Reprinted with permission from ECHOCARDIOGRAPHY, Volume 18, No. 1, January 2001 Copyright ©2001 by Futura Publishing Company, Inc., Armonk, NY 10504-0418

Noninvasive Right and Left Heart Catheterization: Taking the Echo Lab Beyond an Image-Only Laboratory Vincent L. Sorrell, M.D., F.A.C.C., F.A.C.P., and William C. Reeves, M.D., F.A.C.C., F.A.C.P. Sections of Cardiology and the Cardiovascular Center of East Carolina University, Brody School of Medicine, Greenville, North Carolina The assessment of cardiovascular hemodynamics is an extremely important component of managing patients with cardiac diseases. For years, this has been accomplished primarily through the use of right and left heart catheters placed within the cardiac chambers. Since this is an invasive technique, it should only be used when necessary; patient discomfort, infections, and overall risks for physicians would be reduced if noninvasive methods were utilized when available. Echocardiography (echo) provides the greatest ability to determine cardiovascular hemodynamics noninvasively, but requires the utmost precision and care to avoid misinterpretation. When used correctly, echocardiographic modalities provide an even greater assessment of the cardiac patient than invasive techniques. A safer and more comprehensive interpretation is available, and thus, echo should be considered the modality of choice—the new gold standard. (ECHOCARDIOGRAPHY, Volume 18, January 2001) Doppler, echocardiography, hemodynamics, intracardiac pressure Hemodynamics are deŽned as “the study of the movements of the blood and of the forces conceived therein.”1 The Žrst evaluation of hemodynamic assessment is usually achieved through a careful physical examination. This remains clinically important, but is often incomplete or unreliable, even with experienced specialists.2 Further information requires either an invasive direct intracardiac assessment using venous and/or arterial catheters, or a noninvasive echocardiographic approach combining two-dimensional (2-D), M-mode, and Doppler modalities. This article is a guide to the careful assessment of cardiac hemodynamics using echocardiography (echo). Quantitation of valve regurgitation and stenosis is primarily performed with echo; therefore, the determination of intracardiac pressures and cardiac output, primarily performed with invasive techniques, is the chosen focus. Through a comparison of invasive and noninvasive techniques, it also conŽrms that echocardiography

Address for correspondence and reprint requests: Vincent L. Sorrell, M.D., F.A.C.C., Medical Director, Graphics and Exercise Physiology Labs, University Health Systems of Eastern North Carolina, Mail route: TA-B 378, Greenville, NC 27858. Fax: 252-816-5884; E-mail: [email protected]

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can be considered a viable alternative to the historical gold standard of cardiac catheterization in many clinical situations. Background No echo method detects cardiac pressures directly. Doppler echo noninvasively estimates pressure gradients across valves or through chamber defects. Through a modiŽcation of the Bernoulli equation, highly reliable, reproducible, and clinically accurate estimated intracardiac pressures are obtained. This method remains the principal echo technique used today. Despite eliminating the ow acceleration and viscous friction factors from the original Bernoulli equation, the modiŽed, or simpliŽed, version is accurate (P 5 4v2 ).3,4 Fortunately, physiologic regurgitation is extremely common and allows measurement of gradients even in normal individuals. As hearts become diseased, regurgitation is increasingly more frequent, allowing an even greater likelihood for these measurements. The noninvasive Doppler determination of cardiac output was validated in man more than 15 years earlier. During this period, ultrasound equipment, clinical experience, and additional validation in various disease states expanded the utility of this basic principal.5

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Figure 1. Subcostal two-dimensional image of a dilated inferior vena cava during quiet expiration (left panel) and during forced inspiration (“sniff”) (right panel). The right atrial pressure was markedly elevated.

