Does dobutamine improve ventricular function in dogs with regional myocardial dysfunction?

Modeling ischemia-induced dyssynchronous myocardial contraction

Left ventricular (LV) contraction dyssynchrony is not easily quantified. We previously described a model for quantifying LV dyssynchrony that referenced regional amplitude and phase angles to global LV systole using esmolol-induced regional dyskinesis. We tested the hypothesis that our sine wave model and phase angle analysis of regional dyssynchrony in a canine model could also assess dyssynchrony of contraction during regional ischemia. Hence we compared intracoronary esmolol and matched regional ischemia in 10 anesthetized open-chest dogs. Regional and total LV volumes (conductance catheter), piezoelectric crystal shortening, and LV pressures were measured before, during, and after esmolol-induced apical dyskinesis and matched regional ischemia. We defined regional phase angle of contraction (alpha) as the relative distance, measured in degrees, that regional minimal volume differed from global end-systole. We also compared maximal stroke volume (SV), observed effective SV (that portion of regional SV contributing to total SV for each treatment), and calculated effective SV (total regional SV x cosine alpha). Dobutamine infusion increased homogeneity of regional alpha relative to baseline. Both esmolol and ischemia significantly delayed (P < 0.05) apical contraction as quantified by increased alpha (12.4 degrees +/- 28.1 degrees to 27.4 degrees +/- 30.4 degrees and 54.2 degrees +/- 32.6 degrees , respectively) (mean +/- sd) and decreased regional effective SV (4.7 +/- 2.5 mL to 3.6 +/- 2.2 mL and 4 +/- 2.5 mL, respectively) relative to baseline. Our study indicates that intracoronary esmolol and ischemia induced qualitatively similar mechanical effects on myocardial function and that a sine wave model to estimate regional effective SV is a sensitive method to detect and quantify regional dyssynchrony induced by ischemia. Potentially, phase angle and regional amplitude analyses may prove to be effective measures to identify and quantify the beneficial effects of resynchronization therapies on myocardial function.

Interaction between left ventricular wall motion and intraventricular flow propagation in acute and chronic ischemia

Myocardial ischemia has been associated with left ventricular (LV) postsystolic shortening. The combination of tissue Doppler imaging and high frame-rate acquisition of two-dimensional color flow makes it possible to study the interaction between LV wall motion and intraventricular flow propagation. The aim of this study was to examine in a clinical model the impact that acute myocardial ischemia and prior myocardial infarct might have on LV flow patterns and to explain the underlying mechanisms from the tissue Doppler data. LV flow propagation and tissue velocities during early diastole were studied in 18 healthy individuals, 17 patients with prior anterior myocardial infarct, and 16 patients before and during percutaneous coronary intervention (PCI) of the left anterior descending artery. Normal individuals had intraventricular flow propagation toward the apex during isovolumic relaxation. During this early diastolic time phase, myocardial velocities measured at mid- and apical septal segment were directed away from the apex. Before PCI, patients without myocardial infarction had similar findings as in normal individuals. In contrast, each patient with either prior myocardial infarction or PCI-induced acute ischemia had flow propagation opposite to normal individuals, and tissue velocities reversed toward the apex during early diastole. Reversal of early diastolic LV flow propagation in acute and chronic anterior myocardial ischemia reflects postsystolic shortening in the dyskinetic apical and septal myocardial segments.

Quantification of left ventricular mechanical dyssynchrony by conductance catheter in heart failure patients

Mechanical dyssynchrony is an important codeterminant of cardiac dysfunction in heart failure. Treatment, either medical, surgical, or by pacing, may improve cardiac function partly by improving mechanical synchrony. Consequently, the quantification of ventricular mechanical (dys)synchrony may have important diagnostic and prognostic value and may help to determine optimal therapy. Therefore, we introduced new indexes to quantify temporal and spatial aspects of mechanical dyssynchrony derived from online segmental conductance catheter signals obtained during diagnostic cardiac catheterization. To test the feasibility and usefulness of our approach, we determined cardiac function and left ventricular mechanical dyssynchrony by the conductance catheter in heart failure patients with intraventricular conduction delay ( n = 12) and in patients with coronary artery disease ( n = 6) and relatively preserved left ventricular function. The heart failure patients showed depressed systolic and diastolic function. However, the most marked hemodynamic differences between the groups were found for mechanical dyssynchrony, indicating a high sensitivity and specificity of the new indexes. Comparison of conductance catheter-derived indexes with septal-to-lateral dyssynchrony derived by tissue-Doppler velocity imaging showed highly significant correlations. The proposed indexes provide additional, new, and quantitative information on temporal and spatial aspects of mechanical dyssynchrony. They may refine diagnosis of cardiac dysfunction and evaluation of interventions, and ultimately help to select optimal therapy.