Abstract
Several indexes of myocardial contractility have been proposed to assess ventricular function in the isovolumetrically beating isolated heart. However, the conclusions reached on the basis of these indexes may be influenced by ventricular geometry rather than contractility itself. The objective of the present study was to assess the performance of widely used contractility indexes in the isovolumetrically beating isolated heart in two experimental models of hypertrophy, the spontaneously hypertensive rat (SHR) and infrarenal aortocava fistula. Compared to normotensive controls (N = 8), SHRs with concentric hypertrophy (N = 10) presented increased maximum rate of ventricular pressure rise (3875 +/- 526 vs 2555 +/- 359 mmHg/s, P < 0.05) and peak of isovolumetric pressure (187 +/- 11 vs 152 +/- 11 mmHg, P < 0.05), and decreased developed stress (123 +/- 20 vs 152 +/- 26 g/cm(2), P < 0.05) and slope of stress-strain relationship (4.9 +/- 0.42 vs 6.6 +/- 0.77 g/cm(2)/%). Compared with controls (N = 11), rats with volume overload-induced eccentric hypertrophy (N = 16) presented increased developed stress (157 +/- 38 vs 124 +/- 22 g/cm(2), P < 0.05) and slope of stress-strain relationship (9 +/- 2 vs 7 +/- 1 g/cm(2)/%, P < 0.05), and decreased maximum rate of ventricular pressure rise(2746 +/- 382 vs 3319 +/- 352 mmHg, P < 0.05) and peak of isovolumetric pressure (115 +/- 14 vs 165 +/- 13 mmHg/s, P < 0.05). The results suggested that indexes of myocardial contractility used in experimental studies may present opposite results in the same heart and may be influenced by ventricular geometry. We concluded that several indexes should be taken into account for proper evaluation of contractile state, in the isovolumetrically beating isolated heart.
Highlights
Myocardial hypertrophy represents an important adaptive mechanism to hemodynamic overload [1]
The results suggested that indexes of myocardial contractility used in experimental studies may present opposite results in the same heart and may be influenced by ventricular geometry
Left ventricular weight normalized to V0 (LVW/ V0) was significantly higher in the spontaneously hypertensive rat (SHR) group, indicating concentric hypertrophy
Summary
Myocardial hypertrophy represents an important adaptive mechanism to hemodynamic overload [1]. Murad and Tucci [15] considered peak isovolumetric developed pressure to be unreliable for the assessment of myocardial contractility in pressure overload-induced concentric hypertrophy in rats, favoring the developed stress index. These investigators did not consider ventricular dilation. Maximal rate of pressure rise and stress-strain relationship have been used by several investigators to assess myocardial contractility in the hypertrophied rat heart (6,7,1517) Both pressure-volume and stress-strain relationships provide a load-insensitive measure of contractile state. The former may reflect contractility in terms of cardiac pump and the latter, in terms of muscle capacity of force generation
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