Methods Initially, either the physician or the sonographer performs an evaluation of the patient. It is essential for optimal hemodynamic assessment that the blood pressure be recorded routinely during each echo study. The height and weight also should be obtained to calculate the body surface area (BSA). Additionally, our sonographers routinely record whether the patient is in any visible distress. For example, the presence of orthopnea warrants careful investigation for the presence of an elevated left atrial pressure (LAP), while distended neck veins are important clues to an elevated right atrial pressure (RAP). The ICU patient with an arterial line, central venous line, or pulmonary artery (PA) catheter provides important data for the echocardiographer. The sonographer should record the most recent measurements at the time of the echo study. An exact arterial blood pressure is reassuring when providing noninvasive hemodynamic data. The PA catheter provides an opportunity for quality assurance (QA) of echo techniques by comparing the noninvasive and invasive results and may identify large discrepancies. If this occurs, careful evaluation of all the available noninvasive (and invasive) parameters must ensue to determine the most valid result. RAP RAP is most often estimated by the inferior vena cava (IVC) as imaged in the subcostal window in the sagittal plane. The ultrasound beam penetrates the abdominal wall and hepatic tissue, and a sonolucent space behind the 32

liver is readily imaged. The IVC is a highly compliant vessel that changes diameter with changes in the volume of venous return and central venous pressure. With inspiration, the IVC collapses (normal: , 50% reduction in lumen diameter). The absence of IVC narrowing , 50% of the maximal expiratory diameter (plethora), indicates an elevated RAP . 10 mmHg.6 Markedly dilated IVC diameter (. 20 mm) in addition to the lack of inspiratory variation is suggestive of an even greater elevation of RAP. In the mechanically ventilated patient, a dilated IVC less accurately predicts elevated RAPs, but the presence of a small IVC does exclude a signiŽcantly elevated RAP.7 Patients with quiet respiration and minimal IVC variation can be asked by the sonographer to suddenly inhale (“sniff ”), and the subsequent IVC motion is recorded (Fig. 1). Other qualitative correlates of an elevated RAP include enlarged RA chamber (. 20 cm2 ), prominent patent foramen ovale (PFO) with right-to-left shunting, or a dilated coronary sinus (best seen in the parasternal long-axis image). Right Ventricular Pressure The most commonly utilized method to calculate the right ventricular systolic pressure (RVSP) is through the use of the tricuspid regurgitant (TR) Doppler maximum velocity envelope. The gradient between the right ventricle (RV) and the RA is measured with Doppler and the peak velocity is converted to a pressure gradient with the modiŽed Bernoulli equation. The RVSP is then determined by adding the pressure gradient obtained to the “receiving

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Figure 2. Two-dimensional parasternal short-axis image of the LV during diastole (left panel) and systole (right panel). Note the attened septum suggesting elevated right ventricular pressure (and volume overload).

chamber,” in this case, the RAP (RVSP 5 4[TRV m ax ]2 1 RAP). This technique is the basic concept utilized throughout Doppler imaging to determine intracardiac pressures. Color ow Doppler is helpful in obtaining an accurate beam alignment and minimizes underestimation related to nonparallel angles. Contrast agents (even simple agitated saline) allow enhancement of the Doppler envelope and ensure a more accurate peak velocity measurement.8 We have found it important to evaluate the TR jet from multiple transducer locations, including the following: the apical fourchamber view; the parasternal long-axis RV inow view; the parasternal short-axis basal view; and the subcostal long-axis view. The Doppler envelope achieved with the highest velocity and the least Doppler dispersion (“cleanest” Doppler envelope) is usually the most accurate. When a ventricular septal defect is noted, an additional opportunity for estimating the RVSP exists, in the absence of left ventricle (LV) outow tract obstruction. With continuous-wave Doppler placed across the color ow Doppler-identiŽed shunt, the LV to RV gradient is measured. The cuff pressure represents the LV pressure and the RVSP is calculated with subtraction (RVSP 5 cuff SBP 2 4 [VSD grad]2 ).9 Doppler methods are the only means for quantitative assessment of cardiac pressures, but other indirect, qualitative measures of an elevated RVSP include a dilated RV chamber, RV myocardial hypertrophy, or attening of the interventricular septum (IVS) during sysVol. 18, No. 1, 2001

