The effects of left ventricular load and contractility on mitral regurgitant orifice size and flow in the dog.

Abstract

Acute mitral regurgitation (MR) was produced in 12 dogs by closed chest partial valvulectomy and the relative contributions of MR pressure gradient (MRG), the time for regurgitant flow (VSI), and the MR orifice area (MRA) to mitral regurgitant volume (MRV) assessed. Aortic and left atrial pressures, biplane left ventricular (LV) angiography, forward flow and mitral regurgitant flow (MRF) were measured following MR induction and following augmentation of left ventricular end-diastolic volume (EDV), increased aortic resistance (angiotensin), and in the presence of increased ventricular contractility (calcium or epinephrine). Mitral regurgitation orifice area was determined by calculation and the diameters of the mitral anulus and subvalvular areas measured angiographically. Angiotensin and volume infusion induced a substantial increase in MRF which was largely dependent on an increase in MRA but not MRG, while augmentation of contractility decreased MRF accompanied by a decrease in MRA, relatively independent of MRG. Left ventricular size and shape are major determinants of MRA and resultant MRF in acute mitral regurgitation. These findings may help to explain the effects of such factors as ventricular loading and volume on the clinical course of mitral regurgitation in man.

Mildly symptomatic chronic mitral regurgitation. Analysis of left ventricular systolic function and mitral regurgitant fraction under pharmacological influence: echocardiographic study

“…Although it was previously proposed that the size of the regurgitant orifice diminished in situations with increased ventricular contractility or reduced intraventricular volume 26,27 , or both, this theory could not explain our results, because the velocity of the jet and not the regurgitation volume was the factor determining the size of the regurgitant area in color flow mapping 28 . Based on this, the mechanism of the difference observed between digoxin and enalapril could be explained by the capacity of the former to reduce the systolic preejection period 29,30 .…”

Progressive nature of chronic mitral regurgitation and the role of tissue Doppler-derived indexes

“…The size of the effective regurgitant orifice is dependent on annular dimensions, leaflet length, and the integrity of the papillary muscle apparatus. Acutely, augmentation of loading conditions leads to ventricular enlargement, mitral annular dilatation, and increased regurgitant flow (5,35). Although a similar process has been suggested chronically (16), it has never been confirmed.…”

“…The prognosis associated with MR varies directly with the severity of the regurgitation and the effect of the incompetent valve on LV systolic function (6,9). In acute experimental MR, the regurgitant orifice varies with loading conditions, ventricular size, and annular dimensions, as well as within the cardiac cycle (5,15,34,35). However, it is unclear in chronic MR whether the regurgitant orifice is dynamic and can further influence ventricular remodeling.…”

Contribution of Exercise-Induced Mitral Regurgitation to Exercise Stroke Volume and Exercise Capacity in Patients With Left Ventricular Systolic Dysfunction

“…Several factors, including LV size, extent of emptying, mitral annular diameter, papillary muscle function, and left atrial size, have been implicated. 9,[25][26][27] Experimental and clinical studies have also shown that the severity of functional MR often varied over time as a result of dynamic changes in the mitral regurgitant orifice, changes in ventricular-atrial pressure gradients, or both. 24 -27 For instance, the severity of functional MR has been shown to increase during isometric exercise and to decrease during dobutamine and nitroglycerin infusion.…”