LEFT ATRIAL MYOPATHY IN IDIOPATHIC DILATED CARDIOMYOPATHY

To investigate whether left atrial systolic dysfunction in dilated car diomyopathy is the result of left atrial dilatation, atrial involvemen t in the myopathic process, or both, 20 patients with aortic stenosis, 14 patients with idiopathic dilated cardiomyopathy, and 10 normal con trol subjects were studied. Left atrial volumes (cubic centimeters) we re echocardiographically measured at mitral valve opening (maximal), m itral valve closure (minimal), and onset of atrial systole (P wave of the electrocardiogram) with the biplane area-length method. Atrial sys tolic function was assessed by calculating the active emptying fractio n, equal to (volume at onset of atrial systole minus minimal volume)/v olume at onset of atrial systole. Heart rate was similar in patients w ith aortic stenosis and dilated cardiomyopathy (83 +/- 11 vs 86 +/- 15 beats/min, respectively). Maximal volume was similar in patients with aortic stenosis (74.8 +/- 26.4 cm(3)) and dilated cardiomyopathy (79. 7 +/- 25.3 cm(3)) but greater (p < 0.0001) than in control subjects (4 6.4 +/- 11.9 cm(3)). Active emptying fraction was inversely related to volume at onset of atrial systole and to tension at end of atrial sys tole (aortic stenosis r= -0.61 and r= -0.81, respectively; dilated car diomyopathy r= -0.79 and r= -0.66, respectively). At any given level o f volume at onset of atrial systole and tension at end of atrial systo le, however, active emptying fraction was lower in patients with dilat ed cardiomyopathy compared with those with aortic stenosis. Thus left atrial systolic dysfunction in dilated cardiomyopathy is not explained by the degree of left atrial dilatation or left atrial tension at end of atrial systole; this suggests that left atrial myopathy may be inv olved in the dysfunction.