Right heart catheterization allows for the measurement of venous, intracardiac, and PA pressures, which can be used to determine filling pressures, resistance, and transvalvular gradients. To ensure the validity of the data prior to its clinical use, it is imperative to ensure both accuracy and precision of pressure measurements during catheterization. Thus, it is important to correctly set up the transducer system in every case. Typically, the pressure transducer is mounted on the procedure table (or patient bed, if performed outside of the catheterization laboratory) at the mid-chest level. Transducers are connected to the procedural catheter using plastic tubing filled with sterile saline. The catheter, tubing, and transducer are flushed to eliminate any bubbles, which lead to pressure waveform overdamping. After flushing, the transducer is calibrated at the mid-chest level. This process involves opening the transducer to air and allowing the system to “zero” to atmospheric pressure. Thus, measurements must be taken with a high-fidelity pressure transduction system per institutional standards, with fluid-filled tubing and optimal pressure damping to allow for appropriate interpretation of the tracings. Overdamping, often caused by air bubbles, thrombi, loose connections, or kinked catheters, can lead to underestimation of the systolic pressure, loss of the dicrotic notch, and distorted waveforms. On the other hand, underdamping, caused by excess tubing, excess components, or a defective transducer can lead to a falsely elevated systolic peak pressure, underestimated diastolic pressure, and significant waveform artifact.7
Accurate measurements should be taken at end expiration because the negative intrathoracic pressure produced during inspiration will lower intracardiac pressures. Of note, in intubated patients receiving mechanical ventilation with positive end-expiratory pressure, measurements are either taken at end inspiration, or an expiratory hold maneuver is performed with the ventilator to account for the impact of positive pressure. Venous and atrial pressure measurements are taken as a mean over several cardiac cycles, whereas ventricular pressure measurements are described as systolic and end-diastolic values. Arterial pressure measurements (ie, PA, aorta, peripheral arteries), are composed of systolic, diastolic, and mean values. Under fluoroscopic guidance, the flow-directed PA catheter can be advanced through the vena cava, into the RA, RV, PA, and PA wedge positions, with pressure and oxygen measurements taken in each position sequentially, either during forward advancement or during pullback. This information is then integrated with a comprehensive understanding of normal values to elucidate the clinical and hemodynamic picture.
The RA pressure tracing (Figure 40.1
) consists of distinct components, with positive deflections described as “waves,” and negative deflections described as “descents,” with a normal mean RA pressure range of 2 to 6 mm Hg. The “a-wave” represents an increase in RA pressure caused by atrial contraction in late diastole, directly after the P-wave on the electrocardiogram (ECG
). This is followed by the “c-wave,” which represents the displacement of the closed tricuspid valve into the RA during the isovolumic contraction phase of early systole, typically occurring at the end of the QRS complex. As ventricular systole continues, the RA relaxes and the tricuspid annulus is pulled down toward the RV apex, resulting in a drop in atrial pressure known as the “x-descent.” Corresponding to the end of the T-wave on ECG
, the hemodynamic “v-wave” represents a back-pressure reflection from atrial filling against the closed tricuspid valve during ventricular systole. Finally, the “y-descent,” a pressure decrease caused by the tricuspid valve opening in early diastole, occurs before the P-wave on the ECG
. These components combine to form the atrial pressure tracing, and the cause of clinical various presentations can be identified via aberrations in the normal waveform (Table 40.3
TABLE 40.3 Right Atrial Pressure Waveform and Common Abnormalities
Elevated a wave
Decreased RV compliance
Cannon a wave
Third-degree AV block
Absent a wave
Elevated v wave
Reduced RA compliance
Equal a and v waves
Prominent x descent
Prominent y descent
Blunted x descent
Blunted y descent
Of note, left-to-right shunting produces a prominent v-wave in the RA if shunting occurs at the atrial level.
AV, atrioventricular; RA, right ventricle, RV, right ventricle.
FIGURE 40.1 Right heart catheterization positions, waveforms, and normal values.
Crossing the competent tricuspid valve allows measurement of the RV pressure, which is described by its peak systolic pressure (12-24 mm Hg) and end-diastolic pressure (2-6 mm Hg) (Figure 40.1
). However, the pressure tracing can be subdivided into four distinct phases: systole is composed of (1) isovolumetric contraction, from tricuspid valve closure to pulmonic valve opening, and (2) ejection, from pulmonic valve opening to its closure; diastole is composed of (3) isovolumetric relaxation, from pulmonic valve closure to tricuspid valve opening, and (4) filling, from tricuspid valve opening to its closure.
