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
Obstruction
to LV Outflow
It
is of clinical importance to distinguish between the obstructive
or nonobstructive forms of HCM, based on the presence or absence
of a LV outflow gradient under resting and/or provocable conditions
5,7,11,13,41,109,110. Indeed, in most patients, management
strategies have traditionally been tailored to the hemodynamic
state. Outflow gradients are responsible for a loud apical
systolic ejection murmur associated with a constellation of
unique clinical signs 14,72,111, hypertrophy of the basal
portion of ventricular septum and small outflow tract, and
an enlarged and elongated mitral valve in many patients 39,112-114.
Obstruction may either be subaortic 13,71,72 or midcavity
13,115 in location. Subaortic obstruction is caused by systolic
anterior motion (SAM) of the mitral valve leaflets and mid-systolic
contact with the ventricular septum 13,71,113,116-119.
This mechanical impedance to out-flow occurs in the presence
of high velocity ejection in which a variable proportion of
the forward blood flow may be ejected early in systole 120,121.
Systolic anterior motion is probably attributable to a drag
effect 117,122 or possibly a Venturi phenomenon 13,118
and is responsible not only for subaortic obstruction, but
also the concomitant mitral regurgitation (usually mild-to-moderate
in degree) due to incomplete leaflet apposition, which is
typically directed posteriorly into the left atrium 111,123.
When the mitral regurgitation jet is directed centrally or
anteriorly into the left atrium, or if multiple jets are present,
independent abnormalities intrinsic to the mitral valve should
be suspected (e.g., myxomatous degeneration, mitral leaflet
fibrosis, or anomalous papillary muscle insertion) 13,91,115,124.
Occasionally (perhaps in 5% of cases), gradients and impeded
outflow are caused predominately by muscular apposition in
the mid-cavity region—usually in the absence of mitral-septal
contact—involving anomalous direct insertion of anterolateral
papillary muscle into the anterior mitral leaflet, or excessive
mid-ventricular or papillary muscle hypertrophy and malalignment
13,91,115.
Although
it has previously been subject to periodic controversy 72,120,125,126,
there is now widespread recognition that the subaortic gradient
(30 mm Hg or more) and associated elevations in intra-cavity
LV pressure reflect true mechanical impedance to outflow and
are of pathophysiologic and prognostic importance to patients
with HCM 127,128. Indeed, outflow obstruction is a strong,
independent predictor of disease progression to HCMrelated
death (relative risk vs. nonobstructed patients, 2.0), to
severe symptoms of New York Heart Association (NYHA) class
III or IV, and to death due specifically to heart failure
and stroke (relative risk vs. nonobstructed patients, 4.4)
127. However, the likelihood of severe symptoms and death
from outflow tract obstruction was not greater when the gradient
was increased in magnitude above the threshold of 30 mm Hg
127.
Disease
consequences related to chronic outflow gradients are likely
to be mediated by the resultant increase in LV wall stress,
myocardial ischemia and eventually cell death and replacement
fibrosis 7,127,129. Therefore, the presence of LV outflow
obstruction justifies intervention to reduce or abolish significant
subaortic gradients in severely symptomatic patients who are
refractory to maximum medical management 11,14,41,127.
Obstruction
in HCM is characteristically dynamic (i.e., not fixed): the
magnitude (or even presence) of an outflow gradient may be
spontaneously labile and vary considerably with a number of
physiologic alterations as diverse as a heavy meal or ingestion
of a small amount of alcohol 72,73,109. Different gradient
cut-offs have been proposed for segregating individual patients
into hemodynamic subgroups, but rigorous partitioning into
such hemodynamic categories according to gradient can be difficult
because of the unpredictable dynamic changes that may occur
in individual patients 72,73.
Nevertheless,
it is reasonable to divide the overall HCM disease spectrum
into hemodynamic subgroups, based on the representative peak
instantaneous gradient as assessed with continuous wave Doppler:
1) obstructive gradient under basal (resting) conditions equal
to or greater than 30 mm Hg (2.7 m/s by Doppler), 2) latent
(provocable) obstructive—gradient less than 30 mm Hg
under basal conditions and equal to or greater than 30 mm
Hg with provocation, and 3) nonobstructive—less than
30 mm Hg under both basal and (provocable) conditions. By
current clinical convention, LV outflow gradients are routinely
measured noninvasively with continuous wave Doppler echocardiography,
generally obviating the need for serial cardiac catheterizations
in this disease (except when atherosclerotic CAD or other
associated anomalies such as intrinsic valvular disease are
suspected).
It is
important to underscore that a variety of interventions have
been traditionally employed to elicit latent (inducible) gradients
in the echocardiography, cardiac catheterization, and exercise
laboratories (i.e., amyl nitrite inhalation, Valsalva maneuver,
post-premature ventricular contraction response, isoproterenol
or dobutamine infusion, standing posture, and physiologic
exercise) 3,72,73, however, rigorous standardization for
these maneuvers has been lacking, and many have come to be
regarded as nonphysiologic. To define latent gradients during
and/or immediately following exercise for the purpose of major
management decisions, treadmill or bicycle exercise testing
in association with Doppler echocardiography is probably the
most physiologic and preferred provocative maneuver, given
that HCM-related symptoms are typically elicited with exertion.
Intravenous administration of dobutamine is undesirable 130,131,
as discussed under the section on alcohol septal ablation.
©
2003 by the American College of Cardiology and the European
Society of Cardiology |