tole, giving a “D-shape” appearance on the parasternal short-axis image.10 (Fig. 2) Pulmonary Artery Pressure A determination of the pulmonary artery pressure should be a routine part of each echo examination. The normal pressures within the pulmonary artery are systolic 35 mmHg, diastolic 15 mmHg, and mean 25 mmHg. Thus, a TR velocity . 2.8 m/sec represents an elevated RVSP even with a normal RAP. The methods described above to evaluate the RVSP also reect the pulmonary artery systolic pressure (PASP), when right ventricular outow obstruction is absent. Other parameters used to estimate the PA pressures include the M-mode evaluation of the anterior leaet of the pulmonic valve. Normally, a prominent atrial (a) wave is seen and the closing motion is uninterrupted. The a-wave is absent with signiŽcant pulmonary artery diastolic pressure (PADP) elevation, and a mid-systolic closure occurs, producing a “W-shape” M-mode echo with signiŽcant PASP elevation.11,12 (Fig. 3) When the TV closure/opening interval (or the TR duration) signiŽcantly exceeds the pulmonary ejection time (ET), pulmonary hypertension is suggested.13 Inversely, when this interval (or the TR duration) barely exceeds the pulmonary ET, pulmonary hypertension is unlikely. Also, Doppler echo provides insight into the PASP by evaluating the acceleration of the ow by the ejecting RV. Normally, peak ejection velocity occurs in mid-systole (usually more than 120 msec after the onset of ejection) and

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Figure 3. Transesophageal echo image with M-mode of the pulmonic valve. Note the absent a-wave and mild systolic “notching” consistent with elevated pulmonary pressures.

the right ventricular outow tract (RVOT) Doppler envelope has a “rounded” appearance. As the pulmonary pressures increase, the RV pressures rise more sharply and the peak ejection velocity occurs earlier in systole.14 The normally rounded Doppler envelope now has a characteristically “spiked” early waveform appearance. With severe pulmonary hypertension, this acceleration time (AT; time to peak velocity) is , 60 msec. Mahan’s equation utilizes the fact that the acceleration phase of the RVOT Doppler envelope shortens as the mean pulmonary artery pressure (MPAP) increases, and is another tool in the assessment of these pressures (MPAP 5 792 0.45 3 AT).15 This

method is limited by heart rate and should only be considered accurate when the heart rate is between 60 and 100 beats/min. The PADP also can be obtained through noninvasive measures. Since pulmonary regurgitation (PR) is frequently present with pulmonary hypertension, the Doppler envelope of this provides a means of obtaining the PA to RV pressure gradient. Normally, there is an early and late component to this PR Doppler envelope. The late PR velocity, occurring at end-diastole, is converted to pressure and added to the RAP to estimate the PADP (PADP 5 4[PR late]2 1 RAP). 16,1 7 (Fig. 4) The early component of the PR Doppler en-

Figure 4. Continuous-wave Doppler of pulmonary regurgitation with an elevated early (A) and late (B) diastolic velocity. Also note the systolic Doppler envelope (top of Žgure, just below the ECG tracing), with the shortened acceleration time consistent with elevated pulmonary artery pressures.

