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.
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.
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.
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.