Measurement of Regional Myocardial Function in Healthy Small Breed Dogs Using Two-Dimensional Strain Imaging
Conventional echocardiographic indices of left ventricular (LV) systolic function are load-dependent and can be unreliable in mitral regurgitation. Strain and strain rate (SR) are echocardiographic indices of regional myocardial systolic function considered relatively load independent. This study tested the hypothesis that 2D strain could be used to quantify LV systolic function in healthy dogs. Older (>6 years) small-breed dogs (n=24), weighing 16 kg or less, were examined by 2D strain analysis (GE Vivid 7) and conventional echocardiography. Regional longitudinal and radial myocardial strain were quantified in multiple longitudinal (n=6) and radial (n=6) myocardial segments. Global LV longitudinal strain also was evaluated. Intraobserver and interobserver reproducibility were calculated.
Overall, 98.3% (283/288) of myocardial segments could be analyzed. Mean global longitudinal strain was -19.09%. Longitudinal mean strain and SR ranged across the myocardial segments ranged from -9.40% to -28.87% and -1.05 to -3.65 1/s while radial mean strain and SR ranged from 41.50 to 46.79% and 2.82 to 3.01 1/s, respectively. A gradient was identified for longitudinal strain and SR, with values decreasing from apex to base. Radial strain values for the anterior septal and septal segments were significantly lower than for other radial segments. Variability within observers was low (coefficient of variation <10%) but was higher between observers (difference/mean for 9/13 segments <25%).
2D strain analysis is feasible in healthy, awake dogs. Additional studies are needed in dogs with spontaneous mitral valve disease. These investigations should consider reproducibility of this technique and sensitivity of strain for detection of LV systolic dysfunction.