Two-dimensional speckle tracking echocardiography in dogsa focus on unexplored aspects of the technique

Abstract

Two-dimensional (2-D) speckle tracking echocardiography (STE) is a relatively new imaging technique, introduced in veterinary medicine to aid the assessment of cardiac function. The experiments conducted during the Ph. D. focused on different aspects of 2-D STE in dogs, and aimed at improving its applicability and correct interpretation in the canine species. Firstly, the effects of a combination of acepromazine (ACP; 0.02 mg/Kg) and butorphanol (BUT; 0.2 mg/Kg) on 2-D STE-derived strain values were evaluated, to establish whether this combination would be adequate to facilitate echocardiography. Secondly, the use of the right parasternal four-chamber (RP4Ch) view for the assessment of left ventricular (LV) longitudinal strain and strain rate (SR) by 2-D STE, usually performed on left apical four-chamber (LAp4Ch) views, was investigated. Thirdly, the intersoftware variability of longitudinal global strain and SR measurements derived from 2-D STE was assessed, as differences have been demonstrated in human medicine. In the first study, 18 healthy middle and large-sized adult dogs were evaluated. Left ventricular circumferential and longitudinal global and segmental strains were derived via 2-D STE, and comparison between parameters, obtained prior to and after sedation was performed. Between-day measurement variability was also assessed. In the second study, 26 healthy dogs and 25 dogs with various cardiac diseases were examined. Longitudinal global and segmental strains and global SR of the LV were obtained through 2-D STE by use of RP4Ch and LAp4Ch views. Feasibility and reproducibility of the RP4Ch view were investigated, and strain and SR values obtained from the two views were compared. In the third study, echocardiographic images were obtained from two cohorts of dogs. The first cohort included 44 dogs (23 cardiovascularly healthy, 21 with cardiac disease), imaged with a Philips ultrasound system, while the second cohort included 40 dogs (18 cardiovascularly healthy, 22 with cardiac disease), imaged with a General Electric ultrasound system. Echocardiographic images in each cohort were analyzed with vendor specific 2-D STE software, and with TomTec vendor independent software. Global longitudinal strain and SR values obtained with different software from the same LAp4Ch views were compared. Intra- and inter-observer variability was determined, and intersoftware agreement assessed. The results of the first study indicated that the combination of ACP and BUT employed, administered intramuscularly, provides adequate sedation to facilitate echocardiography in healthy dogs, with only a minor influence on 2-D STE variables. In fact, global strain values were not affected by sedation, and only one segmental (apical lateral) strain value decreased significantly. However, systemic arterial pressure and heart rate also decreased, and use of the same sedation protocol in cardiovascularly diseased dogs should be considered with care as undesirable effects could occur. The results of the second study indicated that the RP4Ch view is feasible to measure the variables aforementioned. However, out-of-sector motion of the apical segments can invalidate strain data in some dogs. Furthermore, significant differences between the values obtained from this view and the LAp4Ch view were found, and therefore they should not be used interchangeably. The results of the third study indicated that feasibility is not uniform across software methods, despite the use of good quality images and relatively high frame rate. Furthermore, significant differences among software were found for strain and SR measurements. Therefore, care should be taken when referring to published ranges of normality, or comparing serial measurements in the same patient. Overall, the experiments showed a high reproducibility of longitudinal global measurements, superior to that of segmental strains and global SR.