NHLI (USA)
Cerclage system26 has been trialled in an animal ovine model
with successful protection of coronary arteries from entrapment.
MRI and cine angiogram guide interactive catheter placement
and tension adjustment of the cerclage and coronary artery
protection bridge.
Surgical or Interventional Repair?
Direct Leaflet Techniques
Medical and cardiac resynchronisation therapy reduce
morbidity and mortality via after- and preload modification
and reverse remodelling,18,19 but surgical and interventional
techniques aim to address regurgitation via structural means.
In patients with moderate ischaemic MR, MV repair with
CABG conferred a survival benefit over medical therapy or
revascularisation by percutaneous coronary intervention (PCI)
alone. Even in those with severe functional MR, there has been
documented clinical benefit in addressing MR with mitral valve
Mobius
The percutaneous Mobius device (Edwards Life Sciences)
employed a suture to achieve leaflet plication. Device
development has since been abandoned due to suture
dehiscence and technical problems27 in human trials despite
initial promise in animal studies.
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Mitraclip
The Mitraclip system (Abbott Vascular, USA) delivers via transseptal puncture a rigid clip that directly plicates anterior and
posterior mitral leaflets. In the EVEREST trial28, procedural
success defined as device implantation and MR < grade 2 was
achieved in 74% of 107 patients with < 1% hospital mortality.
There were no clip embolization events although partial clip
detachment occurred in 10%. The composite primary endpoint of freedom from death, MV surgery or MR > grade 2+
was achieved in 66% at one year. Survival at one and three
years was 95% and 90%, respectively; freedom from surgery
was 88% and 76%, respectively (p=NS). In 32 patients who
subsequently required MV surgery, repair was possible in 84%,
demonstrating that the surgical option remained preserved
following percutaneous repair.
The EVERESTII trial29 randomised 279 patients to percutaneous
Mitraclip repair or conventional MV repair surgery in a 2:1 ratio.
The primary composite end point for efficacy (freedom from
death, surgery for MV dysfunction, freedom from MR grade
3+ or 4+) at 12 months was achieved in 55% and 73% in the
percutaneous and surgery groups, respectively (p=0.007).
Death occurred in 6% in each group; MR grade > 3+ in 20%
and 21%, and mitral valve surgery in 20% and 2%, respectively.
Major adverse events at 30 days occurred in 15%vs 48% of
patients in the percutaneous and surgery groups, respectively
(p<0.001). The safety end point incorporating major adverse
event criteria and blood transfusion > 2 units occurred in
9.6%vs 57%, in the percutaneous and surgical groups,
respectively (p< 0.005). Although percutaneous repair was less
effective than surgery for reducing MR, the safety advantage
of percutaneous repair was maintained even after exclusion
of blood transfusion incidence. At 12 months, both groups
reported similar LV dimensions, NYHA class and QoL scores.
The High Risk Surgery arm of the EVEREST II trial30 showed that
the 78 patients in a high-risk surgery group (Euroscore> 12%)
who received Mitraclip intervention had increased survival,
76% vs. 55% (p=0.047), at 1-year compared to the comparator
group who received standard care. LVEDV fell from 172 to
140ml, and LVESV fell from 82 to 73ml (p<0.001), and NYHA
functional class and QoLimproved at 12 months.
Meta-analysis data demonstrated that MitraClip patients were
significantly older (p <0.01), had lower baseline ejection fraction
(EF) (p<0.03), and had higher EuroScore values (p<0.001), with
similar 30-day (1.7 vs 3.5%, p=0.54) and 1-year mortality (7.4 vs
7.3%, p=0.66).
Four-year follow-up data for the EVEREST II trial demonstrated
a non-significant difference in the composite outcome of
freedom from death, surgery, or MR grade 3 / 4 + (39%
vs. 53%, p= 0.07) in the percutaneous vs surgical groups,
respectively. Death rates were similar (17.4 vs. 17.8%, p=0.91)
as was the incidence of MR grade 3 / 4 + (21.7 vs. 24.7%,
p= 0.745), respectively. Surgery for mitral valve dysfunction
occurred in 24 vs. 5.5 %, respectively, (p<0.001) at four years.
The EVEREST II trial confirmed that following MitraClip leaflet
repair, the option of further MV surgery remained for patients
who required it. Further imaging studies have also documented
that epicardial pacemaker lead placement via the coronary
sinus is possible with percutaneous leaflet repair31, 32. The
MitraClip is currently approved for symptomatic patients with
degenerative MR grade 3+ who are too high risk for surgery
who may benefit from fewer hospitalisations, LV remodelling
and symptomatic relief.
Figure 2: 3D reconstruction of the MV annulus, coronary sinus,
aortic root and left circumflex artery 13
Imaging for percutaneous MV repair
The complex mitral valve apparatus and intricate anatomical
relations of the branch coronary arteries necessitate preimplantation, intraprocedural and post-implantation by multiple
imaging modalities. Multi-detector cardiac CT, and more
recently cardiac MRI, are commonly used to image coronary
artery and cardiac vein position. Transoesphageal 2D and
real-time 3D echocardiography is typically used during
device implantation to guide placement, and transthoracic
echocardiograms are used to assess initial patient eligibility
and post-implantation surveillance. Thus,CT and TOE are
used to image structural and real-time anatomical relationships,
respectively, whereas transthoracic echocardiography is used
to screen leaflet morphology and grade MR severity.
