**6. Assessment of cardiac chamber deformation/dyssynchrony**

Strain and strain rate imaging is an advanced echocardiographic technique for estimating myocardial segmental deformation, respectively [12, 91]. Myocardial strain (i.e., deformation of a myocardial segment over time; % change from its original dimension) and strain rate (the rate of myocardial deformation; S<sup>−</sup><sup>1</sup> ) can evaluate more direct intrinsic myocardial function and are less angle-dependent than TDI-based methods [92–94]. Strain and strain rate can be obtained from LV, LA, and RV wall using STE, feature-tracking echocardiography (FTE), or color TDI technology in the longitudinal, radial, and circumferential planes (**Figure 14**) [83]. Speckle tracking can detect the degree of myocardial deformation from the continuous frame-by-frame tracking of speckles (acoustic markers). By tracking these speckles in the myocardium throughout the cardiac cycle, the direction and velocity of myocardial motion can be determined. By comparing the motion of each speckle, the degree of deformation on each segment of the myocardium can be assessed.

Although precise assessment of LV systolic dysfunction is critical for therapeutic intervention and prediction of progression of CHF in dogs with MMVD, assessment of LV function using conventional echocardiography is often complicated

#### **Figure 14.**

*Representative images of left atrial (LA) and ventricular (LV) strain and strain rate imaging for LA and LV deformation analysis in dogs with mitral regurgitation. (A and B) LV (A) and LA (B) strain profiles obtained from GE analysis software algorithm (EchoPAC). (C and D) LV (C) and LA (D) strain profiles obtained from Siemens vector velocity imaging (VVI). (See text for more information).*

*Advanced Concepts in Endocarditis - 2021*

index (RV Tei) (**Figure 13B** and **D**) [89], and Doppler pulmonic outflow profiles (**Figure 13C**) [90] are being used to interrogate PH in dogs. One study found AT, AT/ET ratio, and RV Tei index are strongly correlated with sPAP in dogs without detectable PR [35]. Especially, AT/ET ratios ≤0.25 were predictive of PH, whereas AT/ET ratios >0.42 ruled out PH [86]. However, other study found Doppler estimated mPAP was strongly associated with AT and AT/ET, but weakly associated with RV Tei index [90]. Over 50% of dogs in International Small Animal Cardiac Health Council (ISACHC) II and III had equivocal value of AT/ET indicating PH (0.25–0.42) in this study, suggesting low sensitivity for detecting PH, although most dogs having <0.25 had detectible TR or PR on echocardiography, indicating high specificity for detecting clinically significant PH [90]. This study also found Doppler pulmonic outflow profiles were closely associated with severity of PH in dogs with MMVD, since the Doppler pulmonic outflow profiles (type I/II/III) were 18/0/0 in control, 22/5/1 in ISACHC I, 21/24/2 in ISACHC II, and 17/40/4 in ISACHC III MMVD dogs [90]. The PW Doppler-derived echocardiographic variables of PA flow may have limited value in dogs with hyperdynamic RV condition because Doppler pulmonic outflow profiles can be influenced by RV loading conditions and systolic function [90]. Although RV-TDI may not be a direct indicator of PH, it can be used to evaluate RV systolic and diastolic function in PH patients. It can be obtained from the basal segment of the internal mid-portion of the RV wall in the left parasternal long-axis four-chamber view (**Figure 13D**). One study evaluated the diagnostic value of peak RV myocardial velocities at systole (Stdi), early (Etdi), and late (Atdi) diastole [35]. Also the global TDI index was calculated using the following formula in this study: global TDI index = Stdi × Etdi/Atdi [35].

*Pulse-wave and tissue Doppler interrogation of pulmonary hypertension. (A) PW Doppler-derived acceleration time (AT) to peak pulmonary artery (PA) flow velocity (AT), AT to the ejection time (ET) of PA flow ratio (AT/ET). (B) Tissue Doppler-derived right ventricular Tei index (RV Tei), (C) PW Dopplerderived pulmonic outflow profiles, (D) PW Doppler-derived RV Tei index. (See text for more information).*

**46**

**Figure 13.**

with loading conditions [95]. Several studies demonstrated strain and strain rate obtained from the 2D-STE were useful to grade the progression of dogs with MMVD [95–98]. One study claimed the longitudinal strain with the GE analysis software algorithm (EchoPAC) was inconsistent and less repeatable, while radial strain curves from short-axis images were more consistent and more repeatable (**Figure 14A** and **B**) [95]. Since the software algorithm for strain is automated, special attention should be focused on "(1) timing of the ECG to select the cardiac cycle and the onset and duration of analysis; (2) tracing of the endocardial border for automated detection; (3) inspecting the region of interest; (4) following the tissue tracking in real-time and slow-motion; and (5) inspecting the generated curves relative to the R-waves and aortic valve closure (AVC)" as described in Smith et al. [95]. A velocity vector imaging (VVI) is another form of strain analysis, which can display tissue velocity as a vector showing the amplitude and direction of the movement (**Figure 14C** and **D**) [99].

