Contractility

WikiDoc Resources for Contractility
Articles
Most recent articles on Contractility Most cited articles on Contractility Review articles on Contractility Articles on Contractility in N Eng J Med, Lancet, BMJ
Media
Powerpoint slides on Contractility Images of Contractility Photos of Contractility Podcasts & MP3s on Contractility Videos on Contractility
Evidence Based Medicine
Cochrane Collaboration on Contractility Bandolier on Contractility TRIP on Contractility
Clinical Trials
Ongoing Trials on Contractility at Clinical Trials.gov Trial results on Contractility Clinical Trials on Contractility at Google
Guidelines / Policies / Govt
US National Guidelines Clearinghouse on Contractility NICE Guidance on Contractility NHS PRODIGY Guidance FDA on Contractility CDC on Contractility
Books
Books on Contractility
News
Contractility in the news Be alerted to news on Contractility News trends on Contractility
Commentary
Blogs on Contractility
Definitions
Definitions of Contractility
Patient Resources / Community
Patient resources on Contractility Discussion groups on Contractility Patient Handouts on Contractility Directions to Hospitals Treating Contractility Risk calculators and risk factors for Contractility
Healthcare Provider Resources
Symptoms of Contractility Causes & Risk Factors for Contractility Diagnostic studies for Contractility Treatment of Contractility
Continuing Medical Education (CME)
CME Programs on Contractility
International
Contractility en Espanol Contractility en Francais
Business
Contractility in the Marketplace Patents on Contractility
Experimental / Informatics
List of terms related to Contractility

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Myocardial Contractility is a term used in physiology to describe the performance of cardiac muscle. It is often defined as: the intrinsic ability of a cardiac muscle fibre to contract at a given fibre length.

Determinants of Myocardial Contractility

The five determinants of myocardial performance are:

• Heart rate
• Conduction velocity
• Preload
• Afterload
• Contractility

If myocardial performance changes while preload, afterload, heart rate, and conduction velocity are all constant, then the change in performance must be due to the change in contractility.

It might be thought that a better definition would be that Contractility is the property that represents the strength of myocardial contraction. However, this definition does not separate contractility from the other loading factors that affect the strength of myocardial contraction. In particular, an increase in preload results in an increased force of contraction - this is Starling's law of the heart - but this does not require a change in contractility.

Any chemicals that affects contractility is called inotropic agent. For example drugs such as catecholamines (norepinephrine and epinephrine) that enhance contractility are considered to have a positive inotropic effect.

The concept of Contractility was necessary to explain why some interventions (e.g. an adrenaline infusion) could cause an increase in myocardial performance even if, as could be shown in experiments, the preload, afterload and heart rate were all held constant. Experimental work controlling the other factors was necessary because a change in contractility is generally not an isolated effect.

For example:

• An increase in sympathetic stimulation to the heart increases contractility AND heart rate.
• An increase in contractility tends to increase stroke volume and thus a secondary increase in preload.

All factors that cause an increase in contractility work by causing an increase in intracellular [Ca⁺⁺] during contraction.