Accuracy of electrical impedance cardiography for measuring cardiac output in children with congenital heart defects

This study determined whether noninvasive electrical impedance cardiography accurately measures systemic blood flow (cardiac output) in children with congenital heart defects. A total of 37 patients ranging in age from 2 to 171 months underwent complete right- and left-sided heart catheterizations that included simultaneous Fick and impedance measurement of cardiac output. Based on the diagnosis, 4 groups were formed consisting of a control group (n = 11) with no shunts, a group with intracardiac left-to-right shunting and an atrial septal defect (n = 7), another with a ventricular septal defect (n = 12) and an extracardiac left-to-right shunting with patent ductus arteriosus group (n = 7). Impedance values for systemic blood flow were compared with systemic and pulmonary blood flow obtained by the direct Fick method with measured oxygen consumption. The difference between impedance and Fick systemic blood flow was less than or equal to 5% in each of the 4 groups. The highest correlation between impedance and Fick systemic blood flow was with the atrial septal defect group (r = 0.89) and lowest with the ventricular septal defect and control (r = 0.69) groups. Fick pulmonary blood flow was significantly greater than impedance or Fick systemic flow in all 3 shunt groups. Impedance cardiography accurately measured systemic blood flow in children without shunts or valvular insufficiency. Likewise, systemic blood flow was accurately measured by impedance in the presence of intracardiac left-to-right shunts (atrial and ventricular septal defects) and extracardiac left-to-right shunts (patent ductus arteriosus).(ABSTRACT TRUNCATED AT 250 WORDS)     

Noninvasive diagnosis of mitral regurgitation by impedance cardiography

A total of 46 patients with mitral regurgitation (MR) of varying degrees of manifestation and 84 subjects with no MR were investigated. The possibilities were elucidated of the MR diagnosis by the impedance index (IMR): the ratio of the primary diastolic wave O amplitude to the primary systolic wave amplitude (dz/dt)min of the impedance cardiogram. A significant increase of the IMR was recorded in the MR presence. The degree of such increase depended on the MR manifestation and not on the impairment of the left or right ventricle function. The high specificity and sensitivity of the method, the value of the negative and positive tests as well as their reproducibility evidence that impedance cardiography is a perspective method for the noninvasive diagnosis of MR.     

Reproducibility of cardiac output derived by impedance cardiography during postural changes and exercise

BackgroundEvaluation of cardiac output (CO) and other haemodynamic parameters may aid in understanding factors involved in arterial blood pressure (BP) changes with exercise and postural stress. Impedance cardiography offers a rapid, non-invasive means to acquire this information, however there is limited data assessing the reproducibility of this technique during haemodynamic perturbation. This study aimed to assess reproducibility of CO and other haemodynamic parameters derived from impedance cardiography during exercise and in different postures.Methods51 participants (mean age 57 ± 9 years, 57% male) had CO and other haemodynamic variables (including end diastolic volume, left ventricular work, ejection fraction and systemic vascular resistance) measured via impedance cardiography (Physio Flow) at two visits separated by 12 ± 7 days. Measures were recorded at rest in three postures (supine, seated and standing), during upright cycle ergometry at a fixed workload (40 W), and also during steady state exercise at an intensity of 60% and 70% of age-predicted maximum heart rate (HR_max).ResultsCO reproducibility was assessed over a wide range (5.27 ± 1.00–12.09 ± 2.02 l/min). There was good agreement between CO measured at each visit in all postures and exercise conditions (intra-class correlation coefficient [ICC] range 0.729–0.888, P < 0.05 for all) with a small difference between visits (mean difference 0.06 ± 1.10 l/min). All other haemodynamic variables showed good agreement between visits (ICC range 0.714–0.970, P < 0.05 for all).ConclusionsNon-invasive impedance cardiography provides an acceptably reproducible means to evaluate CO and other haemodynamic variables relevant to arterial BP regulation during different postures and light-to-moderate intensity exercise.     

Noninvasive hemodynamic monitoring in heart failure: utilization of impedance cardiography

The annual health care cost incurred by heart failure patients is about $56 billion, two thirds of which is spent on management of acutely decompensated patients. Hemodynamic evaluation is helpful for optimization of treatment, monitoring clinical outcomes, and overall prognostication of heart failure patients, but historically could only be obtained via costly invasive procedures that carry substantial risks. Impedance cardiography (ICG) is a noninvasive and economical outpatient procedure that has been shown to provide reliable hemodynamic values comparable to those obtained from pulmonary artery catheterization. Recent clinical studies involving hundreds of patients have validated the accuracy and reproducibility of ICG compared with invasive techniques. The direct and derived measurements and the clinical applications of ICG in the diagnosis and treatment of heart failure are presented, as are three clinical case studies demonstrating the utility of ICG in the hemodynamic-guided management of heart failure. ICG is a viable, noninvasive technique in early- and late-stage heart failure that provides assistance in diagnostic evaluation, longitudinal prognostication, and therapeutic decisions.     

