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Pericardial lung ultrasonography for diagnosis of cardiogenic pulmonary edema

We commend the authors of “Usefulness of pericardial lung ultrasonography for the diagnosis of cardiogenic pulmonary edema in dogs”1 for evaluating the usefulness of pericardial lung ultrasonography (LUS) as a rapid diagnostic test for cardiogenic pulmonary edema in dogs with degenerative mitral valve disease. We agree that finding ≥ 4 B lines along the pericardial-pulmonary interface is suggestive of left-sided congestive heart failure. However, there are noteworthy limitations of this technique worth mentioning.

First, we believe that using a single, limited window for LUS may lead to satisfaction-of-search and confirmation-bias errors. Thus, pericardial LUS through this single window should be viewed as a screening test, with positive results prompting a regional, pattern-based LUS approach such as Vet BLUE.2 Determining both the number of B lines (1–3 vs > 3) and their distribution (ie, number of regions positive for B lines) can help guide loop diuretic usage and assessment of therapeutic response in dogs with left-sided congestive heart failure while also allowing screening for other potential causes.3–5 The authors indicated that additional research is needed to determine whether pericardial LUS can differentiate between cardiogenic pulmonary edema and pneumonia, because pneumonia may also cause B lines. However, other differential diagnoses should also be considered, and we recommend the use of LUS to examine the lung surface for additional signs of consolidation (indicative of alveolar disease), including the shred sign (suggestive of air bronchograms), tissue sign (suggestive of lung hepatization), nodule sign, and wedge sign (suggestive of pulmonary thromboembolism). Searching for these LUS findings in 8 additional transthoracic windows may provide more information, allowing better conclusions to be drawn. For example, in panel B of the authors' Figure 2, the perceived B lines could also be pseudo-B lines created by small nodules.6 Real-time evaluation undoubtedly would increase image resolution over a still image. Regardless, adding more LUS windows may lead to more accurate conclusions while avoiding misidentification of small nodules.

The authors also note that pericardial LUS through the same window used to obtain the right parasternal short-axis view of the heart allows for examination of only the left lung and not the right lung. Importantly, B lines are nonspecific and most commonly represent various forms of alveolar-interstitial syndrome (eg, noncardiogenic and cardiogenic edema, pneumonia, hemorrhage, and atelectasis). A regional, pattern-based approach would increase the accuracy of LUS, compared with use of a single view.3,4,6 Other LUS methods for detecting B lines have been reported; however, each lacks the regional, pattern-based approach needed to distinguish important differential diagnoses.5

Lastly, a sector probe, as used by Hori et al,1 is standard for echocardiography. However, a curvilinear probe has a better resolution (because of its higher frequency) and physical basis (beyond the scope of this letter) that are more advantageous for imaging the intercostal pulmonary surface, ensuring more clear visualization of B lines and their numbers, the lung surface, and the subpleural space.2 Thus, when performing LUS, one should change to a curvilinear transducer when moving beyond the pericardial window.

In conclusion, we advocate for increasing the use of point-of-care LUS but suggest the pericardial window best be considered as an adjunct to echocardiography that triggers a more comprehensive and thorough LUS evaluation with a curvilinear transducer.

Gregory R. Lisciandro, DVM

Hill Country Veterinary Specialists, Spicewood, Tex

Kelly A. Mann, DVM, MS

Office of Defense Engagement, Colorado State University, Fort Collins, Colo

Jennifer M. Gambino, DVM

Idexx Laboratories, Inc, Clackamas, Ore, Imagination Imaging, LLC, Philadelphia, Pa

Stephanie C. Lisciandro, DVM

Oncura Partners Diagnostics, Fort Worth, Tex

  • 1. Hori Y, Yamashita Y, Sakakibara K, et al. Usefulness of pericardial lung ultrasonography for the diagnosis of cardiogenic pulmonary edema in dogs. Am J Vet Res 2020;81:227232.

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  • 2. Lisciandro GR, Fosgate GT, Fulton RM. Frequency and number of ultrasound lung rockets (B-lines) using a regionally based lung ultrasound examination named Vet BLUE (veterinary bedside lung ultrasound exam) in dogs with radiographically normal lung findings. Vet Rad Ultrasound 2014;55:315322.

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  • 3. Ward JL, Lisciandro GR, Keene BW, et al. Accuracy of point-of-care lung ultrasonography for the diagnosis of cardiogenic pulmonary edema in dogs and cats with acute dyspnea. J Am Vet Med Assoc 2017;250:666675.

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  • 4. Ward JL, Lisciandro GR, Ware WA, et al. Lung ultrasonography findings in 100 dogs with various underlying causes of cough. J Am Vet Med Assoc 2019;255:574583.

