Percentage Of Systolic Shortening Research Articles

Effects of Pimobendan (UD-CG 115) on the Contractile Function of the Normal and “Postischemic” Canine Myocardium

Pimobendan (UD-CG 115) is a long-acting positive inotropic drug with arterio- and venodilator properties. To determine to what extent this new agent is able to affect contractile function in previously ischemic areas of the left ventricle (LV), the effects of pimobendan on global and regional LV function were studied in eight conscious dogs, 2 days after a 2-h coronary occlusion followed by reperfusion. Before pimobendan, percentage of systolic shortening and mean velocity of shortening were lower in reperfused segments than in control areas (0.41 +/- 0.17 vs. 0.93 +/- 0.07 s-1 and 7 +/- 3 vs. 15 +/- 1%, respectively; both p less than 0.05). Infusion of 1 mg of pimobendan significantly improved peak + dP/dt (3202 +/- 372 to 3848 +/- 498 mm Hg/s; p less than 0.05) and ejection time (166 +/- 13 to 156 +/- 15 ms; p less than 0.05). Cumulative infusion up to 2.5 mg further improved these indexes to 5199 +/- 934 mm Hg/s and to 125 +/- 11 ms, (respectively; both p less than 0.05) without affecting mean arterial pressure (91 +/- 14 to 93 +/- 22 mm Hg; NS). Mean velocity of shortening rose to 1.18 +/- 0.09 s-1 (p less than 0.05) in control segments and to 0.62 +/- 0.18 s-1 (p less than 0.05) in reperfused segments. The ratio between end-systolic pressure and length increased by 26 +/- 9% (p less than 0.05) in the reperfused segments and by 20 +/- 8% (p less than 0.05) in control areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional ventricular segmental dynamics in normal conscious dogs

Left ventricular (LV) subendocardial segmental behavior was analyzed during the whole cardiac cycle for different loading and inotropic conditions in six conscious dogs that were instrumented with ultrasonic crystals in the basal (B) and apical (A) LV regions, a LV micromanometer, and an aortic cuff occluder. There were large variations of A and B segmental behavior during isovolumic contraction and relaxation. In contrast, a linear relationship between A and B was observed during ejection but segmental shortening was larger during control in A than in B, whether it was expressed as a percentage of systolic shortening (34.6 +/- 1.1 and 25.0 +/- 1.2%, respectively; P less than 0.005), or whether segments were normalized for passive resting length. This linear relationship during ejection with a slope of 1.49 was not significantly modified by alterations of loading conditions or inotropic state. The larger A than B shortening, independent of the normalization procedure, is attributed to the regional stress distribution in the LV. The absence of regional and cycle invariance particularly during isovolumic phases prevents the inference of ventricular volume from a limited number of dimensions.

The influence of adenosine triphosphate on left ventricular function and blood flow distribution during aortic crossclamping in dogs

To evaluate the influence of adenosine triphosphate (ATP)-induced vasodilation on myocardial performance and blood flow during aortic crossclamping (XC), ten dogs were instrumented to measure left ventricular (LV) pressure and dimensions. Regional LV function was assessed from the percentage of systolic shortening, whereas the slope of the linear regression of the LV end-systolic pressure-diameter relationship was used as an index of overall contractility. The regional blood flow distribution was measured from sequential injections of radioactive microspheres. Following XC, systemic arterial pressure proximal to the clamp (SAP a), LV end-diastolic pressure (LVEDP), LV end-systolic meridional wall stress (WS), and central venous pressure (CVP) increased significantly, whereas the cardiac index (CI) and heart rate did not change. After 30 minutes of ATP infusion (1 mg/kg/min) SAP a, LVEDP, WS, and CVP returned to control levels, CI increased significantly compared with XC alone, and vascular resistance fell below the control level. ATP produced a threefold increase in myocardial blood flow and shifted the intramural distribution in favor of the endocardial layer. In conclusion, our investigation of the effect of ATP on aortic XC in a canine model showed the drug to produce a smooth, predictable, and rapid reduction in left ventricular preload and afterload. This was accomplished with minimal changes in distal organ perfusion, some improvement in measured cardiac performance, and a large increase in myocardial blood flow.

Relations between myocardial blood flow and postextrasystolic potentiation in epicardial and endocardial left ventricular regions early after coronary occlusion in dogs.

Postextrasystolic potentiation was studied during control and 5 minutes after coronary occlusion in epicardial regions of 12 open-chest dogs. Segmental behavior evaluated with ultrasonic crystals was correlated with regional myocardial blood flow (MBF) measured with radioactive microspheres. A similar correlation was found between the percentage of systolic shortening in postextrasystolic beats and MBF in epicardial (r = 0.64) and endocardial (r = 0.97) regions, although the scatter was much larger in the epicardium. The correlation was similar when segmental function was expressed as the area of the pressure-segment length loop. Three types of segments were described; completely ischemic segments (transmural MBF less than 5% of control), in which end-systolic length was larger than end-diastolic length after postextrasystolic potentiation; severely ischemic segments (5% less than or equal to transmural MBF less than 25% of control), in which the ischemic bulge during control beats was replaced by active shortening after premature ventricular complexes; and marginal segments (25% less than or equal to transmural MBF less than 100% of control), in which depressed shortening was enhanced close to control after a premature ventricular complex. These data reconcile conflicting studies, which did not consider similar degrees of ischemia and show a rapid loss of postextrasystolic potentiation in completely ischemic segments.

Adenine nucleotide content and regional function during ischemia and reperfusion in canine ventricular myocardium.

We have compared in open-chest dogs the evolution of adenine nucleotides and creatine phosphate to that of regional mechanical function during ischemia and reperfusion. Reperfusion restored normal value of creatine phosphate whereas adenine nucleotide level remained depressed. The percentage of systolic shortening, which after occlusion has a zero or negative value, increased to about 20% of control, after reperfusion similarly the pressure-length loop areas decreased to 14.9% of control during ischemia and increased to 39.3% of control during the early phase of the reperfusion period. No individual correlation was found between the ATP content and segmental function during ischemia or reperfusion, suggesting that a low level of ATP did not prevent some restoration of mechanical function. However, the ATP content measured at the end of the ischemic period was correlated with mechanical function measured 75 min after reperfusion, and thus ATP depletion could appear as an indicator of the severity of ischemic damage.

Automated analysis of the left-ventricular diameter time curve from echocardiographic recordings

In order to analyze the left-ventricular diameter time curve, a computer method has been developed. It includes a cursor hand-controlled digitization and optimization of calibration which is valid for a majority of digitization devices. The advantages of well-spaced multiple point calibration are improvement of accuracy, correction of record distortion, and elimination of human error. The left-ventricular endocardial echoes were digitized at a sampling rate of 1 kHz by moving a hand-controlled cursor across a photographic record. Adequate smoothing and derivation of the data leads to recognition of a typical diameter time curve. An automated analysis of this curve can then be performed for several successive beats. In systole, the maximal velocity of circumferential fiber shortening and the percentage of systolic shortening can be defined. During diastole, three phases can clearly be separated: rapid filling, slow filling, and atrial “kick.” The contributions of each of these phases can therefore be quantified from the pattern analysis of the left-ventricular diameter time curve.