Cardiac output measured by impedance cardiography during maximal exercise tests

The overall accuracy of cardiac output measurements made by impedance cardiography during maximum exercise was studied in man. Initially, the systematic error of the technique was assessed over the range 3.5 to 18 litre . min-1 by comparing with simultaneous measurements of cardiac output made using the direct Fick method. No systemic error was demonstrated in 40 estimations made in 20 subjects. The random error was assessed in 4 subjects in a steady state at rest and during exercise at 80 and 130 W and found to be less than 5% in each subject. The reproducibility of maximum exercise response was assessed in six healthy male subjects (age 26.2 +/- 4.4 years, +/- SEM) who underwent maximum exercise tests twice, 1 week apart, on a bicycle ergometer. Simultaneous recordings of cardiac output and oxygen uptake (VO2) at rest and during each 3 min stage of exercise were made. Highly significant correlations were obtained in the stroke volume (r = 0.84, p less than 0.001), cardiac output (r = 0.98, p less than 0.001) and VO2 (r = 0.98, p less than 0.001) between the two tests. Average maximum cardiac output was 27.0 +/- 1.2 litre . min-1 (+/- SEM) and maximum VO2 was 4.4 +/- 0.2 litre . min-1 (+/- SEM). These results show that measurements of cardiac output were reproducible over one week. Impedance cardiography is non-invasive technique which is as accurate as invasive methods and can be used for maximal exercise testing.     

Validity of cardiac output measurement by computer-averaged impedance cardiography, and comparison with simultaneous thermodilution determinations.

The accuracy and reproducibility of noninvasive cardiac output determinations by computer-averaged impedance cardiography were compared with those of simultaneously performed thermodilution cardiac output. In all, 43 patients (14 men and 29 women = 201 pairs) were studied by simultaneously performed impedance and thermal determinations. Individual impedance values correlated with paired thermodilution determinations (r = 0.75; p less than 0.0001). Each patient's average thermodilution values correlated with the average impedance values (r = 0.86; p less than 0.0001). Mean thermodilution output was 4.6 +/- 1.37 liters/min. Mean impedance output was 4.5 +/- 1.27 liter/min Reproducibility was comparable for impedance (0.0059 +/- 0.639) and thermodilution cardiac output (0.023 +/- 0.556). There was high agreement between methods by plot of the difference against mean of the 2 methods. Impedance cardiac output values agree and correlate highly with quality-controlled thermodilution outputs across a wide range of clinical conditions and hemodynamic values.     

Noninvasive assessment of hemodynamics: an emphasis on bioimpedance cardiography

Evaluation of the hemodynamic response in heart failure is a useful adjunct in clinical management. Invasive monitoring has been the accepted gold standard of hemodynamic assessment but carries with it significant associated risks. Noninvasive hemodynamic assessment in heart failure previously has been either unreliable or difficult to obtain. Bioimpedance relies on the proportional change in the conduction of alternating current applied across the thorax as a function of blood volume in the heart and great vessels. Stroke volume, cardiac output, thoracic fluid content, and measures of diastolic function can be determined with bioimpedance. Impedance cardiography is becoming an accepted method for safe, reliable, and reproducible assessment of hemodynamics in heart failure.     

Comparative investigation of cardiac output using impedance rheography and invasive methods

Authors performed comparative measurements of cardiac output using the impedance rheography and Fick's method in healthy men (6) reaching the value of correlation coefficient 0.88 and in patients with acquired cardiac defects (n = 21; r = 0.68). Authors also compared cardiac output values measured at rest and during exercise by means of thermodilution and rheographic methods in patients with heart failure (n = 9). Correlation coefficient was respectively 0.92 and 0.81.     

