Underestimation of cardiac output by thermodilution in patients with tricuspid regurgitation

Thermodilution-derived indices for assessment of left and right ventricular cardiac function in normal and impaired cardiac function

OBJECTIVE

The aim of this study was to assess whether thermodilution-derived parameters of right and left ventricular cardiac function (right ventricular ejection fraction, global ejection fraction, cardiac function index) are able to track changes of cardiac contractile function and whether they are influenced by substantial preload reduction.

DESIGN

Prospective animal study.

SETTING

University-affiliated animal research laboratory.

SUBJECTS

Domestic pigs.

INTERVENTIONS

Sixteen domestic pigs were studied. Right ventricular ejection fraction, global ejection fraction, and cardiac function index were compared to direct measurement of left ventricular rate of maximum systolic pressure rise and the left ventricular rate of maximum systolic pressure rise corrected to preload. Measurements were done with normal cardiac function during normo- and hypovolemia. Thereafter, cardiac function was impaired by continuous infusion of verapamil and measurements were repeated during normo- and hypovolemia (withdrawal of blood 20 mL kg body weight).

MEASUREMENTS AND MAIN RESULTS

With normal cardiac function, hypovolemia led to a significant decrease of right ventricular ejection fraction from 36.7% ± 6.6% to 29.8% ± 5.8% (p < .001), global ejection fraction from 40.5% ± 6.2% to 33.6% ± 7.6% (p < .001), and the left ventricular rate of maximum systolic pressure rise from 2104 ± 390 mm Hg sec to 1297 ± 438 mm Hg sec (p < .001). Cardiac function index (8.92 ± 2.20 min to 7.93 ± 1.54 min) and the left ventricular rate of maximum systolic pressure rise corrected to preload (18.2 ± 4.7 mm Hg sec mL to 15.2 ± 4.3 mm Hg sec mL) did not change significantly. Infusion of verapamil led to a significant reduction of right ventricular ejection fraction, global ejection fraction, cardiac function index, the left ventricular rate of maximum systolic pressure rise, and the left ventricular rate of maximum systolic pressure rise corrected to preload (p < .001). Now, hypovolemia led to a significant decrease of right ventricular ejection fraction (29.1% ± 4.6% to 24.9% ± 5.9%; p < .001), global ejection fraction (37.1% ± 4.7% to 31.9% ± 3.9%; p < .05), cardiac function index (7.58 ± 1.02 to 6.27 ± 1.19 min; p < .05), and the left ventricular rate of maximum systolic pressure rise (733 ± 141 mm Hg sec to 426 ± 108 mm Hg sec; p < .05). Only the left ventricular rate of maximum systolic pressure rise corrected to preload did not change significantly (6.7 ± 1.3 mm Hg sec mL to 4.6 ± 1 mm Hg sec mL; p > .05).

CONCLUSIONS

Right ventricular ejection fraction, global ejection fraction, and cardiac function index enable detection of changes in load-independent, intrinsic cardiac contractility. Importantly, they also reflect changes of contractile function caused by substantial decrease of preload, emphasizing the importance of assessing both cardiac contractile function in coherence with cardiac preload to differentiate between reduced intrinsic contractility and hypovolemia.

[Clinical validation of minimally invasive evaluation of systolic function]

BACKGROUND AND OBJECTIVE

Pulse contour continuous cardiac output (PiCCO) monitoring by means of transpulmonary thermodilution provides 2 indices of systolic function: the cardiac function index and the global ejection fraction. Our aim was to compare these 2 PiCCO indices to the left-ventricular ejection fraction obtained by transthoracic echocardiography.

MATERIAL AND METHODS

This was a prospective clinical study of 35 adult patients in the critical care unit of a university hospital. Each patient provided his or her own control data. Patients with marked changes in regional segment contractility or nonsinus rhythm were excluded. We collected patient variables, reason for admission to the critical care unit, the Acute Physiology and Chronic Health Evaluation II score, the reason for hemodynamic monitoring, and the infusion of vasoactive drugs at the time of the procedure.

RESULTS

Statistically significant correlations were found between the left-ventricular ejection fraction and the global ejection fraction (r=0.79, P<.001) and the cardiac function index (r=0.66, P<.001). The mean (SD) difference between the left-ventricular ejection fraction and the global ejection fraction and the cardiac function index were 1.05% (10.2%) (range, 19.0% to 29.1%) and 0.001% (12.4%) (range, -24.3% to 24.3%), respectively. For predicting a left-ventricular ejection fraction of less than 40%, the area under the curve was 0.879 for the global ejection fraction and 0.805 for the cardiac function index of A global ejection fraction less than 13.5% and a cardiac function index less than 3.15 min(-1) predicted a left-ventricular ejection fraction less than 40% with sensitivities of 97% and 96% and specificities of 85% and 77%, respectively.

CONCLUSIONS

In patients without marked changes in regional segment contractility, the global ejection fraction and the cardiac function index calculated by the PiCCO monitor offer a reliable and simple way to assess left-ventricular systolic function. Low values for these indicators suggest the need for echocardiographic assessment of left- and right-ventricular function.

Non-invasive stroke volume measurement by cardiac magnetic resonance imaging and inert gas rebreathing in pulmonary hypertension

OBJECTIVE

  Right ventricular function determines the prognosis of pulmonary hypertension (PAH). Measurement of stroke volume (SV) non-invasively could be a promising method to monitor disease progression. Cardiac magnetic resonance (CMR) imaging is recognized as an accurate and reproducible method to measure SV. Inert gas rebreathing (IGR) using acetylene is a validated but cumbersome method for pulmonary blood flow (PBF) measurement in PAH. A more convenient rebreathing technique using rapid photoacoustic analysis of nitrous oxide has been introduced and validated in left heart failure. We investigated the accuracy of CMR imaging and IGR using photoacoustic analysis to measure SV in patients under investigation for PAH.

METHODS

  Thirty-three patients (16♀:17♂) with suspected PAH following echocardiography had SV measured by CMR imaging (using pulmonary arterial{CMR PA} and aortic {CMR Ao} flow methods) and IGR. The results were compared with our reference standard: thermodilution (TD) measured during right heart catheterization (RHC).

RESULTS

  All methods showed similar correlation for SV. Bland-Altman analysis confirmed acceptable levels of agreement between the four techniques. TD versus CMR Ao flow had bias (limits of agreement) of -5.41 ml (-22.37 to 11.56 ml), TD versus CMR PA flow 0.12 ml (-20.13 to 20.37 ml) and TD versus IGR 6.25 ml (-16.01 to 28.51 ml).

CONCLUSION

  Cardiac magnetic resonance imaging and IGR using photoacoustic analysis in patients with suspected PAH provided non-invasive measurements of SV that agreed closely with those obtained from TD measured during RHC.

Noninvasive Doppler ultrasonography for assessing cardiac function: can it replace the Swan-Ganz catheter?

BACKGROUND

Cardiac function, including cardiac index (CI), traditionally has been measured by a pulmonary artery catheter (PAC). A noninvasive alternative for measuring cardiac function would offer obvious advantages.

