MARON
AND MCKENNA et al., ACC/ESC Expert Consensus Document on Hypertrophic
Cardiomyopathy
JACC 2003; 42:
000-000
American
College of Cardiology/European Society of Cardiology Clinical
Expert Consensus Document on Hypertrophic Cardiomyopathy
A
Report of the American College of Cardiology Foundation Task
Force on Clinical Expert Consensus Documents and the European
Society of Cardiology Committee for Practice Guidelines
Treatment
Options for Drug-Refractory Patients
In some patients, medical therapy
ultimately proves insufficient to control symptoms, and the
quality of life becomes unacceptable to the patient. At this
point in the clinical course, after administration of maximum
drug treatment, the subsequent therapeutic strategies are
dictated largely by whether LV outflow obstruction is present
(Fig. 1). Surgery. Patients in a small
but important subgroup comprising only about 5% of all HCM
patients in non-referral settings (but up to 30% in tertiary
referral populations), are generally regarded as candidates
for surgery. These patients have particularly marked outflow
gradients (peak instantaneous usually greater than or equal
to 50 mm Hg), as measured with continuous wave Doppler echocardiography
either under resting/basal conditions and/or with provocation
preferably utilizing physiologic exercise. In addition, these
patients have severe limiting symptoms, usually of exertional
dyspnea and chest pain that are regarded in adults as NYHA
functional classes III and IV, refractory to maximum medical
therapy (7,8,11,14,41,90,92,102,103).
Over the past 40 years, based on the experience of a number
of centers throughout the world, the ventricular septal myectomy
operation (also known as the Morrow procedure) (8)
has become established as a proven approach for amelioration
of outflow obstruction and the standard therapeutic option,
and the gold standard, for both adults and children with obstructive
HCM and severe drug-refractory symptoms (7,11,14,15,41,70,78,81,84,85,90
–95,102–106,214).
The myectomy operation should be confined to centers experienced
in this procedure.
Myectomy
is performed through an aortotomy and involves the resection
of a carefully defined relatively small amount of muscle from
the proximal septum (about 5 to 10 g), extending from near
the base of the aortic valve to beyond the distal margins
of mitral leaflets (about 3 to 4 cm), thereby enlarging the
LV outflow tract (215) and,
as a consequence in the vast majority of patients, abolishing
any significant mechanical impedance to ejection and mitral
valve SAM immediately normalizing LV systolic pressures, abolishing
mitral regurgitation, and ultimately, reducing LV end-diastolic
pressures. Such an abrupt relief of the gradient with surgery
(in contrast to slower reduction with alcohol septal ablation
in many cases) is particularly advantageous in patients with
severe functional limitations.
Some
surgeons have utilized a more extensive myectomy procedure
for obstructive HCM, with the septal resection widened and
extended far more distally than in the classic Morrow procedure
(i.e., 7 to 8 cm from the aortic valve to below the level
of papillary muscles) (70,91).
In addition, the anterolateral papillary muscle may be dissected
partially free from its attachment with the lateral LV free
wall to enhance papillary muscle mobility and reduce anterior
tethering of the mitral apparatus (91).
Alternatively, mitral valve replacement or repair has been
employed in selected patients judged to have severe mitral
regurgitation due to intrinsic abnormalities of the valve
apparatus (such as myxomatous mitral valve) (124).
Previously,
some surgeons found it advantageous in selected patients to
perform mitral valve replacement (216,217)
when the basal anterior septum in the area of resection is
relatively thin (e.g., less than 18 mm) and muscular resection
was judged to present an unacceptable risk of septal perforation
or inadequate hemodynamic result (93).
However, currently, some surgical centers experienced with
myectomy do not advocate mitral valve replacement (in the
absence of intrinsic mitral valve disease), even in the presence
of a relatively thin ventricular septum; carefully performed
surgical septal reduction is the preferred method.
Mitral
valvuloplasty (plication) in combination with myectomy has
been proposed for some patients with particularly deformed
or elongated mitral leaflets (84).
Muscular mid-cavity obstruction due to an anomalous papillary
muscle requires an extended distal myectomy (91)
or alternatively mitral valve replacement (115).
