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European Journal of Echocardiography 2007 8(6):474-479; doi:10.1016/j.euje.2006.09.004
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Copyright © 2007, The European Society of Cardiology

Clinical and echocardiographic determinants of ultrasound lung comets

Francesca Frassia,c, Luna Gargania,c, Suzana Gligorovab,c,d, Quirino Ciampia,c,e, Gaetano Mottolab,c and Eugenio Picanoa,*,c

aInstitute of Clinical Physiology, Via Moruzzi 1, Pisa 56010, Italy
bClinica Cardiologica "Montevergine", Mercogliano, Italy
cFF, LG and SG performed the data acquisition; QC was mainly responsible for the data analysis; GM contributed to data acquisition and study protocol design; EP proposed the study and contributed to data discussion. All authors critically reviewed the manuscript.
dSG is recipient of a training fellowship of European Society of Cardiology for the year 2005.
eQC is a visiting scientist to Pisa CNR Echo lab from the Division of Cardiology, Fatebenefratelli Hospital, Benevento.

Received 17 May 2006; received in revised form 15 September 2006; accepted after revision 30 September 2006.

* Corresponding author. Tel.: +39 050 315 2400; fax: +39 050 315 2374. picano{at}ifc.cnr.it


   Abstract
Top
 Abstract
Introduction
 Materials and methods
 Results
 Discussion
 References
 
Background: Ultrasound lung comets (ULCs) are an echographic sign of extravascular lung water, that originate from water-thickened interlobular septa.

Aim: To establish the echocardiographic correlates of ULCs.

Methods 340 in-hospital patients (68±12years, 115 females) admitted to adult cardiology department underwent upon admission a separate evaluation of chest ULCs and a comprehensive 2D and Doppler echocardiography assessment, including the degree of left ventricular diastolic dysfunction (from 0=normal to 3=restrictive pattern). A patient ULC score has been obtained by summing the number of ULCs from each of the scanning spaces in the anterior right and left chest, from second to fifth intercostal space.

Results: Multivariate linear regression analysis identified New York Heart Association (NYHA) class (OR=2.1, CI=1.4–2.9), ejection fraction (OR 0.954, CI=0.928–0.981) and degree of diastolic dysfunction (OR=2.438, CI=1.418–4.190) as the only parameters independently associated to the number of ULCs.

Conclusion: ULCs are a simple echographic sign of extravascular lung water, more frequently associated with left ventricular diastolic and/or systolic dysfunction. ULCs can usefully integrate the clinical and pathophysiological information provided by conventional 2D and Doppler echocardiography, in patients with known or suspected heart failure and dyspnoea as a presenting symptom.

Keywords: Dyspnoea; Ultrasound lung comets; Echocardiography


   Introduction
Top
 Abstract
 Introduction
Materials and methods
 Results
 Discussion
 References
 
Ultrasound Lung Comets (ULCs) consist of multiple comet tails originating from water thickened interlobular septa1 and are a simple echographic sign of extravascular lung water.2 In patients with known or suspected heart failure, they might usefully complement the morphological and functional information derived from a comprehensive cardiac 2D echo Doppler exam.3 In fact, pulmonary congestion is a key parameter in the management of patients with chronic heart failure4 and an early warning sign of impending acute heart failure.5 At this time, a better understanding of the functional determinants of ULCs seems to be a prerequisite prior to its large-scale application in the clinical arena. Aim of this study was to assess the clinical and echocardiographic determinants of ULCs in a consecutive series of 340 in-hospital patients admitted in a cardiology-pneumology department on an emergency or elective basis.


   Materials and methods
Top
 Abstract
 Introduction
 Materials and methods
Results
 Discussion
 References
 
Patient's population
We enrolled 340 patients (age 68±12years, 115 females) admitted to Clinica Cardiologica Montevergine in Mercogliano (Avellino) or to the Institute of Clinical Physiology of Pisa. All patients had a cardiac and thoracic ultrasound scan recorded upon admission (during the first day) by an expert cardiologist and/or European Association of Echocardiography certified sonographer with specific training on ULCs. We ruled out patients with no echocardiogram at admission. Patients’ main demographic characteristics are presented in Table 1.


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  		Table 1 The baseline clinical and echocardiographic characteristics of the patients

 
At admission, 11% of patients had acute heart failure.

The hospital's institutional review board approved the study, and all patients gave informed consent.