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velope provides an opportunity for QA. This early velocity, when converted to pressure and added to the RA pressure, reects the MPAP. The PA systolic and diastolic pressures have already been obtained noninvasively, and the MPAP can be calculated (MPAP 5 [PASP 2 PADP]/3 1 PADP). This result can then be compared with the directly measured MPAP (from the early PR gradient) and allows a comparison of two methods. Determination of the MPAP with Mahan’s equation allows another opportunity for QA. When a patent ductus arteriosus (PDA) is present, the PADP is estimated through an evaluation of the Doppler gradient. Knowing the aortic diastolic pressure (diastolic cuff pressure) allows one to subtract the PDA-derived diastolic pressure gradient and obtain the estimated PADP (PADP 5 4 [PDA] 2 1 RAP).18 LAP Direct LAP can only be obtained with a catheter placed across the atrial septum, a technique that is associated with signiŽcant complications. PA wedge catheters are often used for indirect estimates of the LAP. It is important to remember that these catheters measure the pulmonary artery occlusive pressure (PAOP), which accurately reects the LAP only when there is no signiŽcant transpulmonary gradient. Unfortunately, a number of the patients undergoing PA catheter placement for LAP estimation have concomitant parenchymal and vascular lung disease, and may have a signiŽcant transpulmonary gradient and hence, an inaccurately determined LAP.19 A lack of proper catheter usage, damping from the uid-Žlled catheters, or errors related to calibration techniques also can cause inaccuracies. These facts emphasize the importance of QA methods with both invasive and noninvasive techniques.20 A number of noninvasive methods have been developed, and although imprecise in their absolute LAP, they accurately determine low, normal, and elevated LAP. The most commonly utilized method for this assessment is the pulsed-wave Doppler analysis of the mitral valve inow and pulmonary venous waveform patterns. A common error of mitral inow evaluation is misalignment of the ultrasound beam or sample volume and underestimation of the early (E) and atrial (A) Doppler envelopes. This often can be corrected with a more lateral placement of the transducer position and placeVol. 18, No. 1, 2001

ment of the sample volume at the leaet tips when recording the Doppler inow signal. The Žnding of an elevated E-wave velocity (. 1.5 m/sec) or a “restrictive” pattern (prominent E wave; high E/A ratio[ $ 3:1]; shortened deceleration time[# 140 msec]; diminutive A wave) strongly suggests an elevated LAP. The M-mode echo of the mitral valve motion provides important information for the purpose of evaluating the LAP. Premature closure (before the QRS complex) is a reliable indication of an increased left ventricular end-diastolic pressure (LVEDP). 21 A “b-bump” (extra anterior motion between the A and C points) noted on the anterior MV leaet M-mode echo is representative of an elevated LAP (often . 20 mmHg).22 (Fig. 5) Detailed evaluation of the pulmonary vein (PV) ow has been very helpful in determining the LAP. It is important to have a consistent approach to the PV analysis. The technique found most useful in our laboratory for this assessment has been to angulate the transducer inferiorly while imaging with the color ow Doppler to enhance the color ow pattern in the right upper PV adjacent to the base of atrial septum in the apical four-chamber view. Then, the sample volume size is increased to 3– 4 mm and placed 1–2 cm into the PV. The patient is told to hold his breath at end-expiration to minimize respiratory motion and reduce wall-motion artifact, which may be confused with the atrial reversal (AR) wave. In many individuals, the sample volume location may need to be moved for optimal recording of the systolic (S) and diastolic (D) Doppler envelopes and then moved to another location to record the AR Doppler envelope. An AR velocity . 0.35 m/sec or an AR duration exceeding the mitral A wave duration (by more than 30 msec) strongly suggests an elevated LAP. A PV D wave . S wave is further suggestive of an elevated LAP. The Žnding of a systolic fraction (contribution of S wave velocity time integral [VTI]) , 55% was able to consistently predict an LAP , 15 mmHg in a hemodynamic study using transesophageal echocardiography (TEE).23 Other investigators have recently shown that a systolic fraction . 40% in chronic heart failure represents a LAP . 18 mmHg.2 4 When aortic regurgitation is present, the aorta to LV diastolic gradient is obtained with continuous-wave Doppler and the late diastolic velocity can be measured. Using the cuff diastolic pressure as an estimate of the aortic di-

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Figure 5. M-mode echo of the mitral valve showing a prominent “b-bump” just before closure. This Žnding is consistent with an elevated LAP.

