What is heart failure?
When the left ventricular muscle is damaged and not able to pump efficiently, then the systemic blood pressure and cardiac out put fall. This is compensated for by an increase in the heart rate in order to try to increase the cardiac output back to normal. Renal blood flow is decreased and this triggers the release of hormones which are designed to force up the blood pressure by causing vasoconstriction of the systemic arteries and by causing the kidneys to retain sodium and water. One of the side effects of this is fluid retention. If the left ventricle is unable to pump blood forward it tends to dam back into the filling chamber (the left atrium) and prevents the forward flow of blood returning from the lungs. The blood pressure in the lungs increases and they become congested resulting in breathlessness. Eventually the right ventricle becomes compromised as it has to generate a higher pressure in order to counter-act the damming back effect from the left. This results in congestive cardiac or bi-ventricular failure.
What are the symptoms of heart failure?
The symptoms of heart failure relate to both poor cardiac output (fatigue, tiredness) as blood supply to exercising skeletal muscles is reduced, and to lung congestion (breathlessness). This of often worse when lying down (called orthopnoea) and may cause breathlessness at night forcing a wakening from sleep (paroxysmal nocturnal dyspnoea). Congestion of the liver causes nausea and anorexia.The signs of heart failure are tachycardia, relatively low systemic blood pressure, high venous filling pressure (raised jugular venous pressure) and pitting oedema of the ankles and progressively up the legs. The heart enlarges as it has to accommodate a larger residual volume because the ejection fraction falls, and this results in stretching of the valve rings making them leak. Thus, systolic murmurs may be heard of functional tricuspid and mitral incompetence. Extra heart sounds (third and fourth) may also be heard illustrating that the heart is struggling to work properly.
These events and effects occur in all causes of heart failure.
Acute left ventricular failure causes a sudden onset of marked breathlessness from pulmonary oedema, low blood pressure and reactive tachycardia. Right sided chambers are normal initially and only deteriorate after some time.
What are the causes of heart failure?
The commonest cause is damage to the heart muscle from myocardial infarction or heart attack. However, long standing and poorly controlled hypertension will cause heart failure. Problems with the heart valves also result in heart failure (see below). Occasionally the heart muscle is damaged by viruses or toxins like too much alcohol, and some people are born with a genetic tendency to develop early heart failure.