LV Contractility is significantly more nuanced than we make it out to be. Usually, providers look at the ejection fraction (EF) on the echo and that becomes the entire function of the LV. However, ejection fraction is not a good marker for LV contractility, but it is good when used to look at LV function. Is there really a difference between LV contractility and LV function? The left ventricle systolic phase, or LV inotropy, can be broken down three different ways.
1. LV contractility: The strength of the cardiac myocytes independent of preload and afterload.
2. LV function: The LV contractility when preload and afterload are included,
3. LV performance: The LV’s ability to do work. Work is defined as force times distance (F x d). It is the force of the squeeze of the LV multiplied by the displacement of the blood out of the ventricle.
Depending on which definition you want to focus on, there are different measurements you can look at to determine how well the LV is performing.
Table 1: LV Inotropic Measurements
ESPVR and â–³P/â–³t were both discussed in part 2a. ESPVR and â–³P/â–³t can be calculated. They are both difficult to calculate, and not practical for the bedside. The clinical measurements will look at the function and performance of the LV as opposed to the contractility.
LV Contractility (Part 2a):
1. End-Systolic Pressure Volume Relationship (ESPVR)
2. â–³P/â–³t
LV Function:
1. Ejection Fraction (EF): EF is the function of the LV and is dependent on the preload and afterload. Too little preload will decrease LVEF, whereas increasing preload can increase or decrease the LVEF depending on the Starling Curve. When there is increased afterload the LVEF will decrease, but with decreased afterload the EF will look artificially high and can even look hyperdynamic. Looking at LV function during septic shock or severe mitral regurgitation will obviously look much better compared to when the mitral valve is replaced or the sepsis treated.
Ejection fraction is one of the easiest measurements to obtain, and is done non-invasively, which is why it has become the most commonly used measurement for LV inotropy. The most common method to measure EF is Simpson’s biplane method. This is done with echo and the area of the LV during diastole and systole are drawn in two planes and the volume is estimated. The difference in volume between diastole and systole is the EF.
Figure 1: Simpson’s Biplane Method
https://www.researchgate.net/figure/2-D-measurements-for-volume-calculations-using-the-biplane-method-of-discs-modified_fig3_5933803
2. Fractional Shortening (FS):
This method is also done with echo and is probably the most common method used in bedside point-of-care echo. FS looks at the decrease in the diameter of the base of the left ventricle. This fractional shortening method is usually done in parasternal long-axis view (PLAX), but can be done in short axis as well. The diameter of the base of the LV in diastole is measured and then measured again in systole. The perctantage change in the distance is the fractional shortening. This change in diameter is used to calculate an estimated LV volume during diastole and systole and estimate an EF. In the example in Figure 2, the FS was calculated to be 42.7%, which correlated to an EF 74.1%.
Figure 2: Fractional Shortening
3. Global Longitudinal Strain (GLS):
GLS is being used more often, and can be done with with transthoracic and transesophageal echo (TEE) and looks at the movement of the LV during systole. Typically, GLS looks at the change in the length of the ventricle compared to its length at the end of diastole. This percentage change gives an indication of the contractility of the ventricle. Different regions can be looked at as well, which is then plotted out and can visualize wall motion abnormalities. One benefit of GLS is that it often changes before the EF changes. The equation is the length in systole minus length in diastole divided by the length in diastole, which gives it a negative percentage.
GLS (%) = (Ls-Ld)/Ld
This is done with special software within the ultrasound device. Additionally, the software can do speckle tracking which can allow the ventricle to be looked at independent of the angle, and the circumferential or radial strain can be calculated instead of just longitudinal.
More recently people have been reporting GLS as an absolute number so the smaller the number the worse the ventricular function.
Figure 3: Global Longitudinal Strain
Abou R, van der Bijl P, Bax JJ, et al Global longitudinal strain: clinical use and prognostic implications in contemporary practice Heart 2020;106:1438-1444.
4. Mitral Annular Plane Systolic Excursion (MAPSE):
MAPSE is the amount of movement of the mitral annulus during systole. This is done in the apical 4 view on a basic echo. Using M-Mode, the mitral annulus movement is tracked over time. The mitral annulus does not move as much in the longitudinal plane as the tricuspid annulus. Normal value is ≥ 1cm and < 1cm is considered abnormal.
Figure 4: Mitral Annular Plan Systolic Excursion (6)
5. Mitral Annular Tissue Doppler (TDI)
Looking at the velocity of the mitral annulus during systole is another way to objectively measure LV function. The TDI of the mitral annulus is called Sa or s’. It is not often done with a traditional echo but does have a good correlation in a more binomial function of yes or no. If it is <6 cm/sec then there is LV dysfunction. This is done in the apical 4 view as well with Tissue Doppler (TDI) at the base of the mitral annulus.
Figure 5: LV Systolic Tissue Doppler
LV Performance:
1. LV Stroke work index (LVSWI):
Figure 6: Stroke Work of the Left Ventricle
The best way to look at the performance of the LV is to look at its ability to do work. LV Stroke work looks at the force of contraction and the ability to unload its volume. To calculate stroke work (SW) of either ventricle it is the end pressure minus the beginning pressure multiplied by the stroke volume and a constant. To calculate stroke work index (SWI) the stroke work is divided by body surface area (BSA).
