Meghann Zapcic, MS4
The Article: Ricci, F. et al. “Role and importance of ultrasound lung comets in acute cardiac care.” European Heart Journal: Acute Cardiovascular Care 2015; 4(2): 103-112.
Background: Given the inability of ultrasound to penetrate lung tissue, it was long considered useless in the evaluation of the lungs. The lung essentially acting as a reflective surface creates horizontal artifacts deemed A-lines, which are part of a normal healthy lung. In 1982, Wendell and Athey described vertical artifacts that resembled a comet tail thus being given the name ultrasound lung comets (ULCs) or B-lines. These artifacts were then published by Lichtenstein et al. about the relationship of alveolar-interstitial syndrome and the B-lines giving a foundation for further studies involving correlation of traditional imaging methods with B-lines and extravascular water. This review examines the fundamentals of lung ultrasound as well as examining the clinical research and application of lung ultrasound. Based on this evaluation, a new algorithm is proposed for suspected acute heart failure.
Focus: This review includes pertinent articles on the physical origin of the ULCs as well as their role in acute care settings.
Analysis: The blending of the gas and fluid distribution leads to artifacts starting at the visceral-parietal pleural interface(VPPI), which is a horizontal echogenic line behind the costal level. A normal pleural line can be seen gliding (gliding sign), and this motion creates horizontal isometric repetitions called A-lines. Hyperechoic, vertical artifacts that erase the A-lines and move along with the lung sliding are called B-lines and can be divided into two types. Septal rockets are scattered and usually appear about 7mm apart and are the ultrasound equivalent of Kerley B-lines. Ground glass rockets are within 3mm and are correlated with ground-glass areas on CT scan. B-lines can be confused with E-lines, which are multiple reverberations originating external to the pleural line from subcutaneous emphysema, as well as z-lines, which are vertical ill-defined artifacts that quickly vanishes and are not correlated to lung sliding or erasure of A-lines.
B-lines have been shown to be a reliable alternative diagnostic tool in acute heart failure. Effective management of the congestion that results from left ventricular diastolic pressure elevation relies on the ability to monitor the amount of fluid in the lungs. When compared to other methods such as chest x-ray, thermodilution techniques, and CT, B-lines have been shown to have high diagnostic accuracy. Studies have shown a positive linear correlation between B-lines and elevated PCWP. The detection of B-lines after an implantable cardiac defibrillator with fluid status monitoring alert was also correlated with impending heart failure decompensation. B-lines have also been positively correlated with serum levels of natriuretic peptides as well as the level of diastolic dysfunction seen on echocardiogram. The direction of the B-lines can lead you towards cardiogenic vs noncardiogenic causes of B-lines as well with a type A pattern of homogenous distribution with gravitation distribution is more likely to be cardiogenic pulmonary edema while type B pattern with unclear gradient and dyshomogenous distribution is more likely to be non-cardiogenic.
Applications: Given the high diagnostic value, the authors propose a new algorithm; a patient with suspected heart failure is evaluated with an ECG and lung ultrasound and if one or both are abnormal then you immediately go to an echocardiogram, but if no B-lines or ECG changes are detected then serum BNP or NT-pro BNP are evaluated. If NT-pro BNP is >300pg/ml or BNP >100pg/ml then move onto an echo, if not then acute heart failure is unlikely and consider other diagnosis and possibly get a chest x-ray.
The Takeaway: B-lines are a reliable diagnostic tool in evaluating patients presenting to the emergency department with dyspnea. In patients with suspected heart failure, the presence of B-lines can confirm that there is pulmonary edema leading to more targeted, immediate treatment. The B-lines are also dynamic in nature, so follow-up lung ultrasounds can indicate whether the treatment was effective or more diuretics are necessary. The new algorithm proposed gives a clear path for evaluation of acute heart failure to help streamline the testing needed for these patients in the emergency department.