Effect of changes in contractility on the index of myocardial performance in the dysfunctional left ventricle.
BACKGROUND
The index of myocardial performance has prognostic power in patients with cardiomyopathy and following myocardial infarction. As the index of myocardial performance has been shown to be preload and afterload dependent, the effect of altering contractility on IMP and its components with left ventricular dysfunction has been incompletely delineated.


METHODS
Chronic left ventricular dysfunction was induced in 10 canines using coronary microsphere embolization. Each dog was instrumented and imaged with 2D echo and Doppler. At the same atrially paced rate, contractility was increased with a dobutamine infusion and then following 4 weeks of oral digoxin.


RESULTS
With chronic left ventricular dysfunction, a reduced left ventricular ejection fraction (42 +/- 3%, p < 0.001) and increased index of myocardial performance (0.58 +/- 0.17, p < 0.01) due to isovolumic contraction time lengthening and shortened left ventricular ejection time were noted. Dobutamine increased ejection fraction (p < 0.001), reduced left ventricular end diastolic pressure (p < 0.01), and reduced the index of myocardial performance (0.33 +/- 0.17, p < 0.001) due to isovolumic contraction time, isovolumic relaxation time, and left ventricular ejection time shortening. Digoxin increased ejection fraction (p < 0.05), reduced left ventricular end diastolic pressure (p < 0.05), and reduced the index of myocardial performance (0.42 +/- 0.13, p < 0.01) due to isovolumic contraction time shortening (p < 0.001). Both dobutamine and digoxin lengthened the diastolic filling period (p < 0.01).


CONCLUSIONS
Increased inotropy with digoxin and dobutamine reduced the index of myocardial performance in dogs with left ventricular dysfunction. Shortened isovolumic contraction time, increased diastolic filling period, and reduced left ventricular end diastolic pressure with digoxin may provide insight into its efficacy in heart failure.
Lavine
Steven J
SJ
Department of Medicine, Division of Cardiology, Wayne State University and University of Florida/Jacksonville, Detroit, Michigan and Jacksonville, Florida, USA. steven.lvine@jax.ufl.edu
D000818:Animals; D004285:Dogs; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D009200:Myocardial Contraction; D009203:Myocardial Infarction / Q000150:complications* / Q000000981:diagnostic imaging*; D012720:Severity of Illness Index; D013318:Stroke Volume; D014463:Ultrasonography; D018487:Ventricular Dysfunction, Left / Q000000981:diagnostic imaging* / Q000209:etiology*