Monitoring the Chest with Impedance

Water, Joseph M. Van De; Mount, Bruce E.; Barela, James R.; Schuster, Roger; Leacock, Ferdinand S.

doi:10.1378/chest.64.5.597

Cited by 97 publications

(55 citation statements)

References 17 publications

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“…In such a situation, however, the precordial ECG (P wave, QRS complexes, and T waves) leads are expected to show attenuation, and this insight (in the form of thoracic resistance changes, not the ECG, although there is no difference) has been employed in the monitoring of pulmonary congestion both by external and implantable devices. [18][19][20][21] …”

Section: Discussionmentioning

confidence: 99%

T‐Wave Amplitude Attenuation/Augmentation in Patients With Changing Edematous States: Implications for Patients With Congestive Heart Failure

Madias

2007

Congestive Heart Failure

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Since peripheral edema impacts the entire electrocardiographic curve, it was hypothesized that it would also affect T waves. The amplitude of T waves were measured in all electrocardiographic leads and a sum (ΣT) was calculated in 28 patients with and 28 patients without peripheral edema (controls). For patients with peripheral edema, ΣT on admission was 21.9±10.6 mm and ΣT at peak weight was 8.3±6.3 mm (P=.0005). For patients with peripheral edema who subsequently lost weight, ΣT at peak weight was 7.2±6.1 mm and ΣT at the lowest weight was 14.1±12.2 (P=.006). For controls, ΣT from admission and ΣT from discharge were 24.4±16.9 mm and 24.7±15.7 mm (P=.82), respectively. Percent change (Δ%ΣT) from admission to peak weight correlated with Δ% in weight (r=0.58; P=.001) and Δ% in the sum of QRS complexes (ΣQRS) (r=0.71; P=.00005). Δ%ΣT from peak weight to the lowest weight correlated with the corresponding Δ%ΣQRS (r=0.65; P=.02). Changes in T waves with development and alleviation of peripheral edema mirror the changes shown by the QRS complexes and may be useful in the treatment of patients with congestive heart failure or other edematous states.

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Section: Discussionmentioning

confidence: 99%

T‐Wave Amplitude Attenuation/Augmentation in Patients With Changing Edematous States: Implications for Patients With Congestive Heart Failure

Madias

2007

Congestive Heart Failure

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“…Early studies have validated the potential usefulness of this method to reflect the amount of intrathoracic fluid in animal models 8,9 and in humans with pulmonary edema. 10,11 However, this method does not allow the acquisition of chronic, ambulatory data, and serial comparison of measurements is difficult because the impedance is affected by electrode placement. 12 In our early work in dogs, measurement of intrathoracic impedance by a modified pacemaker correlated closely with heart failure severity as reflected by the LV end-diastolic pressure.…”

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confidence: 99%

Intrathoracic Impedance Monitoring in Patients With Heart Failure

et al. 2005

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Background-Patients with heart failure are frequently hospitalized for fluid overload. A reliable method for chronic monitoring of fluid status is therefore desirable. We evaluated an implantable system capable of measuring intrathoracic impedance to identify potential fluid overload before heart failure hospitalization and to determine the correlation between intrathoracic impedance and standard measures of fluid status during hospitalization. Methods and Results-Thirty-three patients with NYHA class III and IV heart failure were implanted with a special pacemaker in the left pectoral region and a defibrillation lead in the right ventricle. Intrathoracic impedance was regularly measured and recorded between the lead and the pacemaker case. During hospitalizations, pulmonary capillary wedge pressure and fluid status were monitored. Ten patients were hospitalized for fluid overload 25 times over 20.7Ϯ8.4 months. Intrathoracic impedance decreased before each admission by an average of 12.3Ϯ5.3% (PϽ0.001) over an average of 18.3Ϯ10.1 days. Impedance reduction began 15.3Ϯ10.6 days (PϽ0.001) before the onset of worsening symptoms. There was an inverse correlation between intrathoracic impedance and pulmonary capillary wedge pressure (

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“…Although indices derived from the chest impedance signal track cardiac stroke volume very well [4][5][6] , the absolute values of stroke volume in units of milliliters of blood per heartbeat have been considered unreliable and suspect [7][8][9][10] , especially in the case of congestive heart failure, when ventricular ejection fraction is greatly diminished 8,11,12 , or in patients with either reduced or increased peripheral vascular resistance 13 . In addition, comparisons of impedance based stroke volume and cardiac output with results from the green dye dilution or the Fick methods show that the impedance cardiogram tends to overestimate stroke volume by 5 to 10 percent, with rather wide standard deviations, leading to the conclusion that the impedance method is not accurate 4 .…”

Section: Introductionmentioning

confidence: 99%

“…The resulting demodulated root mean square potential, U, is measured between a pair of similar inner electrodes, labeled 2 and 3, at the top and bottom of the chest cavity proper. (This is known as tetrapolar -or 4 electrodetechnique 11 .) If the impedance, Z, of the chest increases, then U will increase, because current is constant and voltage is the product of current and impedance (U = i Z).…”

Section: Introductionmentioning

confidence: 99%

“…If the impedance, Z, of the chest increases, then U will increase, because current is constant and voltage is the product of current and impedance (U = i Z). This tetrapolar technique provides much more stable and reliable signals than the original twoelectrode technique, particularly those due to respiration, which occur as a result of contact resistance changes in a bipolar systems 11 .…”

Section: Introductionmentioning

confidence: 99%

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Anterior-Posterior Impedance Cardiography: A New Approach to Accurate, Non-Invasive Monitoring of Cardiac Function

Babbs

2010

Cardiovasc Eng

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The conventional impedance cardiogram is a record of pulsatile changes in the electrical impedance of the chest with each heartbeat. The signal seems intuitively related to cardiac stroke volume. However doubts persist about the validity of stroke volume measurements based on electrical impedance. This paper presents a new electrical axis for impedance cardiography that is perpendicular to the conventional head-to-foot axis in an anterior-posterior direction. Dual chest and back electrodes are concentric, permitting tetrapolar technique. A relatively simple analytical model is developed, and this model is validated in a three-dimensional finite element model of current flow through the human chest. Three-dimensional simulations show predictable relationships between the fractional increase in anterior-posterior chest impedance and the ventricular ejection fraction (cardiac stroke volume / ventricular end-diastolic volume). Ejection fraction can be computed accurately with a roughly 30-fold increase in signal level compared to the conventional impedance cardiogram. Breathing causes only modest changes in the signal. When the axis of current flow is optimized, one can interpret the impedance changes during the cardiac cycle with greater confidence as a painless, noninvasive, beatby-beat indicators of ventricular ejection fraction in a wide variety of clinical settings.

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Monitoring the Chest with Impedance

Cited by 97 publications

References 17 publications

T‐Wave Amplitude Attenuation/Augmentation in Patients With Changing Edematous States: Implications for Patients With Congestive Heart Failure

T‐Wave Amplitude Attenuation/Augmentation in Patients With Changing Edematous States: Implications for Patients With Congestive Heart Failure

Intrathoracic Impedance Monitoring in Patients With Heart Failure

Anterior-Posterior Impedance Cardiography: A New Approach to Accurate, Non-Invasive Monitoring of Cardiac Function

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