Early Increase in Left Ventricular Compliance after Myocardial Infarction

Abstract

A B S T R A C T The left ventricular (LV) pressurevolume (P-V) relationship is a resultant of several determinants, including initial ventricular volume, geometry, and wall stiffness. A quantitative index of one of these determinants, LV wall stiffness, was developed from a mathematical analysis of the isolated P-V relationship. Since this relationship was exponential, stiffness (dP/dV) could be expressed by the equation dP/dV = aP + b, where a and b are constants. The a constant, termed the passive elastic modulus, was independent of both pressure and volume, was modified only slightly by changes in geometry, and thus was primarily affected by changes in wall stiffness. LV wall stiffness was assessed by determination of the passive elastic modulus in eight normal canine hearts and in five hearts 1 hr after acute myocardial infarction. The value of the passive elastic modulus for the normal canine LV was found to be 0.099 ±0.006 cc'. In the five infarcted hearts there was a modest, but statistically insignificant, shift of the P-V curves from control, such that for the same pressure the infarcted hearts contained greater volume. However, the passive elastic modulus decreased 41% to 0.057 +0.006 cc' (P < 0.001). Thus, although LV wall stiffness may increase later in the course of myocardial infarction, it is concluded that it was significantly decreased 1 hr after infarction. Calculation of the passive elastic modulus provided a sensitive means of detecting such changes, whereas P-V curves alone were generally insensitive.Abstract presented at 20th Annual Scientific Session,

Functional significance of regional ischemic contraction abnormalities.

“…When papillary muscles are subjected to repetitive passive stretch, however, an increase in the tension-length relationship has been observed,6 and early in the course of experimental acute myocardial infarction, an increase in the diastolic pressure-volume relationship has been observed. 6 The observed early increase in diastolic segment length of the ischemic segment in our intact heart study, therefore, may reflect the repeated and substantial stretching of the noncontracting ischemic muscle by adjacent normal fibers. The magnitude of change in regional diastolic segment length in acute ischemia is in the range of 5 to 20% and would be difficult to detect clinically, but the absence of contraction in systole would be manifest as akinesis.…”

Serial changes in left ventricular relaxation and chamber stiffness after large myocardial infarction in rats.

“…77, No. 6, June 1988 tion on left ventricular relaxation. Left ventricular relaxation was prolonged after 10 to 15 min of coronary artery occlusion and then returned to normal by 1 hr.…”

Beneficial effect of salbutamol on cardiac function in severe congestive cardiomyopathy. Effect on systolic and diastolic function of the left ventricle.

“…The decision of whether a given therapeutic agent is an inotropic agent or a vasodilator can be difficult when a study is carried out in Alterations in LV compliance are affected by many factors other than elastic properties of the myocardium. Most accepted factors related to the left ventricle itself altering compliance are ventricular geometry, initial volume, hypertrophy, wall thickness, ventricular filling rate 15,17,19,[24][25][26] and ventricular stiffness. Changes in the behavior of the anatomical constraints to the LV distension, including right ventricular chamber,27 the pericardium and the pleural cavity28 associated with altered pressure and volume-loading conditions, have also been suggested to contribute to the observed displacement of the LV pressure-volume curves.…”