|Abstract or Summary
- Recent developments in the field of clinical echocardiography allow theultrasonographer to objectively quantify both regional and global myocardialfunction. Regional deformation (Strain) and deformation rate (Strain Rate) arenovel indices of ventricular function that can be estimated non-invasively byultrasonographic interrogation of the heart. Deformation Imaging (DI)represents a family of echocardiographic techniques that can be employed todetect
- Recent developments in the field of clinical echocardiography allow theultrasonographer to objectively quantify both regional and global myocardialfunction. Regional deformation (Strain) and deformation rate (Strain Rate) arenovel indices of ventricular function that can be estimated non-invasively byultrasonographic interrogation of the heart. Deformation Imaging (DI)represents a family of echocardiographic techniques that can be employed todetect, quantify and display the characteristics of physical deformation of themyocardium. The objective of the studies described in this thesis was toinvestigate Doppler-derived deformation imaging in dogs.This Master's Degree thesis is structured in two separate studies. The initialstudy compared Doppler-derived DI measures of ventricular function withmore traditional invasive indices of cardiovascular function in healthy adultanesthetized dogs over a range of hemodynamic conditions created by serialpharmacologic manipulations. Five adult healthy dogs underwentsimultaneous cardiac catheterization and transthoracic echocardiographyunder general anesthesia. The following invasive indices were monitoredduring the study: cardiac output (CO), femoral arterial (FA) and left ventricular(LV) pressures, +dP dt[subscript]max, -dP dt[subscript]max, right atrial (RA) and pulmonary arterial(PA) pressures, and pulmonary capillary wedge pressure (PCWP). Sequentialmanipulations of systolic function, afterload and preload were performed,respectively, by means of dobutamine, nitroprusside, and hetastarch infusions.Significant changes were induced in the following invasive hemodynamicparameters: cardiac output (p<0.0001, range 2.600 - 9.340 L min), +dP dt[subscript]max(p=0.0152, range 953.7 - 3822 mmHg s), left ventricular end-diastolic pressure(LVEDP) (p<0.0001, range 0.210 -16.43 mmHg), mean right atrial pressure(p<0.0004, range -2.490 - 9.920 mmHg), systemic vascular resistance (SVR)(p<0.0001, range 510.0 - 2652 dyne*sec cm⁵), and pulmonary vascularresistance (PVR) (p<0.05, range 256.4 -1635 dyne*sec cm⁵). All dogsunderwent a complete echocardiographic exam before anesthesia, afterinduction of general anesthesia and after each hemodynamic manipulation. Atotal of 750 regions of interest (ROIs) were included in the final analysis.Measurable plots were obtained in 741 (98.67%) out of 750 ROIs. Peaksystolic strain rate (SSR) values obtained at the 6 ROIs did not differsignificantly from each other and the avSSR (average of the 6 ROIs)negatively correlated with +dP dt[subscript]max (r=0.9792, p=0.0208). Individual values ofSSR from the different ROIs also negatively correlated with +dP dt[subscript]max, with theexception of ROI 4 (basal portion of the interventricular septum). The lack ofcorrelation was attributed to high variability in the measurements obtainedfrom this specific ROI. The avSSR was significantly reduced, i.e. systolicfunction was increased, by the dobutamine infusion, but was not significantlychanged during nitroprusside and hetastarch infusions. The LVEDP wassignificantly reduced during infusion of nitroprusside, apparently notinfluencing avSSR, and suggesting the possible preload independence of thisparameter in the hemodynamic range generated in the study. Nitroprussideinfusion effected a significant reduction of systemic vascular resistance withoutalteration of avSSR, suggesting a possible afterload independence of thisparameter, at least in the hemodynamic range obtained in this study.Study 2 was conducted on healthy adult non-sedated dogs divided into fourgroups (group 1: Body weight (BW) < 15 kg, group 2: BW 15 - 30 kg, group 3:BW > 30 kg, and group 4: Doberman pinscher dogs). The aim of the studywas to collect information on the feasibility, repeatability and reproducibility ofDoppler-derived DI performed in a clinical setting. Of the initial 56 dogs fromwhich echocardiographic data were collected, 7 dogs (12.5%) were excludedbecause of poor image quality, and data from 49 (87.5%) dogs were includedin the final analysis. Of a total of 1470 ROIs analyzed, 4.65% yielded goodquality curves, 88.3% were characterized by a significant amount of noise butretained a discernible pattern, and 7.14% were considered non-interpretable.Some pair-wise comparisons of the SSR values obtained from the 6 ROIsreached statistically significant difference. DI values in the Doberman pinschergroup did not differ significantly compared to values obtained from a BWmatchedgroup. DI values in group 1 dogs, but not the traditional indices FSand EF, were significantly higher compared to groups 2 and 3. Results from aBland-Altman analysis revealed overall poor clinical repeatability andreproducibility, as a result of the wide variability of the data.Based on the results of study 1 we conclude that Doppler-derived SSRrepresents a useful load-independent index of global systolic function, asdemonstrated in anesthetized dogs. However study 2 suggests that, in apopulation of non-sedated dogs, with a relatively wide range of breeds andBW, Doppler-derived DI measurements are characterized by less than optimalintra-operator and inter-operator variability which may limit its value as a toolto evaluate myocardial function in a clinical setting. Comparison to other newlydeveloped non-invasive techniques to estimate regional myocardialdeformation is needed to determine the eventual clinical utility of the method.