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.
