Pulsed Doppler echocardiographic determination of stroke volume and cardiac output: clinical validation of two new methods using the apical window

Two methods of measuring stroke volume and cardiac output with pulsed Doppler two-dimensional echocardiography were developed and validated against the thermodilution technique in 39 patients, 33 of which were in an intensive care unit. With the use of the apical four-chamber view, a mitral inflow method combined the velocity of left ventricular inflow at the mitral anulus with the cross-sectional area of the anulus calculated from its diameter at middiastole (area = pi r2). From the apical five-chamber view a left ventricular outflow method combined the velocity of left ventricular outflow with the cross-sectional area of the aortic anulus calculated from its diameter during early systole (parasternal long-axis view). Measurements with the mitral inflow and left ventricular outflow methods were obtained in 35 of 39 (90%) and 39 of 39 (100%) patients, respectively. Validation of the mitral method excluded patients with mitral regurgitation (n = 11) and validation of the left ventricular outflow method excluded those with aortic regurgitation (n = 4). Good correlations were observed between thermodilution and Doppler measurements of stroke volume and cardiac output for both the mitral anulus method (R = .96 and .87, respectively) and the left ventricular outflow method (R = .95 and .91, respectively). The results of the two methods correlated well with each other in patients without regurgitant valve lesions. A greater interobserver variability was observed with the mitral anulus method, which was related solely to greater variability in measuring the annular diameter.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of Doppler echocardiographic methods of determining cardiac minute volume

In 40 patients without valvular disease, cardiac output was determined by pulsed Doppler echocardiography and thermodilution simultaneously. The sample volume was located in the center of the mitral valve ring, at the tips of the mitral leaflets and in the left ventricular outflow tract, directly proximal to the aortic valve leaflets. Circular cross-sectional areas of the mitral valve ring, aortic ring and bulbus of the aorta were calculated from the M-mode and two dimensional echocardiographic diameters. The mitral orifice was assumed to be an ellipse with varying short axes, determined as the mean diastolic leaflet separation in the M-mode and a constant long axis, derived from the maximal mitral orifice area or mitral ring diameter. Cardiac output was calculated by multiplying time-velocity integrals with different areas and heart rate. Cardiac output, measured by the thermodilution technique, ranged from 4.0 l/min to 10.2 l/min. Cardiac output determined by the different Doppler methods correlated significantly with the thermodilution measurements. Cardiac output measurements in the left ventricular outflow tract provided the best correlation coefficient (0.93) and a standard error of the estimate of 0.589 l/min, when the circular flow area was derived from the M-mode echo of the aortic ring.(ABSTRACT TRUNCATED AT 250 WORDS)     

Noninvasive determination of stroke volume with spectral Doppler echocardiography

To assess the determination of volume flow by Doppler echokardiography 15 patients were studied twice in intervals of 2 to 6 hours. Cardiac output was determined simultaneously by thermodilution and by Doppler echocardiography. In three patients (20%) no Doppler signal could be recorded. In the 24 successful determinations a correlation of r = 0.93 was found between the two techniques. Mean deviation was 0.57 l/min (0.15-1.16), 9% (1-20%) respectively. With serial measurements the correlation for changes in cardiac output was 0.94. Mean deviation was found to be 0.47 l/min (0.12-1.16), or 75% (9-395%). Thus, gross estimation of cardiac output by Doppler echocardiography seems possible. However, it cannot be judged as of yet whether a more than semiquantitative estimation of individual cardiac output changes is possible nor whether further information can be obtained besides that which is clinically available.     

Feasibility and variability of six methods for the echocardiographic and Doppler determination of cardiac output

The feasibility and the intrinsic variability of six different methods of echocardiographic and Doppler flow determination of cardiac output were analysed in 34 healthy volunteers. Four were excluded because of poor quality echocardiograms. The mean (range) age of the remaining 30 (12 women, 18 men) was 21 years (13-36 years). Cardiac output was calculated by six methods as a product of echocardiographically determined cross sectional area of the aorta (apical and suprasternal views), pulmonary trunk, tricuspid annulus, and mitral annulus (circular and corrected for diastolic variations), and the flow velocity integral measured by Doppler. Cardiac output ranged from 2.79 to 6.56 1/min (4.45 (1.29) 1/min) (mean (SD)). The feasibility of the methods ranged from 87% (26 patients) for the aorta from the suprasternal notch to 100% (30 patients) for the mitral orifice corrected for diastolic variations and for the tricuspid valve. The corresponding results for all 34 individuals were 76% and 88% respectively. Three way analysis of variance was performed in the 23 healthy volunteers in whom all six methods were feasible. Interobserver and intraobserver interpretative variabilities were 6.8% and 5.9% respectively. The intrinsic variability of each single measurement of cardiac output, independently of the observer and the method used, was 25%. Provided the image was suitable for analysis echocardiographic and Doppler flow determination of cardiac output was feasible in most healthy volunteers. But there was significant intrinsic variability for each of different methods. A single value of cardiac output in an individual should be interpreted with caution.     

