Heart failure occurs when the heart is unable to provide sufficient blood to meet the body’s
needs.
Heart failure is not a disease on its own but rather a consequence of other underlying
conditions.
The impairment of the heart function can be due to an inability to PUMP effectively during
systole, called SYSTOLIC heart failure, or inability to FILL properly during diastole,
called DIASTOLIC heart failure.
Heart failure can be right-sided or left-sided depending on the side that is affected.
About two thirds of all left–sided heart failures are caused by systolic dysfunction.
In systolic heart failure, ventricular contraction is compromised.
This may be caused by any condition that weakens the heart muscle or creates more difficulty
for the ventricle to pump.
The most common include: - Coronary artery disease and its consequences:
Plaque buildup narrows the coronary artery, reducing blood supply to the heart muscle.
Complete blockage can cause heart attacks which often leave behind non-functional scar
tissue.
- Dilated cardiomyopathy: The Ventricular wall is dilated, becomes thin and weak.
- Hypertension: higher systemic pressure makes it harder for the ventricle to eject blood.
This is because the pressure in the left ventricle must EXCEED the systemic pressure for the
aortic valve to open.
- Valvular heart disease: Damage to the valves, such as stenosis, also makes it more difficult
for the ventricle to pump.
The effectiveness of ventricular contraction is measured by the EJECTION fraction.
Typically, the left ventricle is filled with about 100ml of blood, but only 60ml is ejected
during contraction.
This corresponds to an ejection fraction of 60%.
The normal range of the ejection fraction is between 50 and 70%.
When ventricular contraction is impaired, the volume of ejected blood is REDUCED, and
so is the value of the ejection fraction.
In systolic heart failure, it drops below 40%.
In DIASTOLIC heart failure, the ventricle is filled with LESS blood.
This may be because it is smaller than usual, or it has lost the ability to relax.
The ejection fraction may be normal, but the blood output is reduced.
The ejection fraction is therefore commonly used to differentiate between SYSTOLIC and
DIASTOLIC dysfunction.
Examples of conditions that can lead to diastolic heart failure include:
- Hypertrophic cardiomyopathy: the heart muscle grows thicker than usual, leaving LESS room
for blood filling.
- Restrictive cardiomyopathy: the heart muscle becomes rigid, unable to stretch.
- Hypertension can also cause diastolic dysfunction INdirectly, via compensation mechanisms.
As higher systemic pressures make it more difficult for the ventricle to pump, the heart
compensates by growing thicker muscle to try harder.
Larger muscle means REDUCED space for blood filling.
Regardless of being systolic or diastolic in nature, left-sided heart failures share
a common outcome: LESS blood pumped out from the heart.
As a result, blood flows back to the lungs, where it came from, causing CONGESTION and
INCREASED pulmonary pressure.
As this happens, fluid leaks from the blood vessels into the lung tissue, resulting in
PULMONARY EDEMA, a hallmark of left-sided heart failure.
Accumulation of fluid in the alveoli IMPEDES the gas exchange process, resulting in respiratory
symptoms such as shortness of breath, which worsens when lying down, and chest crackles.
RIGHT-sided heart failure is most commonly caused by LEFT-sided heart failure.
This is because the INCREASED pulmonary pressure caused by left-sided heart failure makes it
harder for the right ventricle to pump INTO the pulmonary artery.
This results in SYSTOLIC dysfunction.
In compensation, the right ventricle grows thicker to pump harder, which reduces the
space available for filling, eventually leading to DIASTOLIC dysfunction.
Other common causes of right-sided heart failure include chronic lung diseases which also raise
pulmonary blood pressure.
As the right ventricle pumps out less blood, the blood, again, backs up to where it came
from, and in this case, the SYSTEMIC circulation.
This results in abnormal fluid accumulation in various organs, most notable in the feet
when standing, sacral area when lying down, abdominal cavity and liver.
The fluid status can be assessed by examining the distension level of the jugular vein.
Heart failure is usually managed by treating the underlying condition, together with a
combination of drugs.
ACE inhibitors, beta blockers are used to reduce blood pressure in patients with systolic
dysfunction.
Diuretics are used to reduce water retention.