There are several pitfalls of this method; asymmetric wall motion abnormalities may be difficult to evaluate, and LVEF may not be a good indicator of cardiac output in cases of valvular disease such as aortic stenosis or mitral regurgitation.2 It is also unclear how many studies one must perform to become proficient at this estimation.
Explore This IssueACEP News: Vol 31 – No 10 – October 2012
Other methods of estimating LVEF require some measurements and may be more time consuming and require more practice to become comfortable with, but they are still useful for emergency physicians.
Mitral valve E-point septal separation (EPSS) is a relatively simple measurement, the use of which by emergency physicians has also been studied. EPSS is measured as the distance in millimeters between the anterior leaflet of the mitral valve and the interventricular septum in the parasternal long axis view during the early opening point of the mitral valve in early diastole. Images are obtained in M-mode by placing the white vertical line over this area. EPSS measurements of 6 mm or less are seen in patients with normal LVEF; an EPSS measurement greater than 7 mm indicates poor LV function. This method can be particularly useful in patients with coronary artery disease and resultant regional wall motion abnormalities, which can make subjective visual estimation difficult.5
The M-mode LV dimensional or Teichholtz method is also performed using the parasternal long axis view, with images obtained of the left ventricle in M-mode.6 Measurements are made of the right ventricle (RV) internal dimension, inter-ventricular septal thickness, LV internal dimension, and LV posterior wall thickness at end-diastole and end-systole. These measurements are then analyzed by the biostatistical software of the ultrasound machine, which calculates the LVEF. The Teichholtz method uses only a single diameter of the LV in the calculation, and therefore its accuracy depends on assumptions about chamber symmetry. This method is far more time consuming and complex, making it less practical for quick assessments of LV function in critical patients.
The two-dimensional border tracing method also depends on biostatistical calculations by the ultrasound machine. An apical four-chamber view is obtained, and an image is captured at end-systole and end-diastole. For each of these images, the inside border of the left ventricle is traced and the software estimates the volume of the left ventricle, subsequently calculating the EF based on these estimates.
Use in Combination with IVC Evaluation
Sonographic estimation of LVEF can be even more clinically useful in determining a patient’s hemodynamic state when combined with evaluation of intravascular volume status using measurements of the inferior vena cava. As noted in a previous Focus On (ACEP News, June 2011), the degree of collapse of the IVC with respiratory variation can indicate whether the patient is intravascularly volume depleted or hyper- volemic. Using these two sonographic assessments together can help to differentiate among cardiogenic, hypovolemic, and other forms of shock and can help direct resuscitation in cases where there may be multiple concurrent processes – for example, a patient with underlying heart failure who is acutely septic.