Feasibility and variability of six methods for the echocardiographic and Doppler determination of cardiac output.

The feasibility and the intrinsic variability of six different methods of echocardiographic and Doppler flow determination of cardiac output were analysed in 34 healthy volunteers. Four were excluded because of poor quality echocardiograms. The mean (range) age of the remaining 30 (12 women, 18 men) was 21 years (13-36 years). Cardiac output was calculated by six methods as a product of echocardiographically determined cross sectional area of the aorta (apical and suprasternal views), pulmonary trunk, tricuspid annulus, and mitral annulus (circular and corrected for diastolic variations), and the flow velocity integral measured by Doppler. Cardiac output ranged from 2.79 to 6.56 1/min (4.45 (1.29) 1/min) (mean (SD)). The feasibility of the methods ranged from 87% (26 patients) for the aorta from the suprasternal notch to 100% (30 patients) for the mitral orifice corrected for diastolic variations and for the tricuspid valve. The corresponding results for all 34 individuals were 76% and 88% respectively. Three way analysis of variance was performed in the 23 healthy volunteers in whom all six methods were feasible. Interobserver and intraobserver interpretative variabilities were 6.8% and 5.9% respectively. The intrinsic variability of each single measurement of cardiac output, independently of the observer and the method used, was 25%. Provided the image was suitable for analysis echocardiographic and Doppler flow determination of cardiac output was feasible in most healthy volunteers. But there was significant intrinsic variability for each of different methods. A single value of cardiac output in an individual should be interpreted with caution.     

Two-dimensional echocardiographic methods for assessment of left atrial volume

Left atrial (LA) size is an important predictor of cardiovascular events. Various methods of LA volume assessment exist, but their differences have not been defined. This prospective study included 631 patients (331 men; mean age of 68 +/- 14 years) without a history of atrial arrhythmias, stroke, valvular heart disease, pacemaker implantation, or congenital heart disease. All underwent echocardiography with comprehensive diastolic function assessment and LA volume measurement by 3 commonly used methods: biplane area-length, biplane Simpson's method, and the prolate-ellipsoid method. Mean LA volumes were 39 +/- 14 ml/m2 by the area-length method, 38 +/- 13 ml/m2 by the Simpson's method, and 32 +/- 14 ml/m2 by the prolate-ellipsoid method. In 92% of patients, the prolate measurement was smaller than the 2 biplane methods. Pairwise correlations (r) were 0.98 for area-length versus Simpson's, 0.85 for prolate versus area-length, and 0.86 for prolate versus Simpson's (all p values <0.001). For distinguishing normal (n = 62) from pseudonormal diastolic function (n = 240) using receiver-operating curve analysis, areas under the curves were 0.76, 0.78, and 0.75 for the area-length, Simpson's, and prolate methods, respectively (all p values <0.001, no significant intermethod differences). In conclusion, our findings suggest that there are systematic differences among existing LA volume methods. Biplane area-length and Simpson's methods compare closely, whereas the prolate-ellipsoid method generally yields smaller volumes.     

Feasibility and accuracy of transthoracic Doppler echocardiographic estimation of pulmonary capillary wedge pressure applying different methods

BACKGROUND: Pulmonary wedge pressure (PWP) is an established index of cardiac function and an essential component in the management of patients with congestive heart failure and in critically ill patients. AIM: To evaluate feasibility and accuracy of non-invasive prediction of PWP by Doppler echocardiography in daily clinical practice. METHODS: Agreement was assessed between values predicted by Doppler vs. invasively measured PWP. Forty-five consecutive patients [mean (S.D.) age 62 (10) years] with CAD (44%), DCMP (40%) and without structural heart disease (16%) were studied (EF< or =40% in 58% of the patients). Doppler transmitral and pulmonary venous flow velocity profiles were recorded. For binary and quantitative prediction of PWP, four different methods and five different linear equations, suggested previously in the literature, were evaluated. RESULTS: Predictive values to identify elevated PWP were highest for pulmonary venous flow reversal exceeding the duration of forward mitral flow during atrial systole (PPV 1 and NPV 0.96). Likewise, agreement with measured PWP was highest for equations comprising both transmitral and pulmonary venous flow variables (relative mean difference 0.11, S.D.+/-4.01 mmHg for the most accurate equation). Feasibility was slightly, but not statistically, lower when pulmonary venous flow was considered vs. transmitral flow parameters alone for binary prediction (87 vs. 93%) as well as for quantitative assessment (82 vs. 93%). CONCLUSION: Semiquantitative prediction of elevated PWP by Doppler echocardiography is feasible as well as accurate in daily clinical practice. However, accuracy of numeric estimates is limited. Hence, invasive measurement of PWP is still necessary in certain clinical settings.     

