Comparison of thermodilution and indirect Fick cardiac outputs in pulmonary hypertension

Pulmonary hypertension in hereditary hemorrhagic telangiectasia: A clinical review

Hereditary hemorrhagic telangiectasia (HHT) is a rare autosomal dominant hereditary disorder characterized by recurrent spontaneous epistaxis, mucocutaneous telangiectasias, and solid organ arteriovenous malformations (AVMs). Pulmonary hypertension (PH) is an increasingly recognized complication in patients with HHT, most often precipitated by high-output heart failure in the presence of hepatic AVMs as well as pulmonary arterial hypertension in the form of a proliferative vasculopathy. The presence of PH in patients with HHT is associated with significant elevations in rates of morbidity and mortality. Additionally, there is growing recognition of a thromboembolic propensity in this population that increases the risk of chronic thromboembolic PH, posing unique clinical considerations regarding the use of anticoagulation. Patients with HHT are also at risk of PH due to disorders commonly seen in the general population, including left-sided heart and lung disease. The etiology of PH in HHT is multifaceted and complex; the diagnostic approach and treatment strategies must consider the underlying pathophysiology of HHT. This comprehensive review summarizes current knowledge of PH in HHT, detailing the pathogenesis of known etiologies, diagnostic evaluation, and suggested treatment modalities as well as emerging therapies that may be of future interest.

Correlation of Impedance Cardiography-Derived and Cardiac Magnetic Resonance-Derived Stroke Volumes

Cardiac output (CO) and other hemodynamic parameter measurements play an important role in the management of cardiovascular conditions; however, due to limitations of current day technologies, such measurements are either not routinely performed or incorporated into clinical practice. Moreover, measurement of these hemodynamic parameters in the outpatient setting at different time points to assess interval change is currently not feasible. We attempted to validate total-body impedance cardiography-based Non-Invasive Cardiac System (NICaS) derived stroke volume (SV) with that from cardiac magnetic resonance (CMR), a current day gold standard method of assessment. We compared SV, as it is the primary unit of measurement utilized by both technologies. Forty-one consecutive patients undergoing CMR were also investigated by NICaS following CMR. The consistency of non-invasive technology-derived SV measurement was validated by NICaS measurement in 10 subjects, both before and after CMR. Of the 41 enrolled patients; data from 38 patients was adequate for comparison (motion artifact prevented CMR measures in 3 patients). Fourteen patients (37%) were female; mean age was 55 ± 15 years (28-87 years) and body-mass index was 28.7 ± 5.5 kg/m² (20.5-41.9 kg/m²). Hypertrophic cardiomyopathy (9/41) was the most common study indication for CMR. NICaS-derived SV strongly correlated with CMR [NICaS 77 ± 20 ml (31-123 ml) and CMR 84 ± 23 ml (47-132 ml); P < 0.001; r = 0.77; ICC = 0.73]. The Bland-Altman limits of agreement between NICaS and CMR were -26.7% and 39.9%. NICaS-derived SV collected before and after MRI did not differ [80 ± 18 ml (51-102 ml) pre and 76 ± 17 ml (50-99 ml) post; P = 0.0007, Kappa = 1]. Agreement between NICaS-derived and CMR-derived SV was within the acceptable range of boundaries set by the US Food and the Drug Administration. Consistency in SV measurement at different time-points may allow use of this technology to identify interval hemodynamic changes noninvasively.

The Influence of Methods for Cardiac Output Determination on the Diagnosis of Precapillary Pulmonary Hypertension: A Mathematical Model

Background: precapillary pulmonary hypertension (PH, PcPH) is now defined as a mean pulmonary artery pressure (mPAP) > 20 mmHg, a pulmonary artery wedge pressure (PAWP) ≤ 15 mmHg and a pulmonary vascular resistance (PVR) > 2 WU. For PVR calculation, the measurement of cardiac output (CO) is necessary. It is generally measured using thermodilution. However, recent data showed that the agreement with direct Fick method, historically the gold standard, is less than previously reported. We aimed to create a mathematical model that calculated the probability of being classified differently (PcPH or unclassified PH) if CO measured by direct Fick was used instead of thermodilution for any individual patients with a mPAP > 20 mmHg and a PAWP ≤ 15 mmHg. Methods: The model is based on Bland and Altman analysis with a normally distributed difference of cardiac output, fixed 1.96 standard deviation of bias, bias and physiological cardiac output limits. Results: Following a literature review of the studies comparing CO measured with direct Fick and thermodilution, we fixed the 1.96 standard deviation of bias at 2 L/min, bias at 0 L/min and physiological resting CO limits between 1.3 L/min and 10.2 L/min. Conclusions: This model can help the clinician to evaluate the potential benefit of measuring CO using direct Fick during the diagnostic work-up and its utility in confirming or ruling out a diagnosis of PcPH in any given patient with a mPAP > 20 mmHg and a PAWP ≤ 15 mmHg.

