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This article will discuss several features of cardiac
catheterization, specifically right-heart catheterization,
as they relate to patients with pulmonary arterial hypertension
(PAH).
The accepted gold standard definition of pulmonary hypertension
is defined by most experts as a mean pulmonary arterial
pressure of =25 mmHg, with a concomitant pulmonary capillary
wedge (PCW) pressure of =15 mmHg, and pulmonary vascular
resistance of >3 Wood units. These criteria are derived
from the National Institutes of Health registry of pa-tients
with primary pulmonary hypertension.1 Thus, by
definition, cardiac catheterization is required to definitively
estab-lish the diagnosis of PAH.
Cardiac catheterization should be considered essential
for documenting of hemodynamic severity, as well as completing
a standard workup for pulmonary hypertension. The information
obtained from cardiac catheterization in combination with
clinical findings can be used to monitor therapeutic and
adverse effects of medical interventions.
Measurement of  hemodynamics
in patients with PAH via cardiac catheterization can also
provide added prognostic value. For example, in patients
with primary pulmonary hypertension whose mean right atrial
pressure was <10 mmHg, median survival was nearly 50 months
without pulmonary vasodilator therapy, compared with less
than 3 months in patients whose mean right atrial pressure
was =20 mmHg (Figure 1).2
While echocardiography has been shown to be useful for
estimating pulmonary arterial pressure, this modality
has certain limitations that can ultimately lead to errors
in diagnosing PAH without the use of cardiac catheterization
to validate the measurements. Specifically, while echocardiographic
estimates of pulmonary artery systolic pressures have
been shown to correlate with pressures measured by catheterization,3,4
for individual patients, the error of measurement may
be signifi-cant. This is especially important when making
the initial diagnosis of PAH, since overestimates and
underestimates may lead to an incorrect diagnosis.
In addition to limitations in pressure estimates, the
lack of ability of echocardiography to measure PCW pressure
(and thus left ventricular end diastolic pressure) bears
important clinical significance, since it is essential
to exclude pulmonary venous hypertension when making the
diagnosis of PAH.
The Catheterization Procedure
The Catheter
The pulmonary artery (right heart) catheter is designed
for use in the ICU or in the cardiac catheterization laboratory
to measure right-heart and pulmonary arterial hemodynamics,
to estimate left ventricular end diastolic pressure, and
to meas-ure cardiac output. The catheter is usually 120
cm long and has multiple lumens so that pressure recordings
and infusions can be made from various locations in the
heart and pulmon-ary arteries. In addition, a small plastic
balloon that is located at the tip of the catheter can
be inflated and used to “float” the catheter in the direction
of blood flow in order to facilitate catheter advancement.
This balloon is also used to occlude the pulmonary artery
in order to obtain estimates of left atrial pressure (see
below). Finally, a thermistor (temperature indi-cator)
is also located at the tip of the catheter; it is used
to detect changes in blood temperature when performing
ther-modilution cardiac output measurements (see below).
When performing right-heart catheterization specifically
for patients with PAH, the catheter used often has several
modifications that are designed to facilitate the catheterization
process. The catheter is stiffer than the standard right-heart
catheter and contains a blind-end port, which allows passage
of a guidewire for additional stiffness, if desired. This
extra stiffness is often needed because advancing the
catheter into the pulmonary artery can be technically
difficult in the presence of a dilated right ventricle,
elevated pulmonary arterial pressure, and tricuspid regurgitation.
Precautions
When planning cardiac catheterization for a
patient with sus-pected PAH, it is important to understand
the risks associated with the procedure, and to have an
emergency treatment plan in place should these risks occur.
In addition, the desired measurements should be planned
in advance, with careful consideration of the specific
operational procedures that are to be done during the
procedure.
Clinicians should be very familiar with how to interpret
the measurements obtained at cardiac catheterization,
and be able to troubleshoot suspected inaccuracies. Anticipation
of complications and unexpected findings is essential,
so that immediate action can be taken. Finally, the clinician
must continuously scrutinize the findings and question
the meas-urements for both accuracy and clinical relevance.
Patients with PAH may present with relatively few physical
signs of PAH, yet have significant cardiovascular abnormalities.
These patients, with “compensated right-heart failure,”
can easily decompensate when subjected to the stressors
of cardiac catheterization. Despite these risks, however,
cardiac catheterization is safe if appropriate precautions
are carried out.
- Staff experience – The physician and nursing
and technical staff must all be familiar with the diagnosis
and man-agement of PAH and with the catheterization
laboratory equipment. The staff must be meticulous about
flushing and level-ing the pressure transducers and
flushing the catheter to ensure that accurate measurements
are recorded.
- Patient sedation – It is generally recommended
that adult patients be kept awake during catheterization.
However, it is important that anxiety, which may induce
tachycardia and hemodynamic embarrassment, be controlled.
Small doses of benzodiazepines are useful for controlling
anxiety. Close attention to continuous pulse oximetry
is required, however, as hypoxemia during catheterization
is not uncommon.
- Atrial and ventricular ectopy – As the catheter
is manip-ulated into positions in the right atrium and
ventricle, ectopic electrical activity is common. Usually,
atrial premature beats and ventricular ectopic beats
are brief and selflimited. Sustained activity including
atrial and ventricular tachycardia may occur, however.
Immediate repositioning or removal of the catheter is
required in these instances, and antiarrhythmic therapy
should always be available should the arrhythmia per-sist.
- Bradyarrhythmias– One of the most troublesome
complications of cardiac catheterization in patients
with PAH is the development of vagally mediated bradycardia
and hypoten-sion. Often, an anxious or sensitive patient
may develop increased vagal tone 1) on viewing the catheterization
instru-ments or during local anesthetic infusion; 2)
on insertion of the catheter; or 3) on removal of the
catheter. When these “vagal episodes” occur, profound
bradycardia and hypotension often ensue within 30 to
60 seconds. It can be extremely difficult to resuscitate
such a patient. Therefore, it is imperative that a vagal
episode is anticipated in all patients, and that it
is recognized and treated with atropine early in its
course. This author always keeps an open vial of atropine
at the bed-side before, during, and after cardiac catheterization
of a patient with pulmonary hypertension.
- Reliability of measurements – Cardiac catheterization
measurements should be made preferably when the patient
is supine, with anxiety minimized (see above), and at
steady state. Spontaneous
 variation
in hemodynamics over time is a known shortcoming of
cardiac catheterization (Figure 2),5 and thus
great care should be taken to ensure that all meas-urements
are taken in close proximity of each other. In general,
waiting at least 15 minutes after catheter insertion
is advisable. Hemodynamic measurements should then be
obtained as close together as possible.
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