[Relationship between the oscillatory contractions and myocardial tonus in patients with heart defects]

Interplay between contraction oscillations and the tone that is seen during rhythmic stimulation was studied in atrial trabeculae of patients with heart diseases. It was disclosed that in 50% of myocardial preparations from patients with rheumatic heart diseases, an increase in the tone (incomplete relaxation) and oscillations appeared at a frequency of 0.2 HZ. As the frequency was raised, the amplitude of the oscillations and the tone increased. Meanwhile in 25% of the preparations the appearance of the oscillations was not followed by the tone rise. In the remaining preparations, the tone and oscillations were not recorded. No growth of the tone or oscillations was commonly seen in the myocardium of patients with congenital heart diseases. Appearance of low-amplitude oscillations in some of the myocardial preparations from this group of patients occurred at a frequency of 1-2 HZ and was not accompanied by the tone rise. Catecholamines (noradrenaline, izadrin, dopamine) increased the amplitude of evoked contractions but did not change or even reduced the amplitude of oscillations. It is assumed that catecholamines effects are determined by concurrent enhancement of the ingoing Ca current and sequestration of Ca ions by the sarcoplasmic reticulum (as a result of the adenylate cyclase-cAMP system activation). Strophanthine suppresses the Na-K pump and leads to the accumulation by the myoplasma of Na ions which are exchanged for external Ca. As a result, the Ca concentration in the myoplasma and sarcoplasmic reticulum increases. The ability of the sarcoplasmic reticulum to effective Ca sequestration from the myoplasma correspondingly falls.