METHODS

A prospective study of trauma and nontrauma patients was performed in a surgical intensive care unit over a 3-month period. CI was determined using both a standard PAC and a continuous-wave Doppler ultrasound (UTS). The study had 2 phases: phase I was nonblinded and phase II was blinded; the correlation between UTS- and PAC-derived CI was assessed.

RESULTS

A total of 120 paired measurements of CI were observed in 31 patients. The UTS-derived CI measurements showed agreement with PAC measurements in both phase I and phase II of the study with a bias of .06 L/min/m(2) +/- .4 L/min/m(2). Paired measurements correlated well in both phase I (r = .97, R2 = .95, P < .0001) and phase II (r = .93, R2 = .86, P < .0001) of the study.

CONCLUSIONS

Doppler UTS correlates well with PAC measurements of CI. This noninvasive modality is an accurate and safe alternative to PAC.

Management strategies for patients with pulmonary hypertension in the intensive care unit

OBJECTIVE

Pulmonary hypertension may be encountered in the intensive care unit in patients with critical illnesses such as acute respiratory distress syndrome, left ventricular dysfunction, and pulmonary embolism, as well as after cardiothoracic surgery. Pulmonary hypertension also may be encountered in patients with preexisting pulmonary vascular, lung, liver, or cardiac diseases. The intensive care unit management of patients can prove extremely challenging, particularly when they become hemodynamically unstable. The objective of this review is to discuss the pathogenesis and physiology of pulmonary hypertension and the utility of various diagnostic tools, and to provide recommendations regarding the use of vasopressors and pulmonary vasodilators in intensive care.

DATA SOURCES AND EXTRACTION

We undertook a comprehensive review of the literature regarding the management of pulmonary hypertension in the setting of critical illness. We performed a MEDLINE search of articles published from January 1970 to March 2007. Medical subject headings and keywords searched and cross-referenced with each other were: pulmonary hypertension, vasopressor agents, therapeutics, critical illness, intensive care, right ventricular failure, mitral stenosis, prostacyclin, nitric oxide, sildenafil, dopamine, dobutamine, phenylephrine, isoproterenol, and vasopressin. Both human and animal studies related to pulmonary hypertension were reviewed.

CONCLUSIONS

Pulmonary hypertension presents a particular challenge in critically ill patients, because typical therapies such as volume resuscitation and mechanical ventilation may worsen hemodynamics in patients with pulmonary hypertension and right ventricular failure. Patients with decompensated pulmonary hypertension, including those with pulmonary hypertension associated with cardiothoracic surgery, require therapy for right ventricular failure. Very few human studies have addressed the use of vasopressors and pulmonary vasodilators in these patients, but the use of dobutamine, milrinone, inhaled nitric oxide, and intravenous prostacyclin have the greatest support in the literature. Treatment of pulmonary hypertension resulting from critical illness or chronic lung diseases should address the primary cause of hemodynamic deterioration, and pulmonary vasodilators usually are not necessary.

Regional right ventricular dysfunction in chronic pulmonary hypertension

OBJECTIVE

Right ventricular (RV) failure is the main cause of mortality in patients with pulmonary hypertension (PH). Therefore, there is an increasing interest for the assessment of RV function. This study aimed to evaluate the regional RV function in patients with PH by using ultrasonic strain rate imaging.

METHODS

In all, 27 patients with PH and 27 control subjects were studied by ultrasonic strain rate imaging. The regional longitudinal deformation was measured in the RV free wall divided into two segments. A subgroup of 16 patients had concomitant invasive hemodynamic measurements.

RESULTS

In patients with PH, deformation parameters were significantly lower compared with that of control subjects (basal strain rate -2.28 +/- 0.9 vs -2.94 +/- 0.9 s(-1); strain -28 +/- 13% vs -42 +/- 11%; apical strain rate -1.05 +/- 1.38 vs -2.60 +/- 0.9 s(-1); strain -13 +/- 16% vs -41 +/- 11%, respectively). The deformation parameters in the apical segment were reduced more than in the basal segment (the segment-wise comparison with P < .002 for strain rate and P < .0001 for strain) in the patient group. The reduction of the apical deformation was related to the severity of RV afterload. Strong correlations were found between the apical strain and invasively measured mean pulmonary arterial pressure (R = 0.82, P < .0001) and pulmonary vascular resistance (R = 0.73, P < .001) and echocardiographically estimated hemodynamic parameters, RV size and global function, and exercise capacity (evaluated by a 6-minute walk test expressed as a percentage of the expected value).

CONCLUSION

Strain rate imaging provides a new tool to quantify regional RV dysfunction in patients with PH and reveals a characteristic regional pattern of abnormal RV free wall function.

Simultaneous determination of the accuracy and precision of closed-circuit cardiac output rebreathing techniques

Foreign and soluble gas rebreathing methods are attractive for determining cardiac output (Q(c)) because they incur less risk than traditional invasive methods such as direct Fick and thermodilution. We compared simultaneously obtained Q(c) measurements during rest and exercise to assess the accuracy and precision of several rebreathing methods. Q(c) measurements were obtained during rest (supine and standing) and stationary cycling (submaximal and maximal) in 13 men and 1 woman (age: 24 +/- 7 yr; height: 178 +/- 5 cm; weight: 78 +/- 13 kg; Vo(2max): 45.1 +/- 9.4 ml.kg(-1).min(-1); mean +/- SD) using one-N(2)O, four-C(2)H(2), one-CO(2) (single-step) rebreathing technique, and two criterion methods (direct Fick and thermodilution). CO(2) rebreathing overestimated Q(c) compared with the criterion methods (supine: 8.1 +/- 2.0 vs. 6.4 +/- 1.6 and 7.2 +/- 1.2 l/min, respectively; maximal exercise: 27.0 +/- 6.0 vs. 24.0 +/- 3.9 and 23.3 +/- 3.8 l/min). C(2)H(2) and N(2)O rebreathing techniques tended to underestimate Q(c) (range: 6.6-7.3 l/min for supine rest; range: 16.0-19.1 l/min for maximal exercise). Bartlett's test indicated variance heterogeneity among the methods (P < 0.05), where CO(2) rebreathing consistently demonstrated larger variance. At rest, most means from the noninvasive techniques were +/-10% of direct Fick and thermodilution. During exercise, all methods fell outside the +/-10% range, except for CO(2) rebreathing. Thus the CO(2) rebreathing method was accurate over a wider range (rest through maximal exercise), but was less precise. We conclude that foreign gas rebreathing can provide reasonable Q(c) estimates with fewer repeat trials during resting conditions. During exercise, these methods remain precise but tend to underestimate Q(c). Single-step CO(2) rebreathing may be successfully employed over a wider range but with more measurements needed to overcome the larger variability.

Use of 3-Dimensional Color Doppler Echocardiography to Measure Stroke Volume in Human Beings: Comparison with Thermodilution

BACKGROUND

The availability of accurate noninvasive measurements of cardiac output (CO) would be useful in assessing disease severity and the effects of therapeutic interventions in many different clinical settings. Current noninvasive methods are limited by their dependence on geometric assumptions. We tested the feasibility of a new technique for CO measurements based on 3-dimensional color Doppler echocardiographic (3D-CD) imaging.

OBJECTIVE

We sought to compare the accuracy of CO determination in human beings as measured by 3D-CD and conventional 2-dimensional echocardiography (2DE) using thermodilution as the gold standard for comparison.

