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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3612_Библиотеки_им_академика_М_И_Перельмана
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Key Questions in CONGENITAL CARDIAC SURGERY
A wave
V wave
y descent
210
x descent
Figure 4. Right atrial pressure waveform.
The v wave results from an increase in right atrial pressure during
•
right ventricular systole and is generated by passive venous filling of
the atrium while the tricuspid valve is closed. The peak of the wave
follows the T wave in the surface ECG.
A c wave (3rd wave) is occasionally present and follows the a wave
•
by the same time as the PR interval on the ECG. It represents a rise
in pressure due to ventricular contraction and bulging of the closed
tricuspid valve.
The x descent represents the pressure decline following atrial
•
contraction due to atrial relaxation.
The y descent is the result of a fall in pressure due to the opening of
•
the tricuspid valve and the beginning of rapid ventricular filling.
Several conditions alter the shape and position of these waves,
•
including a:
a) cannon a wave — which is seen in A-V asynchrony, such as
complete heart block, when the atrium contracts against a
tricuspid valve that is held closed by right ventricular systole;
6 Congenital angiography and catheter interventions
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b) elevated a wave — which is found in cases of restricted atrial
emptying into the right ventricle, such as tricuspid atresia or
stenosis, and when there is decreased right ventricular
compliance from any cause;
c) elevated v wave — which is found in right ventricular failure,
severe tricuspid regurgitation and patients with reduced atrial
compliance (restrictive physiology);
d) increased c wave — which is found in patients with AV block;
e) prominent x descent — which may suggest constrictive
physiology or right ventricular ischaemia;
f) blunted x descent — which may be seen in patients with atrial
fibrillation;
g) prominent y descent — which is seen in constrictive
pericarditis and restrictive myopathy;
h) blunted y descent — which is found in tamponade and right
ventricular ischaemia.
6 What are the characteristics of the right ventricular
pressure waveform?
The right ventricular (RV) pressure tracing normally exhibits a peak
•
systolic pressure equal to that in the main pulmonary artery and
ranges between 15-30mmHg. The right atrial and the right ventricular
end-diastolic pressures (RVEDP) are equal, usually between 28mmHg.
The RV waveform consists of a systolic and diastolic curve (Figure
•
5). During right ventricular systole, the pressure rapidly rises with
resulting closure of the tricuspid valve and opening of the pulmonary
valve with blood exiting the chamber. The systolic waveform is rapid
in upstroke and occurs immediately after the QRS complex on the
surface ECG. At the end of systole, the ventricular relaxation begins
and as the pressure falls below pulmonary artery pressure, the
pulmonary valve closes.
Right ventricular diastole generates three waveforms:
•
a) early rapid-filling wave — which occurs at tricuspid valve
opening;
b) slower-filling period;
c) right atrial systole — which produces an a wave that is
identical to the a wave in the atrial pressure tracing, with the
end of the a wave corresponding to the right ventricular end-
diastolic pressure (RVEDP). Atrial systole accounts for 25% of
right ventricular diastolic filling.
211
212
Key Questions in CONGENITAL CARDIAC SURGERY
RV systolic pressure
RVEDP
Figure 5. Right ventricular pressure waveform. RVEDP = right ventricular
end-diastolic pressure.
7 What is the pulmonary capillary wedge pressure?
The pulmonary capillary wedge pressure (PCWP) is obtained during
•
right heart catheterisation and is an occluded pressure reflecting
downstream left atrial pressure (Figure 6).
In the absence of pulmonary venous obstruction or mitral valve
•
disease, the PCWP is a reflection, but not a direct measure, of left
ventricular end-diastolic pressure (LVEDP).
The normal waveform includes an:
•
a) a wave — which represents atrial contraction;
b) v wave — which represents left atrial filling during left
ventricular contraction;
c) c wave — which represents mitral valve closure but may not be
seen on the PCWP tracing;
d) x descent — which represents left atrial relaxation;
e) y descent — which represents left ventricular diastole.
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Wedge
LVDP
pressure
213
Figure 6. Pulmonary capillary wedge pressure. LVDP = left ventricular
diastolic pressure.
Normal PCWP ranges from 4 to 12mmHg.
•
PCWP is measured during diagnostic cardiac catheterisation
•
procedures but is also frequently measured in critical care patients
using a Swan-Ganz catheter, which is a flow-directed catheter inserted
without fluoroscopic guidance typically as part of pre-operative and
postoperative management during cardiac surgery.