Non-Invasive Cardiac Output Determination Using Magnetic Resonance Imaging and Thermodilution in Pulmonary Hypertension

Magnetic resonance imaging (MRI) can be used to measure cardiac output (CO) non-invasively, which is a paramount parameter in pulmonary hypertension (PH) patients. We retrospectively compared stroke volume (SV) obtained with MRI (SV_MRI) in six localisations against SV measured with thermodilution (TD) (SV_TD) and against each other in 24 patients evaluated in our PH centre using Bland and Altman (BA) agreement analyses, linear correlation, and intraclass correlation (ICC). None of the six tested localisations for SV_MRI reached the predetermined criteria for interchangeability with SV_TD, with two standard deviations (2SD) of bias between 24.1 mL/beat and 31.1 mL/beat. The SV_MRI methods yielded better agreement when compared against each other than the comparison between SV_MRI and SV_TD, with the best 2SD of bias being 13.8 mL/beat. The inter-observer and intra-observer ICCs for CO_MRI were excellent (inter-observer ICC between 0.889 and 0.983 and intra-observer ICC between 0.991 and 0.999). We could not confirm the interchangeability of SV_MRI with SV_TD based on the predetermined interchangeability criteria. The lack of agreement between MRI and TD might be explained because TD is less precise than previously thought. We evaluated a new method to estimate CO through the pulmonary circulation (COp) in PH patients that may be more precise than the previously tested methods.

A novel approach to determine aortic valve area with phase-contrast cardiovascular magnetic resonance

BACKGROUND

Transthoracic echocardiography (TTE) is the diagnostic routine standard for assessing aortic stenosis (AS). However, its inaccuracies in determining stroke volume (SV) and aortic valve area (AVA) call for a more precise and dependable method. Phase-contrast cardiovascular magnetic resonance imaging (PC-CMR) is a promising tool to push these boundaries. Thus, the aim of this study was to validate a novel approach based on PC-CMR against the gold-standard of invasive determination of AVA in AS compared to TTE.

METHODS

A total of 50 patients with moderate or severe AS underwent TTE, cardiac catheterization and CMR. AVA via PC-CMR was determined by plotting momentary flow across the valve against flow-velocity. SV by CMR was measured directly via PC-CMR and volumetrically using cine-images. Invasive SV and AVA were determined via Fick-principle and Gorlin-formula, respectively. TTE yielded SV and AVA using continuity equation. Gradients were calculated via the modified Bernoulli-equation.

RESULTS

SV by PC-CMR (85 ± 31 ml) correlated strongly (r: 0.73, p < 0.001) with cine-CMR (85 ± 19 ml) without significant bias (lower and upper limits of agreement (LLoA and ULoA): - 41 ml and 44 ml, p = 0.83). In PC-CMR, mean pressure gradient correlated significantly with invasive determination (r: 0.36, p = 0.011). Mean AVA, as determined by PC-CMR during systole (0.78 ± 0.25 cm2), correlated moderately (r: 0.54, p < 0.001) with invasive AVA (0.70 ± 0.23 cm2), resulting in a small bias of 0.08 cm2 (LLoA and ULoA: - 0.36 cm2 and 0.55 cm2, p = 0.017). Inter-methodically, AVA by TTE (0.81 ± 0.23 cm2) compared to invasive determination showed similar correlations (r: 0.58, p < 0.001 with a bias of 0.11 cm2, LLoA and ULoA: - 0.30 and 0.52, p < 0.001) to PC-CMR. Intra- and interobserver reproducibility were excellent for AVA (intraclass-correlation-coefficients of 0.939 and 0.827, respectively).

CONCLUSIONS

Our novel approach using continuous determination of flow-volumes and velocities with PC-CMR enables simple AVA measurement with no bias to invasive assessment. This approach highlights non-invasive AS grading through CMR, especially when TTE findings are inconclusive.

