heart failure

Question 1

define heart failure

Answer 1

a syndrome that can result from any structural or functional cardiac disorder that impairs the ability of the heart to function as a pump to support a physiological circulation

Question 2

define stroke volume

Answer 2

volume of blood ejected by ventricle per contraction

Question 3

what is the Frank-Starling mechanism?

Answer 3

the more a normal ventricle is distended at the end of diastole, the greater the volume that is ejected during the next systolic contraction

Question 4

define preload

Answer 4

the degree of stretch in the ventricles at the end of diastole

Question 5

define end diastolic volume

Answer 5

The amount of blood in the ventricles at the end of diastole

Question 6

what does stretching of muscle fibres do?

Answer 6

optimises the overlap of the filaments and increases the force of contraction

Question 7

what is preload increased by?

Answer 7

Ventricular filling, so is increased by:

Increased central venous pressure

Increased venous return (with increased respiratory pump or skeletal muscle pump activity or when lying down)

Question 8

what is preload reduced by?

Answer 8

Decreased central venous pressure (e.g. dehydration)

Increased heart rate (reduced time for filling)

• Decreased afterload (less ejection leads to reduced return – see Afterload)
• Inflow (mitral and tricuspid) valve stenosis)

Decreased compliance of the ventricle (due to ventricular hypertrophy or impaired ventricular relaxation)

Question 9

define afterload

Answer 9

pressure needed to be overcome in order to pump blood out of ventricles

Question 10

define compliance

Answer 10

how easy a chamber is to fill

Question 11

what 2 conditions is afterload increased in?

Answer 11

when there is a higher pressure to overcome during ejection e.g. in high blood pressure (hypertension), in increased systemic vascular resistance, or if there is stenosis (narrowing) of the aortic valve

when the radius of the ventricle is increased (e.g. when the ventricle is abnormally dilated)

Question 12

when is afterload reduced?

Answer 12

ventricular hypertrophy - develops to compensate when there is increased afterload (helpful at first but contributes to heart failure)

Question 13

name the four ways of classifying heart failure

Answer 13

systolic vs diastolic
left vs right
acute vs chronic
cardiovascular vs systemic causes

Question 14

define systolic heart failure

Answer 14

impairment of ventricular emptying due to poor contractility or increased afterload

Question 15

define diastolic heart failure

Answer 15

impairment of diastolic relaxation or ventricular filling

Question 16

name the main causes of systolic heart failure

Answer 16

Ischaemic heart disease / myocardial infarction - destruction of myocytes

Hypertension – high blood pressure increases left ventricular afterload so the heart compensates by becoming hypertrophic. This initially helps pumping but the hypertrophied ventricle is more prone to failure.

Abnormal myocyte function (cardiomyopathy).

Question 17

what are the effects of systolic heart failure?

Answer 17

1.        The ability of the left ventricle to pump is reduced
2.        Stroke volume falls, so more blood remains in the ventricle at the end of systole
3.        Normal systemic venous return is added to this extra blood, increasing preload. A normal ventricle would increase stroke volume to remove the excess, but the ventricle is impaired so it cannot. (Frank-Starling mechanism).
4. The persistently elevated ventricular pressure is transmitted to the left atrium through the mitral valve then to the pulmonary veins and capillaries. This causes higher hydrostatic pressure, which causes a transudate of fluid across into the pulmonary tissue, leading to pulmonary oedema.