astolic pressure, the LVEDP is readily estimated (LVEDP 5 cuff DBP 2 4 ARVm ax 2 ).25 In the absence of mitral stenosis, the LVEDP reects the end-diastolic LAP. It is important to carefully evaluate the interatrial septum and its motion with 2-D echo. The absence of the expected interatrial shift towards the LA that occurs during inspiration with positive pressure mechanical ventilation is suggestive of a LAP . 15 mmHg.26 When an atrial septal defect is present, the LA to RA velocity can sometimes be measured with pulsed or continuous-wave Doppler via the subcostal window. This velocity-derived pressure gradient can be added to the RAP to estimate the LAP. An indirect estimate of the LAP is the LA size. When this is enlarged (. 20 cm2 ) for no obvious cause (e.g., atrial Žbrillation), an elevated LAP should be considered.27 Lastly, the LAP pressure can be measured theoretically using the following formula: LAP 5 6 AR VTI 1 0.1 E V EL - 1.5 (IAS) 1 3.6. (IAS 5 0 if the septum bows to the right; 1 with left bowing during inspiration; 2 to left).2 8 Using this formula with TEE, the investigators were able to accurately predict the LAP during various hemodynamic challenges (partial aortic crossclamp; partial IVC compression; saline infusion) with a minimal standard error of 1.1 6 2.7 mmHg. Assessment of Ventricular Function Cardiac output (CO) is most commonly measured invasively through the use of a right heart 36

catheter using the thermodilution method.29 Noninvasively, one can trace the Doppler envelope obtained by placing a pulsed-wave Doppler sample volume in the left ventricular outow tract (LVOT). The VTI is obtained by tracing the systolic velocity Doppler envelope (cm) and this distance is multiplied by the sampled cross-sectional area (LVOT diam x LVOT diam x 0.785 5 cm2 ) to obtain the stroke volume (SV) (cm3 ). This can be multiplied by the heart rate to obtain a noninvasive estimate of the CO results (L/min). This divided by the BSA (m2 ) will give the cardiac index (normal 5 2.8 2 4.2 L/m/m2 ). With the recently increased awareness of the potential hazards, the known incidence of complications, and the lack of proven beneŽt from right heart catheterization, coupled with the safety and accuracy reported with this Doppler echo method, it is not unreasonable to consider the echo method the procedure of initial choice. Conners et al. reported a nearly 40% greater likelihood of death in patients receiving a Swan-Ganz catheter on day 1 versus patients without such a monitoring device.3 0 Despite heavy criticism regarding the potential bias from the retrospective design of their trial, they used advanced statistical analyses to make certain patients were closely matched for disease and illness severity. Still, it is likely that a certain proportion of patients’ poor outcome was related to comorbidities that mandated the placement of the catheter, rather than the catheter itself. Inaccuracies may occur with this Doppler

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method of noninvasive CO calculation if significant valve regurgitation (or other intracardiac shunting) is present, but these errors also occur with PA catheter measurements.3 1,32 The availability of imaging with pulsed Doppler for CO calculation provides a signiŽcant advantage over catheter-derived techniques. Similar errors in measurements occur from valve regurgitation with both techniques, but the degree of regurgitation is readily identiŽed with echo, using color ow Doppler. This allows the interpreter the opportunity to modify the CO assessment. With signiŽcant aortic regurgitation (moderate or greater), the commonly measured aortic SV is falsely overestimated, and another valve should be used to calculate the CO. Usually the pulmonic valve is the next Doppler site of choice since the RVOT is often simpler to measure and provides a more geometrically consistent shape than either the mitral or tricuspid annulus. In a closed cardiac system (no atrial or ventricular septal shunting), any valve could be used for the CO measurement since the SV measured at each location should be the same. M-mode echo also provides important insight into the CO. Without signiŽcant aortic valve disease, the Žnding of the initiation of aortic valve closure prior to complete closure implies a reduced SV unable to maintain blood ow at an equal rate throughout systole.33 An empiric observation suggestive of a reduced CO has been that the total amplitude of mitral valve motion is reduced.3 4 If signiŽcant MR exists, then Doppler-derived estimates of the ventricular function can be expanded to include an evaluation of the Doppler envelope of MR. Since the LAP changes relatively little during early ventricular systole, the rate of change of the MR velocity is determined primarily by the rate of change of simultaneous LV pressure. Hence, the change in pressure of 32 mmHg divided by the interval of time (D t), during which MR velocity increases from 1–3 m/sec, determines the noninvasive dP/dt (Normal 5 . 1200 m/sec/ sec).3 5 QA Since the diameter measured for stroke volume calculations must be squared to obtain the cross-sectional area, any error in measurement is then squared. Care must be made to minimize any errors in this measurement. With second harmonic imaging now routinely availVol. 18, No. 1, 2001