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  • 5. Rademacher N, Pariaut R, Pate J, et al. Transthoracic lung ultrasound in normal dogs and dogs with cardiogenic pulmonary edema: a pilot study. Vet Radiol Ultrasound 2014;55:447452.

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  • 6. Lisciandro GR. Vet BLUE—clinical integration. In: Lisciandro GR, ed. Point-of-care ultrasound techniques for the small animal practitioner. 2nd ed. Ames, Iowa: Wiley-Blackwell, in press.

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The authors respond:

The authors thank Lisciandro et al for their comments. First, we proposed a novel method named pericardial lung ultrasonography (LUS) that could be performed concomitant with echocardiography. Unlike standard LUS, including the Vet BLUE protocol,1 pericardial LUS is used only to detect cardiogenic pulmonary edema (CPE), not to evaluate the entire lung field. Therefore, pericardial LUS uses a sector probe and is performed with dogs in a recumbent position, unlike standard LUS. It not necessary to change the probe or posture after echocardiography, and CPE status can be determined rapidly. However, the window is limited. Our method is not an alternative to standard LUS; both thoracic radiography and standard LUS are required to evaluate the entire lung field.

Second, as is the case with standard LUS, small nodules may create pseudo-B lines on pericardial LUS images, as shown in Figure 2A of our report. However, these hyperechoic artifacts originating from the pericardium do not extend to the bottom of the screen, unlike B lines caused by CPE, as seen in Figure 2B. Additionally, real-time evaluation is useful to distinguish artifacts from lesions; we always perform real-time echocardiographic and pericardial LUS evaluations.

Third, B lines are nonspecific and most commonly represent various forms of alveolar-interstitial consolidation. Therefore, CPE cannot be diagnosed only on the basis of B lines. However, because pericardial LUS is performed concomitant with echocardiography, we can evaluate several risk factors for CPE, including heart disease and left atrial enlargement, simultaneously. We expect that the diagnostic accuracy of CPE will be improved by combining pericardial LUS with evaluation of these factors. In our experience, B lines commonly appear around the pericardium in dogs with CPE but are less common in dogs with respiratory diseases. When we used pericardial LUS to distinguish CPE from pneumonia, 10 of 11 dogs with CPE, but 0 of 6 with pneumonia, exhibited B lines (unpublished data). We cannot comment on whether other respiratory diseases can be distinguished from CPE; further studies are needed.

Finally, we recommend the use of a curvilinear probe when the entire lung field requires assessment (standard LUS). Standard LUS using a curvilinear probe is more advantageous for imaging the intercostal pulmonary surface, the lung surface, and the subpleural space.2–4 However, in general, high-frequency probes are not suitable to assess deeper areas, such as the pericardial lung field. In fact, to the best of our knowledge, standard LUS has never been employed to evaluate the pericardial lung field.1–4 Pericardial LUS can evaluate this region. The clinical utility of pericardial LUS differs from that of standard LUS. Clinicians are able to choose pericardial LUS or standard LUS depending on the situation.

Yasutomo Hori, DVM, PhD

Otsuka-ekimae Animal Hospital, Cardiovascular Medical Clinic, Tokyo, Japan

Tadashi Sano, DVM, PhD

Ai Hori, DVM

School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Hokkaido, Japan

Yohei Yamashita, DVM

Ebisu Animal Hospital, Miyagi, Japan

Keiichiro Sakakibara, DVM

North Animal Clinic Sapporo, Hokkaido, Japan

  • 1. Lisciandro GR, Fosgate GT, Fulton RM. Frequency and number of ultrasound lung rockets (B-lines) using a regionally based lung ultrasound examination named Vet BLUE (veterinary bedside lung ultrasound exam) in dogs with radiographically normal lung findings. Vet Radiol Ultrasound 2014;55:315322.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2. Ward JL, Lisciandro GR, DeFrancesco TC. Distribution of alveolar-interstitial syndrome in dogs and cats with respiratory distress as assessed by lung ultrasound versus thoracic radiographs. J Vet Emerg Crit Care (San Antonio) 2018;28:415428.

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  • 3. Rademacher N, Pariaut R, Pate J, et al. Transthoracic lung ultrasound in normal dogs and dogs with cardiogenic pulmonary edema: a pilot study. Vet Radiol Ultrasound 2014;55:447452.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Ward JL, Lisciandro GR, Keene BW, et al. Accuracy of point-of-care lung ultrasonography for the diagnosis of cardiogenic pulmonary edema in dogs and cats with acute dyspnea. J Am Vet Med Assoc 2017;250:666675.

    • Crossref
    • Search Google Scholar
    • Export Citation
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