Usefulness of ultrasound lung comets as a nonradiologic sign of extravascular lung water

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Abstract

The “comet-tail” is an ultrasound sign detectable with ultrasound chest instruments; this sign consists of multiple comet-tails fanning out from the lung surface. They originate from water-thickened interlobular septa and would be ideal for nonradiologic bedside assessment of extravascular lung water. To assess the feasibility and value of ultrasonic comet signs, we studied 121 consecutive hospitalized patients (43 women and 78 men; aged 67 ± 12 years) admitted to our combined cardiology-pneumology department (including cardiac intensive care unit); the study was conducted with commercially available echocardiographic systems including a portable unit. Transducer frequencies (range 2.5 to 3.5 MHz) were used. In each patient, the right and left chest was scanned by examining predefined locations in multiple intercostal spaces. Examiners blinded to clinical diagnoses noted the presence and numbers of lung comets at each examining site. A patient lung comet score was obtained by summing the number of comets in each of the scanning spaces. Within a few minutes, patients underwent chest x-ray, with specific assessment of extravascular lung water score by 2 pneumologist-radiologists blinded to clinical and echo findings. The chest ultrasound scan was obtained in all patients (feasibility 100%). The imaging time per examination was always <3 minutes. There was a linear correlation between echocardiographic comet score and radiologic lung water score (r = 0.78, p <0.01). Intrapatient variations (n = 15) showed an even stronger correlation between changes in echocardiographic lung comet and radiologic lung water scores (r = 0.89; p <0.01). In 121 consecutive hospitalized patients, we found a linear correlation between echocardiographic comet scores and radiologic extravascular lung water scores. Thus, the comet-tail is a simple, non–time-consuming, and reasonably accurate chest ultrasound sign of extravascular lung water that can be obtained at bedside (also with portable echocardiographic equipment) and is not restricted by cardiac acoustic window limitations.

Section snippets

Patients

From January to April 2002, 121 consecutive patients (aged 67 ± 12 years; 43 women and 78 men) admitted to our adult cardiology-pneumology department were included in the study. The inclusion criteria were: (1) in-hospital patients (admitted to our department), (2) chest x-ray on admission or repeated chest x-ray, and (3) echocardiogram for specific assessment of lung comets performed within a few minutes of chest x-ray. Exclusion criteria were: (1) time lag between chest x-ray and chest

Results

In all, 135 paired echos (chest x-ray evaluations) were obtained in 121 patients. Thirteen patients were studied twice (at admission and on discharge), and 1 patient was studied 3 times. Reasons for hospital admission were acute coronary syndrome in 10 patients, stable angina in 37, dyspnea in 33, exacerbation of chronic heart failure in 9, and miscellaneous causes (worsening of chronic pulmonary disease after coronary artery bypass surgery, atrial fibrillation, palpitation, pulmonary embolism,

Discussion

Previous studies have clarified the likely biophysical mechanism underlying the comet-tail artifact.1, 2 All diagnostic ultrasound methods are based on the principle that ultrasound is reflected by an interface between media of different acoustic impedance.6 In normal conditions, with the transducer positioned on the chest wall, the ultrasound beam finds the lung air (i.e., high impedance and no acoustic mismatch on its pathway through the chest) (Figure 7). In the presence of extravascular

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Dr. Jambrik is a visiting fellow from the University of Szeged, Szeged, Hungary, and is supported by the “Eötvös” Educational Grant from the Hungarian Government Budapest, Hungary, and by the “Research and Training Fellowship” of the European Society of Cardiology, Nice, France.

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