8 What are the characteristics of the aortic pressure
waveform?
During ventricular contraction, pressure in the ascending aorta
•
parallels left ventricular (LV) pressure. Once the aortic valve closes,
the aortic pressure declines somewhat more slowly than the LV
pressure. This reflects the capacitance of the aorta and is influenced
by pressure waves from the thoracic aorta and its branches.
The rate and magnitude of decline of the aortic pressure during
•
diastole are dependent on a number of factors, including aortic valve
integrity (aortic regurgitation), capacitance and resistance of the
214
Key Questions in CONGENITAL CARDIAC SURGERY
peripheral circulation, and the presence of abnormal aortopulmonary
connections, such as a patent ductus arteriosus.
Pulse pressure is defined as the systolic pressure minus the diastolic
•
pressure.
A diastolic aortic pressure lower than the pulse pressure signifies a
•
widened pulse pressure, which may be caused by aortic valve
regurgitation, a patent ductus arteriosus, ruptured sinus of Valsalva
aneurysm, large aortopulmonary collaterals, aortopulmonary window,
peripheral vasodilation or arteriovenous malformations.
Conversely, a reduced pulse pressure, defined as a pulse pressure
•
less than 50% of the diastolic value, may be caused by tamponade,
heart failure, cardiogenic shock and aortic stenosis.
9 Describe how pressure gradients are measured in the
catheterisation laboratory
The most frequently utilised cardiac pressure data are the amplitudes
•
of the measured pressures themselves and the pressure differences
(gradients) between two adjacent areas, such as the ascending and
descending aorta (Figure 7).
Left ventricle Ascending aorta
Descending aorta
Peak
pressure
drop
Figure 7. Left heart cardiac catheterisation pressure measurement
demonstrating coarctation of the aorta characterised by a significant
gradient on pulling back the catheter from the ascending aorta to the
descending aorta. The gradient is calculated by comparing the systolic
peak to peak pressures across the affected area.
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Gradients between adjacent chambers or areas result from fixed or
•
dynamic obstructions within or between chambers or vessels. The
magnitude of the gradient generally reflects the severity of the
obstruction.
The pressures are measured using fluid-filled catheters and
•
manometers calibrated to the patient’s mid-chest height.
Peak to peak systolic gradients measured in the catheterisation
•
laboratory assess the difference between peak systolic pressures in
two different adjacent chambers or areas.
Echocardiographic Doppler measurements, however, assess the
•
maximum instantaneous pressure gradient across sites which occurs
before the peak pressures.
Therefore, by default, a Doppler-derived pressure gradient is
•
different (higher) than a catheter-derived peak to peak pressure
gradient. For this reason, mean pressure gradients from both
Doppler and cardiac catheterisation represent better comparison.
It is important to understand that a Doppler-derived pressure gradient
•
across an obstruction is not an ‘overestimate’. It is obtained at a
chronologically different time in the cardiac cycle than a peak to peak
gradient measured by cardiac catheterisation.
Furthermore, it is also important to appreciate that the vast majority
•
of Doppler-derived gradients are measured on unsedated patients,
whereas those at cardiac catheterisation are almost always
measured on a sedated or anaesthetised patient, whose cardiac
output is likely lower as a consequence.
215
10 What is the role of transoesophageal echocardiography
in the context of cardiac catheterisation?
Transoesophageal echocardiography (TOE) is an imaging technique
•
that helps with pre-operative assessment and intra-procedural
guidance.
It is most commonly used to guide sizing and device positioning in
•
the closure of an atrial septal defect (ASD, Figure 8), patent foramen
ovale (PFO) or ventricular septal defect (VSD).
It is also used to guide transseptal puncture and closure of the left
•
atrial appendage and mitral paravalvar leaks (PVLs).
Less commonly, it is used to guide closure of and creation of Fontan
•
baffle fenestrations.
In recent years, it is the imaging of choice for reparative interventions
•
on the mitral valve, such as the application of a MitraClip™ and
similar devices.
In patients weighing more 16kg, 3D TOE has been shown to be a
•
useful tool to guide catheter manipulations in the right heart, thereby
decreasing the exposure to radiation.
216
Key Questions in CONGENITAL CARDIAC SURGERY
A
B
Figure 8. Transoesophageal echocardiographic
images demonstrating: A) flow across a large atrial
septal defect; and B) no residual shunting after device
closure of the defect.
