Laplace's law

Q: What is Laplace's law and how does it relate to cardiac hypertrophy?

A:

• Laplace's law is as follows: T = (P × R)/M where T is the tension in the walls, P is the pressure difference across the walls, R is the radius of the vessel and M is the thickness of the wall.
• In dilated cardiomyopathy, after prolonged increases in afterload (in the setting of hemodynamic stress such as hypertension), the heart becomes distended and the radius of the ventricle increases.
• To create the same pressure during ejection of the blood, much larger wall tension has to be developed by cardiac muscle and the ventricular wall thickens.
• The dilated hypertrophic heart requires more energy (and oxygen consumption) to pump the same amount of blood as compared to the heart of normal size.
• Dilated cardiomyopathy causes increases in the risks of ischemia and arrhythmias.

Teaching topics from the New England Journal of Medicine - Vol. 358, No. 13, March 27, 2008