METHODS

Simultaneous 3D-CD, 2DE, and thermodilution data were acquired in 47 patients postcardiac transplantation with good acoustic windows who required routine hemodynamic evaluation with a pulmonary artery catheter. Data were stored on compact disc and analyzed offline using custom software. Echocardiographic data were compared against thermodilution using linear regression and Bland-Altman analysis.

RESULTS

Correlation coefficients for 3D-CD and 2DE of the left ventricular outflow tract were r = 0.94 and r = 0.78, respectively. Correlation coefficients for 3D-CD and 2DE of the mitral valve were r = 0.93 and r = 0.75, respectively. Compared with 2DE, 3D-CD demonstrated a smaller bias and narrower limits of agreement in the left ventricular outflow tract (-1.84 +/- 16.8 vs -8.6 +/- 36.2 mL) and mitral valve inflow (-0.2 +/- 15.6 vs 10.0 +/- 26 mL).

CONCLUSION

The 3D-CD determination of CO is feasible and accurate. Compared with previous noninvasive modalities, 3D-CD has the advantages of independence of geometric assumptions and ease of image acquisition and analysis.

Measurement of total pulmonary arterial compliance using invasive pressure monitoring and MR flow quantification during MR-guided cardiac catheterization

Pulmonary hypertensive disease is assessed by quantification of pulmonary vascular resistance. Pulmonary total arterial compliance is also an indicator of pulmonary hypertensive disease. However, because of difficulties in measuring compliance, it is rarely used. We describe a method of measuring pulmonary arterial compliance utilizing magnetic resonance (MR) flow data and invasive pressure measurements. Seventeen patients with suspected pulmonary hypertension or congenital heart disease requiring preoperative assessment underwent MR-guided cardiac catheterization. Invasive manometry was used to measure pulmonary arterial pressure, and phase-contrast MR was used to measure flow at baseline and at 20 ppm nitric oxide (NO). Total arterial compliance was calculated using the pulse pressure method (parameter optimization of the 2-element windkessel model) and the ratio of stroke volume to pulse pressure. There was good agreement between the two estimates of compliance ( r = 0.98, P < 0.001). However, there was a systematic bias between the ratio of stroke volume to pulse pressure and the pulse pressure method (bias = 61%, upper level of agreement = 84%, lower level of agreement = 38%). In response to 20 ppm NO, there was a statistically significant fall in resistance, systolic pressure, and pulse pressure. In seven patients, total arterial compliance increased >10% in response to 20 ppm NO. As a population, the increase did not reach statistical significance. There was an inverse relation between compliance and resistance ( r = 0.89, P < 0.001) and between compliance and mean pulmonary arterial pressure ( r = 0.72, P < 0.001). We have demonstrated the feasibility of quantifying total arterial compliance using an MR method.

Pulsed dye densitometry with two different sensor types for cardiac output measurement after cardiac surgery: a comparison with the thermodilution technique

BACKGROUND

Assessment of cardiac output (CO) by the indocyanine green (ICG) dye dilution technique (IDD) with transcutaneous signal detection may be a less invasive alternative to the pulmonary artery catheter (PAC). The aim of this study was to determine the accuracy and reliability of the DDG2001 analyzer (Nihon Kohden Corp, Tokyo, Japan) using a finger (IDDf) and a nose (IDDn) sensor as compared with the thermodilution technique by PAC.

METHODS

In 31 consecutive patients after routine cardiac surgery, CO measurements were performed by IDD compared with the thermodilution technique following postoperative haemodynamic stabilization in the intensive care unit. Repeated measurements were made at 30-min intervals. CO was determined by iced water bolus (IWB: mean of three repeated injections) and IDDf or IDDn, respectively (mean of three repeated ICG injections).

RESULTS

Thirty-three per cent of all measurements for IDDf and 9% for IDDn failed due to a missing signal detection. Mean bias for IDDf to IWB was -0.5 l min(-1).m(-2) (limits of agreement: -1.8/0.8 l min(-1).m(-2)) and for IDDn to IWB was -0.1 l min(-1).m(-2) (limits of agreement: -1.6/1.5 l min(-1).m(-2)). Correlation between IDDf and IWB (r = 0.2) was found to be inferior to the correlation between IDDn and IWB (r = 0.5).

CONCLUSION

The IDD showed a systematic bias compared with the IWB and its performance was limited due to signal detection failure. Therefore, the DDG2001 analyzer cannot be recommended as a substitute for the PAC in routine monitoring of cardiac output after cardiac surgery.

Estimation of left ventricular systolic function by single transpulmonary thermodilution

OBJECTIVE

The single-indicator transpulmonary thermodilution technique (PiCCO system) provides two derived indices of cardiac systolic function: the cardiac function index and the global ejection fraction. We used transesophageal echocardiography to compare theses indices with left ventricular fractional area of change only for patients with no isolated right ventricular dysfunction. (The global cardiac systolic function may be decreased despite preserved left ventricular function in this situation.)

DESIGN

Prospective, open, clinical study.

SETTING

Intensive care unit (ICU) in a university hospital.

PATIENTS

Thirty-three mechanically ventilated patients.

INTERVENTION

Left ventricular fractional area of change (LVFAC) was measured using transesophageal echocardiography. The cardiac function index (CFI) and the global ejection fraction (GEF) were determined from transpulmonary thermodilution-derived cardiac output and thoracic volumes.

MEASUREMENTS AND MAIN RESULTS

Transesophageal echocardiography identified 3 patients with isolated right ventricular failure (PiCCO underestimated LVFAC in this situation). Significant correlations were established between LVFAC and CFI (r=0.87, n=30, p<0.0001) or GEF (r=0.82, n=30, p<0.0001). The mean differences between measured LVFAC and LVFAC estimated with CFI or GEF were 0.8+/-8.5% (range: -17 to 14%) and 0.8+/-9.0% (range: -21 to 19%), respectively. Area under the receiver operating characteristics curves for the estimation of LVFAC >/=40% using CFI or GEF was 0.92. CFI >4 and GEF >18% estimated LVFAC >/=40% with respective sensitivities of 86 and 88% and specificities of 88 and 79%. Significant correlations were established between changes of LVFAC and CFI/GEF over time.

CONCLUSIONS

In mechanically ventilated ICU patients, PiCCO-derived cardiac function index and global ejection fraction provide reliable estimations of LV systolic function but may underestimate it in the cases of isolated right ventricular failure.

Neither the accuracy nor the precision of thermal dilution cardiac output measurements is altered by acute tricuspid regurgitation in pigs

Whether measurement of cardiac output using the thermal dilution technique (TDCO) is valid in the presence of tricuspid regurgitation (TR) is controversial. We assessed the accuracy and precision of the technique in pigs by comparison with data from an electromagnetic flowmeter on the aorta (EMCO). TR was created with sutures that immobilized the free-wall leaflets of the tricuspid valve, and cardiac output was adjusted with dobutamine to give values comparable to control measurements. TR reduced forward stroke volume from 17.2 to 12.6 mL/beat and caused the right atrium to dilate and pulse in synchrony with the right ventricle. Acute TR did not affect the linear regression relation between TDCO and EMCO and did not alter the correlation coefficient (r = 0.94 during both control and TR). These data demonstrate that acute TR does not affect the accuracy or precision of TDCO in pigs.

