The use of echocardiography for cardiac disease in the field setting CRASH: A Point-Of-Care Ultrasound Protocol for Cardiorespiratory Assessment

A POCUS protocol for the evaluation of the thorax is referred as TFAST. In the horse a similar protocol is being developed and validated for the evaluation for the horse with cardiorespiratory disease as is sometimes referred to as CRASH- cardiorespiratory assessment with sonography of the horse. This is a POCUS protocol to assess the cardiovascular and respiratory system of horses in a goal-oriented, time-sensitive approach. Echocardiographic windows described for this protocol are standard echocardiographic windows as recently summarized by Schwartzwald.

This is the summary of the CRASH windows (Figure 1).

1 - Right parasternal long axis 4-chamber view (4C) - The transducer is positioned in the right fourth intercostal space at a level slightly above the olecranon, angled caudally, and rotated clockwise to the 1-o-clock position. The ventricles, atrioventricular valves and atria are imaged. Imaging the left ventricular (LV) apex is prioritized and the dorsal aspect of the atria may not be imaged in its entirety in all horses. This view is used to assess the structures and dimensions of the LV and left atrium (LA).

2 - Right parasternal long axis view of the left ventricular outflow tract (LVOT) - Starting from a 4-chamber view, the transducer is angled cranially, and rotated to the 2-o-clock position. It is used to assess the structure and dimensions of the aorta (Ao) and the pulmonary artery (PA). Specific attention is paid to the relative size of the PA and the Ao as a marker for pulmonary hypertension.

3 - Right parasternal short axis view at the level of the chordal attachments (SACA, Image 3). This view is obtained by rotating the transducer clockwise to the 3- to 4-o-clock position from a 4-chamber view. It is used to assess ventricular size.

4 - Right parasternal short axis view at the level of the aorta (SAAo) -This view is obtained by moving the transducer dorsally from the SACA and rotating the probe to the 5- to 6- o-clock position. The Aorta (Ao) is seen centrally with the left atrium (LA) and left atrial appendage (LAa) visualized caudally toward the far field. The size of the LA can be directly compared with the Ao similarly to the LA:Ao ratio described in small animals.

5 - Caudoventral thoracic (CAV) window (right and left) - The caudo-ventral thorax from right side is viewed in a longitudinal plane over the 7th intercostal space. A hyperchoic echo of lung, A lines and gliding respiratory motions are the expected normal appearance. The diaphragm is viewed at the ventral aspect of the window to ensure ventral position.

6 - Caudodorsal thoracic (CAD) window (right and left) - The caudo-dorsal thorax from right side is viewed in a longitudinal plane over the 15th intercostal space. A hyperchoic echo of lung, A-lines and gliding respiratory motions are the expected normal appearance.

7 - Left parasternal long-axis 2-chamber view (2C) - The transducer is positioned in the 5th or 4th left intercostal space slightly above the olecranon. The left ventricle (LV), left atrium (LA), and mitral valve are viewed. Imaging of the LA is prioritized, and the apex of the LV may not be viewed. This view has traditionally been used for assessment of LA dimensions.

The objectives of the examination are to answer the 8 specific questions below:

1. Is there increased pleural fluid? Increased pleural fluid is seen as fluid in the pleural space. Fluid is considered relevant to report if it is more than in the lateral aspect of the most ventral lung tip and more than approximately 1 cm in depth.
2. Is there increased pericardial fluid? Increased pericardial fluid is seen as fluid visible in the pericardial space that is more than a few millimeters in depth
3. Is there moderate or severe lung pathology such as, consolidation, masses, abscesses and severe or coalescing B-lines or comet tails. Consolidation is defined as hypoechoic area of lung with present bronchial or vascular markings. Mass and abscesses are defined as well circumscribed areas in the lung or pleural space that do not contain normal bronchial or vascular markings. Moderate or severe B-lines or comet tails are defined as interruptions of the smooth and regular hyperechoic echo of lung that merge or create patches.
4. Is there a pneumothorax? Pneumothorax is the presence of air in the pleural space. This is visible as a hyperechoic echo of gas free in the pleural space (outside of the lung) and therefore the hyperechoic echo of lung is not seen sliding with respiratory motions
5. Is there evidence of moderate or severe pulmonary hypertension? These are a pulmonary artery that is larger than the aorta’s sinotubular junction or shape of the interventricular septum becoming concave right to left
6. Is there evidence of moderate to severe left side heart disease? These are a left ventricular apex that is rounded and not cone shaped, the left ventricle is severely enlarged and compressing the right ventricle, or the left atrium is moderately or severely enlarged losing its rectangular shape and being disproportionate to the size of the right atrium.
7. Is there moderate or severe left ventricular hypertrophy or pseudohypertrophy? The left ventricle is thicker in relationship to the left ventricular internal diameter. This corresponds to RWT larger than 0.55.
8. Is there abnormal echogenicity of the myocardium or valves? This is defined as the presence of hyperechoic, hypoechoic or nodular areas in the myocardium, mitral, tricuspid, or aortic valves.

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