Clinically, elevations in RV systolic pressure occur most commonly in the setting of pulmonary hypertension, but can also be owing to left ventricular (LV) pressure overload, pulmonic valve stenosis, RV outflow tract (RVOT
) obstruction, or hemodynamically significant left-to-right shunting. Conversely, reductions in RV systolic pressure can be caused by cardiogenic shock, hypovolemia, or cardiac tamponade.
Similarly, elevations in RV end-diastolic pressure occur most commonly in the setting of volume overload of any cause, such as congestive heart failure, but can also be caused by decreased chamber compliance, ventricular hypertrophy, tricuspid regurgitation, pericardial constriction, or cardiac tamponade. Low RV end-diastolic pressure is primarily caused by hypovolemia but can also occur in the setting of tricuspid valve stenosis.
Beyond the pulmonic valve and into the main PA, the PA tracing is described by its peak systolic pressure (12-24 mm Hg), diastolic pressure (6-12 mm Hg), and mean pressure (10-22 mm Hg) (Figure 40.1
). Similar in appearance to the aortic tracing, albeit with lower pressures, a dicrotic notch is seen in the PA, representing closure of the pulmonic valve.
An elevated PA systolic or diastolic pressure can occur in the setting of pulmonary hypertension (of any cause), mitral stenosis, mitral regurgitation, volume overload, left-to-right
shunting, and pulmonary embolism (PE). A reduced PA systolic or diastolic pressure can occur in the setting of hypovolemia or any lesion restricting PA inflow (tricuspid valve stenosis, pulmonic valve stenosis, RVOT
obstruction, tricuspid atresia, Ebstein anomaly). An isolated reduction in PA diastolic pressure (and therefore a wide PA pulse pressure) can occur because of pulmonic valve regurgitation, whereas a reduced PA pulse pressure occurs in the setting of cardiogenic shock, RV infarct, PE, or cardiac tamponade.
Pulmonary Artery Wedge Pressure.
estimates left atrial (LA) pressure and is used as a measure of left-sided intracardiac filling pressure. In the absence of mitral valve disease or cardiac disease, mean PAWP
is similar to mean LV end-diastolic pressure. However, these pressures may be disparate in patients with aortic valvular disease, systemic arterial hypertension, and coronary artery disease, in whom LV end-diastolic pressure exceeds mean PAWP
because of LV noncompliance and a prominent a wave. Hence, in patients with mitral valve disease or cardiac disease, mean PAWP
cannot be used reliably to assess LV end-diastolic pressure.
To obtain a wedge pressure, the inflated, balloon-tipped catheter is advanced into a branch PA with the intent of blocking PA inflow. This allows the end hole of the catheter to indirectly measure the LA pressure. Therefore, the PAWP
tracing is similar to the left atrial pressure tracing, consisting of the same a-c-x-v-y waveform (Table 40.4
). Similar to the RA, the PAWP
“a-wave” represents atrial systole, the “c-wave” represents the displacement of the closed mitral valve into the LA, and the “x-descent” represents LA relaxation. The “v-wave,” which is intimately related to atrial compliance, represents atrial filling occurring during ventricular systole. Finally, the “y-descent” is caused by mitral valve opening in early diastole. Importantly, the PAWP
tracing is often less distinct than the RA waveform and delayed compared with the ECG
, as the pressure is transmitted through the pulmonary vascular system before being measured by the catheter.
With a normal mean of 6 to 12 mm Hg at end expiration, the PAWP
is 0 to 6 mm Hg less than the PA diastolic pressure under normal conditions (ie, no increased pulmonary vascular resistance [PVR
]). An appropriate “wedge” position should be confirmed by measuring greater than 95% oxygen saturation of blood drawn through the catheter end hole while in the wedge position. If the oxygen saturation is lower than 95%, the balloon is likely “underwedged,” leading to what is essentially a damped PA measurement. Conversely, the catheter can also be “overwedged,” leading to a damped PAWP
waveform (nearly flat) and an estimated PAWP
pressure that is higher than the PA diastolic pressure. Thus, in cases where the mean PAWP
exceeds the PA diastolic pressure, “overdamping” should be considered.
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