It was while watching sailboats float one summer day in the late 1960s on the Santa Monica beaches that Dr.Jeremy Swan and Dr.Willam Ganz got the idea of “floating” a balloon-tipped catheter through the right heart chambers into the pulmonary vasculature to record pressures. The Swan-Ganz (SG) catheter, also known as a pulmonary artery (PA) catheter or right heart catheterization (RHC), has revolutionized care in cardiology, pulmonary, and critical care medicine.
The indications for a RHC to be performed have changed over the last fifteen years. RHC is often performed in the evaluation of advanced heart failure, heart and lung transplantation, and in the evaluation of pulmonary hypertension. In critical care medicine, the use of PA catheters has been reduced dramatically. Much of this is related to multiple large studies that showed outcomes did not improve (and may even be worsen) the care of critically ill patients who undergo RHC. Whether this is related to varying expertise and comfort levels with adequate catheter placement and data interpretation is open to debate. However, RHC is still considered in the evaluation of “mixed” shock states where it is unclear whether a cardiogenic or septic cause may be the leading etiology. A RHC can be performed if noninvasive tests do not clarify the etiology or if the patient does not respond to empiric therapy.
The RHC allows direct evaluation of the central venous, right ventricular, and pulmonary artery pressures. Measurements of the pulmonary capillary wedge pressure (PCWP) or the pulmonary artery occlusion pressure (PAOP) allows an indirect or surrogate evaluation of the left atrial pressure. Calculations can be used to determine the pulmonary vascular resistance, cardiac output, and cardiac index via thermodilution through a thermistor or using the Fick formula.
The RHC is a crucial step in the evaluation of patients with pulmonary arterial hypertension. The World Health Organization has divided the etiologies of pulmonary hypertension by pathophysiology into five broad groups. The majority of cases of pulmonary hypertension are secondary to left heart diseases such has congestive heart failure and valvular diseases (WHO Group 2) or chronic pulmonary diseases (WHO Group 3). Though the prevalence of idiopathic pulmonary arterial hypertension (PAH) may be low, the increasing recognition of liver and autoimmune diseases as well as the prolonged latency of anorexigen-induced PAH is likely to increase the number of individuals diagnosed with this disease.
Since the introduction of Epoprostenol (Flolanâ) in 1996, the pharmacological therapies available in our armamentarium to treat pulmonary hypertension have increased dramatically over the last eighteen years. In the past year alone, three new medications have been approved for treatment of Group 1 PAH as well as one specifically for chronic thromboembolic pulmonary hypertension (CTEPH; WHO Group 4).
With more treatment options, the responsibility to adequately characterize the disease has increased. It is well known that the echocardiogram is the best screening test in pulmonary hypertension but not as the sole diagnostic test. Echocardiograms can both underestimate and overestimate right heart pressures. The right heart catheterization is crucial in the evaluation of not only the pressures but an assessment of the pulmonary vascular resistance and cardiac output. Also, the pulmonary wedge pressure allows a differentiation between pulmonary hypertension secondary to elevated left heart pressures versus intrinsic pulmonary disease. The pulmonary vascular resistance allows both an initial evaluation and a prognostication of the risk of right ventricular failure for patients with pulmonary hypertension. This also provides an assessment of the degree of vascular remodeling in the pulmonary vasculature. The cardiac output often correlates with the patient’s functional class and degree of cardiac decompensation secondary to the disease process.
As more pulmonary hypertension is identified on echocardiograms, it is important for patients to be referred to a pulmonary hypertension specialist for further evaluation. This allows a thorough assessment of the patient’s risk factors for other causes of pulmonary hypertension and the need for a potential right heart catheterization for further information and data. With better characterization of patients with pulmonary hypertension and newer treatment options, the quality of life and exercise capacity can be improved for these patients.
By Hadi Chohan, M.D.