Contractility

Contractility refers to the inherent strength of the myocardium (ability to shorten). Inotropy is the term used to describe the contractile state of the heart.

How do changes in contractility change cardiac performance?

An increase in contractility results in:

• an increase in stroke volume (amount of blood ejected from the chamber with each beat).
• a reduction in preload (more complete emptying of the chamber). If pulmonary edema or effusions were present they may resolve with the reduction in preload.
• an increase in myocardial oxygen consumption. Thus, if a perturbation results in an increase in contractility, hopefully cardiac output increases sufficiently to provide for the increased demand for oxygen that the increase in contractility will require.

As contractility falls one can anticipate the opposite effects.

As contractility increases the Frank-Starling function curve shifts upward and to the left. The opposite occurs with a reduction in contractility.

How are changes in contractility detected on physical examination?

A fall or an increase in contractility can not be detected on physical examination as different from any other cause of a decrease or increase in cardiac output.

The best diagnostic aid to detect a change in contractility is the echocardiogram (cardiac ultrasound examination).