Calcium sensitivity and unloaded shortening velocity of hypertrophied and non-hypertrophied skinned human atrial fibres.

The mechanical properties of myocardium of different animals are modified by a chronic increase in haemodynamic load. In this study differences in calcium sensitivity and maximum unloaded shortening velocity of hypertrophic and non-hypertrophic chemically skinned human atrial fibres are characterized. Investigating right atria of 34 patients, possible correlations are studied between preoperative atrial pressure, degree of hypertrophy (estimated from the muscle fibre diameter), calcium responsiveness (pCa50 eliciting half-maximum contraction) and Vmax (unloaded shortening velocity). Hypertrophic fibres from atrial appendages of patients having an increased right atrial pressure (RAP 8.5 +/- 1.6 mm Hg) and suffering from mitral valve disease (stenosis and insufficiency combined) had a fibre diameter of 18.0 +/- 0.9 microns. They also had a higher calcium sensitivity (pCa50 5.65 +/- 0.08) and a lower unloaded shortening velocity (1.7 +/- 0.1 muscle lengths/s) than non-hypertrophic fibres from the appendages of patients with normal right atrial pressure (RAP 3.2 +/- 0.5 mm Hg) and coronary heart disease (CHD: pCa50 5.45 +/- 0.04; Vmax = 3.4 +/- 0.2 muscle lengths/s; fibre diameter 12.8 +/- 0.4 microns). Thus non-hypertrophic fibres from control CHD patients differed significantly (p less than 0.01) from hypertrophied atrial fibres of patients with mitral valve disease and with combined valve disease (MAV, pCa50 = 5.58 +/- 0.05, Vmax 2.0 +/- 0.3 muscle lengths/s, fibre diameter 14.6 +/- 0.9 microns) or aortic valve disease (stenosis combined with insufficiency, fibre diameter 14.8 +/- 1.4 microns, pCa50 5.56 +/- 0.03, Vmax 2.0 +/- 0.24 muscle length/s; RAP 11.0 +/- 2.6 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)