Body Habitus Considerations During Right Heart Catheterization

Background

Obese and overweight body habitus are common among patients undergoing right heart catheterization for suspected pulmonary hypertension, but previous studies have described only patients with severe obesity. This study examined the effect of body habitus on intracardiac pressures, thermodilution cardiac output (TDCO), indirect Fick (iFick) cardiac output (CO), and pulmonary vascular resistance (PVR) in subjects with normal cardiopulmonary hemodynamics.

Methods

A retrospective analysis was conducted on healthy volunteers and patients referred for right heart catheterization for dyspnea of unknown origin with normal hemodynamics. Of the 65 subjects (53 ± 14 years; 51% female), 31% were normal weight, 49% were overweight, and 20% had obesity, as defined by a body mass index of 30-39.9 kg/m². Mixed venous oxygen saturations and intracardiac pressures were compared across body mass index categories. Agreement between iFick CO calculated by 3 formulae, and TDCO and PVR was examined.

Results

No differences in intracardiac pressures were observed, but mixed venous oxygen saturations were lower in the obese group. iFick CO underestimated TDCO, particularly with the LaFarge formula, with a systematic difference of 0.33 L/min for every 1 L/min increase in CO. This difference was largest in the obese group—on average by 23% ± 10%, translating to an overestimation of PVR by 34% ± 16% on average.

Conclusions

In individuals without severe obesity, intracardiac pressures are not different, but mixed venous oxygen saturations are lower. Obesity confounds estimations of CO and PVR by iFick methods, which could result in inappropriate hemodynamic classification. These data can inform best practices in hemodynamic assessment of populations with obesity.

Cardiac Output Determination in Precapillary Pulmonary Hypertension: A Systematic Review

BACKGROUND

Cardiac output determination is essential in precapillary pulmonary hypertension. While direct Fick is the gold standard, thermodilution is commonly used as the reference method. Moving to noninvasive methods would be highly beneficial for patients, avoiding repetitive invasive assessments. This systematic review followed 3 objectives: (1) assessing the validity of indirect Fick and thermodilution in precapillary pulmonary hypertension, (2) assessing the interchangeability of noninvasive cardiac output measurement methods against reference methods in precapillary pulmonary hypertension, and (3) detecting methodological heterogeneity in the included studies.

METHODS

We systematically reviewed the literature using medical databases and following PRISMA guidelines. We included articles comparing an invasive or noninvasive cardiac output measurement method with thermodilution or direct Fick in precapillary pulmonary hypertension patients. Cutoffs of limits of agreement and percentage error derived from the Bland and Altman graph were used to accept interchangeability. To study methodological heterogeneity, we extracted 9 quality criteria from all studies.

RESULTS

Eleven studies were included. None reached the suggested interchangeability criteria. The median number of the 9 assessed quality criteria was 2 with interquartile range (0-4).

CONCLUSIONS

Further studies evaluating the reliability of thermodilution and the consequences of its use in precapillary pulmonary hypertension patients are necessary. No evidence supports the use of indirect Fick in precapillary pulmonary hypertension. The studied noninvasive methods could not be considered interchangeable with invasive methods. A robust methodology should be used to draw sensible conclusions.

Impact of targeted pulmonary arterial hypertension therapy in patients with combined post- and precapillary pulmonary hypertension

BACKGROUND

Combined post- and precapillary pulmonary hypertension (CpcPH) portends poor outcomes in pulmonary hypertension related to left heart disease (PH-LHD). While recent evidence does not support the use of targeted pulmonary arterial hypertension (PAH) therapy in PH-LHD, there is a lack of clinical data on their use in CpcPH. We evaluated the outcomes in patients with CpcPH treated with PAH therapies.

METHODS

Retrospectively, 50 patients meeting hemodynamic criteria of CpcPH and started on PAH-targeted drugs were identified. Fifty age- and gender-matched PAH patients were chosen as controls. We evaluated the change in 6-minute walk distance, World Health Organization functional class (FC), tricuspid annular plane systolic excursion, BNP or NT-proBNP, and pulmonary artery systolic pressure at 3, 6, 12, and 24 months of follow-up.

