Download Right ventricular function

RIGHT VENTRICULAR FUNCTION
Andrew N Redington MD FRCP
Introduction
The results of an electronic search of the literature of the last three decades underscore the lack
of attention paid to right ventricular form and function, publication’s concerning the left ventricle
outnumbering those of the right ventricle by approximately 10 to 1 (figure 1).
Nonetheless, the
last decade has seen increased recognition of the
importance of right ventricular (RV) function in the
circulation. The negative impact of coexisting RV
dysfunction in dilated and ischemic cardiomyopathy is
well established, for example (17), but it is in congenital
heart disease where right ventricular dysfunction is now
accepted as being pivotal to the natural and unnatural
history of so many of the disease complexes. Now that
operative mortality of the early repair has fallen to very low levels, attention has turned to
improving longer-term outcomes and preservation of function, not least that of the right ventricle.
However, because of the unique haemodynamics associated with RV dysfunction, its impact may
only become apparent clinically after decades of follow-up. It is in this regard that the study of
adolescent and adult survivors can be so instructive. Indeed, many of the concepts now being
applied to the early treatment of congenital heart diseases, have evolved from the study of the
long term survivors in adult congenital heart clinics. Our changing management of tetralogy of
Fallot is a perfect example. Inappropriate concerns regarding the importance of residual RV
outflow tract obstruction, and ignorance of the adverse effects of pulmonary incompetence,
resulted in the frequent use of generous transannular patches in the 1960’s, 70’s and 80’s. Early
mortality fell progressively during these first three decades of tetralogy surgery, but as we learned
more about the protean late complications associated with pulmonary incompetence in the
1990’s, contemporary surgical strategies have been redirected towards preserving pulmonary
valve function.
While ignorance of the potential impact of dysfunction may explain some of the lack of attention
paid to the right ventricle, there is another pragmatic, but no less important, reason for the relative
scarcity of mechanistic research. There can be no doubt that the adequate assessment of RV
performance is more difficult than that of its left ventricular counterpart. While the prolate ellipsoid
of the left ventricle lends itself to geometric assumptions and mathematical interpretation, the
shape, geometry, and anatomical location, of the right ventricle all conspire against precise
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assessment. Add to this the effects of coexisting congenital abnormalities, beat to beat changes
occurring with respiration, the profound changes that may occur with abnormalities of the
pulmonary vascular bed, and right/left heart interactions, and it is easy to see why understanding
of RV function has lagged behind that of the left.
Nonetheless, each of these issues is of
fundamental importance to the physiology of the circulation as a whole, and a variety of methods
are now available for the assessment of RV performance.
In this chapter we explore some of the more important aspects of right ventricular physiology, and
how these may be modified by the natural ‘experiments’ imposed by congenital heart disease,
and its treatment.
Right Ventricular Physiology
With the exception of small physiologic shunts, the average cardiac output from the right ventricle
must, of course, be the same as the cardiac output from the left ventricle. The mechanism by
which right ventricular stroke output is achieved, is very different from that of the left however.
This is almost entirely a consequence of the very different vascular beds into which the right and
left ventricles empty.
Energetically, the external work performed by the right
ventricle to generate the cardiac output is approximately one
quarter to one fifth of that expended by the left ventricle. This
is illustrated perfectly by analysis of right and left ventricular
pressure volume relations (fig 2a).
The left ventricle is
essentially a square wave pump, and its external stroke work
can therefore be approximated to the stroke volume
multiplied by the diastolic to systolic pressure difference.
While the left ventricular pressure volume diagram was
elucidated in the 1960’s (4), it was not until the 1980’s, that
the pressure-volume relationship of the normal right ventricle
was described (23). Earlier observations by Shaver and
coworkers (30), examining simultaneous micro-manometer
pressure recordings from the right ventricle and pulmonary
artery, suggested that the normal right ventricle might operate
under an entirely different set of pressure-volume conditions
to that of the left ventricle. The ‘hang out’ period between the
onset of right ventricular pressure decline, and the dichrotic notch of pulmonary valve closure
suggested that right ventricular ejection was occurring well beyond the development of peak RV
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pressure. This was confirmed by direct analysis of RV pressure-volume relationships constructed
using a bi-plane angiographic method to measure RV volume combined with micromanometertipped pressure catheter recordings (23). Figure 2b shows a typical example. Compared with the
normal left ventricle, ejection from the right ventricle occurs early during pressure rise (with an
abbreviated period of isovolumic contraction) and continues as right ventricular pressure declines.
