Clinical value of pulmonary congestion detection by lung ultrasound in patients with chronic heart failure

Abstract Chronic heart failure is one of the common causes of hospitalization and death. Pulmonary congestion is the common disease feature of patients with chronic heart failure, which could be correctly diagnosed by lung ultrasound. Efficacy of lung ultrasound‐guided pulmonary congestion management for patients with acute heart failure is well documented, however, more evidence is needed to establish the clinical value of pulmonary congestion detection by lung ultrasound examination in patients with chronic heart failure. This review summarized current evidence related to the use and clinical value of pulmonary congestion assessment by lung ultrasound in patients with chronic heart failure, aiming to provide new suggestions on promoting the widespread use of lung ultrasound in patients with chronic heart failure to improve the quality of life and outcome of patients with chronic heart failure.


| INTRODUCTION
Chronic heart failure (CHF) is a clinical syndrome with various etiologies and associated with multiple comorbidities, frequent hospitalization, reduced quality of life and high mortality. 1 Mortality was about 2%-17% during the first admission with heat failure, 17%-45% at 1 year, and >50% within 5 years. 2 Heart failure resulted in considerable and growing economic burden on the health care systems. 3 Mortality of patients with acute myocardial infarction and myocarditis is significantly reduced due to effective therapy options during the last decade. 4,5 However, survived patients with residual myocardial injury might gradually develop CHF and contribute to the increased prevalence of CHF. Population aging serves as another important reason for the increased prevalence of CHF. Despite advances in diagnosis and treatment of CHF, the 5 years mortality of CHF remained as high as around 50%. 4 Given the irreversible nature of heart failure, it is of importance to take additional efforts to reduce the adverse impact of CHF on health care system and to improve the quality of life and outcome of CHF patients. 6 Pulmonary congestion (PC) is a common disease feature and associated with poor outcome in patients with heart failure, including CHF. 7 According to the results of a two-center cohort study, about 23% of heart failure patients were discharged with residual PC and residual PC at discharge was related to poor outcome. 8 Timely monitoring and effectively relieving of PC might thus serve as an important strategy of heart failure management during hospitalization and post hospital discharge.
Clinically, PC could be evaluated with multiple approaches. 9 Physicians may palpate the jugular pulse and auscultate the lung rales to estimate PC, but the sensitivity of these signs is not satisfactory. 10 Chest X-rays could be used to detect PC by observing radiographic signs of fluid accumulation in the lung interstitium or alveolar space, but bedside X-ray equipment, which would be an optimal tool for the examination of CHF patients, is not always available in daily clinical Na Li and Yunlong Zhu Contributed equally to this work. practice setting. PC could be properly assessed by measuring pulmonary capillary wedge pressure (PCWP) with right heart catheterization, but the invasive feature of this procedure limits its widespread use in the daily clinical practice. 11 Lung ultrasound (LUS) is another semiquantitative method for the evaluation of PC. LUS could detect PC at bedside, the sensibility and specificity of LUS on detecting PC are 46% and 95%, respectively. Gullett et al. 12  Furthermore, both expert/expert pairs and expert/novice pairs showed substantial agreement in the right and left anterior/superior thoracic zones (expert/expert, 0.904 and 0.777, respectively; expert/ novice, 0.862, and 0.834, respectively). Interrater agreement was best in the anterior/superior thoracic zones followed by the lateral/ superior zones for both expert/expert and expert/novice pairs. Agreement in the lateral/inferior lung zones was overall inferior. Intrarater agreement was highest at extreme high or low numbers of B-lines. Table 1 summarized the advantages and limitations of LUS, CT, and right heart catheterization on the evaluation of PC.
LUS has been increasingly used in clinical practice for monitoring the status of PC nowadays, especially in patients with acute heart failure. 11,13,14 Evidence related to PC monitoring and the impact of LUSguided PC management in CHF patients is also accumulating now.
Based on obtained clinical experience with the use of LUS, several guidelines and expert consensus recommended the use of LUS in the clinical setting (Table 2). It is to note more randomized large cohort clinical trials are needed to enhance the recommendation level of applying this examination technique in daily clinical practice. Exacerbation of PC could be evaluated by multiple modalities, including invasive PICCO, Swan-Ganz pulmonary artery catheters, implantable devices (CardioMEMS™ system, OptiVol™ Fluid Status Monitoring) and non-invasive pulmonary resistance assessment equipment, chest X-ray, chest CT, echocardiography, LUS and wearable health equipment), which are reviewed in detail by Bekfani 15 and Bashi. 16 Among them, LUS serves as the simplest and most timesaving non-invasive method for the sequential monitoring of PC changes. This point of view is gaining more and more acceptance recently. 17,18 We recommend the use of the 6-point and 8-point methods for the assessment of PC, LUS detected B lines ≥3 could be used as a reliable cutoff value, 19 25 the post hoc analysis of the LUS-HF trial showed that that up to 40% of patients considered "dry" according to pulmonary auscultation presented LUS-evidenced PC at hospital discharge, and these patients also experienced worse prognosis at 6-month followup. 21 Platz and colleagues examined 195 NYHA class II-IV HF patients during routine cardiology outpatient visits with LUS, and 185 patients with adequate LUS images in all zones were analyzed, the results showed that prevalence of patients with ≥3 B-lines on five-or eight-zone LUS was around 32%, and these patients faced about fourfold increased risk of 6-month HF hospitalization or death. 19 They also found that PC count was also positively linked with other clinical and laboratory markers of HF. 19  to the bottom of the screen 31 (Figure 1), which can move synchronously with lung sliding. 32 Impedance of lung gas is high is high in the healthy status, so ultrasound could hardly penetrate the lung field. In case of PC, lung gas and fluids could form an air-liquid interface, which changes acoustic impedance and favors the penetration of ultrasound in the lung field. 33 The clinical value of detecting LU-BL in chronic heart failure patients is gaining the attention of physicians worldwide now. 24

| PULMONARY CONGESTION DIAGNOSIS BY LUNG ULTRASOUND IN PATIENTS
LUS has now been used in the diagnosis of ARDS, pneumonia, pulmonary embolism, pneumothorax, COPD, asthma, and interstitial pulmonary fibrosis. In particular, LUS B-lines could indicate the presence of pulmonary congestion in patients with pulmonary edema, ARDS, and pneumonia 20 (Table 5).   CI 44-94%), but lower specificity (50%, 95% CI 28-72% vs. 88%, 95% CI 76-100%). As a whole, similar number of detectable B-lines was reported by both pocket device and high-end ultrasound system. 37 Figure 2 showed B-lines detected in an 84-year-old male patient admitted to our department due to acute decompensated chronic heart failure. Five B-lines were counted by 8-point methods ( Figure 1A). The patient's B-line disappeared and A-line was obvious at discharge ( Figure 1B).

| IMPACT OF MONITORING AND TARGETING PULMONARY CONGESTION IN CHRONIC HEART FAILURE PATIENTS
LUS offers specific visualization of B-lines of pulmonary congestion.
Theoretically, monitoring PC might be helpful for the adjustment of the dosage of medication, especially the diuretics in CHF patients.
Another merit of PC assessment with LUS is to avoid stopping diuretic