Impedance Cardiography Offers Noninvasive Insight Into PAH Progression

With the current standard of care to direct treatment for pulmonary arterial hypertension (PAH) being invasive thermodilution during right heart catheterization, additional methods are needed for routine risk assessment of these patients. A recent analysis of 93 patients with pulmonary hypertension—54 of whom were diagnosed with Group 1 PAH and 39 with chronic thromboembolic pulmonary hypertension—found potential for impedance cardiography to fill this gap.

In the study published in Anatolian Journal of Cardiology, cardiac output and stroke volume positively correlated with the findings from right heart catheterization, indicating impedance cardiography’s potential to identify low-risk patients and those with a greater risk of clinical deterioration.¹ The patients included in this study underwent right heart catheterization between September 2018 and December 2022. Of the 54 patients with Group 1 PAH, 31 had idiopathic PAH, 10 had connective tissue disease–associated PAH, and 13 had repaired congenital heart disease–associated PAH.

Impedance cardiography is a painless, noninvasive method of measuring heart and blood vessel function through cardiac output, systemic vascular resistance, and fluid status, the results of which indicate blood pressure; the test can take between 5 and 10 minutes to administer.² The technique was first introduced in 1966.³

The overall mean (SD) patient age was 47.38 (16.08) years (P < .001), and 63.4% (P = .002) were female patients. Their mean weight and BMI were 61.56 (9.07) kg (135.71 [20.00] lb) and 22.93 (2.98).

In this study, body mass index, heart rate, hemodynamic parameters, pericardial effusion, peripheral edema, arrhythmia, and PAH etiology did not affect the accuracy of cardiac output from thermodilution and impedance cardiography. | Image Credit: © Tima-stock.adobe.com

Cardiac outputs as measured by thermodilution and impedance cardiography were a mean of 4.93 (1.06) L/min and 4.41 (1.23) L/min, respectively, indicating moderate correlation between the methods (r = 0.49; P < .001). This was demonstrated to be even stronger in the patients who had Group 1 PAH: the mean cardiac output for these patients was 5.13 (1.10) L/min by thermodilution and 4.57 (1.22) L/min by impedance cardiography (r = 0.52; P < .001). Agreement between the 2 methods was evaluated via the Bland-Altman method, and the overall bias was 0.52 L/min, with the limits of agreement ranging from −1.76 to 2.80 L/min, and the percentage error was 49.89%.

The results for overall stroke volume also showed modest correlation (r = 0.53; P < .001). Using thermodilution, this was 64.63 (17.10) mL, and by impedance cardiography, 60.94 (18.03) mL. Among the patients who had Group 1 PAH, the measures were 67.54 (19.04) mL and 61.88 (17.94) mL, respectively—again indicating moderate correlation (r = 0.51; P < .001). Again using the Bland-Altman method for agreement between the methods, the results were a bias of 3.69 mL, with the limits of agreement ranging from −30.16 to 41.48 mL, and the percentage error was 56.50%.

Accounting for potential confounders, the investigators determined that body mass index, heart rate, hemodynamic parameters, pericardial effusion, peripheral edema, arrhythmia, and PAH etiology did not affect the accuracy of cardiac output from thermodilution and impedance cardiography.

Eight patients experienced clinical deterioration over the 1-year follow-up, and findings from an ROC analysis show the cardiac index and stroke volume index results from impedance cardiography are modestly accurate at predicting this outcome:

• Cardiac index:
  • Area under the curve (AUC): 0.76 (95% CI, 0.59-0.94)
  • Cardiac index cut-off value: 2.45 L/min/m²
  • Sensitivity: 70.0%
  • Specificity: 81.8%
• Stroke volume index:
  • AUC: 0.81 (95% CI, 0.63-0.98)
  • Cardiac index cut-off value: 32.25 mL/m²
  • Sensitivity: 76.0%
  • Specificity: 81.8%

Strengths in these findings are that cardiac output as measured by both methods was compared using guidance and the latest definition of pulmonary hypertension from the 2022 European Society of Cardiology/European Respiratory Society pulmonary hypertension guideline. Also, this analysis specifically focused on PAH. Limitations of note are that the 2 methods could not be executed simultaneously and the ability to reproduce the cardiac output results from a patient at another time was not tested.

The authors concluded that their data are “potent to identify low-risk status and predict clinical deterioration in PAH patients.”

References

1. Zhang Y, Bu F, Qi Y, Zhang D, Zhang H, Cui X. Impedance cardiography is a potent non-invasive method in cardiac output measurement and pulmonary arterial hypertension risk assessment. Anatol J Cardiol. Published online May 12, 2025. doi:10.14744/AnatolJCardiol.2025.5108

2. Impedance cardiography. UF Health. Accessed May 14, 2025. https://ufhealth.org/conditions-and-treatments/impedance-cardiography-bioz

3. Kubicek WG, Karnegis JN, Patterson RP, Witsoe DA, Mattson RH. Development and evaluation of an impedance cardiac output system. Aerosp Med. 1966;37(12):1208-1212.