Superiority of two-dimensional measurement of aortic vessel diameter in Doppler echocardiographic estimates of left ventricular stroke volume

Attempts to measure left ventricular stroke volume utilizing the Doppler aortic flow method have found varying correlations between invasive thermodilution and non-invasive Doppler methods. Because stroke volume is the product of the Doppler flow velocity integral (that is, the area under the flow velocity curve) and the cross-sectional area of the vessel through which blood flows, both variables are potential sources of error. Previous studies have shown that the Doppler flow velocity integral can be measured with acceptable reproducibility in the ascending aorta. Consequently, in this study an attempt was made to determine empirically the optimal method for measuring aortic diameter and area. The diameter of the ascending aorta was measured utilizing four M-mode and seven two-dimensional echocardiographic conventions. Doppler aortic flow velocity patterns were recorded with a 2.25 MHz M-mode echocardiographic transducer from the suprasternal notch by mapping the ascending aorta until aortic peak flow velocity was recorded. In 19 adult patients undergoing cardiac catheterization for clinical indications, Doppler stroke volume estimates utilizing the various echocardiographic conventions for measuring aortic root diameter and area were compared with simultaneous measurements of stroke volume by the thermodilution technique. The best correlation (r = 0.87) with thermodilution stroke volume was obtained by estimating aortic area from the two-dimensional parasternal long-axis images with the aortic dimension measured distal to the aortic sinuses from the inner to inner wall. The data were related by the equation: Thermodilution stroke volume = (0.73) X (two-dimensional Doppler stroke volume) + 17 cc.(ABSTRACT TRUNCATED AT 250 WORDS)     

New echocardiographic windows for quantitative determination of aortic regurgitation volume using color Doppler flow convergence and vena contracta

Color Doppler images of aortic regurgitation (AR) flow acceleration, flow convergence (FC), and the vena contracta (VC) have been reported to be useful for evaluating severity of AR. However, clinical application of these methods has been limited because of the difficulty in clearly imaging the FC and VC. This study aimed to explore new windows for imaging the FC and VC to evaluate AR volumes in patients and to validate this in animals with chronic AR. Forty patients with AR and 17 hemodynamic states in 4 sheep with strictly quantified AR volumes were evaluated. A Toshiba SSH 380A with a 3.75-MHz transducer was used to image the FC and VC. After routine echo Doppler imaging, patients were repositioned in the right lateral decubitus position, and the FC and VC were imaged from high right parasternal windows. In only 15 of the 40 patients was it possible to image clearly and measure accurately the FC and VC from conventional (left decubitus) apical or parasternal views. In contrast, 31 of 40 patients had clearly imaged FC regions and VCs using the new windows. In patients, AR volumes derived from the FC and VC methods combined with continuous velocity agreed well with each other (r = 0.97, mean difference = -7.9 ml +/- 9.9 ml/beat). In chronic animal model studies, AR volumes derived from both the VC and the FC agreed well with the electromagnetically derived AR volumes (r = 0.92, mean difference = -1.3 +/- 4.0 ml/beat). By imaging from high right parasternal windows in the right decubitus position, complementary use of the FC and VC methods can provide clinically valuable information about AR volumes.     

Impedance cardiography for repeated determination of stroke volume in elderly hypertensives: correlation with pulsed Doppler echocardiography

In this double-blind, crossover study the authors have validated stroke volume determination by impedance cardiography against the pulsed Doppler echocardiographic method in elderly hypertensives. They found a good correlation between the stroke volume values obtained by the two methods over a range of values from 30 to 130 mL. The coefficient of linear regression was about .95 at each visit. The mean of the differences was -0.73 mL with a standard deviation of 8.46. Given that individual differences are normally distributed, the values corresponding to 2 standard deviations of the mean define a range covering 95% of the observed differences. From the distribution of the data around the mean plot it appears that, in comparison with pulsed Doppler, impedance cardiography tends to slightly underestimate stroke volumes of greater than 90 mL and to overestimate values of less than 50 mL. The results of this study indicate that impedance cardiography may represent a reliable alternative to pulsed Doppler echocardiography for the noninvasive estimation of cardiac output at rest in elderly patients.     