able in many echo laboratories, lateral resolution has signiŽcantly improved, and this may assist in more accurate measurements. It is helpful to practice in patients with very normal LV function as well as those with severe LV dysfunction, since these two groups are the easiest to visually assess and derive a rough estimate. Another method of QA is to compare calculated CO using the LVOT area with the CO from the RVOT area (these should be equal in the absence of AR or PR).3 6 Performing multiple LVOT measurements in the same individual may help identify the standard error of the individual interpreter and echo laboratory. Most studies have shown that invasive catheters have an accuracy of 6 10%, and this is an achievable goal with noninvasive techniques.37 Although the majority of the studies cited a high correlation with invasively determined data, some individual data points were significantly different. Most of these measurements are dynamic variables and can change from moment to moment. The majority of studies comparing these methods were not done simultaneously and this fact may have contributed to some of the noted differences. Importantly, the absence of an ideal reference standard also limits any comparative Žndings. Even when a single “reference standard” technique is used in the same patient, repeat measurements show imperfect agreement. Determinations of CO by thermodilution indicator (TDI) often differ from each other as much as determinations by Doppler and TDI methods differ. PA measurement is a highly complex skill with numerous technical variables that can effect the reliability and validity. Individuals using these techniques must maintain the ability to trouble-shoot errors in measurements. Accurate Doppler velocity measurements require examination of blood owing parallel to the ultrasound beam, as angulation errors will incrementally underestimate peak velocity and VTI. (Figs. 6A and 6B) Optimal Doppler signals can be obtained only with experience and attention to detail. Precise velocity recordings are a prerequisite for reliable derivations of intracardiac pressures. The sonographer should use intravenous-agitated saline without hesitation to enhance a weak right heart Doppler signal. Parallel alignment can be improved using CFD as a guide. The physician should utilize multiple echo Žndings to support any measured data and initially correlate the Žnd-

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Figure 6. A. Continuous-wave Doppler envelope of TR. Although the Doppler envelope appears complete and accurate (right panel), note the angle of the Doppler cursor and the direction of the TR jet. The peak velocity was 3.0 m/sec (peak gradient 5 36 mmHg). B. Continuous-wave Doppler envelope of TR in the same patient as Figure 6A. Note the Doppler cursor angle is now parallel with the jet direction (inset). The peak velocity was 3.6 m/sec (peak gradient 5 52 mmHg).

ings with invasive data. Eventually, invasive data should be minimized. Future Perspectives Each of the methods described is currently available in most echo laboratories and only requires the commitment of the sonographer and the physician to maintain QA. The majority of the techniques described have been available for more than a decade and were speciŽcally referenced to emphasize their long-standing clinical validity and utility (see reference dates). Newer methods of advanced 2-D echo, 38

M-mode, and Doppler techniques are constantly being developed; they will further improve our ability to perform a complete noninvasive assessment of cardiac hemodynamics. Proximal isovelocity surface area (PISA) calculations are being simpliŽed for the clinical arena and show promise for quantitative measurements of regurgitant volume. Some institutions have begun performing color M-mode through the mitral valve or pulmonary vein (e.g., TEE), and have found this a reliable marker for estimating LAP.38 Other newer utilization of old techniques will continue to be

