Myocardial Contractility: Historical and Contemporary Considerations.

Area of Science:

• Cardiovascular Physiology
• Biophysics

Background:

• The term "myocardial contractility" has been used for over 125 years but lacks a universally accepted definition.
• Existing definitions are often conflated with cardiac performance or inotropy, leading to confusion among researchers and clinicians.
• New discoveries highlight the load-dependent nature of cardiac contraction, necessitating a clearer understanding of contractility.

Purpose of the Study:

• To re-examine historical and contemporary interpretations of cardiac performance and inotropy.
• To propose a modern, precise definition of myocardial contractility.
• To address the ambiguity surrounding myocardial contractility in light of recent scientific advancements.

Main Methods:

• Review of historical and contemporary literature on myocardial contractility, cardiac performance, and inotropy.
• Analysis of the load-dependent kinetics of cardiac contraction and its implications.
• Reconsideration of definitions based on sarcomeric protein interactions and chemo-mechanical processes.

Main Results:

• Historical definitions of myocardial contractility are often operational and fail to distinguish it from loading conditions.
• The Starling mechanism describes length-dependent force development, distinct from length-independent contractility.
• A proposed definition emphasizes intrinsic, kinetically controlled chemo-mechanical processes.

Conclusions:

• A precise definition of myocardial contractility is crucial for advancing cardiovascular research and pharmacology.
• The proposed definition clarifies contractility as independent of preload, afterload, and muscle length.
• This definition accommodates new discoveries regarding sarcomeric protein modulation of cardiac function.