The left atrium functions as a reservoir for blood stored during ventricular systole, a conduit for pulmonary venous flow during ventricular diastole, and as a pump augmenting left ventricular filling during atrial systole. Cardiac angiography and Doppler echocardiography have been used in the assessment of atrial function. These measurements are, however, quite sensitive to ventricular and atrial loading conditions. Instantaneous pressure-volume relations of the left atrium have been described by a time-varying elastance model in the isolated left atrium and intact circulation in animal models. The mitral stenosis can be characterized hemodynamically as increased afterload of the left atrium. Percutaneous mitral balloon valvuloplasty, which results in a dramatic increase in the mitral orifice area in patients with mitral stenosis, is a well-suited clinical model for physiological assessment of the left atrial function in response to acute change of the left atrial afterload. The purpose of this study was 1) to evaluate the feasibility of the left atrial pressure-volume loop using automatic boundary detection method, 2) to obtain the left atrial pressure-volume loop in patients with mitral stenosis and to compare with that of normal controls, and 3) to assess the changes of the left atrial wall tesion and stroke work after percutaneous mitral balloon valvuloplasty in patients with mitral stenosis using the left atrial pressure-volume relations.

Twelve patients had simultaneous measurements of left atrial pressure and left atrial volume using trasseptal catheterization and two-dimensional echocardiography with automatic boundary detection technology. The left atrial pressure-volume was constructed by a computer workstation interfaced with an ultrasound system. Left atrial volumetric parameters, areas of A and V loops, and peak wall tension were measured and compared before and after percutaneous mitral balloon valvuloplasty.

1) The left atrial pressure-volume loop could be obtained without complications in the control group as well as in patients with mitral stenosis. 2) The left atrial peak wall tension and A and V loop areas were significantly increased in mitral stenosis compared to the control group. 3) Left atrial maximal volume, minimal volume and volume before active atrial contraction were significantly increased in mitral stenosis compared to control group. 4) Left atrial ejection fraction and left atrial active emptying fraction were significantly reduced in mitral stenosis. Left atrial passive emptying fraction was slightly reduced in mitral stenosis compared to control group without statistical significance. 5) Left atrial peak wall tension and A loop area were significantly reduced after percutaneous mitral balloon valvuloplasty. 6) There were no significant changes in left atrial maximal volume, minimal volume, volume before active atrial contraction, total volume change, passive emptying volume, active emptying volume, passive emptying fraction, active emptying fraction, V loop area and left atrial ejection fraction after percutaneous mitral balloon valvuloplasty.

The left atrial stroke work and peak wall tension can be assessed quantitatively using left atrial pressure-volume relations in patients with mitral stenosis and those are significantly reduced after percutaneous mitral balloon valvuloplasty. The analysis of left atrial pressure-volume loop is a potentially useful means in the assessment of left atrial function.