Biological variation of the cardiac index in patients with stable chronic heart failure: inert gas rebreathing compared with impedance cardiography

Validity of Hemodynamic Monitoring Using Inert Gas Rebreathing Method in Patients With Chronic Heart Failure and Those Implanted With a Left Ventricular Assist Device

OBJECTIVE

The present study assessed agreement between resting cardiac output estimated by inert gas rebreathing (IGR) and thermodilution methods in patients with heart failure and those implanted with a left ventricular assist device (LVAD).

METHODS AND RESULTS

Hemodynamic measurements were obtained in 42 patients, 22 with chronic heart failure and 20 with implanted continuous flow LVAD (34 males, aged 50 ± 11 years). Measurements were performed at rest using thermodilution and IGR methods. Cardiac output derived by thermodilution and IGR were not significantly different in LVAD (4.4 ± 0.9 L/min vs 4.7 ± 0.8 L/min, P = .27) or patients with heart failure (4.4 ± 1.4 L/min vs 4.5 ± 1.3 L/min, P = .75). There was a strong relationship between thermodilution and IGR cardiac index (r = 0.81, P = .001) and stroke volume index (r = 0.75, P = .001). Bland-Altman analysis showed acceptable limits of agreement for cardiac index derived by thermodilution and IGR, namely, the mean difference (lower and upper limits of agreement) for patients with heart failure -0.002 L/min/m² (-0.65 to 0.66 L/min/m²), and -0.14 L/min/m² (-0.78 to 0.49 L/min/m²) for patients with LVAD.

CONCLUSIONS

IGR is a valid method for estimating cardiac output and should be used in clinical practice to complement the evaluation and management of chronic heart failure and patients with an LVAD.

Biological variation of extracellular matrix biomarkers in patients with stable chronic heart failure

BACKGROUND

Extracellular matrix (ECM) biomarkers such as matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) are pathophysiological key, prognostic marker and therapeutic target in chronic heart failure (HF). Serial measurements of MMPs and TIMPs may be useful for guidance of these applications. However, interpretation of time-dependent changes requires knowledge about the biological variation of ECM biomarkers.

METHODS

We performed measurements of MMP-2, MMP-9, TIMP-1, and TIMP-4 in 50 patients with chronic HF who met rigid criteria for clinical stability at 3-h, 6-h, 1-week and 2-week time intervals. In addition, clinical and haemodynamic assessment was performed at baseline, at 1- and 2-week intervals. Haemodynamic variables were measured using inert gas rebreathing and impedance cardiography. Heart rhythm was monitored with external ECG event recorders throughout the complete study. Reference change values (RCVs) and minimal important differences (MIDs) were determined for MMP-2, MMP-9, TIMP-1, and TIMP-4.

RESULTS

Clinical and haemodynamic variables were stable over time. Depending on the time-interval, RCVs ranged between 4.9 and 11.7% for MMP-2, 26.4 and 56.7% for MMP-9, 10.8 and 30.7% for TIMP-1, and 16.0 and 47.4% for TIMP-4, respectively. The MIDs varied between 43.38 and 65.22 ng/ml for MMP-2, 28.71 and 40.96 ng/ml for MMP-9, 52.32 and 156.07 ng/ml for TIMP-1, and 293.92 and 798.04 pg/ml for TIMP-4, respectively.

CONCLUSION

The biological variation of ECM biomarkers differs with respect to individual biomarkers and time intervals. MMP-2 may be most suitable for serial biomarker measurements, as the biological variation is low irrespective of the time interval between measurements.

Hemodynamic Determinants of the Biologic Variation of N-Terminal Pro-B-Type Natriuretic Peptide in Patients With Stable Systolic Chronic Heart Failure

BACKGROUND CONTEXT

Biologic variation of N-terminal pro-B-type natriuretic peptide (NT-proBNP) in chronic heart failure (CHF) may affect blood levels and risk stratification. The sources of NT-proBNP variation are unknown.

METHODS AND RESULTS

We performed NT-proBNP measurements and clinical and hemodynamic assessments in 50 patients with heart failure with reduced ejection fraction (HFrEF) who met criteria for clinical stability over 2 time intervals. Hemodynamic variables were measured with the use of inert gas rebreathing and impedance cardiography. Heart rhythm was monitored with the use of external electrocardiographic event recorders throughout the study. Determinants of NT-proBNP-levels and both absolute (ΔNT-proBNP_abs) and relative (ΔNT-proBNP_%) changes at 1-week and 2-week intervals were identified with the use of univariable and multivariable linear mixed-effects models and linear regression analyses, respectively. Clinical and hemodynamic variables did not significantly change between study visits. The individual variation of NT-proBNP at 2 weeks was 9.2% (range 3.9%-18.6%). Weight and glomerular filtration rate were independently associated with baseline NT-proBNP concentrations (P = .01 and P = .005, respectively). There was no relationship between absolute and relative changes of NT-proBNP at 1-week intervals and changes in clinical and hemodynamic variables. Absolute change of NT-proBNP at 2-week intervals was associated with absolute change in left cardiac work index (P = .008), and relative change in NT-proBNP at 2-week intervals was determined by relative change of thoracic fluid content index (P = .008) and diastolic blood pressure (P = .01). The coefficients of determination (R²) for the multivariable models with Δ_1wkNT-proBNP_abs, Δ_2-weeksNT-proBNP_abs, Δ_1wkNT-proBNP_%, and Δ_2wksNT-proBNP_% as dependent variables were 0.21, 0.19, 0.10, and 0.32, respectively.

CONCLUSIONS

In patients with stable HFrEF, changes in clinical and hemodynamic variables only marginally contribute to the variation of NT-proBNP.

Biological variation of the cardiac index in patients with stable chronic heart failure: inert gas rebreathing compared with impedance cardiography

AIMS

In chronic heart failure (CHF), changes in cardiac function define the course of the disease. The cardiac index (CI) is the most adequate indicator of cardiac function. Interpretation of serial CI measurements, however, requires knowledge of the biological variation of CI. Because measurements of CI can be confounded by the clinical situation or the method applied, biological variation might be subject to the same confounders.

METHODS AND RESULTS

We prospectively included 50 CHF patients who met rigid criteria for clinical stability. CI was measured by both inert gas rebreathing (IGR) and impedance cardiography (ICG) in weekly intervals over 3 weeks-each measurement performed at rest (IGR_rest/ICG_rest) and during low-exercise 10 Watt pedalling (IGR_10W/ICG_10W). Intra-class correlation coefficients (ICCs), reference change values, and minimal important differences of CI were determined for IGR_rest, ICG_rest, IGR_10W, and ICG_10W. Impedance cardiography and IGR showed moderate agreement at rest (20% (6-36)) and good agreement at 10 Watt (-4% (-23-16)). Depending on time interval, measurement modality for CI, and mode, ICC ranged between 0.42 and 0.78, ICC values for IGR were lower than those for ICG. Reference change value ranged between 3 and 15%, and minimal important difference ranged between 0.2 and 0.5 L/min/m². Values for IGR were lower at rest and higher at 10 Watt than those for ICG.

CONCLUSION

Non-invasive measurements of CI are stable over time. Measurement modalities for CI, however, are not interchangeable. Biological variation is less pronounced when obtained by ICG. The influence of low-level exercise on stability of CI depends on the measurement modality.