Study for the mechanism of mechanical alternans

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Mechanical alternans is a poorly-understood phenomenon of alternating strong and weak beats with a constant beat-to-beat interval. It is a possible linker between failing myocardium and ventricular fibrillation in patients with chronic heart failure. Interval-force relationship, so-called mechanical restitution, is an intrinsic regulatory principle of myocardial contractility depending on sarcoplasmic reticulum (SR)Ca^(2+) cycling. Force-frequency relationship is also considered to reflect Ca^(++) handling of SR. We analyzed interval-force relationship and force frequency relationship in patients with chronic heart failure. In patients with atrial fibrillation, mechanical restitution curves were able to be obtained from beat by beat variance of left ventricular contractility adjusted by pre-preceding coupling intervals. We estimated mechanical restitution curves by fitting to monoexponential curves. Tau of the mechanical restitution curve increased in accord with the decrease of ejection fraction. We analyzed force-frequency relationship. In patients with chronic heart failure, peak force rate shifted to lower heart rate. The force gain of patients was little. A force gain was correlated to the left ventricular ejection fraction. We were able to obtain adequate mechanical restitution curves after both strong beats and weak beats from some patients. Mechanical restitution curves after weak beats steeply rose compared with those after strong beats. The time constant after weak beats were shorter than those after strong beats. Thus mechanical restitution properties were different after strong beats and weak beats during mechanical alternans. This implies that mechanical alternans originates from alternating changes of myocardial Ca^(2+) cycling property.