Ishwarya SivakumarHeart failure

Heart Failure

Definition and Epidemiology

Heart failure develops as an outcome of cardiac disease. It can be described as an abnormality of cardiac structure or function causing inadequate systemic perfusion so the delivery of oxygen does not meet the requirements of the metabolizing tissues. Around 68,000 people in the UK are diagnosed with heart failure each year.1

Causes

Coronary heart disease (CHD) is the most common cause of heart failure with about 23,000 people aged less than 75 dying in the UK each year due to CHD.15 In coronary heart disease the arteries that supply the cardiac muscle with oxygen becomes blocked or severely narrowed by the process of atherosclerosis leading to myocardial infarction. CHD weakens the heart overtime and leads to heart failure. Another common cause of heart failure is hypertension.2 Since hypertension increases afterload, there is a rise in preload as more blood stays in the heart after it pumps. The heart will have to work harder to pump blood around the body. To cope with this, the cardiac muscle becomes harder and stiffer which makes the heart inefficient at doing its job. Usually there is an excessively high preload in heart failure.8, 9

Cardiomyopathy is the term used to define any disease of the cardiac muscle that affects the heart’s ability to pump blood with an adequate force.10 There are three types of cardiomyopathies. In congested cardiomyopathy, the left ventricle becomes dilated and weak. Initially, the chambers of the heart respond to this situation by stretching to hold more blood for systemic perfusion. However, this only temporarily strengthens the heart’s contraction.11 Eventually, the cardiac muscle weakens and is unable to pump blood with the force required. In hypertrophic cardiomyopathy the walls of the ventricles become hypertrophied, the affected cardiac muscle may become stiff. Consequently the ventricles may not fill as effortlessly as normal, so less blood is pumped to the body. Restrictive cardiomyopathy inhibits the heart from sufficiently filling with blood before contracting due to a loss of elasticity. This leads to heart failure. The types of arrhythmia that can lead to heart failure include bradycardia and tachycardia. Bradycardia is when the heart beats at an abnormally slow rate resulting in a low cardiac output that can consequently lead to heart failure.13 Tachycardia is when the heart rhythm is too fast or irregular. The heart rate ranges from 100 beats per minute to 400 beats per minute. The heart will not be able to pump oxygenated blood sufficiently at such high rates.14

Figure 1

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Ishwarya SivakumarHeart failure

Other factors such as alcohol intake, smoking, valve regurgitation, valve stenosis and genes can also increase the chances of heart failure.

Signs and symptoms

Many symptoms of heart failure are linked to the congestion that develops due to the transudation of plasma into alveolar spaces (pulmonary edema). This occurs as a result of the redistribution of blood, which causes an increase in venous blood pressure in the lungs.2 The plasma reduces oxygen movement through the lungs and leads to dyspnea. Other symptoms occur due to insufficient systemic perfusion so not enough oxygenated blood reaches the metabolizing tissues.4 Some of the main symptoms of heart failure can be seen in figure 2.

If right-sided heart failure occurs, the right ventricle loses its ability to pump causing blood congestion in the systemic circulation. The congestion affects the liver, gastrointestinal tract, limbs and lungs causing fatigue, fluid build-up in the feet, ankles, legs and abdomen, liver enlargement, weight gain and dyspnea.

In left-sided heart failure, people experience systolic failure, diastolic failure or both. In systolic heart failure, the heart muscles are unable to contract normally, so not is blood is pumped out of the body. Diastolic heart failure is when the left ventricle cannot fill well. This is because the left ventricle loses the ability to rest properly in between heartbeats.26 Some of the symptoms of left-sided heart failure include fluid congestion in the lungs, dyspnea and fatigue. Orthopnea is also said to occur as the heart condition progresses.

Heart failure is classified into four classes according to the New York Heart Association (NYHA). Descriptions of these four classes would be that35: Class 1 means that there will be no restrictions in the physical activity of the heart failure patient. Class 2 means that there will be a slight restriction to the physical activity of the patients, even normal physical activity causes the patient to experience symptoms of heart failure. Class 3 means that there will be a considerable restriction to the physical activity of the patient and they may only find themselves comfortable when they are resting. Class 4 means that the patient will experience symptoms of heart failure even when they are not taking part in any physical activity. Moreover, their symptoms may increase if they do not rest.