A Doppler echocardiographic method for calculating volume flow across the tricuspid valve: correlative laboratory and clinical studies

In this study we tested a two-dimensional Doppler echocardiographic method for measuring volume flow across the tricuspid valve. Five anesthetized, open-chest dogs had a calibrated electromagnetic flow probe placed on the ascending aorta. Volume flow across the tricuspid valve was controlled by creating a variable femoral-to-pulmonary arterial shunt. Since no standard plane provided a direct view of the tricuspid valve orifice, tricuspid flow area was estimated by calculating a fixed circular flow orifice from the maximal late diastolic diameter of the tricuspid anulus in a four-chamber view. Doppler-determined velocities across the tricuspid valve and tricuspid anulus images in the four-chamber view were obtained in inspiration and expiration. For 24 cardiac outputs (0.6 to 4.0 liters/min), inspiratory tricuspid flow determined by the Doppler method correlated minimally better (r = .90, SEE = 0.30 liter/min) than did expiratory measurements (r = .89, SEE = 0.35 liter/min) with the time-averaged systemic flow determined electromagnetically. Doppler-determined tricuspid volume flows in four-chamber and short-axis two-dimensional echocardiographic views from 10 children were then compared with values determined simultaneously by thermodilution during cardiac catheterization. In the children, Doppler-determined flows in short-axis and four-chamber views, both in inspiration and expiration, were similar; when results for the two views were averaged in inspiration and expiration, the tricuspid flows predicted by the Doppler method were highly correlated (r = .98, SEE = 0.48 liter/min) with the results of thermodilution. The two-dimensional Doppler echocardiographic method provides a means of estimating volume flow across the tricuspid valve noninvasively.     

Noninvasive determination of stroke volume with impulse Doppler echocardiography: comparison with the Fick method

Pulsed Doppler echocardiographic studies were performed in 14 patients (eleven with mitral valve disease, two with coronary artery disease, one with aortic and mitral valve replacement) for determination of cardiac output and the results compared with those obtained from simultaneous measurements carried out according to the Fick principle. Determination of cardiac output and stroke volume was achieved with a pulsed Doppler instrument specifically designed in our laboratory (repetition frequency 10 kHz, maximal penetrance 7.7 cm, ultrasonic beam diameter 3 cm at a distance of 5 cm from the transducer). Doppler measurements of the instantaneous blood flow velocity in the ascending aorta were obtained with the transducer in a suprasternal position. Through integration of the mean spatial velocity over an entire cardiac cycle, the distance traversed by the blood during one heart beat was obtained and then multiplied by the echocardiographically-determined cross-section area of the aorta and the heart rate to yield the cardiac output. There was a statistically-significant linear correlation between the cardiac output determined by Doppler (CO-D) and Fick (CO-F): CO-D = 0.92 CO-F X 0.48, r = 0.85, n = 14. The mean values for the two methods were 3.89 and 3.68 1/min, respectively. The correlation between the two methods improved if only those patients with sinus rhythm were taken into consideration (CO-D = 1.05 CO-F - 0.21, r = 0.93, n = 11). The results show that the pulsed Doppler method used enables accurate determination of cardiac output. The method can be carried out in all patients without aortic stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

New echocardiographic and angiographic methods for right atrial volume determination: In vitro validation and in vivo results

