Michelle Hunter-Behrend MD, Danielle Goodrich MD, and Laleh Gharahbaghian MD, FACEP
The scope of practice for emergency physicians with basic cardiac echo include an assessment for pericardial effusion and tamponade, contractility issues [specifically of the left ventricle (LV)], and chamber size (particularly of the right ventricle (RV). Systolic dysfunction, not diastolic dysfunction, is the focus of basic cardiac echo by emergency physicians. Prior studies have shown that trained emergency physicians can accurately assess LV contractility.1,2 Evaluation of LV contractility may be done by a visual “eye-ball” estimation or by semi-quantitative measurements such as E-point septal separation (EPSS) or fractional shortening. While visual assessment may be the fastest method to estimate LV contractility, this may be limited in patients with asymmetric wall motion abnormalities or severe valvular disease.
Furthermore, emergency physicians may assess for RV strain by visual “eye-ball” estimation or semi-quantitative methods such as RV:LV ratios or tricuspid annulus plane systolic excursion (TAPSE). Visual estimation includes assessment of the septal shift (towards LV), RV dilation or decreased motility, and McConnell’s sign.
Here are some tips and tricks for the various methods for estimating LV contractility and RV strain:
1. Visual estimation of LV contractility. Contractility is categorized as normal, mild to moderately decreased, severely decreased, or hyperdynamic based on the estimated LV volume change from diastole to systole. LV contractility is deemed normal if there is a large change in volume or poor if there is a small volume change, although an exact measurement is not defined. Hyperdynamic contractility refers to vigorous tachycardia and cardiac activity with LV walls close to touching during systole.
Clip 1 (Normal Contractility) & Clip 2 (Poor Contractility)
2. EPSS. EPSS is calculated as the distance in millimeters from the anterior mitral valve leaflet and the ventricular septum in early diastole in parasternal long view using M-mode (Fig 3). EPSS measurements of 7mm or less are seen in patients with normal LV ejection fraction (LVEF) and an EPSS measurement greater than 7mm indicates poor LV function. While emergency physicians can accurately estimate LVEF using EPSS, it is limited by local wall abnormalities such as valvular diseases that restrict the anterior mitral leaflet (mitral stenosis, aortic regurgitation), asymmetric septal hypertrophy, severe left ventricular hypertrophy, and discrete proximal septal thickening. These may inaccurately estimate contractility.3
3. Fractional shortening. This method is calculated by obtaining M-mode measurements across the mid-portion of the LV walls in either parasternal long or short axis views, and assessing the fractional change in diameter from end-systole to end-diastole (Fig 4). A fractional shortening value is between 30-45% and correlates to a normal ejection fraction. A poorly contractile heart will have widened systolic separation and therefore a lower fractional shortening. Although not a calculation of ejection fraction (EF), fractional shortening does correlate with cardiac index and visual estimation of LV contractility.4,5 Limitations of fractional shortening include measuring in a different cross-section of the LV than the correct mid-LV section and severe LV hypertrophy.
4. Visual estimation of RV strain. When assessing for RV strain, visual evaluation of RV size and contractility is easily obtained with standard echo views. RV enlargement, which appears grossly larger than the LV, may cause deflection of the interventricular septum towards the LV. (VIDEO 6) In the parasternal short axis view, this finding may be referred to as the “D-sign” given the flattening of the septum gives a “D”-like appearance to the LV (Fig 5). McConnell’s sign refers to a hypocontractile and enlarged RV with a hypercontractile apex, also indicative of RV strain and most correlated to pulmonary embolism as the source. (VIDEO 7)
Clip 6: PSL RV Strain & Clip 7: McConnell’s Sign
5. RV: LV ratio. For a more accurate assessment of RV size, RV and LV chamber size may be measured and compared in the apical 4-chamber view.6 A normal RV:LV ratio is 0.6:1 with a ratio of 1:1 or greater being indicative of RV strain (VIDEO 6). While this ratio may not be indicative of acute RV strain, one may assess the RV free wall for hypertrophy to help with differentiating acute from chronic RV strain. Normally, a thinner wall less than 7mm will be seen. In the setting of RV strain, a thin wall is more likely to be indicative of an acute process (such as pulmonary embolus) versus a thick wall which is more likely to be indicative of a chronic process (such as pulmonary artery hypertension and cor pulmonale). However, a thick RV free wall does not rule out pulmonary embolus.
6. TAPSE. More precise than a visual assessment of RV motility, TAPSE is a measurement of apex-to-base shortening of the RV that is used to assess global RV systolic function. Measurement is obtained in the apical 4-chamber view by placing M-mode over the tricuspid annulus and assessing the longitudinal movement distance during systole. The normal range is from 16-20mm, with less than 16mm being associated with increased mortality in acute pulmonary embolus patients.7,8
So which methods are best?
Visual estimation of LVEF has shown to accurately predict normal and poor contractility by emergency physicians; however, determining moderate dysfunction is more difficult as there exists wider variation in this category.10,11. Previous studies confirmed that EPSS is closely correlated to the visual estimation of LVEF (3). In fact, EPSS may serve as a continuous variable to estimate LV function as opposed to the categorization used with visual assessment.12,13 Further study found that EPSS is moderately correlated, but not predictive of fractional shortening.14
Currently, the American Heart Association defines RV strain in submassive PE based on a RV:LV ratio of 0.9 or greater.15 On point-of-care cardiac echocardiography by emergency physicians, assessment of the RV:LV ratio for RV dilation is highly specific for RV strain.16 Using TAPSE to estimate RV function has been shown to correlate with traditional echocardiographic parameters.9,17. When comparing TAPSE with RV:LV ratio, TAPSE may be superior to RV:LV ratios for predicting mortality in acute PE patients. 8
In conclusion, emergency physician can use semi-quantitative parameters in addition to visual assessment of LV function and RV strain as an additional evaluative tool for cardiac function and patient outcomes.