Contractility refers to the inherent strength of the heart muscle – referred to as inotropy.
Factors affecting contractility
Factors that increase contractility:
- Increased Beta adrenergic stimulation
- Increased preload
- Reduced vagal tone
- Positive inotropic agents
Factors that reduce contractility:
- Reduced sympathetic stimulation
- Reduced preload
- Increased vagal tone
- Negative inotropic agents
Measures of contractility
Global or whole-heart contractility can be assessed by a variety of invasive or non-invasive ways. Invasive means involve measuring pressure changes directly in the ventricle. Non-invasive means are more commonly used clinically and include variables measured by cardiac ultrasound (echocardiography) or magnetic resonance imaging (MRI).
Effect of contractility on myocardial performance
An increase in contractility results in:
- An increase in stroke volume
- A reduction in preload
- An increase in MVO2
A reduction in contractility will have the opposite effects
Manifestations of abnormal contractility
If contractility is too high:
- This condition will likely go undetected.
If contractility is too low:
- The resultant fall in BP will manifest as signs of hypotension
- Fluid accumulation in the organs that drain into the weak ventricle
Effects of the autonomic nervous system on contractility
The sympathetic nervous system increases contractility. The parasympathetic nervous system decreases contractility.