Thus, the normal right ventricular pressure volume relationship is more trapezoidal or triangular,
and the external mechanical work (the area subtended by the loop) proportionately smaller then
that of a square wave pump with similar stroke volume and peak developed pressure. This
capacity to eject during pressure rise and decline is mechanically very efficient, but crucially
dependent on the low hydraulic impedence imposed by the normal pulmonary vascular bed.
Relatively subtle changes in right ventricular afterload can result in large changes in this energetic
efficiency. Increased pulmonary vascular resistance promptly alters the shape of the right
ventricular pressure volume relationship to something more akin to that of the left (26). In
conditions such as pulmonary stenosis, or when the RV is the systemic ventricle, the pressurevolume characteristics may be indistinguishable from a normal left ventricle. It should be
remembered however, that while there is a large contractile reserve when its afterload is
increased slowly (ie over weeks or months), the right ventricle is much more prone to acute
failure with relatively modest increases in afterload. Indeed, the afterload sensitivity of the right
ventricle is 2 or 3 times that of the left ventricle (38). Consequently, there is an almost linear
inverse relationship between right ventricular ejection fraction and right ventricular afterload (16).
It should be clear therefore that the application of concepts derived from the understanding of left
ventricular contractile physiology, need not necessary apply directly to that of the right. Similarly,
the diastolic properties of the right ventricle are very different from those of the left ventricle.
Interestingly, while the diastolic phase of right ventricular filling, as assessed from the pressure
volume relationship, may remain stable even with relatively large changes in afterload, it is
markedly pre-load dependant. For example, the pressure volume trajectory in response to an
acute volume load is much steeper in the right ventricle compared to the left, suggesting greater
inherent myocardial stiffness or reduced chamber compliance. Paradoxically, the right ventricle
adapts more readily to a chronically increased pre-load. Gross right ventricular dilatation (of a
greater degree, and tolerated for much longer than would be possible by the left ventricle) can
occur with little or no apparent change in basal compliance characteristics. That is, despite a
doubling or tripling of right ventricular end diastolic volume, there may be little or no change in
right ventricular end diastolic pressure. It must be remembered however that, unlike the left
ventricle, the right ventricle is not necessarily a closed system in diastole. The high aortic diastolic
pressure maintains aortic valve closure throughout diastole, even in the presence of a markedly
raised left ventricular end-diastolic pressure. The low pulmonary artery end-diastolic pressure
associated with a low pulmonary vascular resistance is easily exceeded by right atrial systolic
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pressure under some circumstances. As a result, real changes in myocardial compliance may not
reflected by changes in either ventricular pressure, volume or pressure-volume characteristics.
As will be discussed later, restrictive right ventricular physiology may therefore be associated with
normal trans-tricuspid flow characteristics, normal right ventricular end-diastolic pressure and
volume, and normal right ventricular pressure volume relations, despite markedly abnormal right
ventricular myocardial properties (6).
So far, the differences between right and left ventricular physiology have been described as if the
two ventricles were separate entities. While this is convenient, it is physiologically inappropriate.
Left and right ventricular systolic and diastolic ventricular performance is affected by phenomena
occurring on the contralateral side of the heart. These right-left heart interactions are amplified by
the effect of congenital heart disease, but are present in all of us as part of normal ventricular
physiology.
Right Ventricular – Left Ventricular Interaction
While the deeper layers of myocardial fibres are separated, there are shared superficial fibers
that encircle the normal left and right ventricle. Furthermore, in some forms of congenital heart
disease the deeper layers or the right and left ventricle may be contiguous within the
interventricular septum (28). The function of the two ventricles is therefore inextricably linked, in
both the structurally normal and abnormal heart.
The potential for left to right ventricular myocardial ‘cross-talk’ was beautifully demonstrated in an
experimental study of intact explanted hearts in which electrical, but not mechanical, continuity
between the right and left ventricles had been interrupted (7).
Pacing the right ventricular
myocardium, lead to little detectable mechanical activity (measured as developed pressure) in the
left ventricle. Conversely however, pacing-induced contraction of the electrically isolated left
ventricle was associated with the development of an almost normal right ventricular pressure
trace (7). Indeed, it was estimated that over 50% of the mechanical work of the right ventricle,
may be generated by ‘left ventricular’ contraction. Hoffman and coworkers shed more light on
this phenomenon in a series of in vivo experiments (15).