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Figure 7. Summary Žgure showing a representative waveform obtained with a right heart catheter. Each of the various echocardiographic parameters is also labeled for direct comparison. Boxes (invasive date): RAP 5 right arterial pressure; RVSP 5 right ventricular systolic pressure; RVDP 5 right ventricular diastolic pressure; PASP 5 pulmonary artery systolic pressure; PADP 5 pulmonary artery diastolic pressure; PCWP 5 pulmonary capillary wedge pressure. Other abbreviations: CS 5 coronary sinus; IVC 5 inferior vena caval size and respiratory variation; RA size 5 right atrial size; IVS 5 interventricular septal motion; TR velocity 5 tricuspid regurgitation velocity-generated gradient; VSD 5 ventricular septal defect gradient; PV 5 pulmonic valve M-mode motion; PR velocity 5 pulmonic regurgitation gradient; AT (RVOT) acceleration time of the right ventricular outow tract Doppler envelope; PDA 5 patent ductus arteriosus gradient; E/A 5 mitral inow E and A wave evaluation; LA size 5 left atrial size; S/D 5 pulmonary vein S and D wave evaluation; IAS 5 interatrial septal motion; AR 5 pulmonary vein atrial reversal velocity and duration; AI velocity 5 aortic insufŽciency gradient; MV 5 mitral valve M-Mode motion; * 5 LAP formula (see text).

investigated and will likely prove helpful in the noninvasive assessment of cardiac hemodynamics. With newer contrast agents, we may soon be able to diagnose intracardiac pressures by the persistence of the agent. Since one of the variables that determine the duration of microbubble visibility is the pressure within the heart chamber, it may become possible to use this information to develop an algorithm to solve for this unknown pressure. Knowing the number of bubbles injected allows a calculation of the washout, which may soon provide an estimate of the CO. Even more simply, the video intensity of the bubbles as they traverse the LV can be measured. Fifteen years earlier, prior to the availability of the Žrst Food and Drug Administration approved third-generation microbubble (Optison, 1998), this method was correlated with thermodilution CO.39 It is this type of foresight that helps solidify echo as the gold standard of the new millennium. As newer microbubbles become approved for clinVol. 18, No. 1, 2001

ical use, additional hemodynamic data is likely to evolve. One stated advantage of the invasive method is the ability for continuous monitoring of the critically ill patient. Continuous monitoring remains an indication for invasive catheterization, but may soon also be available with newer transnasal, esophageal echo probes. These probes are slightly larger than nasogastric tubes and allow monitoring for longer periods of time.4 0 Many ultrasound systems now offer automated, immediate CO determinations and these are likely to become even more clinically useful as validation studies are reported. Finally, three-dimensional echocardiography is attaining clinical utility and will soon become the likely noninvasive method of choice for accurate cardiac output calculations. With precise diastolic and systolic area measurements, geometric assumptions that currently limit this volumetric method are minimized.

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Summary Some representative intracardiac pressure waves obtained during cardiac catheterization are shown in Figure 7. The various echocardiographic modalities able to assist in the estimation of these pressures also are listed. It is important not to rely too heavily on any single measurement, but instead utilize multiple parameters whenever possible. One major advantage of echo over catheter techniques is related to its inherent imaging capabilities. A frequent clinical scenario is the hypotensive patient with a lowered CO and an elevated PAOP. This patient may beneŽt from inotropic agents aimed at improving the LV systolic function and diuretic therapy to lower the preload, if indeed LV systolic dysfunction is present. Equally plausible, however, is a hyperdynamic LV systolic pump with cavity obliteration that prevents adequate LV Žlling. This patient, if treated like the Žrst, would likely deteriorate with inotropic agents that further reduce the LV cavity size and increase the heart rate. Although the hemodynamic “numbers” are indistinguishable, this clinical dilemma is readily identiŽed and treated more appropriately with the imaging capabilities of echo. This became evident with the increased use of intraoperative TEE evaluations during the postoperative period. These patients had both routine PA catheters and TEE imaging probes in place, and the above clinical situation, previously thought to be rare, was found to be much more common than anticipated. Since no noninvasive method of ventricular performance has been determined to be the single best method, it is important to utilize all available techniques in each individual patient. This is one of the single greatest advantages over invasively derived methods that rely too heavily on a single measurement. Through a careful, practiced, stepwise approach using all echocardiographic modalities (e.g., 2-D echo, M-mode echo, color and conventional Doppler; and contrast echo), the majority of cardiac hemodynamics can be measured routinely and provide important useful clinical information. Of course, if patients were offered a choice of the preferred method for hemodynamic assessment, invariably echocardiography would prevail over invasive techniques. This method is safer, faster, and cheaper (especially if the economic impact of anticipated complications are considered) and provides comparably accurate 40

