RIGHT HEART CATHETERIZATION
Right heart catheterization generally involves the introduction of a balloon-tipped catheter into the right atrium (RA), right ventricle (RV), and pulmonary artery (PA). The use of an inflatable balloon on the tip enables rapid and safe passage of the catheter through the venous system and right heart chambers; this technique was developed in the 1970s by Dr. Harold Swan, Dr. William Ganz, and colleagues. A PA catheter has a port at the distal tip, a port that is approximately 30 cm proximal from the distal tip, an inflatable balloon at the distal tip, and a thermistor near the distal tip. The distal and proximal ports can be used to transduce pressure, or serve as access for fluids and medications. The balloon can be inflated to temporarily occlude the PA, which allows the distal port to transduce a “wedge” pressure. The thermistor can be used to measure the temperature change of fluid injected into the proximal port; this measurement is used in the calculation of cardiac output. A comprehensive preprocedural evaluation that includes history, physical examination, routine laboratory data, a 12-lead ECG, and a transthoracic echocardiogram can help guide appropriate patient selection, procedural planning, and data interpretation.
The American College of Cardiology, the American Heart Association, the
American College of Chest Physicians, the American Thoracic Society, the
Society of Critical Care Medicine, and the American Society of
Anesthesiologists have published guidelines and consensus statements on the
indications for right heart catheterization. Box 13.1 lists the common
indications for right heart catheterization. Although right heart
catheterization is indicated for the diagnostic evaluation of many disease
processes, there is much debate on the routine use of PA catheters to guide
clinical management of critically ill patients. Several randomized trials have
investigated the efficacy and safety of ongoing PA catheter-based clinical
management in patients with heart failure, patients who have undergone
high-risk noncardiac surgery, and patients with acute respiratory distress
syndrome. These studies demonstrated that there is no improvement in survival,
and that there is an increased risk of complications in patients randomized to
PA catheter-based management. However, these studies have been criticized for
their study design, improper patient
selection, and variably experienced physicians who performed the catheter placement and data interpretation. As a
result, there is no clear consensus on whether PA catheters are beneficial or
harmful for guiding clinical management over time.
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FIG 13.1 Hemodynamic findings in constrictive pericarditis. Simultaneous pressure tracings from the left ventricle and right ventricle. In
this patient with constrictive pericarditis, there are
elevated and equalized diastolic pressures and discordant right and left
ventricular systolic pressures.
Contraindications
There are several absolute contraindications to right heart
catheterization. First, lack of informed consent. Patients with a terminal
illness in whom an invasive hemodynamic evaluation will not affect treatment or
prognosis should not undergo right heart catheterization. Patients with a
mechanical prosthetic tricuspid or pulmonic valve are at risk for catheter
entrapment within the valve apparatus, and should not undergo right heart
catheterization. Finally, patients with right-sided endocarditis, thrombus, or
intracardiac tumor should not undergo right heart catheterization. Relative
contraindications to right heart catheterization include active infection,
active bleeding, severe thrombocytopenia, severe coagulopathy, and under-lying
left bundle branch block (which increases the risk of complete heart block if
the PA catheter causes a right bundle branch block).
Procedural Technique and Data Interpretation
Right heart catheterization can be performed in the cardiac catheterization
laboratory, intensive care unit, or operating room. Central venous access can
be obtained via percutaneous puncture of the common femoral vein, the internal
jugular vein, the brachial vein, or the subclavian vein. Before the procedure,
the patency of the access vein should be assessed by vascular ultrasound. The
patient is then prepared and draped in the usual sterile fashion. After a
time-out is performed and local anesthesia is administered, a needle is
introduced into the access vein. A sheath is placed in the access vein by means
of the modified Seldinger technique with ultrasound guidance.
A PA catheter is introduced into the venous sheath. When the PA catheter
advances beyond the sheath, the distal balloon is inflated, and the PA catheter
is advanced into the RA, the RV, and the main PA. Direct fluoroscopic
visualization or pressure monitoring can be used to guide advancement of the PA
catheter. The pressure waveform in each chamber is carefully examined and
recorded before advancing the PA catheter into the next chamber. After the PA
catheter has reached the main PA, it is advanced into a distal PA until it has
occluded the distal PA. At this point, the pressure transduced from the distal
port is defined as the pulmonary capillary wedge pressure (PCWP) and reflects
the estimated left atrium (LA) pressure and the LV diastolic pressure (when
there is no obstruction between the LA and LV). Once the PCWP is recorded, the
balloon is deflated, and the PA catheter is withdrawn back into the proximal
PA. Finally, blood samples are collected from the PA to measure the mixed
venous saturation.
