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Common Congenital Heart Lesions - page 81 / 126





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81 of 126

Heart Failure

Chapter 9 p.218-236, reading from Monday 27th

Heart Failure: inability of the heart to pump blood forward at a sufficient rate to meet the metabolic demands of the body (forward failure), or the ability to do so only if the cardiac filling pressures are abnormally high (backward failure), or both. Impaired left ventricular function is the most common cause of heart failure.

Review of cardiac physiology:

Frank-Starling Relationship: The higher the preload, the greater the ventricular output. In English, an increase in the amount of blood in the ventricle before contraction (during diastole) results in an increase in the amount of blood the ventricle pumps into the aorta during systole. This relationship is a good thing because it allows the ventricle to pump more blood when it sees an increased volume (like during exercise).

Why this happens: think of the ventricles as a new balloon. The more air you put in the balloon, the more the balloon has to stretch to hold the air. In the heart, this stretching comes from the overlap of actin and myosin filaments and a subsequent increase in the number of crossbridges linking the two filaments. An increase in crossbridges results in an increase in the force of contraction and an increase in Ca2+ sensitivity, which further increases the force of contraction. Again, think of the balloon. If you blow the balloon up a lot and let it go, it flies around the room because the air comes out with a lot of force. But if you only blow the balloon up a little bit, the air leaves with less force, and it’s no fun because the balloon just falls on the floor. :0) See p.215 Fig 9.3

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