Accurate and real-time LAP measurement is an important factor in formulating and adjusting clinical treatment plans, but it is almost impossible to obtain LAP directly in clinical practice. Therefore, many critically ill patients can use PAWP instead of LAPC through floating catheter. However, the application of floating catheter is also invasive and cannot be used routinely. A non-invasive method has been explored to evaluate left atrial pressure. The combined application of tissue Doppler of atrioventricular valve annulus, pre-mitral flow spectrum and pulmonary vein spectrum can be used for qualitative or semi-quantitative assessment of LAP [14, 15], and some can be used for quantitative assessment of LAP [16], but the correlation with LAPC is only moderate [6, 17]. This study focused on the methodology of quantitative and real-time measurement of left atrial pressure using mitral regurgitation spectrum. We synchronously compared two methods of quantitative measurement of LAP using mitral regurgitation spectrum with PAWP, and analyzed the advantages and disadvantages of these two methods.
One is the early “Doppler + sphygmomanometer” method, that is, LAPBP method, which uses the peak pressure difference of mitral regurgitation spectrum to measure the left atrial pressure quantitatively. The other has been developed by our team according to Weiss exponential equation and simplified Bernoulli equation. LAPEq is calculated by measuring any two intervals of the descending branch of the mitral regurgitation spectrum and bringing them into the equations. We collected the mitral regurgitation spectrum (TTE) and PAWP synchronously after placing the floating catheter before cardiac surgery, so that we can simultaneously use three methods to measure LAP. We compared the measurement results of LAPC with those of the other two methods, and analyzed the advantages and disadvantages of these methods and their clinical values.
It was found that LAPBP method and LAPC method have good correlation in some patients, such as ischemic heart disease, myocarditis, and patients without aortic stenosis [5]. By analyzing the data of patients with mitral valve prolapse, we found that LAPBP and LAPC were well correlated in 7 patients with A2 and/or P2 prolapse, while LAPBP in 11 patients with P1 or P3 prolapse was lower than LAPC. Considering that the accuracy of LAPBP is related to the mitral regurgitation angle and the regurgitation angle is related to the prolapse site, LAPBP method is only applicable to some patients with mitral valve prolapse. To sum up, LAPBP is a more practical method for quantitative measurement of LAP, which has better clinical application value in patients with central mitral regurgitation.
In theory, LAPEq method can measure LAP quantitatively in real time. However, the accuracy of LAP measurement depends on the accuracy of t1−t2 and t1−t3 measurement. In this study, the deep learning model of big data training was used to establish a software with automatic tracking envelope and automatic calculation capabilities to improve the repeatability of LAPEq measurement. The LAPC of subjects in this study was between 8 and 29 mmHg. Paired t-test showed that there was no significant statistical difference between LAPEq and LAPC (t = 0.954, P = 0.348), and there was a high correlation between the results of the two measurement methods (r = 0.908, P < 0.001), that is, LAPEq method can be used to measure LAP quantitatively in real time. The previous animal experiments [12] and our clinical trials have proved that the left atrial pressure can be measured quantitatively using mathematical equations, and our theoretical derivation is reasonable.
LAPEq method is less affected by other factors such as valve disease, systemic blood pressure, angle of mitral regurgitation, etc. The LAPBP method is easily affected by the eccentric angle of the mitral regurgitation beam, and underestimates the peak pressure difference of MR. LAPEq method is used to measure the rate of left ventricular pressure decline. Whether the mitral regurgitation spectrum is eccentric has little influence on the accuracy of this method. However, it was found that LAPEq method needs to measure mitral regurgitation when the spectral edge of mitral regurgitation is clear enough, so it requires more mitral regurgitation than LAPBP method. Therefore, we have continuously improved our measurement software. For patients with large mitral regurgitation, the software has good repeatability; for cases with relatively few mitral regurgitation, we first drew the edge manually, and then used the software to draw the mitral regurgitation spectrum curve to measure and calculate LAP, so as to improve the repeatability of this measurement method.
In addition, the LAPEq method derived from the mathematical formula is a direct quantitative measurement of LAP. In some cases, PAWP measured by floating catheter method is not equal to left atrial pressure, such as mechanical ventilation under PEEP, endotoxic shock [18], pulmonary embolism [19], ARDS, etc. Therefore, the application of PAWP instead of LAP in clinical practice is also limited. LAPEq method based on the descending branch of mitral regurgitation spectrum is a direct quantitative measurement of left atrial pressure, which has good repeatability and is worth popularizing.
To sum up, combining the advantages and disadvantages of various non-invasive methods for measuring left atrial pressure, we propose the following process for non-invasive quantitative measurement of left atrial pressure: first, use qualitative evaluation methods to determine the possibility of elevated left atrial pressure, and then decide which method to use for LAP measurement according to the amount of mitral regurgitation and the angle of regurgitation beam. LAPEq method can be used for patients with large regurgitation or eccentric regurgitation. For patients with small reflux, LAPBP method can be considered for measurement. Repeated measurements are required to increase the repeatability of measurement and obtain more reliable left atrial pressure.