Echocardiographic study
All patients underwent comprehensive transthoracic echocardiography examination at rest. End-systolic, end-diastolic volumes, ejection fraction and systolic pulmonary artery pressure were calculated. The left ventricular volumes and ejection fraction were measured by modified biplane Simpson's method according to the American Society of Echocardiography and adjusted for body surface area.6 The systolic pulmonary artery pressure was derived from maximal velocity of tricuspid Doppler tracing adding the value of the right atrial pressure. The right atrial pressure was estimated on the basis of inspiratory collapse index of the inferior vena cava.7 Diastolic function was determined from the pattern of mitral and pulmonary venous flow velocity by pulsed Doppler echocardiography,8 complemented by mitral annular velocity by tissue Doppler imaging, when needed.9 Diastolic dysfunction was staged as being "absent" (grade 0), "mild" (grade 1, impaired relaxation), "moderate" (grade 2, pseudonormalized filling pattern), and "severe" (grade 3, restrictive filling pattern). All echocardiographic examinations were performed using commercially available instruments with a cardiac probe (2.5–3.5MHz): Sonos 5500 and 7500 machine (Philips Technology, Andover, Massachusetts), Acuson Sequoia (Mountain View, Ca.), Esaote Mylab (Genoa, Italy) or Vingmed Vivid 7 (Trondheim, Norway).

Chest ultrasound
By selection, the echocardiographic and thoracic echo examination were performed during the first day of hospital stay (8±4h from admission), with patients in the supine or near-to-supine position at the end of the standard 2D-echocardiogram. The ultrasound scanning to find the signs of ULCs was previously described.2,3 Briefly, the ultrasound scanning of the anterior and lateral chest was obtained on the right and left hemithorax, from the second to fourth (on the right side to the fifth) intercostal space, and from parasternal to mid-axillary line. In each intercostal space, the number of ULCs was recorded at the parasternal, midclavear, anterior axillary, and mid-axillary lines. The sum of ULCs yielded a score denoting the extent of the extravascular fluid of the lung. Zero was defined as a complete absence of ULCs on the investigated area. A lung comet was defined as a hyperechogenic, coherent bundle with a narrow basis, spreading from the transducer to the further border of the screen. The lung comets described here extend to the edge of the screen and arise only from the pleural line (Fig. 1). The examinations were performed with the same probe used for the echocardiographic study.


Figure 1
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  		Figure 1 Ultrasound lung comets.

 
The intra- and interobserver variabilities of the echo comet score were previously assessed by two independent observers in a set of 20 consecutive cases and were 5,1% and 7,4%, respectively.2

Observers unaware of the results of the other scan obtained all echocardiography and ULCs measurements independently of one another.

Statistics
Continuous variables are presented as means±SD or medians (25th, 75th percentiles) when indicated. Categorical variables are presented as counts and percentages. Univariate and multivariate logistic regression analyses were performed to assess the association of ULCs with continuous clinical and echocardiographic parameters. Chi-square test with Yates's correction for continuity was used to analyze the association of the presence of ULCs with categorical variables.

A p value of <0.05 was considered statistically significant. All statistical analysis were performed by SPSS for Windows, release 12.0 (Chicago, Illinois).


   Results
Top
 Abstract
 Introduction
 Materials and methods
 Results
Discussion
 References
 
Clinical characteristics
The clinical and echocardiographic characteristics of the 340 patients are shown in Table 1. Mitral regurgitation was moderate in 24% and severe in 7% of the patients.

Ultrasound lung comets
ULCs assessment was obtained in all patients (feasibility=100%). The imaging and analysis time was always <3min. The median of ULCs number was 13 (2–75).

Correlation between ultrasound lung comets and clinical and echocardiographic parameters
The NYHA functional class at admission was significantly related to number of ULCs (Fig. 2). Follow-up ULCs data were available, before discharge, in 121 patients, at 6±4days after the initial assessment on admission. In the subset of 70 patients who showed a clinical response to treatment at the end of hospitalization (decrease of NYHA functional class ≥1), the number of ULCs observed at admission decreased before discharge (42±32 vs. 15±18, p<0.0001). In the subset of 51 patients with no change or worsening of NYHA functional class, the number of ULCs was similar upon admission and before discharge (37±36 vs. 25±31, p=ns).


Figure 2
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  		Figure 2 Ultrasound lung comets number increases with increasing dyspnoea severity.

 
The 37 patients admitted with acute heart failure had a higher number of ULC's when compared to the 303 patients without acute heart failure (50±37 vs. 20±29, p<0.0001).

There was a significant, although weak, linear correlation between ULCs at admission and creatininemia (r=0.202, p=0.002), and creatinine clearance estimated with the Cockroft-Gault equation (r=–0.286, p<0.001).

There was a significant linear correlation between ULCs and left atrial dimension (r=0.294, p<0.0001), left ventricular end-diastolic diameter, wall motion score index (r=0.336, p<0.0001), pulmonary artery systolic pressure (r=0.264, p<0.0001). The presence of ULCs was related to the severity of mitral (96% vs. 4% p=0.001) and tricuspidal regurgitation (92% vs. 8% p<0.0001) and to impaired diastolic function (Fig. 3). There was an inverse relationship between ULCs number and ejection fraction (Fig. 4).