IMPLICATIONS

Cardiac output is a valuable measurement that guides the medical care of patients with heart and lung disease. This study demonstrates that the thermal dilution technique of determining cardiac output is valid when acute tricuspid valve regurgitation is present in pigs.

Measured versus estimated oxygen consumption in ventilated patients with congenital heart disease: the validity of predictive equations

OBJECTIVE

To determine the validity of predictive equations in calculating oxygen consumption (Vo(2)) in ventilated patients with congenital heart disease.

DESIGN

Prospective study.

SETTING

Cardiac catheterization laboratories and intensive care units of two university teaching hospitals.

PATIENTS

A total of 126 patients with congenital heart disease were studied. Of these, 75 patients received anesthesia in the pediatric cardiac catheterization laboratory, and 51 were deeply sedated in the intensive care unit after open heart surgery.

MEASUREMENTS AND MAIN RESULTS

Vo(2) was measured directly in all patients using respiratory mass spectrometry. Estimated values for absolute Vo(2) (mL/min) and indexed Vo(2) (mL.min-1.m-2) were calculated from the four predictive equations published by LaFarge and Miettinen, Lundell et al., Wessel et al., and Lindahl. The agreement between measured and estimated Vo(2) was evaluated by calculating their bias and limits of agreement. A failure of agreement between measured and estimated Vo(2) was noted in both groups of patients, irrespective the equation used, and the agreement was poorer in patients in the intensive care unit. The equation by LaFarge and Miettinen produced the closest estimation in patients at cardiac catheterization with a bias of 4.5 mL/min for absolute Vo(2) and 6.9 mL.min-1.m-2 for indexed Vo(2). A systematic error of overestimating lower and underestimating higher indexed Vo(2) mL.min-1.m-2 was introduced in both groups.

CONCLUSION

Predictive equations do not accurately estimate Vo(2) in ventilated patients with congenital heart disease.

Comparison of cardiac output measured with echocardiographic volumes and aortic Doppler methods during mechanical ventilation

OBJECTIVE

To compare two transesophageal echocardiographic methods of cardiac output and stroke volume measurement in mechanically ventilated patients.

DESIGN

Prospective clinical study.

SETTING

Operating room (group I) and intensive care unit (group II) in two university hospitals.

PATIENTS

Fifteen deeply anesthetized patients undergoing gynecological laparoscopy for sterility (group I) and 40 patients with septic shock (group II).

INTERVENTIONS

Transesophageal echocardiography with modification of hemodynamic conditions.

MEASUREMENTS AND RESULTS

Left ventricular (LV) volumes, cardiac (CI) and stroke index (SI) were measured with two methods using either LV volumes or aortic Doppler. These values were significantly lower in group I compared to group II. Using ANOVA and paired t-tests, there were no significant differences between the two methods of measurement. Correlation between these methods was better in group II than in group I, although not significantly so. In group I, bias for CI measurements was low (0.05 l/min per m(2)), with a weak agreement in terms of the 95% confidence interval (-1.17; 1.06 l/min per m(2)) compared to the mean values obtained with both methods (1.3 l/min per m(2)). In group II, bias for CI measurements was lower (0.2 l/min per m(2)). Agreement was weak, regarding 95% confidence intervals (-1.7; 1.3 l/min per m(2)) compared to the mean values (3 l/min per m(2) with the LV volumes method and 3.2 l/min per m(2) and with the Doppler method).

CONCLUSIONS

Cardiac output and stroke volume can be measured from LV volumes in mechanically ventilated patients, yielding relevant information. However, the accuracy of LV volume measurements is not excellent compared to the aortic Doppler method. Thus, this latter technique should still be considered as the gold standard.

Flow dependency of error in thermodilution measurement of cardiac output during acute tricuspid regurgitation

OBJECTIVE

To evaluate the effect of variable degrees of tricuspid regurgitation on thermodilution cardiac output measurements during changes in venous return.

DESIGN

Prospective, controlled animal study.

SETTING

University laboratory.

PARTICIPANTS

Eight anesthetized mongrel dogs instrumented for simultaneous measurement of cardiac output by thermodilution and ascending aortic electromagnetometry.

INTERVENTIONS

Data were collected before and after induction of moderate and severe tricuspid regurgitation. Under each condition, measurements were obtained at baseline and after opening 2 peripheral arteriovenous shunts to increase venous return.

MEASUREMENTS AND MAIN RESULTS

Baseline electromagnetic flow ranged from 1.74 to 3.62 L/min (median 2.73 L/min). Moderate and severe regurgitation reduced median electromagnetic flow values by 31% and 51%. Applying generalized estimating equations to model thermodilution cardiac output as a function of electromagnetic flow, arteriovenous shunt, and severity of tricuspid regurgitation revealed that (1) moderate and severe regurgitation changed the slope and intercept of the thermodilution/electromagnetic regression, but the differences between them were not significant, and (2) arteriovenous shunt alone had no effect under any condition. A simplified model independent of shunt and containing just 2 levels of tricuspid regurgitation (none or present) crossed with electromagnetic flow was applied. This analysis showed that regurgitation caused thermodilution to significantly underestimate electromagnetic flow at cardiac outputs > 2.27 L/min (99 mL/kg/min) and overestimate it at flows < 1.02 L/min (44 mL/kg/min).

CONCLUSIONS

These data show that acute tricuspid regurgitation may produce underestimation of cardiac output by thermodilution when flow is relatively high, produce overestimation when flow is relatively low, or have minimal effect when flow is in the midrange.

Noninvasive whole-body electrical bioimpedance cardiac output and invasive thermodilution cardiac output in high-risk surgical patients

OBJECTIVE

To evaluate the reliability of whole-body impedance cardiography with two electrodes on either both wrists or one wrist and one ankle for the measurement of cardiac output compared with the thermodilution method.

DESIGN

Prospective, clinical investigation

SETTING

Surgical intensive care unit of a university-affiliated community hospital.

PATIENTS

Simultaneous cardiac output measurements by noninvasive whole-body impedance cardiography (nCO) and invasive thermodilution (thCO) in 22 high-risk surgical patients scheduled for extended surgery requiring perioperative pulmonary artery catheter monitoring.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 109 sets of measurements consisting of 455 single comparison measurements between nCO and thCO were included in the analysis. The mean cardiac output difference between the two methods was 1.62 L/min with limits of agreement (2 SD) of +/- 4.64 L/min. The inter-measurement variance was slightly higher for nCO. The correlation coefficient between nCO and thCO was r2 = 0.061 (p < .001) for single measurements and r2 = 0.083 (p < .002) for sets of three to six measurements. The two most predictive factors for between-method differences were the absolute thCO value (r2 = 0.13; p < .001) and whether or not a continuous nitroglycerin infusion was used (p < .05, Student's t-test).

CONCLUSIONS

Agreement between whole-body impedance cardiography and thermodilution in the measurement of cardiac output was unsatisfactory. Factors that can explain these differences are differences between the populations used for calibration of nCO and the study population, the influence of changing peripheral perfusion, and the effect of a supranormal hemodynamic state on the bioimpedance signal. Whole-body impedance cardiography cannot be recommended for assessing the hemodynamic state of high-risk surgical patients as studied in this investigation.

