18. Dilatative hypertrophy of the left ventricle of the heart

Organ: Heart

Description:

A slice of the heart can be seen. Most notably the left ventricle is severely dilated. Note that the ventricular wall isn’t abnormally thick.

Diagnosis: Dilatative hypertrophy of the left ventricle

Causes:

• Increased preload
  • Aortic insufficiency
  • Mitral insufficiency

Theory:

This topic is best understood in tandem with preparation 17.

When there is an increased preload, more blood volume will enter the heart. This can cause volume-overload of the heart. The ventricles must respond to this by undergoing dilatative hypertrophy. In this type of hypertrophy new sarcomeres are added in series after the existing sarcomeres, which causes the muscle fibre to lengthen instead of thickening. Consequently, the ventricle wall won’t become thicker but the ventricle itself will become dilated. To measure this type of hypertrophy the weight of the heart and not the thickness of the ventricle must be determined.

Like explained in topic 17, the ventricle will continue to dilate to compensate for the increasing preload. However, due to the Laplace law, the increasing dilation causes increasing tension in the ventricular wall, which reduces the contractility. The ventricle will eventually not be able to pump enough blood to the systemic circulation, causing a state of decompensation.

To sum up:

1. Increased preload causes dilatative hypertrophy
2. The Laplace law states that increased dilation of the ventricle causes increased strain on the ventricular wall. This increased strain causes a decrease in contractility.
3. The decreased contractility eventually results in the ventricle not being able to compensate for failing heart, causing decompensation.

   

   Dilative hypertrophic left ventricle prep