Figure 3
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  		Figure 3 Ultrasound lung comets number increases with increasing diastolic dysfunction.

 


Figure 4
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  		Figure 4 Ultrasound lung comets number increases with decreasing ejection fraction.

 
At multivariate analysis independent predictors of the presence of ULCs were: NYHA functional class on admission, ejection fraction and diastolic dysfunction (Table 2).


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  		Table 2 Independent predictors of the presence of ultrasound lung comets

 

   Discussion
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
References
 
ULCs are a simple echographic sign of extravascular lung water, more frequently associated with left ventricular diastolic and/or systolic dysfunction. ULCs can usefully integrate the clinical and pathophysiological information provided by conventional 2D and Doppler echocardiography in patients with known or suspected heart failure and dyspnoea as a presenting symptom.

Comparison with previous studies
Previous studies found a correlation – albeit only fair or moderate – between the amount of extravascular lung water (assessed by chest X-ray, positron emission tomography or bioimpedance changes) and dyspnoea severity,10 systolic dysfunction,11 or pulmonary capillary wedge pressure.12 These data are in broad agreement with the data of the present study, and confirm that extravascular lung water is a pathophysiological variable correlated with the severity of heart failure, as reflected by increased filling pressures.13 It is also well established that the degree of diastolic dysfunction is a non-invasive marker of high filling pressures, correlated to the hemodynamic and prognostic severity of heart failure.14–16 It is therefore not surprising that the degree of diastolic dysfunction proved to be the strongest predictor of ULCs. The data corroborate previous findings describing a significant linear correlation, both at rest and at peak stress, between ULC score and E/E1 ratio, a surrogate marker for left sided filling pressures.17

Practical implications
Pulmonary congestion resulting from elevated left atrial and left ventricular filling pressures is the most common event requiring hospitalization in patients with heart failure.18 It occurs often before the appearance of clinical manifestation of heart failure: it has been demonstrated that lung fluid overload, monitored by intrathoracic impedance, appears before the onset of patient symptoms and before hospital admission, and may provide an early warning of impending decompensation. Thus, the possibility that sufficiently sensitive and accurate techniques could be used to detect pulmonary oedema even before it becomes clinically apparent "is so inherently attractive that the effort to develop and validate such techniques still continues".19 Nevertheless, to date, none of the methods for measuring extravascular lung water, other than chest X-ray, has been incorporated into clinical practice. Unfortunately the most accurate and reproducible methods are also the most expensive and difficult to be implemented for purposes of routine clinical practice. At present, chest X-ray represents the clinical standard for assessing extravascular lung water, but the relationship between radiological signs and haemodynamic findings may be dependent on the duration as well as on the severity of cardiac dysfunction. There may be significant inter-observer variations in the interpretation of chest X-ray changes.4 Chest X-ray also requires a radiological apparatus and uses ionising radiation.20 The recent 2005 guidelines of the American Heart Association/American College of Cardiology clearly state that several chest radiographs are not recommended in the management of chronic heart failure. Changes in the radiographic assessment of pulmonary vascular congestion are too insensitive to detect but the most extreme changes in fluid status.21

ULCs assessment provides an appealing alternative to the available methods for the detection of pulmonary congestion. It is reasonably well correlated with extravascular lung water assessed by computerized tomography,1 chest X-ray,2 and double-indicator dilution method,22 especially when intrapatient variations are considered on serial assessment. It is easy to obtain and to measure, even with hand-held instruments, and requires only basic bedside ultrasound technology.23 It seems attractive for an integration of Doppler-echocardiography in the evaluation of patients with known or suspected heart failure. ULCs may also possibly complement the information provided by cardiac natriuretic peptides in heart failure patients.24 Under time pressure in the emergency setting, ULCs assessment at admission can be drastically simplified by scanning just a single representative chest segment, that is the right third intercostal space, along the anterior axillary line, as previously described.2,3 In the emergency room, ULCs can also complement the critical information of thoracic echocardiography on pleural effusion, lung contusion, and pneumothorax.25 As a possible limitation of the ULCs sign, one must consider that cardiogenic watery comets can be difficult to distinguish from pneumogenic fibrotic comets, which can be found in bronchiectasia, emphysema, pleural or interstitial lung disease.1,3

In conclusion, ULCs look promising for a simple assessment of pulmonary congestion, which is a major predictor of both morbidity and mortality in heart failure and a key pathogenetic trigger in acute heart failure.18 Identification of hemodynamic congestion, before the clinical manifestations appear, may potentially prevent hospitalization and allow life-saving interventions to be implemented sooner.26


   References
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 

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