Noninvasive cardiac output monitoring during exercise stress test

A computerized continuous wave Doppler instrument was used to monitor changes in cardiac output during symptom limited supine bicycle exercise in 41 individuals. Eight (19%) had technically unsatisfactory Doppler signals. Of the remaining 33 patients, 21 had clinical and 18 had angiographic evidence of coronary artery disease (group 1) and 12 age-matched asymptomatic subjects served as controls (group 2). In eight group 1 patients, cardiac output determined simultaneously by Doppler and thermodilution technique correlated well at rest and peak exercise (Y = 1.71x + 0.69, SEE = 0.57, r = 0.86, P less than 0.001). During exercise, group 1 patients increased their cardiac output from 5.2 +/- 1 to 6.9 +/- 1.4 (mean +/- SD), group 2 subjects increased their cardiac output from 5.5 +/- 1.3 to 10.9 +/- 2. Group 1 patients, when compared to group 2 control subjects, had a lesser increase in cardiac output (34% versus 103%, P less than 0.05), a shorter duration of exercise (6.1 versus 9.7 mins, P less than 0.05) and a lower double product (172 +/- 18 versus 211 +/- 27, P less than 0.05). This new Doppler technique provides reasonably accurate estimates of cardiac output at rest and on moderate exercise in selected patients. In selected clinical situations, it may be a valuable addition to other measurements that are usually determined during exercise.     

Beyond auscultation--acoustic cardiography in the diagnosis and assessment of cardiac disease

the evaluation of patients with known and suspected cardiac disease. The subsequent development of phonocardiography provided an analogue visual display that permitted a more detailed analysis of the timing and acoustical characteristics of heart sounds, murmurs, clicks and rubs. In addition, the measurement of systolic time intervals enabled a valuable non-invasive assessment of left ventricular function. Acoustic cardiography, a much more recently developed technology, has enabled the simultaneous acquisition of ECG and cardiac acoustical data. This user-friendly and cost-effective technology permits acquisition of detailed information regarding systolic and diastolic left ventricular function and provides both a computerized interpretation and a visual display of the findings. Its clinical applications include the evaluation of patients with suspected heart failure, ischaemia and cardiac arrhythmias and the optimization of cardiovascular drug and device therapies. It can also be used in a wide variety of ambulatory and inpatient monitoring applications.     

Noninvasive measurement of cardiac output during surgery using a new continuous-wave Doppler esophageal probe

The ability of a new continuous-wave Doppler esophageal probe to measure cardiac output noninvasively during surgery under general anesthesia was tested and compared with simultaneously measured thermodilution cardiac output. A Doppler computer, calibrated for the aortic diameter and the transcutaneously measured cardiac output from the suprasternal notch, computed the Doppler cardiac output from the descending aortic blood flow velocity signal. A total of 246 paired Doppler cardiac output and thermodilution cardiac output measurements were made in 14 patients during surgery. The average thermodilution cardiac output was 5.90 +/- 3.27 (standard deviation) liters/min (range 1.20 to 19.18); the average Doppler cardiac output was 6.21 +/- 4.0 liters/min (range 2.30 to 28.20). The difference between the cardiac output measured by the 2 techniques was 1.38 +/- 2.2 liters/min (range 0.04 to 16.8). Two to 5 cardiac output measurements were averaged and arranged into "time periods." The average standard deviations for thermodilution and Doppler cardiac outputs within each time period were 0.64 and 0.47 liters/min, respectively. There was a correlation between the 2 measurements over a range of cardiac output values (r = 0.76, Doppler cardiac output = 0.93 x thermodilution cardiac output +0.7, standard error of the estimate = 1.76). Reproducible measurements of Doppler cardiac output were obtained during intraobserver (mean difference 0.64 +/- 0.52 liter/min) and interobserver (mean difference 0.41 +/- 0.36 liter/min) studies (n = 8). Cardiac output measurement by the Doppler esophageal probe could be used for hemodynamic monitoring during surgery in selected patients with cardiopulmonary disease.     

Noninvasive measurement of cardiac output using two-dimensional Doppler echocardiography and analysis of sources of error

