LEFT ATRIAL MECHANICAL ADAPTATION TO LONG-STANDING HEMODYNAMIC LOADS BASED ON PRESSURE-VOLUME RELATIONS

Left atrial (LA) adaptation during the development of left ventricular (LV) dysfunction is not fully understood. We performed echocardiograp hic assessment of LA volumes simultaneously with recordings of pulmona ry wedge pressures in 60 patients. Twenty patients had no structural o r functional LV abnormalities, 20 had a recent myocardial infarction w ith LV dysfunction, and 20 suffered from congestive heart failure (CHF ). Pressure-volume loops were obtained at baseline and during increase s in in LA pressure produced by normal saline infusion. LA afterload w as estimated by the effective LV elastance (E-LV). Atrioventricular co upling was calculated by the E-LV/E-es ratio (where E-es is the end-sy stolic elastance). E-es increased in patients with myocardial infarcti on (0.80 +/- 0.09 mm Hg/ml, p <0.001); whereas it decreased in patient s with CHF (0.22 +/- 0.05 mm Hg/ml, p <0.001) compared with controls ( 0.61 +/- 0.07 mm Hg/ml). Similarly, stroke workload increased in patie nts with myocardial infarction (60.7 +/- 7.3 mm Hg.ml, p <0.001), wher eas it decreased in patients with CHF (25.4 +/- 2.2 mm Hg.ml, p <0.001 ) compared with controls (44.8 +/- 5.5 mm Hg.ml). In all patients LA s tiffness (slope of the relation of the filling portion of the pressure -volume loop) was increased compared with controls (controls: 0.13 +/- 0.04, patients with myocardial infarction: 0.22 +/- 0.05, and patient s with CHF: 0.27 +/- 0.05 mm Hg/ml, p <0.001 for both comparisons). Mo reover, the E-LV/E-es ratio increased gradually as LV function deterio rated (controls: 1.06 +/- 0.10, patients with myocardial infarction: 1 .35 +/- 0.16, and patients with CHF: 6.90 +/- 0.84, p <0.001). Thus, e arly in heart failure, LA pump function is augmented but LA stiffness increases and work mismatch occurs. With further progression of LV dys function, LA pump function decreases as a result of increased afterloa d imposed on the LA myocardium. (C) 1998 by Excerpta Medica, Inc.