By replacing the right ventricular
myocardium with a non-contractile prosthesis, they were able to show virtually normal right
ventricular pressure generation, as a consequence of normal left ventricular shortening. Just as
interesting, was the observation that intact right ventricular geometry is crucial for normal left
ventricular mechanical performance. During gradual enlargement of the non-contractile RV free
wall, there was a progressive reduction in both right ventricular mechanical work, but also left
ventricular mechanical work, i.e. as the right ventricle dilated, RV pressure development and
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stroke work fell. This simple observation may have huge implications for our understanding and
management of left ventricular dysfunction in the presence of the chronic right heart disease (and
vice-versa) in congenital and acquired defects.
All of these effects are amplified by the superimposition of pericardial constraint. While
chronically, the pericardium usually has the capacity to enlarge, commensurate with the size of
the ventricular mass, this cannot occur acutely. Just as an acute pericardial effusion can impose
major, life threatening, hemodynamic abnormalities, the rapid dilation of a cardiac chamber can
have similar effects.
Brookes et al examined the effects of acute right ventricular dilation
(imposed by selective right coronary ischemia) on both right and left ventricular performance
measured by conductance catheter (2).
With an intact pericardium, acute right ventricular
dilatation led, unsurprisingly, to a commensurate reduction in left ventricular size, and loadindependent indices of contractility. This effect was mediated primarily by septal shift. This
change in left ventricular volume was obviated by release of the pericardium. A similar of degree
of right ventricular dilatation occurred, but there was a non-significant fall in left ventricular
volume. Going along with Hoffman’s observations (15) however, acute right ventricular dilatation
under these circumstances was also associated with a significant fall in load-independent
measures of left ventricular myocardial contractility. This could not be explained on the basis of
changes in left ventricular geometry, and almost certainly reflected abnormalities of myocardial
cross talk under the circumstances of acute right heart dilatation.
These relatively recent observations from experimental studies have potential resonance in adults
with congenital heart disease. An understanding of the mechanisms of right-left heart interaction,
may ultimately help us better manage the biventricular effects of chronic right or left ventricular
volume overload, for example.
Furthermore, these mechanisms maybe harnessed in an
advantageous way. In patients with a sub-aortic right ventricle for example, the impact of septal
shift on systemic tricuspid valve performance, is increasingly understood, and can be modified by
changing the hemodynamics of the subpulmonary left ventricle. The tricuspid valve is
characterized morphologically by its attachments to the septum. As the septum moves towards
the left ventricle, valvar incompetence is almost inevitable. Thus, increasing left ventricular
pressure by banding the pulmonary artery, can reverse septal shift and relieve tricuspid
incompetence in some patients (34).
Cardio-pulmonary Interactions
The importance of the relationship between right and left heart function, described above, is
matched by a similarly intimate relationship between the right heart and the lungs. The effect of
cyclical changes in venous return on right heart hemodynamics has already been discussed, and
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will be further emphasized throughout this chapter. This cardio-venous relationship, is just one of
the manifestations of cardio-pulmonary interaction however.
Changes within the lungs
themselves, as a result of the mechanical work of breathing, changes in pulmonary vascular
resistance (with the secondary effects on RV contractile physiology described earlier), and intrathoracic pressure can all be equally important in both the ambulatory patient and, in particular, the
patient requiring positive pressure ventilation. Although perhaps outside the remit of this chapter,
these effects of ventilation on pulmonary blood flow are amplified in the Fontan circulation lacking
a subpulmonary ventricle.
Normal inspiration, supplies work to the circulation.
It has been
estimated that approximately 30% of pulmonary blood flow (and therefore cardiac output) in
Fontan circulation can be directly attributed to this inspiratory work (20). Unsurprisingly, this
effect is more marked in those patients with cavopulmonary anastomosis, compared to those with
atriopulmonary anastomosis (25,12).
exercise.
This cardio pulmonary adaptation is manifest also on
Compared with patients after atriopulmonary anastomosis, patients with total
cavopulmonary anastomosis develop a higher respiratory rate, at all stages of exercise (27). This
is despite similar minute volume, anatomic deadspace, and carbon dioxide production. They
therefore seem to be harnessing the work of breathing to generate pulmonary blood flow, and
hence cardiac output, during exercise (27).
The adverse effects of positive pressure ventilation are also most marked in patients lacking a
sub-pulmonary right ventricle. There is essentially a linear inverse relationship between mean
airway pressure and pulmonary blood flow (39,31). As mean airway pressure rises (because of
the imposition of positive end expiratory pressure, the use of prolonged inspiratory or plateau
times, or auto-PEEP) the cardiac output will fall. The perioperative management of these patients
should therefore be to establish normal respiration as soon as possible, and in those requiring
positive pressure ventilation, to minimize the mean airway pressure, while maintaining adequate
ventilation and small airway patency.
