Cardiac failure develops when the heart cannot maintain the circulation When the
pumping effort of the heart falls short of sustaining a circulation sufficient for
metabolic needs, cardiac failure is said to have occurred.
Conditions in which the circulation fails because of a low blood volume,
e.g. bleeding or fluid loss, are excluded from this definition.
The main broad groups of conditions causing cardiac failure are those demanding
extra work of the heart (e.g. hypertension, valve diseases) and those
that damage heart muscle (e.g. ischaemia).
Cardiac failure can be either acute or chronic}
Acute cardiac failure takes place when there is a sudden onset of pathology.
There is abrupt failure of chamber emptying, the failing chambers dilate, and
compensatory mechanisms cannot be brought into operation.
Circulatory collapse with low blood pressure is termed 'cardiogenic shock.
Chronic cardiac failure takes place when there is gradual increase in severity
of a disease.
It has a major impact on organ systems other than the heart, and is manifest by
tiredness, breathlessness and development of oedema.
In the face of inadequate circulation,several compensatory responses take place:
• The ventricles of the heart enlarge in size, and contract more effectively.
• Constriction of arterioles causes re-distribution of blood flow.
• Activation of sympathetic and renin-angiotensin systems causes retention of
salt and water, and changes in vascular tone.
• There is desensitization of cardiac muscle to sympathetic stimulation.
Acute on chronic failure may develop when compensatory mechanisms break down.
Failure of the left side of the heart leads to poor systemic arterial perfusion and
increased pressure in the pulmonary venous and capillary system.
When the left heart fails to pump efficiently, the chambers fail to empty completely
at systole and they become dilated.
A dilated chamber is a failing chamber. Incomplete emptying leads to a progressive
rise in pressure in one chamber, which is reflected back into the chamber or vessels
preceding it in the circulation.
In the left heartnthis leads to dilatation of the left atrium, dilatation and
increased pressure in the pulmonary veins and, eventually, to increased pressure
in the pulmonary capillaries.
The high pressure in the pulmonary capillary system forces the fluid component of
blood out into the alveolar air sacs, which become filled with low-protein fluid.
This is manifest clinically as pulmonary oedema, and presents with acute
breathlessness due to fluid in the air sacs.
Another consequence of left heart failure is that insufficient blood is pumped out
into the aorta and arterial system, which leads to hypotension, poor perfusion
of tissues, and poor tissue oxygenation.
Failure of the right side of the heart leads to poor perfusion of the lungs and
increased pressure in the systemic venous system.
As the right side of the heart fails, the chambers dilate and there is increased
intra-chamber pressure, preventing adequate emptying of the systemic venous blood
from the superior vena cava and inferior vena cava into the right atrium.
This rise in systemic venous pressure has a number of clinical manifestations:
• The raised pressure in the superior vena cava can be observed in the neck in the
form of jugular vein engorgement (raised jugular venous pressure).
• The raised pressure in the inferior vena cava is reflected back into the venous
system of the liver and other organs,and may manifest as a tender, enlarged,
congested liver, palpable beneath the right costal margin.
• The raised pressure in the small venules and capillaries of the lower limb,
supplemented by the effect of gravity,eads to increased pressure in the lumen
of these small vessels, with transudation of fluid into the interstitial
tissues producing subcutaneous oedema, particularly around the ankles.
Congestive cardiac failure is failure of both the right and the left side of the heart
Failure of both sides of the heart is termed 'congestive cardiac failure'.
Biventricular failure most commonly arises when there is right heart failure
secondary to pulmonary capillary congestion as a result of primary left heart failure.
When left heart failure is long-standing and severe, the back pressure effects cause
permanent congestion and increased pressure in the pulmonary capillary system.
This gives rise to increased back pressure in the pulmonary arterial system,
which leads to right heart failure as a result of the right heart having to
pump against an increased peripheral resistance.
Congestive cardiac failure may also be caused by unusual diseases that simultaneously
affect the muscle of both ventricles.
Congested liver - right heart failure
Chronic passive venous congestion of the liver causes dark areas where centrilobular
zones are congested by blood, contrasting with pale periportal areas.
This appearance is similar to that of the cut surface of a nutmeg, hence the
term 'nutmeg liver'.