Diagnostic tests are used to reveal whether a person suffers from heart failure. Some of the various tests used to diagnose heart failure are explained below.32 A B-type natriuretic peptide (BNP) blood test can be carried out. When heart failure progresses, the heart secretes BNP due to the changes in pressure. BNP levels are higher in heart failure patients. This highlights that a BNP blood test will reveal whether a person suffers from heart failure. A chest x-ray can be carried out to check for fluid

Figure 2

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Ishwarya SivakumarHeart failure

congestion in the lungs and heart and to see whether the heart is enlarged. An electrocardiogram can be used to determine the heart’s ejection fraction and also check if there is any abnormality in the electrical activity of the heart. An echocardiogram uses ultrasound waves to check blood flow across the valves by the Doppler effect. A stress test is when the pumping of the heart is increased by physical activities or medication to determine whether there are blocked arteries. Other tests include cardiac catheterization and CT coronary angiogram to check if the person has coronary heart disease, which can lead to heart failure.

Prognosis

The prognosis of heart failure is dependent on the health of the patient. However, heart failure prognosis is generally poor with nearly 50% of patients dying within 5 years of being diagnosed.16 Smoking and alcohol intake tend to contribute to early demise in people with heart failure. Some studies have revealed that there are heart failure patients who don’t even live up to their life expectancy28: Despite the prediction that 50% of heart failure patients live for 5 years after diagnosis, studies in Scotland showed that the five-year survival rate only applied to 25% of the population. Furthermore, an American study showed that 54% of heart failure patients died within three days even though they were expected to live for six more months.

Treatment

There is no cure for heart failure. However, there are many treatments that exist to improve the symptoms and/or prognosis of heart failure. The body produces a very powerful peptide hormone called angiotensin II, which causes vasoconstriction, and a subsequent raised blood pressure. Therefore, most heart failure patients are prescribed an angiotensin-converting enzyme (ACE) inhibitor.1 They work by slowing down the activity of the ACE leading to a decline in

the production of angiotensin II. As a result, vasodilation occurs which in turn, lowers blood pressure. This makes it easier for the cardiac muscle to pump blood, as there is an improvement in the oxygen supply/demand ratio. ACE inhibition induces progress in the function of the failing heart by predominantly decreasing the demand for oxygen by reductions in afterload and preload.6, 7

Diuretics work by increasing the volume of urine. Diuretics that are commonly used to treat heart failure include loop diuretics and thiazide diuretics. Different diuretics are said to work at different parts of the kidney tubules; this gives rise to the benefit of being able to use a combination of different diuretics to get the best treatment. Diuretics alleviate symptoms of fluid congestion and lower high blood pressure by eliminating excess sodium and water. The blood pressure reducing effect is increased due to the dilating effect of diuretics on the blood vessels.19 These events reduce the demand of oxygen-rich blood pumped from the heart allowing it to work less hard.

Figure 3

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Ishwarya SivakumarHeart failure

Beta-blockers cause the heart to beat with less force by slowing it down and reducing afterload. This prevents arrhythmias from developing and therefore improves the prognosis of heart failure.20 Digoxin is also a drug used to improve the symptoms of heart failure. Digoxin blocks the sodium-potassium ATPase enzyme subsequently rising the amount of calcium and potassium in heart cells.21 This makes the heart muscle contract more forcefully.22 Consequently, systemic perfusion is more efficient.

If medication isn’t working, surgery may be considered. Coronary angioplasty or coronary artery bypass may be used if the person’s heart failure is caused by coronary heart disease.24 Valve replacements may be considered if valve regurgitation or stenosis is the root cause of heart failure. A cardiac defibrillator can be surgically implanted in the chest to treat arrhythmia and lessen some of the symptoms of heart failure. Despite the advancement in medical and surgical treatments for heart failure, patients continue to move to end-stage failure.23 During this stage, when all other treatments have failed, heart transplantation is used as a last resort given that there is chance of long-term transplantation success.

Possible future direction

Human pluripotent stem cells (human embryonic stem cells or reprogrammed somatic cells) have the ability to generate cardiomyocytes to replace the dead cells and restore cardiac function.25 Figure 4 shows how embryonic stem cells an be derived and examples of the various types of cells it can differentiate into. Cardiomyocytes are heart muscle cells that contract to pump blood out of the ventricles. Researchers have shown that cardiomyocytes derived from human embryonic stem cells can be used to restore cardiac function in non-human primate hearts. They showed

that the intra-cardial transfer of one billion human embryonic stem cells remuscularized a significant amounts of the infarcted monkey heart.17 This suggests that human pluripotent stem cells have a future as potential treatment for heart failure in humans. However, more research has to be done on whether a similar remuscularization of the human heart is likely. Moreover, the use of stem cells can cause controversy. Examples of the issues that would arise from stem cells are that: The long-term effects of using stem cells are still not known. Stem cells involve the usage and destruction of a potential life but using reprogramed somatic cells may not be so controversial but people don’t know if adult stem cells are as effective as embryonic stem cells.

Bibliography

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Figure 4

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Ishwarya SivakumarHeart failure

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