Esophageal Doppler monitor determinations of cardiac output and preload during cardiac operations

BACKGROUND

Perioperative management of cardiac surgical patients frequently mandates measurements of cardiac output and left ventricular filling. This study compared cardiac output and left ventricular filling measured by pulmonary artery (PA) catheter and esophageal Doppler monitor (EDM).

METHODS

Thirty-four patients undergoing coronary artery bypass grafting were prepared by implanting a PA catheter, an EDM, and a transit-time ultrasonic flow probe around the ascending aorta. In 20 patients, left ventricular end-diastolic short-axis area (EDA) was measured by transesophageal echocardiography. At five time points, cardiac output was measured from the flow probe, the EDM, and the PA catheter (by thermodilution), and left ventricular filling was assessed from the PA catheter (as PA diastolic pressure), the EDM (corrected flow time), and the EDA. For cardiac output, concordance correlations relating EDM to flow probe and PA catheter to flow probe were calculated, transformed (Fisher's z transformation), and compared by Student's t test. For left ventricular filling, regression coefficients were created between corrected flow time and EDA and between PA diastolic pressure and EDA. Spearman correlations were compared by Wilcoxon rank sum test.

RESULTS

The EDM and the PA catheter exhibited similar relationships to the flow probe (concordance correlations, 0.55 +/- 0.35 [mean +/- standard deviation] and 0.49 +/- 0.34, respectively; p = 0.088). The correlation between corrected flow time and EDA was better than the correlation between PA diastolic pressure and EDA (concordance correlations, 0.49 +/- 0.55 versus 0.10 +/- 0.43, respectively; p < 0.01).

CONCLUSIONS

These data suggest that the EDM may offer a less invasive technique for evaluating cardiac output and a more accurate estimate for preload compared with the PA catheter.

Comparison of two semicontinuous cardiac output pulmonary artery catheters after valvular surgery

OBJECTIVE

To compare semicontinuous cardiac output (CCO) with bolus cardiac output (BCO), in the immediate postoperative period after valvular surgery, under hypothermic cardiopulmonary bypass with two CCO pulmonary artery catheters, based on the pulsed warm thermodilution technique, i.e., Opti-Q from Abbott or IntelliCath from Baxter-Edwards (Abbott and Baxter groups, respectively).

DESIGN

Prospective study.

SETTING

University hospital.

PATIENTS

Forty-four adult patients scheduled for mitral and/or aortic valve surgery were randomized into two groups. Tricuspid or pulmonary valvulopathy diagnosed by echocardiography was excluded.

INTERVENTIONS

Cardiac output was measured every 20 mins during the 3 postoperative hrs. BCO was the mean of three boluses (10 mL) of an ice-cold saline solution injected within 3 secs. CCO was the mean of two CCO values obtained in normal mode immediately before and after BCO measurements.

MEASUREMENTS AND MAIN RESULTS

Two groups of 22 patients underwent 198 pairs of cardiac output measurements. The mean difference or bias was calculated as the difference between BCO and CCO, and precision was the SD of the mean bias. The limits of agreement were defined as bias +/- 2 SD. A two-sample Wilcoxon's test was used for comparison of bias and precision in sinus and non-sinus rhythm, and stable and unstable mean arterial pressure in each group and between the two pulmonary artery catheters. The coefficient of correlation was also calculated. Bias +/- precision was 0.066+/-0.526 L/min, r2 = .83, for the Abbott group, and 0.015+/-0.490 L/min, r2 = .85 (not significant), for the Baxter group. There was no significant difference within and between groups for bias and precision in sinus and non-sinus rhythm, nor in stable and unstable mean arterial pressure.

CONCLUSIONS

This study, during the immediate postoperative period in valvular surgery under hypothermic cardiopulmonary bypass, showed a satisfactory correlation between CCO and BCO with the two systems.

Determination of cardiac output by the Fick method, thermodilution, and acetylene rebreathing in pulmonary hypertension

Assessment of cardiac output is an important part of the management of patients with pulmonary hypertension. The accuracy of the thermodilution technique in patients with low cardiac output or severe tricuspid regurgitation has been questioned. To address this issue, we simultaneously compared 105 cardiac output measurements by the Fick method and thermodilution in 35 patients with pulmonary hypertension. Moreover, we evaluated the acetylene rebreathing technique, a noninvasive method of determining cardiac output. The mean difference +/- 95% limit of agreement between thermodilution and the Fick method was +0.01 +/- 1.1 L/min. The mean difference +/- 95% limit of agreement between acetylene rebreathing and the Fick method was -0.23 +/- 1.14 L/min. Neither the mean agreement nor the 95% limits of agreement of both thermodilution and acetylene rebreathing with the Fick method were affected by the presence of low cardiac output or severe tricuspid regurgitation. We conclude that thermodilution and acetylene rebreathing are useful tools for assessing cardiac output in patients with pulmonary hypertension, even in the presence of low cardiac output or severe tricuspid regurgitation.

Hemodynamic effects of fluid loading in acute massive pulmonary embolism

OBJECTIVE

To assess the hemodynamic effects of fluid loading in patients with acute circulatory failure caused by acute massive pulmonary embolism (AMPE).

DESIGN

Prospective study.

SETTING

Respiratory critical care unit of a university hospital.

PATIENTS

Thirteen patients free of previous cardiopulmonary disease with angiographically proven AMPE (Miller index = 24 +/- 1), with acute circulatory failure defined by a cardiac index (CI) lower than 2.5 L/min/m2.

INTERVENTION

Infusion of 500 mL of dextran 40 over 20 mins.

MEASUREMENTS AND MAIN RESULTS

Fluid loading induced a substantial increase in right atrial pressure from 9 +/- 1 mm Hg to 17 +/- 1 mm Hg and in right ventricular end-diastolic volume index from 123 +/- 14 mL/m2 to 150 +/- 11 mL/m2 (p < .05 for both comparisons). The increase in right ventricular preload was associated with an increase in Cl from 1.6 +/- 0.1 to 2.0 +/- 0.1 L/min/m2 (p < .05), whereas right ventricular ejection fraction (15 +/- 3% at baseline vs. 16 +/- 3% after fluid loading) and total pulmonary vascular resistance index (1689 +/- 187 dyne x sec/cm5 x m2 at baseline vs. 1492 +/- 166 dyne x sec/ cm5 x m2 after fluid loading) remained unchanged. The increase in Cl induced by fluid loading was inversely correlated to baseline right ventricular end-diastolic volume index (r = -.89 ; p< .05).

CONCLUSIONS

These results suggest that fluid loading can improve hemodynamic status in patients with acute circulatory failure caused by AMPE.

