Assessing the Prognostic Value of Lung Ultrasound in Detecting Pulmonary Congestion in Acute Heart Failure Patients

Introduction

Heart failure (HF) is a prevalent and serious condition, characterized by the heart’s inability to pump effectively, leading to significant morbidity and mortality. Hospitalizations due to acute heart failure (AHF) have risen dramatically, with pulmonary congestion emerging as a predominant factor contributing to these admissions. Unlike low cardiac output, clinical congestion, manifested by symptoms such as dyspnea and edema, serves as the most frequent cause of hospitalization for heart failure and is a strong predictor of adverse outcomes, including increased mortality.^1,2

Despite advancements in the management of heart failure, patients often experience residual congestion at the time of discharge, which is not adequately addressed by conventional diagnostic methods. Traditional assessments such as clinical evaluations and chest X-rays have limitations in sensitivity and specificity for detecting elevated cardiac filling pressures.³ Moreover, other biomarkers, like natriuretic peptides, can be influenced by various factors unrelated to cardiac dysfunction—such as renal function and body mass index—while patients are often on stable diuretic regimens.⁴

Lung ultrasound (LUS) has emerged as a promising, non-invasive, and semi-quantitative tool for evaluating pulmonary congestion. This technique involves detecting vertical echogenic lines known as B-lines, which represent extravascular lung water and signify pulmonary congestion. Recent studies have suggested that the quantity of B-lines correlates with patient outcomes, identifying those at higher risk for adverse events after discharge.^5,6

The objective of this study is to assess the prognostic significance of pulmonary congestion as assessed by LUS in patients hospitalized for AHF. Specifically, we aim to evaluate how the presence of B-lines at the time of discharge correlates with short-term outcomes, including rehospitalization and cardiac mortality. Furthermore, we will describe the dynamic changes in LUS findings throughout the patient’s hospital stay.

Through this investigation, we aim to establish LUS as an integral aspect of routine clinical evaluation in heart failure management, ultimately improving patient stratification and outcomes.

Patients and methods

Study design: This bi-centric prospective observational study was conducted at the Cardiology Departments of Hedi Chaker Hospital in Sfax and Habib Thameur Hospital in Tunis from July 1, 2022, to September 30, 2023. The study aimed to evaluate the prevalence and prognostic importance of pulmonary congestion assessed by lung ultrasound (LUS) in patients hospitalized for acute heart failure (AHF).

Study population: We enrolled consecutive adult patients (≥18 years) admitted for AHF, regardless of the etiology and systolic function. All patients were required to meet the European Society of Cardiology criteria for heart failure diagnosis. Patients were excluded based on the following criteria: age <18 years, dyspnea due to trauma, body mass index >40, history of pneumothorax, lobectomy, or lung cancer, severe interstitial lung disease preventing adequate ultrasonography interpretation, and refusal to consent.

Assessment methods: Upon hospital admission, each patient underwent a comprehensive evaluation, which included:

Acute interstitial pulmonary syndrome was defined, according to the International Consensus Conference on LUS, by the presence of two or more positive regions in each hemithorax.⁷ A positive region was defined by the presence of three or more B-lines in transverse intercostal plane.^8,9

The examination involved assessment of eight distinct thoracic zones to identify B-lines—vertical, echogenic lines extending from the pleura, indicative of pulmonary congestion. Operators performing LUS were blinded to the patients’ clinical data to prevent bias.

Data analysis: Following discharge, patients were closely monitored for 180 days to document the occurrence of adverse outcomes, defined as a composite of urgent care visits, rehospitalization due to acute decompensation of heart failure, or cardiac death. Continuous variables were analyzed using appropriate statistical tests (e.g., Student’s t-test for normally distributed data and Mann-Whitney U test for non-normally distributed data). Categorical variables were evaluated using the Chi-squared test or Fisher’s exact test where applicable. Prognostic factors were assessed using univariate and multivariate Cox regression analyses to derive hazard ratios (HR) and confidence intervals (CI).

Event-free survival was calculated using Kaplan-Meier curves, with differences between groups assessed using the log-rank test. A significance level of p < 0.05 was established.

Results

Study population: A total of 116 patients were included in the analysis, with a median age of 69 years (interquartile range: 62-75), and 62 patients (53%) were male. The mean left ventricular ejection fraction (LVEF) was 40% ± 10%. Patient demographics and clinical characteristics at baseline are summarized in Table I.

Baseline characteristics: Of the enrolled patients, key clinical characteristics included a history of hypertension in 67 patients (57.8%), diabetes in 45 patients (38.8%), and chronic kidney disease in 32 patients (27.6%). The mean plasma NT-proBNP level at admission was 1500 pg/mL (range: 500-4500 pg/mL). Table II presents a detailed overview of these clinical characteristics.

Lung ultrasound findings: At the time of discharge, the mean number of B-lines detected was 6.6 ± 3.3. Notably, during the hospital stay, the number of B-lines significantly decreased from a mean of 31.9 ± 12.7 upon admission to 6.6 ± 3.1 at discharge (p < 0.001). This decline demonstrates effective pulmonary decongestion among patients during their hospitalization. The distribution of B-lines was assessed bilaterally across the eight zones, with ≥3 B-lines recorded in 45 patients (38.8%) at discharge.

Adverse clinical outcomes: During a mean follow-up period of six months, a total of 72 adverse events were documented. These included:

In-hospital mortality was recorded at 4.3%. The follow-up events for heart failure hospitalization or death were significantly associated with the number of B-lines detected at discharge.