LVSWI = [(MAP – LAP) x SV x 0.0136]/BSA
2. Myocardial Performance Index (MPI):
The MPI is not looked at in a traditional echo. It is a ratio of the non-ejection time compared to the ejection time during LV systole. This is often referred to as the Tei index.
Figure 7: Measuring MPI (8)
MPI = (IVCT + IVRT) / ET
Summary:
Decreased contractility is considerably more complicated than just looking at the EF and moving on. When we are talking about the inotropy of the LV we often talk about LV contractility but we are actually referencing measurements that look at LV function. From an education standpoint, the stroke volume is dependent on LV contractility, but this is very difficult to directly measure clinically. This means that in the ICU we will usually be referencing LV function or LV performance. As long as we understand that these measurements can vary depending on preload and afterload conditions, they can be used safely. The EF of a systolic heart failure patient in septic shock may improve to 55-60% if the echo is done early on. Then, once the shock resolves, it will return to baseline or potentially even worse than before. It is important to keep this in mind when making inotrope and vasopressor choices in the ICU.
Figure 8: LV Contractility
Table 2: LV Inotropic Assessment Values
Figure 9: LV Inotropic Breakdown
Left Ventricular Heart Failure Series:
Part 1a: Introducing Preload
Part 1b: Measuring Preload
Part 2a: Physiological Contractility
Part 2b: Clinical Contractility
Part 3: Afterload
Part 4: Managing LV dysfunction
Other Left Sided Heart Failure:
Part 1: Valvular disease
Part 2: LVOT obstruction/SAM
Cardiogenic Shock:
Part 1: Why a Protocol is Needed
Part 2: Cardiogenic Shock Protocols
Part 2b: Contractility at the Clinical Level
References:
1. Davidson, B.P., Giraud, G.D., 2012. Left Ventricular Function and the Systemic Arterial Vasculature: Remembering What We Have Learned. Journal of the American Society of Echocardiography 25, 891–894.. doi:10.1016/j.echo.2012.06.020
2. Solaro RJ. Regulation of Cardiac Contractility. San Rafael (CA): Morgan & Claypool Life Sciences; 2011. Available from: https://www.ncbi.nlm.nih.gov/books/NBK54078/
3. Hamlin RL, del Rio C. dP/dt(max)--a measure of 'baroinometry'. J Pharmacol Toxicol Methods. 2012;66(2):63-65. doi:10.1016/j.vascn.2012.01.001
4. Zhong, Liang & Tan, Ru San & Ghista, Dhanjoo & Ng, Eddie & Chua, Leok & Kassab, Ghassan. (2007). Validation of a novel noninvasive cardiac index of left ventricular contractility in patients. American journal of physiology. Heart and circulatory physiology. 292. H2764-72. 10.1152/ajpheart.00540.2006.
5. Navtej S. Chahal, Tiong K. Lim, Piyush Jain, John C. Chambers, Jaspal S. Kooner, Roxy Senior, Normative reference values for the tissue Doppler imaging parameters of left ventricular function: a population-based study, European Journal of Echocardiography, Volume 11, Issue 1, January 2010, Pages 51-56, https://doi.org/10.1093/ejechocard/jep164
6. Cameli, Matteo & Mondillo, Sergio & Solari, Marco & Righini, Francesca & Andrei, Valentina & Contaldi, Carla & de marco, Eugenia & Di Mauro, Michele & Esposito, Roberta & Gallina, Sabina & Montisci, Roberta & Rossi, Andrea & Galderisi, Maurizio & Nistri, Stefano & Agricola, Eustachio & Mele, Donato. (2016). Echocardiographic assessment of left ventricular systolic function: from ejection fraction to torsion. Heart Failure Reviews. 21. 10.1007/s10741-015-9521-8.
7. Mittal S. Basics of tissue doppler revisited. Journal of The Indian Academy of Echocardiography & Cardiovascular Imaging. 2017;1(2):126-32.
8. Packard, René & Baek, Kyung-In & Beebe, Tyler & Jen, Nelson & Ding, Yichen & Shi, Feng & Fei, Peng & Kang, Bong & Chen, Po-Heng & Gau, Jonathan & Chen, Michael & Tang, Jonathan & Shih, Yu-Huan & Ding, Yonghe & Li, Debiao & Xu, Xiaolei & Hsiai, Tzung. (2017). Automated Segmentation of Light-Sheet Fluorescent Imaging to Characterize Experimental Doxorubicin-Induced Cardiac Injury and Repair. Scientific Reports. 7. 10.1038/s41598-017-09152-x.
9. Chengode S. Left ventricular global systolic function assessment by echocardiography. Ann Card Anaesth. 2016;19(Supplement):S26-S34. doi:10.4103/0971-9784.192617
10. Abuomara HZA, Hassan OM, Rashid T, Baraka M. Myocardial performance index as an echocardiographic predictor of early in-hospital heart failure during first acute anterior ST-elevation myocardial infarction. Egypt Heart J. 2018;70(2):71-75. doi:10.1016/j.ehj.2017.12.001
11. Caballero L, Kou S, Dulgheru R, et al. Echocardiographic reference ranges for normal cardiac Doppler data: results from the NORRE Study. Eur Heart J