Continuous cardiac output and mixed venous oxygen saturation monitoring

Continuous assessment of cardiac output and SVO2 in the critically ill may be helpful in both the monitoring variations in the patient's cardiovascular state and in determining the efficacy of therapy. Commercially available continuous cardiac output (CCO) monitoring systems are based on the pulsed warm thermodilution technique. In vitro validation studies have demonstrated that this method provides higher accuracy and greater resistance to thermal noise than standard bolus thermodilution techniques. Numerous clinical studies comparing bolus with continuous thermodilution techniques have shown this technique similarly accurate to track each other and to have negligible bias between them. The comparison between continuous thermal and other cardiac output methods also demonstrates good precision of the continuous thermal technique. Accuracy of continuous oximetry monitoring using reflectance oximetry via fiberoptics has been assessed both in vitro and in vivo. Most of the studies testing agreement between continuous SVO2 measurements and pulmonary arterial blood samples measured by standard oximetry have shown good correlation. Continuous SVO2 monitoring is often used in the management of critically ill patients. The most recently designed pulmonary artery catheters are now able to simultaneously measure either SVO2 and CCO or SVO2 and right ventricular ejection fraction. This ability to view simultaneous trends of SVO2 and right ventricular performance parameters will probably allow the clinician to graphically see the impact of volume loading or inotropic therapy over time, as well as the influence of multiple factors, including right ventricular dysfunction, on SVO2. However, the cost-effectiveness of new pulmonary artery catheters application remains still questionable because no established utility or therapeutic guidelines are available.

Noninvasive monitoring of cardiac output in critically ill patients using transesophageal Doppler

Measurement of cardiac output using thermodilution technique in mechanically ventilated patients is associated with significant morbidity. The goal of the present study was to assess the validity of cardiac output measurement using transesophageal Doppler in critically ill patients. Forty-six patients from three different intensive care units underwent 136 paired cardiac output measurements using thermodilution (COTH) and transesophageal Doppler (COTED). In addition, simultaneous suprasternal Doppler and indirect calorimetry (Fick principle) were used to measure cardiac output in 26 patients from one center. A good correlation was found between COTH and COTED (r = 0.95), with a small systematic underestimation (bias = 0.24 L/min) using transesophageal Doppler. The limits of agreement between COTH and COTED were +2 L/min and -1.5 L/min. Variations in cardiac output between two consecutive measures using either transesophageal Doppler or thermodilution techniques were similar in direction and magnitude (bias = 0 L/min; limits of agreement = +/-1.7 L/min). Suprasternal Doppler and indirect calorimetry yielded similar correlations and agreements in the subset of patients in whom they were used. These results confirm that transesophageal Doppler can provide a noninvasive, clinically useful estimate of cardiac output and detect hemodynamic changes in mechanically ventilated, critically ill patients.

Transesophageal Doppler Analysis of Coronary Sinus Flow A New Method to Assess the Severity of Tricuspid Regurgitation

BACKGROUND: Severe mitral regurgitation induces reversal of flow in the pulmonary veins. We hypothesized that severe tricuspid regurgitation may disrupt normal coronary sinus flow. The purpose of this study was to analyze the Doppler flow pattern of the coronary sinus and to determine its value in the assessment of the severity of tricuspid regurgitation. METHODS: The coronary sinus flow was analyzed in 70 consecutive patients with some degree of tricuspid regurgitation (27 mild, 14 moderate, and 29 severe) and in 35 patients without tricuspid regurgitation. The coronary sinus flow was obtained by pulsed-Doppler transesophageal echocardiography in a transverse plane, which showed its drainage into the right atrium. RESULTS: The number of patients with adequate studies of the coronary sinus tended to increase with the severity of the tricuspid regurgitation. In patients without or with only mild tricuspid regurgitation the coronary sinus Doppler flow pattern was formed by two negative waves, a late systolic wave and another diastolic one with higher velocity and longer duration. The systolic wave became reversed in 21 (96%) of the patients with severe tricuspid regurgitation. The sensitivity, specificity, and diagnostic accuracy of the presence of a reversed systolic wave in the coronary sinus for the diagnosis of severe tricuspid regurgitation was 95%, 82%, and 80%, respectively. CONCLUSIONS: Significant tricuspid regurgitation modifies the coronary sinus flow pattern as assessed by transesophageal echocardiography. The presence of a reversed systolic flow in the coronary sinus appears to be a reliable new sign with good sensitivity, specificity, and diagnostic accuracy for the diagnosis of severe tricuspid regurgitation.

Noninvasive measurement of cardiac output by an acetylene uptake technique and simultaneous comparison with thermodilution in ICU patients

A simple, accurate, and noninvasive method of cardiac output measurement can be an extremely useful tool for the clinician and researcher. This study used the acetylene gas uptake technique to measure the absorption of acetylene into the pulmonary circulation during a constant exhalation, which is proportional to the pulmonary capillary blood flow and to the cardiac output, assuming no anatomic shunts. We compared cardiac output measured simultaneously by this and by the standard thermodilution (TD) technique in 21 patients in the ICU with a variety of medical and surgical conditions and a wide range of cardiac outputs. We also compared the two techniques in 19 ambulatory patients with a 2-h interval between the invasive and noninvasive test to assess variability over time. The two tests had an excellent correlation when done simultaneously with a correlation coefficient of 0.89 (p < 0.001). With a 2-h interval between the two tests, the correlation coefficient was 0.66 (p = 0.0018). Nine patients in the simultaneous group had cardiomyopathy. When they were excluded, the correlation coefficient increased to 0.96. Most of these patients had documented tricuspid regurgitation (TR), which may underlie the greater difference between acetylene uptake and TD values, with consistently higher TD values in these patients. This study confirms the correlation between the acetylene uptake and the standard invasive TD techniques in sick patients with various medical and surgical conditions and a wide range of cardiac outputs. Furthermore, we believe this would be a more accurate method for measuring cardiac output in patients with cardiomyopathy and TR because it is based only on pulmonary capillary blood flow.

Whole-body impedance cardiography in the measurement of cardiac output

OBJECTIVE

To evaluate the reliability of whole-body impedance cardiography with electrodes on wrists and ankles in the measurement of cardiac output compared with the thermodilution method.

DESIGN

Prospective, clinical investigation.

SETTING

Surgical intensive care unit and operating room at a university hospital.

PATIENTS

Simultaneous cardiac output measurements by thermodilution and whole-body impedance cardiography were performed in 74 patients undergoing a coronary artery bypass grafting operation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 97 triplicate, simultaneous cardiac output measurements were carried out with thermodilution and whole-body impedance cardiography: 74 measurements were conducted in patients who were awake and 23 measurements were conducted during anesthesia but before the commencement of surgery. The mean cardiac output difference (bias) between the two methods was 0.25 +/- 0.81 (SD) L/min; the limits of agreement (2 SD) were-1.37 and 1.87 L/min, respectively. The repeatability value (rv = 2.83 x SD) for whole-body impedance cardiography (rv = 0.46 L/min) was considerably better than for the thermodilution method (rv = 1.05 L/min). Whole-body impedance cardiography reliably detected cardiac output changes induced by head-up tilt before anesthesia, by anesthesia induction, and by intubation. Two factors predicted the between-methods stroke volume difference: hematocrit (correlation coefficient r = -.36, r2 = .13; p < .001); and body mass index (r = .29, r2 = .08; p < .01). Using the multiple linear regression equation for correcting the stroke volume by hematocrit and body mass index, the limits of agreement (2 SD) between the methods studied were reduced to +/-1.28 L/min for cardiac output and +/-0.72 L/min/m2 for cardiac index.