All of these effects are seen in the bi-ventricular circulation, effected by right ventricular disease
(6,33,31). As mentioned earlier, systolic function of the right ventricle is exquisitely dependant on
load.
Even relatively small changes in mean airway pressure can significantly increase the
afterload on the failing right ventricle. Likewise, in those with restrictive physiology, antegrade
diastolic flow will be in enhanced by normal ventilation and reduced as mean airway pressure
rises (33). A similar ventilator strategy as to that used in Fontan patients (e.g. low or no PEEP,
short inspiratory time, short plateau time) is applicable to patients with right heart disease
undergoing surgery.
It can be seen from the brief discourse above, that measurement of right ventricular performance
in adults with congenital heart disease must take into account many factors. There are many
techniques available, each with its own set of advantages and limitations. In general, static
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imaging techniques measuring ventricular volume and its derivatives, will fail adequately to
describe either right ventricular systolic or diastolic performance, and therefore be unable
consistently to predict need for intervention. Ideally, dynamic assessment of load independent,
as well as these load dependant phenomena will be required. None of the individual techniques
described below can therefore be considered to provide a comprehensive evaluation. Used
together however, many of the questions asked of right ventricular performance can now be
addressed, if not yet answered definitively.
Assessment of Right Ventricular Performance.
A review such as this necessarily concentrates on the technologically innovative methods, but the
importance of physical examination, the electrocardiogram and, in particular, the chest radiograph
cannot be underestimated.
The latter can be an enormously effect tool in the general
assessment of progressive right heart disease. For all of the advances made in invasive and
non-invasive techniques, few indices have been shown to be more robust than a simple
measurement of heart size on the chest radiograph. That having been said, the chest radiograph
cannot hope to provide the mechanistic information required to describe the pathogenesis of right
heart disease, or the refinement needed to predict and select treatment in the individual. For this
ever to be achieved, more sophisticated assessment will be required
Cardiac Catheterization
It would be an overstatement to suggest that cardiac catheterization is redundant in the clinical
assessment of right heart disease, but invasive assessment of hemodynamics aside, the
calculation of right ventricular volume using single plane and bi-plane geometric algorithms (23)
have been consigned to medical history. At best, these techniques were time consuming and
laborious, and many were conceptually flawed and inaccurate. For static measurements of right
ventricular volume, magnetic resonance imaging is now unsurpassable. However, for dynamic
right heart volume assessment, although remaining an experimental tool, conductance catheter
assessment must now be the state of the art. The strength of the technique is its ability to
measure beat-by-beat changes in pressure-volume relationships acutely during interventions.
Validated for RV volume measurement (40,41), it has been used, for example, to quantify
pulmonary regurgitant volume in response to simulated pulmonary artery stenosis in tetralogy of
Fallot patients (5), and to assess RV contractility using load-independent end-systolic indices
based on the elastance model of function (3). Indeed, it is only with such measurements that
intrinsic myocardial dysfunction can be separated from the sometimes complex load-dependent
changes that are seen in adults after repair of congenital anomalies, eg after the atrial switch
procedure for transposition of the great arteries (9).
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Clinically, diagnostic right heart catheterization is therefore reserved for the assessment of
hemodynamics unmeasurable by other techniques (e.g. RVEDP, complex gradients, etc) or
increasingly frequently, as a prelude to trans-catheter therapy of structural abnormalities (eg
ASD, pulmonary artery stenosis) which secondarily impose adverse effects on right ventricular
performance.
Radionuclide Studies
Equilibrium and first pass radio-nuclide assessment of right ventricular volumes and ejection
fraction have been used for many years.
While the validity of such techniques has been
established in the normal bi-ventricular heart, there are relatively few studies assessing their
accuracy in the presence of intracardiac shunting, the anatomic and spatial abnormalities
associated with congenital heart disease, and under the circumstances of important secondary
hemodynamic phenomenon such as pulmonary or tricuspid incompetence. For these reasons,
and the compelling data being achieved using the alternative techniques of echocardiography
and magnetic resonance imaging, again radio-nuclide studies are becoming a thing of the past.