Atrial myocardial deformation profiles estimated by TDI and 2D-STE (e.g. strain and strain rate) have been recently emerged as a good alternative method of exploring LA mechanics in both humans and dogs [100–103]. Although many drawbacks of this approach were noticed (e.g. suboptimal reproducibility, angle dependence, and the confounding effect of noise artifacts), 2D-STE can be a more advanced angle-independent echocardiographic technique for the direct evaluation of LA function than standard grayscale echocardiographic images [100–103]. The specific STE variables subject to the LA function include peak atrial longitudinal average strain (PALS), peak atrial contraction average strain (PACS), and contraction strain index (CSI), which reflect the LA function during its reservoir, booster pump phase, and the contribution of LA active contraction to the LV filling phase (**Figure 14B**) [104]. In humans, LA strain analysis has been useful for grading patients with valvular diseases, atrial fibrillation, or acute coronary disease [105–107]. However, a recent canine study found the STE variables were not significantly different between ACVIM B1 and B2 groups, although those (especially, PALS) were significantly different between ACVIM B2 and C groups [108]. The use of cut-off for PALS <27.9% enables to perfectly differentiate dogs in ACVIM stage B2 from those in ACVIM stage C with a sensitivity of 100% and specificity of 100% [108]. Another study also demonstrated the STE variables including PALS, PACS, and CSI were significantly decreased with the progression of MMVD [103]. A further study from this study group also found the STE variables (PALS <30% and CSI per 1% increase) were predictors of cardiac death in the univariate analysis [109].

Since the RV chamber is crescent-shaped and is wrapped around the LV, precise echocardiographic assessment of RV function is often difficult. The TDI and STE can overcome this limitation as reported in human studies [110, 111]. Recent canine study found the STE on RV was applicable and repeatable in healthy dogs [93]. Furthermore, other study demonstrated the RV longitudinal strain and the dyssynchrony index were significantly different from control dogs [75]. In this study, the global, free wall, and septal RV longitudinal strain in dogs with precapillary PH were significantly lower than those in control, while free wall and septal systolic shortening time strain were significantly slower [75].

### **7. Conclusion**

In this chapter, we described echocardiographic features of MMVD in dogs along with human echocardiographic criteria of MR. Although there are many similarities for diagnosing and grading the severity of MR in both species,

**49**

**Author details**

, Ta-Li Lu2

, Ran Choi3

4 Changbaig Hyun Special Animal Clinic, Seoul, Korea

\*Address all correspondence to: changbaig@gmail.com

provided the original work is properly cited.

1 Cardiology Section, Haedeun Animal Medical Center, Bucheon, Korea

2 Cardiology Section, Chuan Animal Hospital, Taipei City, Taiwan

3 Cardiology Section, Dasom Animal Medical Center, Busan, Korea

and Changbaig Hyun4

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*

Sang-Il Suh1

*Echocardiographic Features in Canine Myxomatous Mitral Valve Disease: An Animal Model…*

veterinary cardiologists are more focused on the severity of cardiac remodeling and cardiac dysfunction caused by MR, because surgical restoration of defected mitral apparatus is rarely done in dogs. Recent canine studies also found advanced ultrasound technologies, such as strain and strain rate imaging, and two-dimensional speckle tracking echocardiography were also applicable for dogs with MMVD, although more studies are warranted for standardizing the method of assessment in dogs. The authors believe that this chapter would be a valuable reference for veterinary and human cardiologists and researchers for understand-

The authors express great gratitude to Siemens Healthineers (Ms. UnWook Park) for technical support and Drs Jae-Min Suhl and Jin-Hee Noh for sharing space

and resources for preparing echocardiographic images on this chapter.

*DOI: http://dx.doi.org/10.5772/intechopen.91819*

ing mitral valve disease.

**Acknowledgements**

**Conflict of interest**

There is no conflict for this publication.

*Echocardiographic Features in Canine Myxomatous Mitral Valve Disease: An Animal Model… DOI: http://dx.doi.org/10.5772/intechopen.91819*

veterinary cardiologists are more focused on the severity of cardiac remodeling and cardiac dysfunction caused by MR, because surgical restoration of defected mitral apparatus is rarely done in dogs. Recent canine studies also found advanced ultrasound technologies, such as strain and strain rate imaging, and two-dimensional speckle tracking echocardiography were also applicable for dogs with MMVD, although more studies are warranted for standardizing the method of assessment in dogs. The authors believe that this chapter would be a valuable reference for veterinary and human cardiologists and researchers for understanding mitral valve disease.