CONCLUSIONS

There was close agreement between whole-body impedance cardiography and thermodilution in the measurement of cardiac output in patients with coronary artery disease without cardiac shunts and valvular lesions. The repeatability of the impedance method was significantly better than the repeatability of thermodilution. Whole-body impedance cardiography can be recommended for the assessment of cardiac output and its changes in the resting state. Whole-body impedance cardiography is a feasible and handy method for noninvasive and continuous measurement of cardiac output.

Comparison of Doppler echocardiography with thermodilution for assessing cardiac output in advanced congestive heart failure

Noninvasive cardiac output estimation by Doppler echocardiography was compared with thermodilution and Fick oxygen methods in 73 patients with advanced chronic congestive heart failure due to dilated cardiomyopathy. In these patients, Doppler echocardiographic measurements showed a closer agreement with Fick measurements than that of thermodilution.

Pulsed wave Doppler measurement of cardiac output from the right ventricular outflow tract

Doppler ultrasound can be used to measure cardiac output (CO). Intraoperative Doppler cardiac output (DCO) by transesophageal echocardiography (TEE) has been studied using blood flow velocity from the left ventricular outflow tract (LVOT), the mitral valve (MV), and the main pulmonary artery (MPA). The purpose of this study was to compare DCO, measured from a relatively new TEE view of the right ventricular outflow tract (RVOT), with thermodilution cardiac output (TDCO). We also compared changes in DCO from the RVOT to changes in TDCO. A 5.0/3.7 MHz multiplane TEE probe was placed in 45 adult cardiac surgical patients undergoing general anesthesia. Patients were excluded if there was greater than mild tricuspid valve insufficiency. From the transgastric view, at approximately 110-140 degrees, the RVOT was imaged. DCO was calculated from 1) the time-velocity integral (TVI) using pulse wave (PW) Doppler, 2) the area of the RVOT (measured in early systole using the diameter (pi(D/2)2) of the RVOT at the level of the PW Doppler sample volume), and 3) the heart rate. Simultaneous TDCO was performed by a separate examiner. The RVOT was imaged satisfactorily in 84% of patients (38/45). The mean bias between DCO and TDCO was -0.01 L/min (2 SD +/- 0.45 L/min; n = 38). There was good correlation between DCO and TDCO (R2 = 0.97). Changes in TDCO and changes in DCO were compared in 15 patients. The mean bias between changes in DCO and changes in TDCO was 0.04 L/min (2 SD +/- 0.66 L/min). Analysis of the changes in DCO and TDCO showed good correlation (R2 = 0.96). We conclude that there is a good correlation between DCO measured from the RVOT and TDCO. This technique permits cardiac output measurement without the necessity of placing a pulmonary artery catheter, and it also provides a method of evaluating RVOT blood flow.

Acute hemodynamic responses to inhaled nitric oxide in patients with limited scleroderma and isolated pulmonary hypertension

BACKGROUND

Inhaled nitric oxide (NO) is a selective pulmonary vasodilator that reduces pulmonary vascular resistance (PVR) in patients with primary pulmonary hypertension. Their responses to inhaled NO predict their responses to other vasodilators, such as prostacyclin, and provide an estimate of the "fixed" component of their increased PVR. Some patients with limited cutaneous systemic sclerosis develop isolated pulmonary hypertension with a similar clinical course. Therefore, we have measured the acute hemodynamic response to inhaled NO in such patients.

METHODS AND RESULTS

Seven patients were studied during inhalation of increasing concentrations of NO (0 to 80 ppm). Complete hemodynamic data were collected on five patients. They demonstrated a selective, dose-dependent, and rapidly reversible fall in PVR (34%) and mean pulmonary artery pressure (17%). There was a nonsignificant increase in cardiac index but no change in mean arterial pressure or systemic vascular resistance. The mean right atrial pressure fell (27%), but there was no change in pulmonary artery occlusion pressure. Of the seven patients, five responded to inhaled NO ( < or = 40 ppm) with a decrease in total pulmonary resistance of at least 20%.

CONCLUSIONS

Inhaled NO is an effective and selective pulmonary vasodilator in a significant number of patients with pulmonary hypertension associated with limited cutaneous systemic sclerosis. It may be useful in determining the potentially reversible contribution to the increased PVR and should be considered for patients with acute pulmonary vascular crisis.

Value of proximal regurgitant jet size in tricuspid regurgitation

Recent studies have shown good agreement between proximal regurgitant jet size obtained with transthoracic color flow mapping and regurgitant fraction in patients with mitral regurgitation. To evaluate this in patients with tricuspid regurgitation, we analyzed 40 patients in sinus rhythm, 16 with free jets and 24 with impinging jets, comparing proximal jet size (millimeters) with parameters derived from the Doppler two-dimensional echocardiographic method (regurgitant fraction) and the flow-convergence method (peak flow rate, effective regurgitant orifice area, and momentum). Good agreement was noted between peak flow rate (r = 0.80, p < 0.001), momentum (r = 0.80, p < 0.001), and effective regurgitant orifice area (r = 0.78, p < 0.001), with proximal jet size measured in the apical four-chamber view in patients with free jets. The average of jet proximal size in three planes also had good correlation with peak flow rate (r = 0.75, p < 0.001), regurgitant fraction, momentum, and effective regurgitant orifice area (r = 0.74, p < 0.001). In patients with impinging jets, agreement was fair between effective regurgitant orifice (r = 0.65, p < 0.001), peak flow rate (0.65, p < 0.001), and momentum (r = 0.62, p < 0.001) with mean jet proximal size. Jet proximal size obtained with transthoracic color flow mapping is a good semiquantitative tool for measuring tricuspid regurgitation in free jets that correlates well with established measures of the severity and with new parameters available from analysis of the proximal acceleration field. In patients with eccentrically directed wall jets, the correlation weakens but still appears clinically significant.

Clinical estimation of left and right ventricular volume with open chest compared with transesophageal echocardiography and fast-response thermodilution

OBJECTIVE

A clinical measure--inspection of the relation of the heart (acute margin) to the diaphragm--has shown a strong positive correlation to transesophageal echocardiographic (TEE) determination of left ventricular end-diastolic area (LVEDA) during weaning from cardiopulmonary bypass (CPB). The present study examines the correlation between right ventricular end-diastolic volumes (RVEDV) before and after CPB when using the same clinical measure of left ventricular dimension.

DESIGN

Prospective study.

SETTING

Operating room, university hospital.

PARTICIPANTS

Patients scheduled for elective coronary artery bypass grafting.

INTERVENTIONS

After induction of anesthesia and endotracheal intubation, a transesophageal echo-probe was inserted. A pulmonary artery right ventricular ejection fraction/volumetric TD catheter was placed in the pulmonary artery.

MEASUREMENTS AND MAIN RESULTS

Before going on CPB, a mark was made with cautery at the line of contact between the acute margin and the diaphragm. After CPB, the patients were transfused to the same level. At these two times, TEE recordings of the LVEDA and hemodynamic measurements including calculations of RVEDV were obtained. The LVEDA before and after CPB showed a positive correlation, r = 0.81, p < 0.001. The RVEDV after CPB showed a weak correlation, r = 0.54, p < 0.05, to RVEDV before CPB. There were no significant changes in right ventricular (RV) wall tension calculated as right atrial pressure x RVEDV and pulmonary artery systolic pressure x right ventricular end-systolic volume products. The only significant change regarding hemodynamic parameters was a decrease in mean arterial pressure.