Echo-Doppler Assessment
Right Ventricular Dimensions
There is no single M-mode measurement of right ventricular dimension that adequately describes
its overall size. Individual measurements of ventricular inflow, and outflow dimensions, from
apical four-chamber, apical two-chamber and parasternal short axis sections should each be
recorded separately and can be used to provide quantitative evidence of change. One of the
most interesting ways in which M mode echocardiography can be used, as a functional tool, is in
assessing long axis function. The deeper layers of right ventricular myocardium are arranged
longitudinally, and this technique is particularly appropriate for assessment of inflow shortening,
from an apical four chamber view. Motion of the right ventricular atrioventricular ring has been
shown to be abnormal, after surgical, but not device, closure of ASD (10), as well as in more
complex forms for congenital heart disease (8). However, the more readily applicable technique
of tissue Doppler imaging (see below), while measuring myocardial rather than atrioventricular
ring movement and velocity, is likely to supercede such measurements. Indeed, Vogel and
coworkers have recently described a tissue Doppler index of RV contractility which is unaffected
by changes of loading conditions over a wide physiologic range (35). The index, isovolumic
myocardial acceleration ‘IVA’, is almost unique as a non-invasive measurement of intrinsic RV
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contractile function, and should prove very useful in the clinical assessment of acute, and
perhaps chronic, changes in RV function.
Two- and three-dimensional echocardiography is required for accurate determination of right
ventricular volume. The most accurate methods using standard two-dimensional sections employ
a multiple slice, Simpson’s rule, analysis from a 4-chamber view (37). The third dimension is
usually assumed to be circular or elliptical. Despite the obvious limitations, these techniques
provide a relatively robust and reproducible, although incomplete, assessment of right ventricular
volume. More recent approaches (29) have tried to incorporate the volume of the right ventricular
outflow tract in the calculations. Whether the added complexity of such techniques outweighs
any improvement in applicability remains to be seen.
All two-dimensional-based techniques require geometric assumptions.
The Holy Grail of
echocardiographic assessment, is an easily applicable real-time three-dimensional assessment of
right ventricular volume. This is now on the horizon with some of the innovative hardware and
software solutions being incorporated into contemporary machines.
However, the history of
three-dimensional echocardiography now extends approximately 10 years. Despite a plethora of
studies demonstrating the potential for right ventricular volume measurement (36), the technique
remains investigational, at best. Just as with any echocardiographic technique, and amplified
when three-dimensional reconstruction is required, these techniques will be limited by the
adequacy of echocardiographic interrogation. While the transesophageal approach overcomes
many of these issues, it is not yet a technique for everyday use, or sequential assessment.
Doppler Assessment
All Doppler measurements are subject to the changes imposed by varying stroke volume as a
result of respiration.
The pulmonary arterial systolic velocity, right ventricular outflow tract
gradient and tricuspid regurgitant velocity will tend to increase by 5-10% during normal
inspiration. Combined with the inherent error of any measurement technique, only relatively large
changes can reliably be recognized. Improved accuracy can be obtained by making
measurements during suspended ventilation (eg. held end-expiration), or by taking averaged
values from one or more respiratory cycles, but such protocols must be rigorously and
consistently adhered to for them to be valid.
Similar cyclical changes, and subsequent inaccuracies, can be expected in trans-tricuspid
diastolic flow velocities. There are other reasons why trans tricuspid flow velocities may be
unreliable indicators of diastolic function however. The use of the E/A ratio, in combination with
E-wave deceleration time and pulmonary venous flow patterns, has become established as a
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qualitative measure of diastolic performance of the left ventricle (33). As alluded to earlier, the
‘open’ nature of the right ventricle in diastole can invalidate similar interpretation of RV diastolic
performance. This is particularly the case when there is restrictive RV disease. Trans-tricuspid
flow in late diastole need not necessarily equate with right ventricular filling. The right ventricular
may be acting as a conduit between the right atrium and pulmonary artery, under these
circumstances.
Nonetheless, with this caveat, it is still possible to describe qualitatively the
presence of restrictive physiology using Doppler techniques. The small amount of retrograde flow
normally demonstrable in the superior caval vein, inferior caval vein and hepatic veins will all be
amplified in the presence of restrictive disease, and E-wave deceleration time tends to be shorter
than normal (24). Most importantly, in the presence of a normal pulmonary vascular resistance,
restrictive right ventricular disease is associated with antegrade diastolic flow into the pulmonary
artery coincident with atrial systole (6,24). It is important to note that there is often Dopplerdetectable late-diastolic flow associated with forward movement of the pulmonary valve leaflets
during late diastolic RV filling in normals. This is characteristically low velocity (<10cm/sec)
intrapulmonary, translational flow that occurs in the absence of pulmonary valve opening (14). In
restrictive right ventricular physiology, with an intact pulmonary valve, the pulmonary valve
leaflets will reopen in late diastole and laminar flow will be detectable by Doppler ultrasound,
usually with a velocity of greater than 20 cm/sec.
