Alpha-myosin heavy chain isoform and atrial size in patients with various types of mitral valve dysfunction: a quantitative study.

The cardiac myosin phenotype, an important determinant of myocardial contractility, is modified by chronic increases in hemodynamic load. To quantify the proportion of atrial alpha-myosin heavy chain in various types of left atrial overload and to assess the possible relation between this proportion and atrial size, 34 patients were studied, 4 with Wolff-Parkinson-White syndrome, 29 with various types of mitral valve dysfunction and 1 with an atrial septal defect. Four normal autopsy hearts were also studied. The proportion of alpha-myosin heavy chain among total (alpha plus beta) myosin heavy chains was determined in each atrial sample, using an enzyme-linked immunosorbent assay. The size of the left atrium was assessed by one- and two-dimensional echocardiography. Alpha-myosin heavy chain was the main isoform present in the normal atria (85.5 +/- 9% of total myosin heavy chains). Patients with pure tight mitral stenosis (n = 9), mitral stenosis plus mild regurgitation (n = 8) and severe mitral regurgitation (n = 8), who had a higher indexed left atrial transverse diameter than those with Wolff-Parkinson-White syndrome (33 +/- 6, 39 +/- 10 and 46 +/- 5 versus 19.5 +/- 2 mm/m2, p less than 0.01, p less than 0.001 and p less than 0.001, respectively), also demonstrated a much smaller percent of alpha-myosin heavy chain content (28 +/- 20, 23.5 +/- 13 and 12 +/- 10 versus 58 +/- 18%, p less than 0.01, p less than 0.01 and p less than 0.001, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)