Cardiac CT
Cardiac CT is the primary modality for measuring anatomical
relationships. Its fast acquisition times and 3D volume
rendering capabilities have been used to assess anatomy
relevant to annuloplasty techniques, including:
• Coronary sinus(CS) ostium area and calibre
• CS length and its course along MVA / left atrial wall
• CS to mitral annulus distance
• Anatomical relations of CS to LCx/marginal branches and
MV annulus
oDistance (CS ostium to intersection with LCx)
oLCx branch superior/deep to Cs
• Mitral annulus diameter, circumference, area
• Left atrial volume
• Area between CS and AV groove
Sorgenteet al. 16 reported the anatomical relations between
the CS and mitral annulus in 165 patients with varying LV and
LA volumes. Their findings documentedCS remodelling with
chamber enlargement, e.g. CS shifted toward posterior aspect
of MV annulus with progressive dilatation:
• frequent crossing of the LCxartery between the CS and
mitral annulus in 77% of patients, and in particular, 97% of
patients with severe MR.
• area between CS and AV grooves decreased in moderatesevere MR (150 v 260 mm2, p<0.001)
120
Cardiac MRI
Cardiac MRI has been used to evaluate in-vivo CS and MV
relationships. Chiribiri reported the first accurate measurements
with cardiac MRI 15 in a feasibility study in 31 participants (24
normals and 7 patients with known/suspected CAD but no
CABG). Their findings showed:
• CS to LCx crossing point at 71mm (22 to 100mm) from
ostial origin
• LCx between CS and MVA in 25/31 (80.6%)
• CS to MVA distance at LCx crossing greater in patients
than normal (17v 9.6mm, p<0.001)
Qualitatively, the above findings suggested CS located adjacent
to LA wall rather than MV annulus, larger separation between
CS and MVA in 4C view(suggestive of annulus flattening), and
the LCx runs closer to CS than to MVA, and LCx between CS
and MVA in majority.
Echocardiographic Imaging in percutaneous
MV repair
Both transthoracic and transoesphageal echocardiography have
important roles in the screening, implantation, and surveillance
of percutaneous MV repair procedures.33-37 Although CT and
cardiac MRI are predominantly used in anatomical assessment
of the mitral valve, echocardiography is used routinely for
screening entry criteria for percutaneous MV repair. Typical
measurements from the EVEREST I trial34 included:
• MV inflow orifice area (> 4 cm2)
• MV leaflet coaptation length and depth
• MV flail gap and width
• Grading of mitral regurgitation
• (‘integrated’ MR – MR jet area, regurgitant volume/ fraction,
pulmonary venous flow)
Functional assessment of MR severity, as proposed by the
Valve Academic Research Consortium (VARC), is generally
characterised by a standardised ‘integrated’ semi-quantitative
approach incorporating features of MR jet area, regurgitant
volume, regurgitant fraction, and pulmonary vein flow36.
Transoesphageal and transthoracic 3D echocardiography
allows measurement of mitral annulus geometry that is not
typically measured by CT or MRI. Findings from CT and MRI
have indirectly inferred mitral annulus shape change from
variation of the CS to MVA distance in different view planes.
These ‘non-planarity’ measures are readily assessed directly by
3D echo techniques8,33,36.
Multi-modality findings
Collating geometric findings across several anatomical, cardiac
CT and MRI studies revealed consistent findings related to
CS, LCx and mitral annuluar anatomy15. The principle findings
across different modalities were as follows:
• CS-GCV behind LA in 90 to 100%
• LCx crosses between CS and MVA in 68 to 95%
• Distance from CS ostium where LCx crosses occurs at 71 to
78 mm along course of CS
• Decrease in CS to MVA distance in different views suggests
flattening of MV annulus in presence of progressive
moderate-severe MR and LV disease
Summary
Percutaneous MV leaflet repair may be achievable in the
majority of patients, who benefit from reduced MRseverity,
improved quality of life and survival compared to standard
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medical care whilst preserving the option of future surgical
and cardiovascular resynchronisation therapies. Other
indirect annuloplasty techniques remain in a nascent stage
where pre-procedural anatomical assessment is vital due to
potential impingement of coronary vessels. Coronary CT has
the largest evidence base for pre-procedural assessment of
the mitral apparatus, but cardiac MRI appears equally suitable.
Echocardiographic techniques maintain an important role for
patient selection, regurgitation assessment and follow up, as
well as intra-procedural guidance of device deployment.
Current interventional devices for percutaneous mitral repair
have limited approval outside research and special clinical
governance arrangements. Future research should focus
on modelling dynamic anatomical change of the mitral valve
in motion before and after MV repair. Measurement via
MRI and CT is feasible peri-procedurally, butmulti-modality
imaging remains essential to expand the evidence base for this
promising array of techniques.
Correspondence to:
Dr Robin Chung
The Heart Hospital
University College London
W1G 8PH UK
[email protected]
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