10 Left and Right Heart Catheterization
Heart catheterization involves placing a catheter into a cardiac chamber. The primary purpose is generally to obtain hemodynamic information, although other useful information can be gained through catheterization of the atria or ventricles including a measurement of systolic function (e.g., ventriculography can provide important information on left ventricular [LV] function) and detection of abnormal intracardiac connections. Heart catheterization is distinct from coronary angiography in which a catheter is placed in the coronary ostia (and thus external to the heart), although the two procedures provide complementary information and typically are performed as a single procedure.
The pulmonary artery (PA) catheter (also known as the Swan-Ganz catheter or right heart catheter) was developed in the 1970s by Dr. Harold Swan, Dr. William Ganz, and colleagues. When a PA catheter is properly placed with its distal tip in a PA, the proximal port that is approximately 30 cm from the catheter’s tip generally lies in the right atrium (RA). This port can be used to transduce pressure or as central access for infusion of fluids or intravenous medications. The port at the distal tip of the catheter is used to measure PA pressure and pulmonary capillary wedge pressure (PCWP). An inflatable balloon present at the distal end of the PA catheter makes it possible for the catheter to temporarily occlude the PA and for the distal port to measure the pressure distal to the catheter. This pulmonary venous pressure, in most cases, reflects the pressure in the left atrium (LA) and the LV diastolic pressure. A thermistor at the distal tip makes it possible to measure the change in temperature of fluid injected into the proximal port of the PA catheter and to calculate cardiac output (CO), as will be described in more detail. Thus, placement of a PA catheter makes it possible to obtain information on cardiac function, including ventricular preload (RA pressure is a reflection of right ventricular [RV] preload and PCWP is a function of LV preload), afterload (systemic vascular resistance [SVR] and pulmonary vascular resistance [PVR]), and CO.
PA catheters are used primarily in three different settings: in the cardiac catheterization laboratory, in intensive care units (ICUs) and in the operating room. PA catheters are used in the cardiac catheterization laboratory in patients for whom detailed hemodynamic information is needed. Examples include patients with valvular heart disease, cardiomyopathy, and suspected intracardiac shunts. For patients with dyspnea and low CO syndromes in whom the relative contributions of systolic and diastolic function are unknown or in whom the differential diagnosis includes restrictive cardiomyopathy and pericardial constriction, right heart catheterization performed concurrently with left heart catheterization is invaluable because patients with pericardial constriction can improve dramatically with pericardiectomy (see Chapters 20, 42, and 43). There is no consensus on which patients need right heart catheterization, and even in a single catheterization laboratory there may be wide practice variation in which patients undergo right heart catheterization.
It is generally accepted that right heart catheterization can be useful for diagnosis. A separate but related question is whether it is beneficial to make clinical management decisions over hours, days, or weeks using information obtained from an indwelling PA catheter. Several randomized studies have addressed this issue for operative patients and patients in an ICU setting. These studies, which have enrolled patients with heart failure, patients undergoing high-risk noncardiac surgery, and patients with acute respiratory distress syndrome, have shown no beneficial effects of using PA catheter–derived hemodynamic information as a basis for ongoing clinical management decision making. Indeed, there has been no improvement in survival rates and an increased rate of complications in patients randomized to PA catheter–based therapeutic decisions. These studies have been criticized for several reasons, including improper patient selection (e.g., including low-risk patients who would not be expected to benefit), study design (e.g., expecting a monitoring tool to affect outcomes without specified treatment protocols), and the use of variably experienced physicians for both catheter placement and interpretation of data. Therefore, there is no clear consensus on whether PA catheters are beneficial or harmful for ongoing management in the operating room or in the ICU setting. That said, it is clear that in certain clinical settings, important initial diagnoses can be made and/or confirmed with the use of a PA catheter, as described below.
Box 10-1 lists some common indications for PA catheter insertion. As with any invasive procedure, the risks and benefits should be weighed for the individual patient, and a PA catheter should be inserted only if there is a specific question that will be answered with respect to making a diagnosis and/or guiding treatment. For instance, a PA catheter may be used to determine the cause of shock in a hypotensive patient in whom the cause is not evident based on signs, symptoms, and noninvasive testing. Guidelines and consensus statements on indications for PA catheter placement and use have been formulated by numerous groups, including the American Society of Anesthesiologists, an expert panel of the European Society of Intensive Care Medicine, the American College of Chest Physicians, the American Thoracic Society, the American College of Cardiology, the Society of Critical Care Medicine, and a 1998 workshop convened by the U.S. Food and Drug Administration. The reader is referred to these documents for information on the use of PA catheters in specific indications.