Early changes in left ventricular regional dimensions and function during chronic volume overloading in the conscious dog.

Abstract

SUMMARY As the left ventricle dilates during chronic volume overloading, it assumes a more spherical configuration, suggesting a nonuniform regional myocardial response. Accordingly, we studied early alterations in left ventricular geometry and regional function induced by chronic volume overloading in the canine heart subjected to an aortocaval fistula. Nine mongrel dogs were instrumented with ultrasonic crystal pairs placed perpendicularly to the long axis to measure instantaneous segment lengths in the apical, midventricular, and basal portions of the left ventricle; another pair monitored an apical internal diameter. We obtained control measurements of end-diastolic dimensions and percent shortening in the conscious state. An aortocaval fistula was then constructed, resulting in an increase in resting end-diastolic pressure (EDP) from 11 ± 1 (SEM) to 22 ± 2 mm Hg and resting heart rate from 100 ± 4.9 to 131 ± S. O beats/min at 1 month (P < 0.01). At 10-20 days, mid-basal regional end-diastolic dimensions were significantly greater than control (8.8 ± 2.4% increase, P < 0.01), while there were no significant increases in apical dimensions when compared at the same EDP. However, by 20-40 days, all dimensions were significantly increased (11.4 ± 3.3% increase at the mid-base, P < 0.01), 7.8 ± 1.6% at the apex (P < 0.01), and 11.2 ± 4.5% at the diameter (P < 0.05). Regional function as measured by percent shortening at the same EDP exhibited early augmentation in all segments by 2 weeks compared to control (3.8 ± 1.3% increase at the diameter, 3.8 ± 1.9% at the base, 7.2 ± 2.2% at the middle, and 12.2 ± 4.7% at the apex, P < 0.05). Prom 4 to 6 weeks, however, function was not different from control, with a slight reduction in all regions from the peak values obtained at 2 weeks. We conclude that in the canine heart there are regional differences in the rate of left ventricular dilation to chronic volume overload, suggesting differential regional hypertrophy, with the earliest response at the mid-basal level. Furthermore, despite dilation, regional function is preserved or even augmented, although to varying degrees in each region. Circ Re* 45: 420-428, 1979 FOR many years, pathologists and clinicians have appreciated that the shape of the left ventricle is quite spherical late during the course of chronic volume overload (Kirch, 1920(Kirch, , 1930Grant, 1953). Since the normal heart is ellipsoidal in shape, this progressive change in geometry implies regional differences in the rate of left ventricular dilation and hypertrophy, the meaning and implications of which have been unclear. Since the geometry of the heart is an important determinant of ventricular wall stress, which in turn is an important determinant of ventricular performance and energy demands, such shape changes would appear to be key in the eventual adaptation of the heart to the volume overload. Attempts to quantify alterations in cardiac geometry have led to conflicting results, depending on the type of lesions and animal species examined. Ross ...

Abnormalities of dynamic ventricular shape change in patients with aortic and mitral valvular regurgitation: assessment by Fourier shape analysis and global geometric indexes.

“…Studies of several forms of myocardial and valvular disease have revealed abnormalities of dynamic shape deformation. 8 " 12 These and other data have shown that the larger the ventricular chamber volume the rounder the shape and that when the percent of volume ejected is reduced, dynamic shape change is similarly decreased. 8" 1013 The data, however, have not demonstrated that dynamic shape change abnormalities are in any sense separable from volume change, nor have they been consistent about the nature of these abnormalities.…”

Depressed contractile function due to canine mitral regurgitation improves after correction of the volume overload.

“…from the difficulty in longitudinally measuring contractile function in humans (where a contractility deficit is known to occur) and also from the fact that few experimental models of volume overload (where contractile function could be studied longitudinally) consistently produced contractile dysfunction (33)(34)(35)(36)(37)(38) Limitations to assessment of contractile function. A key premise of our study is that we are able to measure contractile function accurately.…”

Morphological and Functional Adaptation of the Maternal Heart During Pregnancy

“…24 In volume overload states, LV dilatation and eccentric hypertrophy are compensatory mechanisms frequently associated with changes in the LV from an ellipsoid to a more-spherical shape. 21,25 Such geometry and loading changes can alter functional evaluation of the LV by classical parameters, such as EF or shortening fraction, 25,26 as well as novel deformation parameters. 21,27 In this study, we performed a comprehensive assessment of the effects of normal pregnancy on LV mechanics using standard and novel morphological and functional echocardiographic parameters while considering LV load and shape.…”