Right heart catheterization provides the following hemodynamic
information through direct measurements and calculations based on these measurements: ventricular preload (RA pressure is a
reflection of RV preload, and PCWP is a function of LV preload), ventricular
afterload (systemic vascular resistance and pulmonary vascular resistance), and
cardiac output. These data can be used to evaluate various disorders, including
shock, valvular disease, cardiomyopathy, pericardial disease (Fig. 13.1), and intracardiac shunts (Table 13.1).
The pressures in the vena cavae, RA, RV, PA, and PCWP position can be
directly measured with the PA catheter. The mixed venous saturation can also be measured with the PA
catheter. The cardiac output (CO) and cardiac index (CI) can be calculated by
two methods: the thermodilution method and the Fick method. To calculate CO by
the thermodilution method, a substance cooler than blood (typically, room
temperature saline) is injected through the proximal port of the PA catheter.
As the injected substance passes through the PA, the blood temperature decreases, and this change is
measured by the thermistor at the
distal tip of the PA catheter. The change in the temperature over time is used
to calculate the CO. The Fick principle, first described by Adolph Fick in
1870, states that the total uptake or release of a substance by an organ is the
product of blood flow to that organ and the arterio-venous concentration of the
substance. With the use of this principle, pulmonary blood flow can be
determined with the arteriovenous difference of oxygen across the lungs and the
oxygen consumption. Oxygen consumption can be assumed, but a more accurate
measure of CO requires measurement of oxygen consumption. Direct measurement of
oxygen consumption can be done with either a Water’s hood or a metabolic cart.
The CI can then be calculated to compare cardiac performance among patients
of various sizes. CI is simply the CO divided by the body surface area (BSA):
CI = CO/BSA.
The resistance across the systemic vasculature and the pulmonary
vasculature can be calculated with the preceding hemodynamic information.
Systemic vascular resistance (SVR) is a measure of systemic afterload. The
equation for SVR is as follows: SVR = (MAP − CVP)/ (CO × 80),where MAP is mean
arterial pressure; CVP is central venous pressure; CO is cardiac output; and 80
is a correction factor to convert units for SVR to dynes/s/cm5. The
pulmonary vascular resistance (PVR) can be calculated in a manner similar to
the SVR substituting (mean PA pressure – PCWP) in place of (MAP – CVP) in the
preceding equation. The PVR is sometimes reported in Wood units, which is calculated
as PVR = (mean PA pressure – PCWP)/80.
Complications
There are three categories of potential complications: (1) complications
associated with central venous access (e.g., bleeding, infection, and
pneumothorax); (2) PA catheter–associated complications; and (3) misinterpretation of the acquired
data. Venous access complications related to PA catheter placement are not any
different from those associated with any procedure that involves percutaneous
access of central veins. Specific PA catheter–associated complications include
the following. (1) Atrial and ventricular arrhythmias or complete heart block
as the PA catheter is advanced through the right heart chambers. These rhythm
disturbances are typically self-limited and resolve after changing the catheter
position. As the PA catheter crosses the tricuspid valve, it can cause trauma
to the right bundle, leading to right bundle branch block, which is usually
transient. If the patient has a preexisting left bundle branch block and
develops a PA catheter–induced right bundle branch block, the patient can
develop transient complete heart block. For this reason, in patients with a
left bundle branch block, temporary pacing capabilities should be readily
available in the event that complete heart block occurs. (2) Direct damage to
the tricuspid or pulmonic valve, catheter-associated endocarditis of either
valve, and catheter-associated thrombus formation, which leads to an increased
risk of pulmonary embolus and infarction. Pulmonary infarction can also occur
from prolonged inflation of the balloon within a branch of the PA. (3) The
complication with the highest mortality rate is rupture of a PA due to either
overinflation of the distal balloon or repeated trauma to the PA. PA rupture is
fatal in approximately 50% of cases. Although rare, this complication occurs
most commonly in patients with PA hypertension. Other factors increasing the
risk of PA rupture include advanced
age, female sex, and frequent wedging of the balloon.
