Good day everyone, today we are going to discuss fully on disease of the heart:
After studying this section, you should be able to
- describe the consequences of failure of either or both sides of the heart
- the compensatory mechanisms that occur in heart failure
- explain the causes and consequences of faulty heart valve function
- define the term ischaemic heart disease
- discuss the main conditions associated with ischaemic heart disease
- describe rheumatic heart disease and its effects on cardiac function
- explain the underlying pathophysiology of pericarditis
- describe, with reference to standard ECG trace, the main cardiac arrhythmias
- describe the principal congenital cardiac abnormalities.
Heart (cardiac) failure
The heart is described as failing when the cardiac output is unable to circulate sufficient blood to meet the needs of the body. In mild cases, cardiac output is adequate at rest and becomes inadequate only when tissue needs are increased, e.g. in exercise. Heart failure may affect either side of the heart, but since both sides of the heart are part of one circuit, when one half of the pump begins to fail it frequently leads to increased strain on, and eventual failure of, the other side. The main clinical manifestations depend on which side of the heart is most affected. Left ventricular failure is more common than right, because of the greater workload of the left ventricle.
Compensatory mechanisms in heart failure
In acute heart failure, the body has little time to make compensatory changes, but if the heart fails over a period of time the following changes are likely to occur in an attempt to maintain cardiac output and tissue perfusion, especially of vital organs:
- the cardiac muscle mass increases (hypertrophy), which makes the walls of the chambers thicker
- the heart chambers enlarge
- decreased renal blood flow activates the renin- angiotensin-aldosterone system , which leads to salt and water retention. This increases blood volume and cardiac workload. The direct vasoconstrictor action of angiotensin 2 increases peripheral resistance and puts further strain on the failing heart.
Acute heart failure
If heart failure occurs abruptly, the supply of oxygenated blood to body tissues is suddenly and catastrophically reduced and there is no time for significant compensation to take place. Death may follow if the brain’s vital centres are starved of oxygen. Even if the acute phase is survived, myocardial damage may lead to chronic heart failure. Common causes include:
- myocardial infarction
- pulmonary embolism, blocking blood flow through the pulmonary circulation – the heart fails if it cannot pump hard enough to overcome the obstruction
- life-threatening cardiac arrhythmia, when the pumping action of the heart is badly impaired or stopped
- rupture of a heart chamber or valve cusp, both greatly increase the cardiac effort required to maintain adequate output
- severe malignant hypertension, which greatly increases resistance to blood flow.
Chronic heart failure
This develops gradually and in the early stages there may The no symptoms because compensatory changes occur as described above. When further compensation is not possible, myocardial function gradually declines Underlying cases include degenerative heart changes with advancing age, and many chronic conditions, eg, anaemia, lung disease, hypertension or cardiac disease.
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Right-sided (congestive cardiac) failure
The right ventricle fails when the pressure developed within it by the contracting myocardium is insufficient to push blood through the lungs.
When compensation has reached its limit, and the ventricle can no longer empty completely, the right atrium and venae cavae become congested with blood and this is followed by congestion throughout the venous system. The organs affected first are the liver, spleen and kidneys. Oedema of the limbs and ascites (excess fluid in the peritoneal cavity) usually follow.
This problem may be caused by increased vascular resistance in the lungs or weakness of the myocardium.
Resistance to blood flow through the lungs. When this is increased the right ventricle has more work to do. The two commonest causes are pulmonary embolism and left ventricular failure, when the pulmonary circulation is congested because the left ventricle is not clearing all the blood flowing into it.
Weakness of the myocardium. This is caused by myocardial damage following ischaemia or infarction.
Left-sided (left ventricular) failure
This occurs when the pressure developed in the left ventricle by the contracting myocardium is not enough to force blood into the aorta and the ventricle cannot then pump out all the blood it receives. Causes include ischaemic heart disease, which reduces the efficiency of the myocardium, and hypertension, when the heart’s workload is increased because of raised systemic resistance. Disease of the mitral (left atrioventricular) and/or aortic valves may prevent efficient emptying of the heart chambers, so that myocardial workload is increased.
Failure of the left ventricle leads to dilation of the atrium and an increase in pulmonary blood pressure. This is followed by a rise in the blood pressure in the right side of the heart and eventually systemic venous congestion.
Exercise tolerance becomes progressively reduced as the condition worsens and is accompanied by cough caused by pulmonary oedema. The sufferer is easily tired and is likely to have poorly perfused peripheral tissues and low blood pressure.
Congestion in the lungs leads to pulmonary oedema and dyspnoea, often most severe at night. This paroxysmal nocturnal dyspnoea may be due to raised blood volume as fluid from peripheral oedema is reabsorbed when the patient slips down in bed during sleep.
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Disorders of heart valves
The heart valves prevent backflow of blood in the heart during the cardiac cycle. The mitral and aortic valves are subject to greater pressures than those on the right side and are therefore more susceptible to damage.
Distinctive heart sounds arise when the valves close during the cardiac cycle. Damaged valves generate abnormal heart sounds called murmurs. A severe valve disorder causes heart failure. The most common causes of valve defects are rheumatic fever, fibrosis following inflammation and congenital abnormalities.