Transthoracic Echocardiography to Assess Post-Resuscitation Left Ventricular Dysfunction After Acute Myocardial Infarction and Cardiac Arrest in Pigs

Transthoracic echocardiography is a non-invasive diagnostic and prognostic tool to assess post-resuscitation myocardial dysfunction, structural changes, and/or acute myocardial infarction extension after resuscitation in the days to follow. In experimental ischemic and non-ischemic cardiac arrest models in pigs, transthoracic echocardiography is frequently used to seriously assess non-invasively cardiac anatomy and function. Echocardiography is used in a broad variety of experimental models in different types of animals related to different cardiac and non-cardiac diseases where the heart might be involved.

Begin by taking mono-dimensional and two-dimensional echocardiographic short and long axis images at the aortic and left ventricular levels. Take a two-dimensional short axis view at the aortic level. This view shows the left atrium aortic valve, right atrium tricuspid valve, right ventricular outflow tract and pulmonary valve.

Place the cursor in the middle of the aorta and left atrium to record the respective M-mode images. Take a two-dimensional parasternal long axis view. This view allows the visualization of the aortic root and aortic valve leaflets, interventricular septum, left ventricle, and left atrium.

The aorta must be in the same horizontal plane and in continuum with the interventricular septum, the aortic leaflets should be clearly visible. Place the transducer in the third or fourth left intercostal space with its indicator toward the right flank making small changes in the probe angulation to obtain a standardized view. Take a two-dimensional short axis view of the left ventricle at the papillary level.

For left ventricle dimension measurements use a short axis view at the papillary or cordis level, this is easier to obtain a standardized image in a ventilated animal than in the long axis view. Place the cursor in the middle of the left ventricle then record an M-mode image of the left ventricle at the papillary level. Repeat this process for the subpapillary and apical level of the left ventricle.

Take an apical four chamber view. The left and right atriums and ventricles will be visible together with the mitral in tricuspid valves in the interatrial and interventricular septum. Position the probe at the level of the cardiac apex, then position the marker on the probe to the left, the structure that helps standardize the view is the interventricular septum, which should be displayed parallel to the ultrasound beam by moving the transducer either medially or laterally.

Take an apical two chamber view. From the apical four chamber view, rotate the transducer 45 to 60 degrees in a counterclockwise direction, only the left atrium and left ventricle must be visible, so avoid the interventricular septum and verify that the cursor passes in the middle of the left atrium and left ventricle. To take an apical three chamber view, rotate the transducer 45 to 60 degrees counterclockwise from the apical four chamber view, the left ventricle apex should be visible together with the anterior septum and posterior lateral ventricular segments.

The other visible structures will be the aortic valve, left atrium. Take an apical five chamber view. Start from the apical four chamber view and angle the probe ventrally and then laterally to visualize an oblique septum, the aorta, left ventricle, right ventricle, and both atria.

For a standardized apical four chamber view, record a sign loop. Place the sample volume at the cusp of mitral leaflets and use the color doppler to place the cursor orthogonally to the mitral flow and align it with the left ventricular long axis. Then, switch to pulsed doppler and record at least three cardiac cycles.

Similarly, obtain a standardized apical five chamber view and record a sign loop with at least three cardiac cycles. Use color doppler to place the cursor orthogonally to the aortic flow, move the sample volume toward the aortic valve until the flow velocity accelerates, record at least three cardiac cycles. Use TDI from a 2D standardized apical four chamber view.

The PW-TDI measures peak longitudinal myocardial velocity from a single segment. For the aortic and left atrium diameter, measure the M-mode of the short axis views at the level of the aortic sinuses using the leading edge to leading edge method. For LVOT diameter, measure it 0.5 to one centimeter below the aortic cusp from a parasternal long axis view.

For end-diastolic, anteroseptal, and posterior diastolic wall thickness at the papillary level, measure at the end-diastole from the border between the myocardial wall and the cavity, and the border between the myocardium wall and the pericardium. To calculate LVEF, define end-diastole as the first frame after mitral valve closure, or the frame in which the left ventricle dimension is most frequently the largest, then, define end-systole as the frame after the aortic valve closure, or the frame where cardiac dimensions are the smallest. Follow the tracings of left ventricular area measurements at the boundary between the myocardium and the ventricular cavity, measure the areas and calculate ventricular volumes by modifying Simpson's single plane rule from the apical four chamber view.

Repeat the procedure in the apical two chamber view for the biplane Simpson method as described in the text manuscript. For PW peak mitral inflow velocity, E and A velocities, and E-wave deceleration time, are measured from the mitral flow spectrum. For TDI systolic S Prime velocities and diastolic E and A Prime velocities, measure from the TDI spectrum images at the apical four chamber view from the septal or lateral annulus and calculate averages at baseline in 96 hours after coronary occlusion.

Heart rate of the animal increased significantly at two hours and four hours post-acute myocardial dysfunction cardiac arrest ROSC compared with the baseline together with the end-systolic volume, while end-diastolic volume did not change significantly at different times. The mean differences in LVEF between baseline and two hours and four hours were approximately minus 40 and minus 39 absolute points percentages respectively. From two to 96 hours post-acute myocardial dysfunction cardiac arrest ROSC, HR tended to normalize, LVEF improved, rising approximately to 25 points percent, but it remained below the baseline.

Changes in left ventricular volumes were minimal and not significant, results were similar for changes between four and 96 hours post-AMI cardiac arrest ROSC. Deceleration time was the only echocardiographic diastolic variable that changed significantly at the different study time points. At two hours, the deceleration time decreased 16%from the baseline and maintained the decrease at four hours post-acute myocardial dysfunction cardiac arrest ROSC.

At 96 hours, DT returned similar to the baseline coordinates. Complimentary methods could be single-photon emission computed tomography or magnetic resonance imaging, without gadolinium or with gadolinium, to evaluate myocardial perfusion and, with the last one, also myocardial edema.