Occasionally, patients, usually children, may demonstrate
an obstruction to right ventricular outflow due to excessive
muscular hypertrophy of trabeculae or crista supraventricularis
muscle (218); resection of
the right ventricular outflow tract muscle, with or without
an outflow tract patch, has abolished the gradient.
Published
reports of over 2,000 patients from North American and European
centers show remarkably consistent results with the ventricular
septal myectomy operation. Isolated myectomy (without concomitant
cardiac procedures such as valve replacement or coronary artery
bypass grafting) is now performed with low operative mortality
in patients of all ages, including children, at those centers
having the most experience with this procedure (reported as
1% to 3%, and even less in the most recent cases) (7,11,15,81,92–95,101–107).
Surgical risk may be higher among very elderly patients (particularly
those with severe disabling symptoms associated with pulmonary
hypertension), patients with prior myectomy, or those undergoing
additional cardiac surgical procedures. Complications such
as complete heart block (requiring permanent pacemaker) and
iatrogenic ventricular septal perforation have become uncommon
(equal to or less than 1% to 2%), while partial or complete
left bundle-branch block is an inevitable consequence of the
muscular resection and is not associated with adverse sequelae
(15,81,85,90
–93,102–106).
Intraoperative guidance with echocardiography (transesophageal
or with the transducer applied directly to the right ventricular
surface) is standard at centers performing surgery for HCM
and is useful in assessing the site and extent of the proposed
myectomy, structural features of the mitral valve, and the
effect of muscular resection on SAM and mitral regurgitation
(93,123,219).
Septal
myectomy is associated with persistent, long-lasting improvement
in disabling symptoms and exercise capacity (i.e., increase
by one or more NYHA classes and demonstrable increase in peak
oxygen consumption with exercise) and decreased frequency
of syncope five or more years after surgery (7,11,13–15,81,90
–95,102–106,220).
Symptomatic benefit following myectomy appears to be largely
the consequence of abolishing or substantially reducing the
basal outflow gradient and mitral regurgitation, and restoring
normal LV systolic and end-diastolic pressures (in more than
90% of patients), which may also favorably influence LV diastolic
filling and myocardial ischemia (204).
Because myectomy may result in a decrease in left atrial size
(221), the likelihood of
AF occurring after surgery may be mitigated (and sinus rhythm
restored with greater ease), especially in patients younger
than 45 years.
Selected
patients in whom severe refractory symptoms are indisputably
linked to marked outflow gradients elicited by exercise (when
resting obstruction is absent or mild) usually also benefit
from myectomy. Reacquisition of SAM and a large resting LV
outflow gradient is exceedingly uncommon after successful
myectomy in either adults or children, and the need for reoperation
to reduce recurrent outflow gradient is extremely uncommon
at centers having the most experience with the septal myectomy
operation (15,81,95,103,105).
By
convention, surgery has not been recommended or performed
in asymptomatic or mildly symptomatic patients with obstructive
HCM for a number of reasons: 1) the effect of surgery per
se on longevity is unresolved, although several surgical series
have reported improved late survival after myectomy compared
with the clinical course of nonoperated medically treated
patients with severe symptoms; 2) operative mortality is now
very low, but in some patients the risk of surgery may exceed
the ultimate risks from the disease; 3) outflow obstruction
is often compatible with normal longevity; and 4) there is
little or no evidence that surgical relief of outflow obstruction
abolishes the risk for progression to the end-stage phase,
which is an independent disease consequence.
Although
definitive evidence is lacking, there is some suggestion in
retrospective non-randomized studies that surgical relief
of outflow obstruction in severely symptomatic patients may
reduce long-term mortality and possibly SCD (10,95,105).
It should be emphasized that surgery is not regarded as curative
but is performed to achieve an improved quality of life and
functional (exercise) capacity.
One
possible exception to this tenet may be young asymptomatic
or mildly symptomatic patients with particularly marked outflow
obstruction (e.g., 75 to 100 mm Hg or more at rest). There
is a paucity of data in this subset, but it is not unreasonable
to at least consider surgical intervention for young patients,
even if they are not severely symptomatic, in the presence
of particularly marked obstruction to LV outflow.
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