The pulmonary artery catheter (РАС), in use for over 30 years and placed in about one million patients yearly, is still the gold standard for obtain ing similar hemodynamic values. But there is little information from large, multicenter randomized trials showing value and improved patient outcome. The potential complications are well documented. They include pulmonary artery (PA) rupture, PA thrombus, infection, and right atrial/ventricular perforation, catheter entrapment that may lead to rupture of the chordae, and tricuspid valve. A large multicenter trial is underway to evaluate effectiveness of PAC’s in CHF—the Escape Trial. When comparing the РАС to the BioZ, some advantages of the BioZ are obvious. It is noninvasive, requires minimal skill to perform, can be conducted in the critical care units, stepdown units, perioperative areas, emergency departments, or the outpatient clinics for a one-time measurement or continuous monitoring.
The cost of utilizing ICG versus РАС to provide hemodynamics is a difference of approximately $1,246-$3,461 per case depending on the hospital’s cost for the procedure. Silver et al. reported on the projected annualized cost savings by percent РАС volume reduction per month. As an example, a facility that performs five РАС procedures per month and decreases the number by one per month can realize a cost savings of $25,572 per year.
A summary of ICG clinical applications for the assessment of HF includes the ability to gauge whether symptoms are due to decompensation and objectively trend the changes of hemodynamic decompensation. ICG assists in the treatment of HF to determine the need for pharmacologic agents, guide in the selection of drug agents and dosing, and measure responses to therapy adjustments.
A study in progress with the BioZ, the PRospective Evaluation and identification of cardiac Decompensation In patients with HF by impedance Cardiography Test (PREDICT trial) proposes to address if the hemodynamic parameters can accurately predict the occurrence of clinically important circulatory deterioration in patients with HF.
The second new diagnostic modality, BNP, may rival the echocardiogram for providing the most useful diagnostic test although, as will be later shown, the role of the echocardiogram is still preserved. BNP is a 32-amino-acid peptide that is released from the cardiac myocytes in response to ventricular pressure or volume overload. Its chief physiologic effects include vasodilatation, increasing sodium and water excretion, and inhibition of the renin angiotensin aldosterone and sympathetic nervous activities. The BNP test is a point-of-care fluorescence immunoassay blood test requiring approximately 5 cc of whole blood or plasma. Quantitative results are generated in about 15 minutes. The utility of BNP in the diagnosis of HF, especially CHF, has been shown in a range of clinical trials. First, the evidence for its role in asymptomatic left ventricular dysfunction (ALVD) will be reviewed.
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Figure 3. Maisel A, DeMaria A, et al. Am Heart J. 2001;141:367-374.
As the ACC/AHA HF classification supports HF prevention as the goal, but when this is not achieved, early identification is the next objective. The problem of asymptomatic HF is not benign. ALVD is at least as prevalent as CHF. In the United States, an estimated 20 million people have asymptomatic left ventricular systolic dysfunction (ALVSD). As mentioned previously, studies have shown that treating asymptomatic HF is beneficial. Treatment slows and may reverse the progression of the disease. Maisel et al. studied subjects referred for echocardiography to evaluate the presence or absence of left ventricular dysfunction and illustrates that BNP, when applied to the right population, may be a reasonable screening test for this entity. BNP was able to differentiate between normal and abnormal left ventricular function. There was a significant increase in BNP seen in patients with echocardio-graphic evidence of systolic or diastolic dysfunction. The subset of systolic dysfunction with evidence of diastolic-restrictive dysfunction had a significantly higher BNP level, 1,077 ± 272 pg/ml, compared with systolic or diastolic only dysfunction which had BNP levels of 567 ±113 pg/ml and 391 ± 89 pg/ml, respectively. Patients with no HF had an average level of 37 ±6 pg/ml (Figure 3). The values of the systolic and diastolic function in this study illustrate that further testing to measure the ejection fraction would be required to differentiate the two disorders.