data. Comprehensive echocardiography is the modality of choice for initial and serial evaluations of cardiovascular hemodynamics. References 1. 2.

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7.

8.

9.

10.

11.

12. 13. 14. 15.

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17.

Dorland’s Illustrated Medical Dictionary, 26th ed. WB Saunders Company, Philadelphia, 1981, p. 593. Risenberg PR, Jaffe AS, Schuster DP: Clinical evaluation compared to pulmonary artery catheterization in the haemodynamic assessment of critically ill patients. Crit Care Med 1984;12:549. Thomas JD, Weyman AE: Seminar on in vitro studies of cardiac ow and their applications for clinical Doppler echo–II. J Am Coll Cardiol 1989;13:221. Stam RB, Martin RP: Quantitation of pressure gradient across stenotic valves by Doppler ultrasound. J Am Coll Cardiol 1983;2:707. Huntsman LL, Stewart DK, Barnes SR, et al: Noninvasive Doppler determination of cardiac output in man: Clinical validation. Circulation 1983;67:593. Kircher BJ, Himelman RB, Schiller NB: Noninvasive estimate of right atrial pressures from the inspiratory collapse of the inferior vena cava. Am J Cardiol 1990; 66:493. Jue J, Chung W, Schiller NB: Does inferior vena caval size predict right atrial pressures in patients receiving mechanical ventilation? J Am Soc Echocardiogr 1992;5:613. Waggoner AD, Barzilai B, Perez JE: Saline contrast enhancement of tricuspid regurgitation jets detected by Doppler color-ow imaging. Am J Cardiol 1990;65: 1368. Silbert DR, Brunson SC, Schiff R, et al: Determination of right ventricular pressure in the presence of a ventricular septal defect using continuous-wave Doppler ultrasound. J Am Coll Cardiol 1986;8:379. Jardin F, Duboury O, Gueret P, et al: Quantitative two-dimensional echocardiography in massive pulmonary embolism: Emphasis on ventricular interdependence and leftward septal displacement. J Am Coll Cardiol 1987;10:1201. Tahara M, Tanaka H, Nakao S, et al: Hemodynamic determination of pulmonic valve motion during systole in experimental pulmonary hypertension. Circulation 1981;64:1249. Nanda NC, Gramiak R, Robinson TI, et al: Echocardiographic evaluation of pulmonary hypertension. Circulation 1974;50:575. Halte L, Angelsen BAJ, Tromsdal A: Noninvasive estimation of pulmonary artery systolic pressures with Doppler ultrasound. Br Heart J 1981;45:157. Dabastani A, Mahan G, Gardin JM, et al: Evaluation of pulmonary artery pressure and resistance by pulsed-Doppler echo. Am J Cardiol 1987;59:662. Mahan G, Dabestani A, Gardin J, et al: Estimation of pulmonary artery pressure by pulsed-Doppler echocardiography. (abstract) Circulation 1983;68 (Suppl. 3):III-367. Masuyama T, Kodama K, Kitabatake A: Continuouswave Doppler echocardiography of pulmonary regurgitation and its application to noninvasive estimation of pulmonary artery pressures. Circulation 1986;74: 484. Lee RT, Lord CP, Plappert T, et al: Prospective Doppler echocardiography evaluation of pulmonary artery

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ECHOCARDIOGRAPHY: A Jrnl. of CV Ultrasound & Allied Tech.

41

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