鈴木 亮平

Objective: The objective of this study was to evaluate the influence of heart rate (HR) on myocardial function assessed by two-dimensional speckle-tracking echocardiography (2D-STE) in healthy dogs. Animals: Thirteen healthy beagle dogs. Methods: Animals were anesthetized and HR was controlled with right atrial pacing. Myocardial function of each dog was assessed using 2D-STE at pacing rates of 120, 140, 160, and 180 bpm. Results: All strain and strain rate variables in the longitudinal, circumferential, and radial directions were not significantly different between pacing rates. Peak early diastolic torsion rate at 180 bpm was significantly increased compared with that at 120 bpm (P = 0.003). Conclusion: Torsion rate in early diastole was elevated at 180 bpm, which may reflect improved myocardial relaxation with higher HR. Changes in left ventricular torsion during tachycardia may play an important role in preserving stroke volume in the presence of shortened ejection and filling times. (C) 2013 Elsevier B.V. All rights reserved.

OBJECTIVES: To evaluate left ventricular geometry in dogs with various stages of myxomatous mitral valve disease. METHODS: Ninety-seven dogs with myxomatous mitral valve disease classified by the International Small Animal Cardiac Health Council system and 20 weight- and age-matched healthy dogs. Left ventricular long-axis to short-axis ratio, sphericity index in end-diastole and end-systole, left ventricular wall thickness to internal dimension ratio and relative wall thickness were assessed. RESULTS: The diastolic sphericity index was lower in classes Ib, II and III than in healthy dogs (P=0.003, P<0.001 and P<0.001) and was also lower in class III than in classes Ia, Ib and class II dogs (P<0.001, P<0.001 and P=0.002). The relative wall thickness was lower in classes II and III than in class Ia (P=0.003 and P<0.001), class Ib (P=0.004 and P<0.001), and healthy dogs (P<0.001 and P<0.001) and was also lower in class III than in class II (P=0.005). CLINICAL SIGNIFICANCE: Sphericity index and relative wall thickness are simple methods for assessing left ventricular geometry using two-dimensional echocardiography that may be useful in myxomatous mitral valve disease dogs as part of risk stratification.

Objective: The objective of this study was to clinically assess myocardial deformations in dogs with chronic mitral valve insufficiency (CMVI) using two-dimensional speckle-tracking echocardiography (2D-STE). Animals: 87 dogs with CMVI. Methods: Dogs were placed into 1 of 3 classes, based on the International Small Animal Cardiac Health Council classification. In addition, 20 weight- and age-matched healthy dogs were enrolled as controls. The dogs were examined for myocardial deformations using 2D-STE, and strain and strain rate in the longitudinal, circumferential, and radial directions were evaluated. Results: Class II and III dogs had higher circumferential strain than class I dogs (P = 0.002 and P = 0.001, respectively) and controls (P &lt 0.001 and P &lt 0.001, respectively). Class III dogs had higher radial strain than class I dogs (P = 0.001) and controls (P &lt 0.001). Class III dogs had higher radial strain rate than class I dogs (P = 0.006) and controls (P = 0.001). Other deformations, including longitudinal deformations, were not significantly different between classes of CMVI or between CMVI dogs and controls. Conclusions: In the clinical progression of CMVI in dogs, myocardial deformations, as assessed by 2D-STE, differed according to myocardial contractile direction. Thus, assessments of multidirectional myocardial deformations may be important for better assessment of clinical cardiac function in dogs with CMVI. © 2013 Elsevier B.V. All rights reserved.

Background Left ventricular torsional motion plays an important role for effective pump function. However, noninvasive clinical assessment of torsional deformations by two-dimensional speckle-tracking echocardiography (2D-STE) in dogs with myxomatous mitral valve disease (MMVD) has not been reported. Hypothesis Left ventricular torsion is determined by the native orientation of the helical myocardial fibers, such that it might provide better assessment of myocardial function than conventional methods. Animals Sixty-seven client-owned dogs with MMVD were classified into 3 classes based on the International Small Animal Cardiac Health Council classification and 16 weight- and age-matched healthy dogs. Methods Dogs were examined for myocardial deformations by 2D-STE and were evaluated for peak systolic rotation and rotation rate at each basal and apical view. Dogs also were evaluated for peak systolic torsion and torsion rate. Results Peak systolic torsion was higher in class II than in class I (P<.001) dogs. Peak systolic torsion was lower in class III than in class II (P=.001) dogs and controls (P=.003). Conclusions and Clinical Importance Torsional deformations assessed by 2D-STE differed among clinical classes of MMVD. Myocardial torsional deformations by 2D-STE may provide more detailed assessment of contractile function in dogs with MMVD.