CONCLUSIONS

It is concluded that there is only a weak correlation regarding RVEDV before and after CPB when the patient is transfused to the line of contact, whereas this clinical measure correlates well with LVEDA.

Incidence of tricuspid regurgitation and vena caval backward flow in mechanically ventilated patients. A color Doppler and contrast echocardiographic study

In 40 patients requiring mechanical ventilation for an episode of respiratory failure of various causes, prevalence of tricuspid regurgitation (TR) or other cause of vena caval backward flow (VCBF) was systematically investigated using transthoracic Doppler echocardiography. Quantification of TR was obtained from planimetry of the regurgitant jet during color Doppler examination. The influence of cyclic mechanical lung inflation was examined by contrast echography of the inferior vena cava and hepatic veins. All the 40 patients studied had TR, which was mild in 21, moderate in 9 and severe in 10. Using a planimetric scale, TR was more marked during mechanical ventilation, when compared with a brief period of spontaneous breathing. Moreover, contrast echocardiography demonstrated that systolic TR reached inferior vena cava and hepatic veins in 16 cases, and also evidenced direct mechanical action of lung inflation producing a pancardiac VCBF in 15 cases. This high incidence of TR and VCBF partially may explain the relatively poor reliability of the thermodilution method for measurement of cardiac output when used in ventilated patients.

Thermodilution left-sided cardiac output for valve area determination after balloon mitral valvotomy

This study was conducted to establish the validity of left-sided cardiac output measurement with a Swan-Ganz catheter and assess its accuracy in estimating mitral valve area (MVA) by the Gorlin formula. The use of right-sided cardiac output after balloon mitral valvotomy (BMV) can give inaccurate measurements for Gorlin-derived MVA because of the atrial septal defect (ASD) created during the procedure. The left-sided cardiac output was measured with a Swan-Ganz catheter (proximal port in the left atrium and then in the left ventricle, and distal port in the ascending aorta) in 10 consecutive patients before and after BMV. Gorlin-derived MVA cardiac output by this method was compared with (1) Gorlin-derived MVA by means of right-sided cardiac output with and without balloon occlusion of the ASD and (2) MVA measured by echocardiography. Before BMV, a close agreement with a good correlation between left-sided and right-sided cardiac output was found (r = 0.83, p = 0.006). Furthermore, Gorlin-derived MVA by cardiac output with either method was comparable with valve area by echo. After BMV, left-sided cardiac output correlated well (r = 0.92, p = 0.0002) and was comparable with right-sided cardiac output with occlusion of the ASD (mean difference 0.17 +/- 0.49 L/min, p = 0.3) but was significantly lower than the value obtained with open ASD (mean difference 0.93 +/- 0.77 L/min, p = 0.004). Comparison of the correspondent MVAs yielded similar results. Gorlin-derived MVA with left-sided cardiac output and MVA by echo were also similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Which physical factors determine tricuspid regurgitation jet area in the clinical setting?

The visual assessment of jet area has become the most common method used in daily clinic practice to evaluate valvular regurgitation. Despite the high prevalence of tricuspid regurgitation, however, few studies have systematically compared TR jet areas with a quantitative standard. To evaluate this, 40 patients in sinus rhythm with tricuspid regurgitation were analyzed: 16 with centrally directed free jets and 24 with impinging wall jets. The size of the maximal planimetered color jet area (cm2) was compared with parameters derived using the pulsed Doppler 2-dimensional echocardiographic method: regurgitant fraction and the flow convergence method (peak flow rate, effective regurgitant orifice area and momentum). Mean tricuspid regurgitant fraction averaged 33 +/- 15%, peak flow rate 76 +/- 54 cm3/s, effective regurgitant orifice area 27 +/- 21 mm2 and momentum 21,717 +/- 15,014 cm4/s2. An average of 4-chamber, and long- and short-axis areas in free jets correlated well with regurgitant fraction (r = 0.81, p < 0.001), better with peak flow rate (r = 0.94, p < 0.001), effective regurgitant orifice (r = 0.92, p < 0.001) and momentum (r = 0.94, p < 0.001). The correlation was worse, but still significant, in wall jets. For the same peak flow rate, wall jets were 75% of the size of a corresponding free jet. Jet area measurement is a good semiquantitative tool to measure tricuspid regurgitation in free jets, which correlates well with regurgitant fraction and better with new parameters available from analysis of the proximal acceleration field. In patients with eccentrically directed wall jets the correlation with planimetered jet area was worse, but still significant.

Why do patients with congestive heart failure tolerate the initiation of beta-blocker therapy?

BACKGROUND

Despite its negative inotropic effects, the initiation of beta-adrenergic blockade is tolerated by patients with congestive heart failure (CHF). Accordingly, we examined the acute hemodynamic effects of beta-adrenergic blockade on systolic and diastolic left ventricular (LV) function and ventriculo-arterial coupling. In addition, isolated myocardium from patients with CHF shows selective beta 1-receptor downregulation, implying a greater role for the beta 2-receptor in maintaining in vivo LV contractility. As a secondary aim, we hypothesized that nonselective beta-adrenergic blockade would have greater negative inotropic effect than beta 1-blockade in patients with CHF.

METHODS AND RESULTS

Patients with clinical CHF (n = 24) and control patients without CHF (n = 24) were given either the nonselective beta-blocker propranolol or the beta 1-selective blocker metoprolol. LV pressure-volume relations were obtained before and after the administration of intravenous beta-blocker, and measures of LV systolic and diastolic function were examined. Patients with CHF had a deterioration in LV systolic function with a fall in LV systolic pressure (139 +/- 6 to 125 +/- 6 mm Hg), cardiac index (2.56 +/- 0.11 to 2.20 +/- 0.11 mL.min-1 x M-1), dP/dtmax (1173 +/- 63 to 897 +/- 50 mm Hg/s), and end-systolic elastance (0.88 +/- 0.10 to 0.64 +/- 0.10 mm Hg/mL), P < .05 for all. Although there was deterioration of active LV relaxation (isovolumetric relaxation 63 +/- 2 to 73 +/- 3 milliseconds, peak filling rate 543 +/- 33 to 464 +/- 28 mL/s, P < .05 for both), there was no change in passive LV diastolic function (pulmonary capillary wedge, 24 +/- 2 to 24 +/- 1 mm Hg; chamber stiffness, 0.0154 +/- 0.0005 to 0.0163 +/- 0.0005 mL-1, P = NS for both), and a decrease in afterload (arterial elastance 3.85 +/- 0.31 to 3.38 +/- 0.24 mm Hg/mL, P < .05). Control patients had no change in these parameters other than a prolongation of isovolumetric relaxation (48 +/- 1 to 55 +/- 2 milliseconds, P < .05). The effects of propranolol (n = 12) versus metoprolol (n = 12) on these parameters in patients with CHF were similar.

CONCLUSIONS

These data do not support a greater in vivo physiological role of the myocardial beta 2-receptor in CHF. The preservation of passive diastolic function and ventriculo-arterial coupling provide possible explanations of why beta-adrenergic blockade is tolerated by patients with CHF.