11 What is the role of cardiac computed tomography and
magnetic resonance imaging in the context of cardiac
catheterisation?
Cardiac computed tomography (CT) and magnetic resonance
•
imaging (MRI) are commonly used for diagnostic anatomical and
functional assessment of the heart prior to cardiac catheterisation
and act as tools of triage (Figure 9).
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Figure 9. Computed tomography coronal image
demonstrating dextrocardia, isomerism, right lung
agenesis, right bronchus agenesis and a single
branch left pulmonary artery following stenting of
the ductus arteriosus.
217
These cross-sectional imaging techniques help limit angiography and
•
diagnostic studies to reduce radiation exposure to the patient.
Recently, cardiac CT and MRI images have been used in conjunction
•
with fluoroscopy to guide cardiac interventions, such as stenting of
coarctation of the aorta. This integration of multimodality imaging with
fluoroscopy, known as fusion imaging, provides an alternative to
traditional fluoroscopically-guided catheterisation.
12 What are the general principles of aortic valvuloplasty?
Class I indications for aortic valvuloplasty include:
•
a) a newborn with duct-dependent, isolated valvular aortic
stenosis (AS);
b) children with isolated valvular AS with depressed LV systolic
function;
c) children with isolated valvular AS with a resting peak systolic
valve gradient (by catheter) ≥50mmHg;
d) children with isolated valvular AS with a resting peak systolic
valve gradient (by catheter) ≥40mmHg and symptoms of
angina or syncope, or ischaemic ST-T wave changes on
electrocardiography at rest or with exercise.
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Key Questions in CONGENITAL CARDIAC SURGERY
Pre-procedural echocardiography provides the most accessible
•
anatomical and physiological data on the morphology of the aortic
valve, peak instantaneous and mean aortic valve gradient, aortic
valve annulus diameter, aortic valve insufficiency and left ventricular
function.
It is important to consider that the severity of the aortic valve
•
gradient may be underestimated in patients with impaired left
ventricular function.
The technique of aortic valvuloplasty includes:
•
a) general anaesthesia;
b) vascular access via the femoral artery but may also be
obtained via the carotid artery (percutaneous or cutdown) or
rarely the umbilical artery;
c) haemodynamic assessment to measure the aortic valve
gradient;
d) aortic angiography to delineate the plane of the aortic valve
which aids balloon positioning and demonstrate the presence
or absence of regurgitation. Although some operators
perform left ventricular angiography, this rarely adds to the
procedure and may cause deleterious effects on left
ventricular function;
e) measurement of the aortic annulus diameter to select the
appropriate balloon diameter (Figure 10). The balloon to
annulus ratio of approximately 0.8-0.9 is perceived to be
appropriate and can be increased in 0.5 or 1mm increments
until an acceptable result is obtained. Oversizing of the
balloon obviously risks severe aortic regurgitation. Tyshak II
(NuMED, Inc.) balloons are low profile and compliant, and
are favoured for this procedure.
®
The criteria for a successful valvuloplasty should be taken in
•
context of the clinical scenario but broadly are:
a) >50% decrease in the pressure gradient across the aortic
valve;
b) >25% increase in the aortic valve area;
c) mild or less aortic regurgitation.
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AB
Figure 10. Angiographic evaluation of an aortic valve annulus: A)
measurements of the aortic valve annulus (arrow) and the sinotubular
junction after retrograde aortic root injection in an adult patient. A pacing
catheter is seen in the right ventricle used at the time of balloon valvuloplasty
for balloon stability; B) measurements of the aortic valve annulus via a
transcarotid approach in neonatal critical aortic stenosis. Thickened leaflets
can be seen within the root (arrow).
219
13 What are the general principles of pulmonary
valvuloplasty in isolated pulmonary stenosis?
Pulmonary valve stenosis may be isolated or as part of a complex of
•
additional lesions, such as septal defects or associated with
univentricular heart anatomy.
Pulmonary valvuloplasty is indicated for a patient with:
•
a) critical pulmonary valve stenosis;
b) stenosis with a peak to peak catheter gradient >40mmHg or an
echocardiographic peak instantaneous gradient >60mmHg;
c) clinically significant pulmonary valvular obstruction in the
presence of RV dysfunction.
The technique of pulmonary valvuloplasty includes:
•
a) general anaesthesia but can be performed under sedation in
older patients;
b) vascular access via the femoral vein. At the discretion of the
operator, an arterial line may be used to monitor the arterial
blood pressure;
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