The purpose of this study was (1) to analyze the factors responsible for errors in the two-dimensional Doppler echographic measurements of cardiac output (C.O.) and (2) to establish a noninvasive method for measuring C.O. The subjects were 50 cardiac patients who had neither aortic valve disease nor intracardiac shunts. The C.O. was calculated using the following formula: C.O. (l/min) = mean flow velocity (cm/sec) x pi(aortic ring diameter/2)2 (cm2) x 60/10(3) Left ventricular ejection flow velocity was recorded in the center of the aortic ring from the apical approach. Mean velocity was calculated by integration of instantaneous mean velocity in the ejection phase divided by the cardiac cycle length, and was corrected by the Doppler incident angle. The inner diameter of the aortic ring was measured in the parasternal long-axis view at the time of the maximum ejection flow velocity. The following results were obtained: 1. Sources of error in the measurement of cardiac output. 1) Accuracy of instantaneous mean velocity calculating circuit: This calculating circuit was accurate in model experiments using pulsatile flow. 2) Effect of high-pass filter: In model circuits, application of high-pass filter overestimated flow velocity. The higher the cut-off frequency of the high-pass filter, the larger the overestimation. This was probably due to the parabolic flow velocity profile in the circuit. 3) Flow velocity profile in the aortic ring: The flow velocity profile seemed to be flat in the aortic ring except near the anterior aortic wall. Therefore, the effect of the high-pass filter was considered to be negligible in case of clinical application. 4) The effects of shift and size of sample volume: The location of sample volume relative to the aortic valve ring shifted about 7 mm during systole. However, the shift and size of sample volume seemed to have little effect on the measured C.O., because the flow velocity profile was nearly flat in the aortic ring. 5) Ultrasound beam incident angle: From a practical viewpoint, it was necessary to set an incident angle of less than 50 degrees for minimizing the error. We were able to set the angle within 50 degrees in all but one of patients. 6) Diameter of the aortic ring: Two-dimensional echographic measurement of the aortic ring diameter was not so accurate; it seemed to become a major source of error in the calculation of C.O.(ABSTRACT TRUNCATED AT 400 WORDS)     

Impedance cardiography for cardiac output estimation: reliability of wrist-to-ankle electrode configuration.

BACKGROUND: Non-invasive measurement of cardiac output (CO) may become an important modality for the treatment of heart failure. Among the several methods proposed, impedance cardiography (ICG) has gained particular attention. There are 2 basic technologies of ICG: thoracic and whole-body ICG whereby the electrodes are applied either to the chest or to the limbs. The present study is aimed to test the effectiveness of the Non-Invasive Cardiac System (NICaS), a new ICG device working with a wrist-to-ankle configuration. METHODS AND RESULTS: To evaluate the reliability of NICaS derived CO (NI-CO), 50 CO measurements were taken simultaneously with thermodilution (TD-CO) and modified Fick (Fick-CO) in 35 cardiac patients, with the TD-CO serving as the gold-standard for the evaluation. Overall, 2-tailed Pearson's correlation and Bland-Altman limits of agreement between NI-CO and TD-CO were r=0.91 and -1.06 and 0.68 L/min and between Fick-CO and TD-CO, r=0.80 and -1.52 and 0.88 L/min, respectively. Good correlation was observed in patients with loading conditions altered by nitroglycerin and also in patients with moderate valvular diseases. CONCLUSION: Agreement between NI-CO and TD-CO is within the boundaries of the FDA guidelines of bio-equivalence. NI-CO is applicable for non-invasive assessment of cardiac function.     

无创血流动力学监测可用于对老年慢性心力衰竭患者心功能的评价

目的通过对老年慢性心力衰竭患者无创血流动力学监测,并与美国纽约心脏病学会（NYHA）心功能分级做对比分析,初步评价判定心功能分级的可靠性。方法选取我院自2004年4月～2005年9月1日收治于老年心血管病科的冠心病、高血压病、扩张型心肌病等患者共120例,按NYHA分级分为Ⅰ、Ⅱ、Ⅲ、Ⅳ共4组,应用Bioz.com无创血流动力学监测得到16种血流动力学参数,进行统计学分析。结果①心输出量（CO）、心排血指数（CI）、左室每博作功指数（LVSWI）、左心作功指数（LCWI）4项参数值按NYHA分级Ⅰ～Ⅳ组有逐渐减低趋势（P<0.05）;②每博输出量（SV）、每博输出指数（SI）、速率指数（VI）按NYHA分级Ⅰ、Ⅱ组间,Ⅲ、Ⅳ组间无显著差异,但Ⅰ、Ⅱ组与Ⅲ～Ⅳ组间有明显减低趋势（P<0.05）;外周阻力（SVR）、外周阻力指数（SVRI）按NYHA分级Ⅰ、Ⅱ组间,Ⅲ、Ⅳ组间无显著差异,但Ⅰ、Ⅱ组与Ⅲ、Ⅳ组间有明显增高趋势（P<0.05）;③胸部液体含量（TFC）、收缩时间比率（STR）按NYHA分级Ⅰ、Ⅱ、Ⅲ组间无显著差异,但Ⅳ组与其他各组比较有明显增高趋势（P<0.05）。结论无创血流动力学监测到的血流动力学参数可作为评估慢性心力衰竭临床分级标准的量化指标。