Download Right heart catheterisation: how to avoid the most common mistakes

Right heart catheterisation: how to avoid the most common mistakes
Dr. Michele D'Alto
Department of Cardiology
Second University of Naples
Monaldi Hospital
Via Leonardo Bianchi, 1
80131 Naples
ITALY
[email protected]
AIMS
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To discuss practical issues: vein cannulation, type of catheter, catheter placement, waveform
interpretation, measurements and calculations.
To identify possible pitfalls and caveat.
To improve the skills in performing a correct diagnosis integrating RHC and other imaging
modalities.
SUMMARY
Right heart catheterization (RHC) represents the gold standard for measuring pulmonary
haemodynamics. RHC is mandatory to confirm the diagnosis of pulmonary hypertension (PH), to
assess the severity of haemodynamic impairment and to perform vasoreactivity testing in selected
patients.
PH is defined as a mean pulmonary arterial pressure (mPAP) ≥25 mmHg by RHC measured at rest,
with pre-capillary PH being defined by a pulmonary artery wedge pressure (PAWP) ≤15 mmHg and
post-capillary PH by a PAWP >15 mmHg. Among post-capillary PH, “isolated post-capillary PH”
(Ipc-PH) is defined by a diastolic pulmonary gradient (DPG) <7 mmHg and pulmonary vascular
resistance (PVR) ≤3 WU, and “combined post- and pre-capillary PH” (Cpc-PH) by DPG ≥7 mmHg
and/or PVR >3 WU.
The term pulmonary arterial hypertension (PAH) describes a group of PH characterized by the
presence of pre-capillary PH and a pulmonary vascular resistance (PVR) >3 Wood units (WU) in the
absence of other causes of pre-capillary PH such as PH due to lung diseases, chronic thromboembolic
pulmonary hypertension (CTEPH) or other rare diseases.
RHC, as an invasive diagnostic tool, is part of a complex alghorhythm for PH diagnosis. The
interpretation of invasive haemodynamics should consider the context of the clinical picture and
imaging, in particular echocardiography.
RHC is a challenging procedure requiring careful attention, meticulous measurement and extensive
expertise. In order to obtain valuable clinical information and to minimize the risk related to the
procedure RHC should be limited to expert centres.
Cannulation of a sufficiently large systemic vein is the first step for performing RHC.
The practice of using surface anatomy and palpation to identify target vessels before cannulation
attempts (“landmark technique”) is based on the supposed location of the vessel, the identification of
anatomic landmarks, and blind insertion of the needle until blood is aspirated. Depending on the site
and patient population, landmark techniques for vascular cannulation are associated with a 60% to
95% success rate. The landmark technique can be augmented by the use of ultrasound; this is
recommended in the case of jugular vein cannulation and very helpful when using the brachial vein
approach.
The gold standard for pressure and blood flow measurement of the pulmonary circulation are
respectively the high-fidelity micromanometer-tipped catheters and the direct Fick method. The fluidfilled flow-directed thermodilution catheters are much more widely used and have been demonstrated
to be accurate though with lack of precision of +/- 1/L/min for cardiac output, +/- 8 mmHg for mPAP
and -15 to +8 mmHg for PAWP. Precision on otherwise accurate measurements can be improved by
repetition and averaging. This is why it is recommended to average 3 to 5 thermodilution cardiac
output measurements with less than 10% variation, and to read pulmonary vascular pressures in
triplicate.
In clinical practice, the catheter commonly used for RHC is a balloon floatation tip catheter, known as
“Swan-Ganz” catheter.
A correct zero level set is pivotal in performing RHC. The wrong zero level set is one of the most
common mistakes and a major confounding factor during RHC. Zero level setting must be meticulous
because it represents the starting point for all pressure measurements. In fact, each pressure measured
during RHC is a difference between the pressure at the chosen zero level and the pressure in the
chamber (or vessel) where the fluid-filled catheter tip is located, assuming there is no obstruction and
no significant flow within the catheter.
The question of zero leveling was raised before the introduction of cardiac catheterization, during the
early measurements of the peripheral and central venous pressure. An ideal zero reference would be
not only independent of chest diameter but also insensitive to changes in body position and represent
a “hydrostatic indifference point”. Recently, it has been proposed a standardized reference point valid
in any body position, defined by the intersection of the mid-thoracic frontal plane with the transverse
plane passing through the fourth anterior intercostal space and the mid-sagittal plane.
Kovacs et al. assessed retrospectively the position on computed tomography the right and left atrial
centre levels in 196 consecutive patients with PH undergoing RHC, found that the centre of the left
atrium was best described by the “mid-thoracic level”. As a consequence, zeroing the system at this
level seems reasonable for the assessment of PAWP.
Accurate measurement of left ventricular filling pressure is essential to distinguish between PAH and
PH due to left heart diseases, mainly heart failure with preserved ejection fraction (HFpEF).
Commonly, PAWP is used as a surrogate measure of left atrial pressure and left ventricular enddiastolic pressure. PAWP is the pressure measured from a catheter wedged in a branch pulmonary
artery. Actually, the term “wedge pressure” derives from the measurement obtained by a “wedged”
catheter without an inflated balloon. Using an inflated balloon we measure a “pulmonary artery
occluded pressure”. Both are usually referred to as a PAWP and used indifferently, but the measured
pressures will be different if there is an increased large vein resistance (such as in sepsis for example).
In clinical practice, determination of CO and CI is typically done by either the Fick method or
thermodilution, in order of reproducibility the direct Fick is preferable to thermodilution which is in
turn preferable to the indirect Fick.
The Fick principle is based on the observation that the total uptake (or release) of a substance by the
peripheral tissues is equal to the product of the blood flow to the peripheral tissues and the arterialvenous concentration difference (gradient) of the substance. In the determination of cardiac output,
the substance most commonly measured is the oxygen content of blood thus giving the arterio-venous
oxygen difference, and the flow calculated is the flow across the pulmonary system.
This provides an easy way to calculate the cardiac output: Cardiac output = oxygen consumption /
arteriovenous oxygen difference.
Measurement of the arterial and venous oxygen content of blood involves the sampling of blood from
the pulmonary artery and from the pulmonary vein. In practice, sampling of peripheral arterial blood
is a surrogate for pulmonary venous blood.
The first step during RHC in congenital heart disease is to obtain pressure measurements at different
levels of the systemic venous return, the right heart, and the pulmonary circulation. This should
include measurements in the superior vena cava, inferior vena cava, right atrium, right ventricle (or
sub-pulmonary ventricle), pulmonary artery, and PAWP. Systemic pressures are also required to
calculate the ratio between pulmonary and systemic artery pressure. The ratio between the systemic
and pulmonary pressures and resistance may be especially useful if shunt closure is contemplated.
RHC in patients with pulmonary hypertension can be very challenging and has been associated with
serious, sometimes fatal, complications. For this reason, RHC should be performed only in expert
centres.
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