We demonstrated that TTE global longitudinal and radial strain values were higher and circumferential strain values were lower than their corresponding values using TEE. TEE longitudinal strain has an excellent agreement with TTE-derived measurements and a modest agreement in circumferential strain but a notable disparity in radial strain values. 2D strain imaging using TTE was more feasible and less time consuming compared with TEE 2D strain measurements. Both modalities were correlated with LV function parameters using conventional echocardiography.
Strain imaging is defined as myocardial deformation imaging, a technique that helps the calculation of both left and right ventricle function. A growing body of evidence shows that the assessment of myocardial strain provides great value in the clinical setting , so guidelines now recommend assessment of strain values during the routine assessment of ventricular function .
Two modalities have been developed to assess ventricular deformation or strain. Tissue Doppler imaging suffers from the limitations of Doppler technique, most notably angle dependence. The second method, speckle tracking echocardiography, measures strain with acoustic markers or “speckles” on B-mode imaging and tracks their motion relative to one another. Although this method requires an adequate frame rate, it has emerged as a more robust method of strain measurement because speckles can be tracked at any angle [11, 12].
In recent years, this technique of strain imaging progressively became more used in the assessment of global ventricular function [11,12,13,14,15]. As it is reproducible, and able to provide quantitative data, the application of 2D strain imaging in the evaluation of ventricular function is further increased. Transthoracic 2D strain imaging has been studied extensively; there are a great number of articles in the literature describing its clinical application.; however, there are a limited number of studies that investigate the relevance of 2D strain imaging during TEE examination [16, 17].
TEE provides important clinical information in the emergency room and patients undergoing cardiac surgery as well as in noncardiac surgery. TEE is used widely often to assess the systolic and diastolic LV functions in the intraoperative and perioperative period [18, 19]. Moreover, TEE is an established imaging modality for patients with inadequate transthoracic acoustic windows in terms of assessing the LV function and management of high-risk patients. That is why, the agreement between TEE and TTE in LV deformation assessment might be an important addition in the echocardiographic laboratory [20,21,22,23,24,25].
The present study is somewhat different from other TEE 2D strain imaging studies. Kurt et al.  studied the reproducibility of TEE 2D strain imaging parameters in 34 healthy individuals with mean age 36 ± 9.2 years, in the absence of any structural cardiovascular disease. The authors concluded that there were generally good agreements between strain and strain rate measurements on TEE and TTE. The inter- and intraobserver agreement for TEE parameters was good.
In the present study, we investigated 2D strain imaging using both TTE and TEE in different cardiac pathologies including valvular heart disease, IHD, cardiomyopathy, congenital heart disease, and stroke which is a real-life daily practice. The age group was close to Kurt et al.’s study age group (16–68 years), and the mean age was 39 ± 11 years. All components of LV strain were investigated longitudinal, circumferential, and radial strain. There was an excellent agreement of longitudinal strain using both TTE and TEE and a modest agreement in circumferential strain and diverting values in radial strain.
In another study, Kukucka et al.  speculated that strain calculation from TEE images was feasible. Their study also included patients undergoing CABG surgery, and only TEE measurements were studied.
Tousignant et al.  performed a study in which 21 patients underwent CABG surgery, and TTE and TEE values were obtained just for the right ventricle. In this study, the global right ventricular strain value was similar using both methods (20.1% vs 20.4%).
In the present study, TEE 2D strain imaging for the assessment of ventricular function was time consuming and less feasible, when compared with TTE 2D strain, because of the requirement of offline analysis with the workstation. The presence of automated functioning imaging program available in Vivid-9 echocardiographic machines, which is the computer-based program that proposed to give similar data about the global and 4CH, long-axis, and 2CH strain imaging in a short time, failed to shorten the analysis time in addition to longer acquisition time as invasive procedure in comparison to TTE 2D strain analysis [28, 29].
In the current study, the authors found notable differences in mean longitudinal strain and radial strain values of all LV segments between the TTE and TEE measurements (higher in TTE LS and RS and lower in CS). This is likely caused by different technology used in transthoracic and transesophageal modalities in obtaining the best transgastric view for measurements of circumferential and radial strain.
Moreover, our study results indicate that both TTE and TEE LS were highly correlated to LV dimension, volumes, and systolic function indices and WMSI assessed by conventional echocardiographic methods; however, the agreement was weaker in TTE- and TEE-derived CS. TTE and TEE RS were incompatible with all these quantitative parameters’ assessment of LV systolic function. Ryczek et al.’s  results were in accordance with our study and demonstrated a strong significant linear correlation between TTE GLS and LVEF.
Aksakal et al.  investigated the agreement between TTE and TEE in the assessment of LV systolic functions by longitudinal myocardial deformation imaging (strain-S and strain rate-Sr) and LV diastolic functions by conventional Doppler parameters. The authors demonstrated that both TTE and TEE were correlated to diastolic function parameters assessed by conventional echo-Doppler parameters.
In accordance with the present study, Simmons et al.  reported good agreement on Doppler-derived strain and strain rate when comparing intraoperative TEE with TTE. In the present study, the number of segments fully analyzed by TTE in all strain components longitudinal, circumferential, and radial was notably higher than that explored by TEE examination (97% vs 90% in longitudinal strain and 93% vs 88% in radial and circumferential analysis).
In comparison with our study, Carlo et al. showed poor agreement between segmental strain measurements assessed by TTE and TEE regarding longitudinal, circumferential, and radial strain; in the long-axis views, only 193 of the 342 segments that were tracked in both TTE and TEE were used to assess agreement on hypokinetic segments. For LS, 78 segments were graded as normal by both techniques, and 23 segments were scored as normal in TTE but hypokinetic in TEE. Sixty segments were found to be hypokinetic by both techniques, and 32 segments graded hypokinetic by TTE were scored as normal by TEE.
Regarding radial strain in their study, TTE and TEE agreed on only 38 segments graded as normal. Forty-nine segments were normal in TTE and hypokinetic in TEE. Sixty-two segments were hypokinetic for both, whereas 44 segments were hypokinetic only for TTE.
In accordance with our results, Cheung et al.  showed that in the animal study during incremental atrial pacing data of TTE and TEE were comparable. In this study, they evaluated peak isovolumic velocity, isovolumic acceleration during isovolumic contraction, and diastolic E and A velocities from data obtained through TTE and TEE-TDI. Using isovolumic acceleration and isovolumic velocity from TTE-TDI, they found that systolic function evaluation had values comparable to those of TEE. However, they concluded that a velocity was incomparably different. Relying on these results, they have reported that TEE-TDI might be suitable for the monitorization of serial changes in LV function.
Our study was carried out on a limited number of subjects. 2D strain imaging is dependent on good 2D image quality. For this reason, poor 2D image quality results in a poor success rate. LV deformation assessment was only for systolic function using speckle tracking, and diastolic function was not analyzed with strain imaging.
Finally, although normal values for TTE strain and strain rate in a general population have been described, “normal” values for healthy individuals using TEE imaging are not available.