Statistical analysis of outcomes: Multivariate Cox regression analysis identified that the presence of ≥3 B-lines bilaterally at discharge was a strong predictor of adverse clinical outcomes, with a hazard ratio (HR) of 11.024 (95% CI: 5.542-21.926, p < 0.001) ( Table III).

Kaplan-Meier survival curves: Figure 1 illustrates the Kaplan-Meier event-free survival curves. The differences in survival between patients with ≥3 B-lines versus <3 B-lines were statistically significant (log-rank test, p < 0.001), further reinforcing the prognostic importance of LUS findings in this cohort.

Figure 1. Event-free survival curves for both death and HF hospitalization regarding the number of B-lines.

Discussion

Previous studies have demonstrated the value of LUS as a diagnostic tool for acute heart failure (AHF). LUS showed a sensitivity of 94.2% and specificity of 77.5% for diagnosing AHF.¹²

This study aimed to assess the prognostic significance of pulmonary congestion evaluated by lung ultrasound (LUS) in patients hospitalized for acute heart failure (HF). Our findings provide compelling evidence that residual pulmonary congestion, quantified through the number of B-lines at discharge, serves as a crucial predictor of adverse short-term outcomes, including rehospitalization and cardiac mortality.

Prognostic significance of B-Lines: The multivariate analysis revealed that having ≥3 B-lines bilaterally at discharge is an independent predictor for the combined endpoint of heart failure hospitalization or cardiac death at the 180-day follow-up, with a hazard ratio of 11.024 (95% CI 5.542-21.926, P < 0.001). This finding corroborates earlier studies which have illustrated that persistent pulmonary congestion correlates with significantly higher risks of rehospitalization and mortality, underscoring the importance of monitoring B-lines as an integral part of patient assessment.^1,2,13–15 The identification of this threshold within our study supports the clinical utility of LUS as a non-invasive and effective method for risk stratification.

Dynamic monitoring of lung congestion: Furthermore, the significant decrease in the number of B-lines from admission (31.9 ± 12.7) to discharge (6.6 ± 3.3, P < 0.001) illustrates the effective therapeutic interventions aimed at alleviating congestion. This dynamic monitoring capability of LUS not only enhances clinicians’ understanding of fluid status but also allows for timely adjustments in treatment strategies.^16,17 The potential to visualize and quantify the resolution of pulmonary congestion can significantly refine patient management, promoting better clinical outcomes in the follow-up phase.

Of note, data on the concomitant decline of B-line counts and natriuretic peptides are conflicting.^18–20 Natriuretic peptide clearance in an acute setting appears to exhibit slower kinetics when compared with B-line variations to therapy, especially in the presence of renal failure. Divergent results have also been reported for E/e’,^18,19 although definitive conclusions cannot be drawn given the small size of these studies.

Event-free survival correlation: Our study further indicates that patients with <3 B-lines at discharge exhibit a markedly improved event-free survival rate of 76.4% over six months. This finding suggests that LUS may be instrumental in identifying low-risk patients, enabling medical teams to tailor follow-up and preventive strategies more effectively. The integration of LUS into routine assessment alongside traditional clinical indicators can enhance the overall management of heart failure.

Multidimensional approach to management: Complementing LUS with traditional assessments and biomarkers, such as natriuretic peptides, represents a significant advancement in the multidimensional management of heart failure. Although NT-proBNP is valuable, its levels can be influenced by various factors unrelated to cardiac function.¹ In contrast, LUS provides a direct evaluation of pulmonary congestion, thereby offering a more reliable prognostic tool.⁴

Longitudinal studies and theoretical framework: Longitudinal studies have shown that the presence of pulmonary congestion, as indicated by B-lines, remains a stronger predictor of adverse outcomes than other biomarkers measured at discharge. Volpicelli et al.²⁰ documented a correlation between B-line clearance and symptomatic relief, demonstrating that rapid resolution of pulmonary edema could significantly improve clinical outcomes. This relationship underscores the importance of LUS not only in initial assessments but also in monitoring treatment efficacy over time.

Limitations and areas for future research: However, this study does have limitations. The lack of routine NT-proBNP assessments at discharge restricts our ability to correlate these findings with changes in neurohormonal status, an important facet of heart failure management. Moreover, while our study focuses on a diverse patient population representative of real-world clinical settings, this diversity could contribute to variability in the prognostic implications of the B-line count. Future studies should aim to validate the prognostic value of LUS in larger, homogenous cohorts, and explore long-term outcomes associated with persistent pulmonary congestion. Additionally, the relative short follow-up duration may limit our understanding of the full impact of persistent pulmonary congestion on long-term outcomes. Extending follow-up periods in future studies could yield insights into the chronic implications of post-discharge congestion assessments.

In summary, our research emphasizes the critical role of LUS in the management of acute heart failure, showcasing its potential to improve patient outcomes through effective monitoring and intervention. By integrating LUS into routine clinical practice, healthcare providers can better identify high-risk patients, facilitate timely treatment adjustments, and ultimately enhance the overall care provided to individuals suffering from heart failure.

Conclusion

In conclusion, this study demonstrates that lung ultrasound (LUS) is a valuable, non-invasive tool for assessing pulmonary congestion in patients with acute heart failure (HF). The quantification of B-lines, particularly at discharge, has shown to be a significant predictor of adverse outcomes, such as rehospitalization and cardiac mortality, within a six-month follow-up period. Specifically, the identification of three or more B-lines serves as a critical indicator of patients at heightened risk for exacerbations, reinforcing the necessity for enhanced monitoring and targeted interventions.

Patient consent

Informed consent was obtained in writing from all participants prior to their inclusion in the study