Lusitropy

Lusitropy is a term used to describe myocardial relaxation. The increase in calcium uptake by cardiomyocytes leads to increased myocardial contractility (positive inotropic effect), but the myocardial relaxation, or lusitropy, decreases.

Positive

Increased catecholamine levels promote positive lusitropy, enabling the heart to relax more rapidly. This effect is mediated by the phosphorylation of phospholamban and troponin I via a cAMP-dependent pathway.

Negative

Relaxation of the heart is negatively impacted by the following factors:

1) Calcium overload - too much intracellular calcium
2) Rate of efflux of calcium through pumps - if calcium is not removed from the cell quickly enough
3) Impaired sarcoendoplasmic reticulum calcium ATPase (SERCA)- this channel in the myocyte pumps calcium from the cytoplasm of the cell into the endoplasmic reticulum.
4) TN-C binding affinity - TN-C (troponin C) is a protein that affects the myosin-actin fibers of the heart. When calcium binds, it triggers contraction of the heart. If calcium binds too easily, relaxation will become more difficult.