RESULTS

After adjusting for age and gender, there was no improvement in World Health Organization FC in CpcPH over 2 years (odds ratio of change to FC I/II 1.01, 95% CI: 0.98-1.04). There was no significant improvement in 6-minute walk distance (β coefficient 0.21, 95% CI: -0.98 to 1.4), reduction in BNP/NT-proBNP (β coefficient -12.16, 95% CI: -30.68 to 6.37), increase in tricuspid annular plane systolic excursion (β coefficient 0.074, 95% CI: 0.010-0.139), or decrease in pulmonary artery systolic pressure (0.996, 95% CI: 0.991-1.011) in CpcPH with therapy. There was higher mortality in CpcPH compared to PAH on treatment (24% vs 4%, P = .003).

CONCLUSIONS

There were no improvements in symptoms, exercise capacity, or echocardiographic parameters with PAH-targeted therapy in CpcPH. Further studies into potential treatments benefiting this population are needed.

Thermodilution vs estimated Fick cardiac output measurement in an elderly cohort of patients: A single-centre experience

Aims

Patients referred to the cath-lab are an increasingly elderly population. Thermodilution (TD, gold standard) and the estimated Fick method (eFM) are interchangeably used in the clinical routine to measure cardiac output (CO). However, their correlation in an elderly cohort of cardiac patients has not been tested so far.

Methods

A single, clinically-indicated right heart catheterization was performed on each patient with CO estimated by eFM and TD in 155 consecutive patients (75.1±6.8 years, 57.7% male) between April 2015 and August 2017. Whole Body Oxygen Consumption (VO2) was assumed by applying the formulas of LaFarge (LaF), Dehmer (De) and Bergstra (Be). CO was indexed to body surface area (Cardiac Index, CI).

Results

CI-TD showed an overall moderate correlation to CI-eFM as assessed by LaF, De or Be (r² = 0.53, r² = 0.54, r² = 0.57, all p < .001, respectively) with large limits of agreement (-0.64 to 1.09, -1.07 to 0.77, -1.38 to 0.53 l/m²/min, respectively). The mean difference of CI between methods was 0.22, -0.15 and -0.42 (all p<0.001 for difference to TD), respectively. A rate of error ≥20% occurred with the equations by LaF, De or Be in 40.6%, 26.5% and 36.1% of patients, respectively. A CI <2.2 l/m²min was present in 42.6% of patients according to TD and in 60.0%, 31.0% and in 16.1% of patients according to eFM by the formulas of LaF, De or Be.

Conclusion

Although CI-eFM shows an overall reasonable correlation with CI-TD, the predictive value in a single patient is low. CI-eFM cannot replace CI-TD in elderly patients.

Accuracy and precision of cardiac output estimation by an automated, brachial cuff-based oscillometric device in patients with shock

Non-invasive monitoring of cardiac output is a technological and clinical challenge, especially for critically ill, surgically operated, or intensive care unit patients. A brachial cuff-based, automated, oscillometric device used for blood pressure and arterial stiffness ambulatory monitoring (Mobil-O-Graph) provides a non-invasive estimation of cardiac output values simultaneously with regular blood pressure measurement. The aim of the study was to evaluate the feasibility of this apparatus to estimate cardiac output in intensive care unit patients and to compare the non-invasive estimated cardiac output values with the respective gold standard method of thermodilution during pulmonary artery catheterization. Repeated sequential measurements of cardiac output were performed, in random order, by thermodilution (reference) and Mobil-O-Graph (test), in 24 patients hospitalized at intensive care unit. Reproducibility and accuracy of the test device were evaluated by Bland–Altman analysis, intraclass correlation coefficient, and percentage error. Mobil-O-Graph underestimated significantly the cardiac output by −1.12 ± 1.38 L/min ( p < 0.01) compared to thermodilution. However, intraclass correlation coefficient was >0.7 indicating a fair agreement between the test and the reference methods, while percentage error was approximately 39% which is considered to be within the acceptable limits. Cardiac output measurements were reproducible by both Mobil-O-Graph (intraclass correlation coefficient = 0.73 and percentage error = 27.9%) and thermodilution (intraclass correlation coefficient = 0.91 and percentage error = 26.7%). We showed for the first time that cardiac output estimation in intensive care unit patients using a non-invasive, automated, oscillometric, cuff-based apparatus is reproducible (by analyzing two repeated cardiac output measurements), exhibiting similar precision to thermodilution. However, the accuracy of Mobil-O-Graph (error compared to thermodilution) could be considered fairly acceptable. Future studies remain to further examine the reliability of this technology in monitoring cardiac output or stroke volume acute changes which is a more clinically relevant objective.