Restrictive physiology is most commonly seen in patients after repair of Tetralogy of Fallot (6,13).
A competent pulmonary valve under these circumstances is rare, but laminar late diastolic
pulmonary arterial flow coincident with atrial systole, throughout the respiratory cycle, is now
considered to be the hallmark of restrictive right ventricular physiology.
It is associated, in
general, with a smaller right ventricle, because the restrictive disease intrinsically protects against
dilatation and associated complications resulting from chronic pulmonary incompetence (13).
Restrictive physiology does not, however, preclude marked right ventricular dilatation. It is simply
a qualitative sign that the resistance to right ventricular filling exceeds the resistance to
pulmonary arterial flow.
Furthermore, this Doppler echocardiographic sign depends on tiny
pressure transients between the right atrium and pulmonary artery. Any coincident disease that
increases pulmonary arterial diastolic pressure (e.g. left atrial hypertension) may prevent
antegrade diastolic flow even when there is restrictive disease (1). Similarly, low right atrial
pressure (e.g. secondary to diuretic use), loss of sinus rhythm, or loss of mechanical atrial
systolic function due to gross dilation or fibrosis, can all reduce or mask this physiologic sign. It is
also easy to over-diagnose restrictive physiology. A small amount of flow into the right ventricular
outflow tract is, of course, normal during right ventricular filling. It is important therefore to use
pulsed wave Doppler interrogation, classically with the sample volume midway between the level
of the pulmonary valve leaflets and the pulmonary artery bifurcation.
Furthermore, a small
amount of antegrade diastolic flow is normal during deep or forced inspiration in patients with
right heart disease.
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While clearly a physiologic spectrum, pragmatically, the definition of
restrictive disease requires antegrade diastolic flow to occur throughout the respiratory cycle.
The long term physiologic implications (mostly beneficial) of restrictive right ventricular physiology
are described elsewhere (chapter ?). However, It was first described as an acute complication,
associated with low cardiac output, after surgical repair of tetralogy of Fallot in children. The
same physiology can occur in adults undergoing primary repair, or revisions. The paradox of
restrictive right ventricular physiology being advantageous in the long term, but highly
disadvantageous in the immediate postoperative period must be understood. Its recognition on
the intensive unit is important as management of fluids, inotropes, and, in particular, positive
pressure ventilation are all crucially important to the hemodynamic management of these
patients. Thus, maintenance of adequate filling pressures, sinus rhythm, a low pulmonary
vascular resistance and low mean-airway pressure (because of the potential for adverse cardiopulmonary interactions – see above) are all-important.
Magnetic Resonance Imaging
Established as a highly important diagnostic modality in adults with congenital heart disease,
magnetic resonance techniques have also rapidly become established as the gold standard for
the measurement of RV volume, and volume-based indices of function in ambulatory patients
(11). The ready measurement of flow, in absolute terms, is also a major advantage. Right and
left heart outputs can be measured to calculate shunts (22), regional flows can be deduced, and
pulmonary regurgitant volume can be calculated (21). These measurements are unaffected by
the geometric and spatial constraints of other techniques, and are reasonably reproducible (19).
Importantly, they are easily repeated to obtain sequential assessment of longitudinal change.
While much of the enthusiasm for magnetic resonance quantification is justified, there are some
practical and philosophical caveats. The capital cost is high, not all can undergo study (e.g. those
with pacemakers, intraoperative patients), and the equipment and, just as importantly, adequately
trained personnel are not available in every institution. Philosophically, while offering much in the
future, the utility of the measurements to clinical decision making are yet to be established. The
need and timing for pulmonary valve replacement late after tetralogy of Fallot is a good example.
The degree of RV dilation, the right ventricular ejection fraction, and the volume of pulmonary
regurgitation can all be measured with precision, but the individual or combined threshold for
intervention on the basis of such measurements remains to be established.
Conclusions
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There is still a lot to learn about the assessment and implications of RV dysfunction in adults with
congenital heart disease. An understanding of the uniqueness of normal and abnormal RV
physiology combined with appropriate application of the available techniques will help to answer
some of the very important questions that challenge these patients and their carers.
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