Until now, right atrial (RA) volume calculation by means of two-dimensional echocardiography (2-DE) has only been attempted in a single plane: the apical four-chamber view. Our study reports a new method for RA volume calculation using two intersecting 2-DE views. For this purpose, silicone rubber casts of 19 human necropsy hearts were obtained and thin-walled natural rubber moulds of the RA casts were prepared. Totally filled with and immersed in water, the moulds could be visualized in the apical four-chamber view and an additional 2-DE plane, the latter corresponding to the subcostal view in vivo. In this view the vertical extension of RA could be estimated. Areas and lengths of RA were determined in the respective planes, and RA volume was calculated by applying the formula, area x length, to two intersecting planes. Finally, volume of the silicone casts was determined angiocardiographically (Angio) using a biplane method (30° RAO, 40° LAO-40° hepatoclavicular). The true RA volume was 106±23 ml (mean±1SD) as determined by water displacement. Using Angio an excellent correlation was found: the calculated volume amounted to 106±23ml; the difference was 5.5±4.8ml (n.s.); Angio vol=0.93 true vol+ 7.77; r=0.95; SEE= 7,4 ml. Volume determination from the apical four-chamber view of 2-DE using a monoplane disk method resulted in a mean volume of 62±17 ml. The mean difference to the true RA volume was 44±16 ml (p < 0.001). When volume calculations were made using the biplane method, a value of 105±22 ml resulted. The mean difference to true volumes was 7.4±4.8 ml: y=0.84x + 15.88; r=0.91; SEE=9.4 ml.In an in vivo study endsystolic RA volumes were calculated in a normal adult population (n=40) from the same intersecting planes as in vitro. A normal value of 38±6 ml/m² was found. In vivo validation using Angio showed a slightly higher normal value of 43=7 ml/m². Thus, 2-DE is highly accurate in determinating RA volume. In the in vitro as well as in the in vivo study the results of monoplane calculations are clearly inferior to a method which also takes account of the vertical extension of RA.     

Doppler echocardiographic determination of the pressure gradient in hypertrophic cardiomyopathy

The continuous wave Doppler ultrasound signal across the left ventricular outflow tract in hypertrophic cardiomyopathy has a characteristic pattern that is in keeping with the dynamic nature of the pressure gradient in this condition. To determine the accuracy and reliability of the peak Doppler flow velocity signal for measuring the peak pressure gradient in this condition, 340 beats were analyzed from five consecutive patients studied with simultaneous continuous wave Doppler ultrasound and dual catheter pressure recordings across the left ventricular outflow tract. Each patient was studied at steady state and during physiologic and pharmacologic manipulations of the pressure gradient. Peak velocity and calculated peak gradient were determined by two independent observers who did not know the catheter measurements. In addition, 18 beats with well defined flow velocity envelopes were digitized for analysis of the magnitude, timing and contour of the instantaneous Doppler ultrasound and catheter gradients throughout systole. Peak catheter gradient in the 340 beats ranged from 12 to 245 mm Hg. The correlations between the Doppler-derived and catheter peak gradients were close (r = 0.96, SEE = 4 mm Hg for Observer 1 and r = 0.97, SEE = 11 mm Hg for Observer 2). Interobserver variability for measurement of peak flow velocity was small (mean +/- SD 0.16 +/- 0.15 m/s). An interobserver difference greater than 0.3 m/s occurred in 25 of the 340 beats analyzed. By retrospective analysis, this was due to contamination of the outflow tract signal by mitral regurgitation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative echocardiographic volume determinations using a dynamic heart model

Using a dynamic and symmetrical cardiac phantom different echocardiographic mathematical models (Simpson 7 slices, area-length method, Simpson 2 slices and method according to Teichholz) were compared. 9 different end-diastolic (EDV) and end-systolic (ESV) volumes, 9 different stroke volumes (SV) and ejection fractions (EF) were used. EDV and ESV varied between 39-298 ml; SV between 29-100 ml and EF between 14-46%. In addition 10 fixed volumes of the same shape were evaluated using the same echocardiographic mathematical models. While symmetrical fixed volumes can be assessed correctly (r = 0.97-0.98), apart from the formula according to Teichholz (r = 0.89, significant underestimation of volumes), the correlation coefficients decrease using a dynamic cardiac phantom. In the modification of Simpson with 7 slices the best correlation was found for all parameters (EDV: r = 0.93; ESV: r = 0.94; EF: r = 0.87; SV: r = 0.81). The biplane area-length method has no advantages over Simpson's rule with 2 slices in the short axis; for symmetrical models both methods are comparable, both having high correlation coefficients (for volumes r = 0.85 and r = 0.88; for EF 0.78 and 0.84). Using the method according to Teichholz symmetrical volumes can be well assessed (r = 0.90), for the determination of EF the correlation coefficient decreases to r = 0.65 and for stroke volume to 0.33, reflecting no significant correlation to the actual SV. Possible causes for a poorer correlation are discussed for moving objects as opposed to the fixed volumes.     

Doppler echocardiographic methods for optimization of the atrioventricular delay during cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) is beneficial for a majority of patients with medically refractory heart failure due to severe left ventricular (LV) systolic dysfunction and prolonged interventricular conduction to improve symptoms and LV performance. An optimally programmed atrioventricular delay (AVD) during CRT can be also important to maximize the response in left ventricular function. Several Doppler echocardiographic methods have been reported to be useful for determination of the optimal AVD. This review will discuss the various Doppler-based approaches to program the AVD in patients that receive CRT.