Heart diseases

Epidemiology

So what is heart disease? Cardiovascular disease (heart diseases) is a class of diseases which include the heart or blood vessels (arteries and veins) with similar symptoms where many of them are related to atherosclerosis. Around 90% of them are preventable and that prevention should begin at an early age because vascular damages are accumulating since the adolescence while some are inherited and are manifested early in life.

Heart diseases represent the number one cause of death in the world surpassing cancer, chronic obstructive pulmonary disease, and lower respiratory infections. While the prevalence in high-income countries is decreasing, the number of deaths caused by them is growing rapidly in low and middle-income countries. They are taking the lives of approximately 18 million people every year, which makes around the 30% of all deaths, and it is estimated that this number will go up to 23 million of deaths each year by the year of 2030. More than 75% of these deaths happen in low and middle-income countries, and 85% of all cardiovascular disease-related deaths are caused by myocardial infarction and cerebrovascular infarction (heart attack and stroke). It has been noticed that the cardiovascular risk in women has increased in the last few decades.

How does the heart work?

The heart is a central organ in the cardiovascular system located in the center of your chest between the lungs, and its function is to deliver the oxygen and nutrition rich blood to all other organs and tissues in your body. It is made of four chambers, left and right atria, and left and right ventricles. The heart valves are keeping the blood to flow in one direction through the atria to ventricles, and through the ventricles to the aorta and pulmonary trunk (arteries), assuring that there is no backflow. The heart has an electrical activity on its own, and it’s keeping a certain rhythm in pumping the blood. The oxygen-depleted blood comes into the right atrium which accepts it through the superior and inferior venae cavae (veins) and passes it to the right ventricle which then pumps it into pulmonary tract where when in lungs it exchanges the gasses renewing the oxygen, and eliminating the carbon dioxide. The oxygenated blood then comes into the left atrium via the pulmonary vein, and it’s being sent by the left ventricle to other tissues and organs through the aorta where it can be used. The oxygen is made into carbon dioxide when it’s used in tissues after what the cycle repeats. Heartbeat is also a cycle. It consists of two parts including the systole and the diastole. In systole, the ventricle contracts forcing the blood out of the heart into the lungs and system circulation, while during the diastole the heart relaxes, and is letting the ventricles to be filled with blood delivered to atrial chambers.

The heart possesses a very strong and rich innervation of the sympathetic nervous system

It has β1 receptors  which are responsible for:

+ inotropic effect (the power of heart contractions)

+ chronotropic effect (the frequency of heart contractions)

+ dromotropic effect (conduction speed of electrical impulses)

+ bathmotropic effect (excitability of the heart)

The cardiac output is the volume of blood which the heart pumps per one minute, and it is measured by multiplying the stroke volume (volume of blood pumped from the left ventricle per heartbeat) with the heart rate (the number of contractions per minute).

The sympathetic nervous system is ”forcing” the heart to beat. SA node (Sinoatrial node) is a group of cells located near the confluence of venae cavae, and it functions as a pacemaker because it generates the electrical impulses. The parasympathetic nervous system also affects the SA node, but contrary to the sympathetic nervous system it slows down the heartbeat, decreases the frequency so the heart is pumping less blood into circulation. The cells in the Sinoatrial node are in continual activity, with no relaxed state, that is why the heart is the only muscle in your body that is always working even when you’re resting. If a cell is stimulated with enough power, a sudden change in membrane potential occur which leads to an action potential. This is a physiological process in which the potential of membrane first depolarize then repolarize, that potential expands through the heart, and causes the heart contractions.

Types of heart diseases

Heart disease is a broad concept, and it includes various diseases related to heart, common categories are:

  • vascular diseases (Coronary artery disease, Cerebrovascular disease, Peripheral arterial disease, Renal artery stenosis, Aortic aneurysm)
  • Heart rhythm disorders (arrhythmia)
  • Heart failure, pulmonary heart disease
  • Heart valve abnormalities
  • Cardiomyopathy
  • Congenital heart disease
  • Rheumatic heart disease
  • Inflammation in the heart

Coronary artery disease

Coronary artery disease is a condition when the endothelial artery tissue loses its function and becomes narrow. The plaque inside the arteries is made, and it interferes with the normal blood circulation. Long-term damage that has been made over the years by cholesterol, diabetes, high blood pressure, or smoking is causing the inflammation and the collection of fat deposits inside the arteries. The blood vessel with an atherosclerotic plaque in itself can’t supply the organ which it is supposed to. Patients can feel this as a dull pain in the chest, and that condition is called angina pectoris. The heart muscle which is inadequately supplied with oxygen may lead to heart failure. If the part of the plaque is torn, a thrombus, which can completely stop a blood supply is made causing a deficiency of oxygen and nutrient substances. This could later evolve into myocardial infarction (heart attack) if it stops the flow in the coronary arteries (heart arteries).

Cerebrovascular disease

Cerebrovascular disease includes various problems that are involved with blood vessels responsible for blood supply of a brain. The main cause is similar to coronary artery disease, atherosclerosis with a difference of location of the stenosis. If arteries have decreased blood flow, smaller blood vessels may completely stop to transfer blood. The brain tissue is not well supplied, and that leads to ischemic stroke (due to insufficient oxygen supply). This may also appear if a thrombus (part of atherosclerotic plaque) or some other particle (embolus) obstruct a blood vessel, and stop the blood circulation. Another type of stroke is called hemorrhagic stroke, and it is related to arterial damage that has been done over the years which causes them to break and initiate bleeding.

Peripheral arterial disease

Peripheral arterial disease includes all acute or chronic disorders in blood supplying which aren’t related to brain or heart supply most commonly noticeable in legs. The main cause for this disorder is atherosclerosis, other inflammations of endothelial tissue, thrombosis or embolism. Due to smoking, hypertension, or diabetes, this process is accelerated and can lead to complications such as heavy gangrene which may outgrow from chronic ischemia, and induce amputation of an ischemic organ.

Renal artery stenosis

This condition is caused by atherosclerosis of renal arteries or fibromuscular dysplasia where the arterial muscle has an unrestricted grown. Renal arteries may have constricted sections intermittently with dilated parts giving it a look of caps on blood vessels. They can be so narrowed down, inducing kidney damage. It can appear on one or both kidneys which can affect the severity of a disease. It is not concluded what does really cause this disorder but it is recognized that it is generally more common in women. This condition can induce renovascular hypertension, kidney failure which requires dialysis, and a fluid stagnation in legs or lungs.

Aortic aneurysm

An aneurysm is a state of blood vessel weakness where a blood vessel is bulging. It can be diffused or localized in one spot giving it a look of a balloon. Aorta is the biggest arterial blood vessel in the human body starting directly from the heart. The most common aneurysm is atherosclerosis on descending part of the aorta. When all of the blood vessel layers are widened the real aneurysm is presented, opposed to the expansion of individual layers which is called pseudoaneurysm. The weakness on an aneurystic wall can break up leading to aortic rupture which is a life-threatening surgical emergency.

Heart rhythm disorders

An arrhythmia is a group of conditions including the irregular heartbeat, which can manifest itself through an individual extrasystole (irregular heartbeats originally from atria or ventricles) or the absolute arrhythmia which comes from atria. Because the heart doesn’t work normally the body is suffering, besides that, the heart is straining itself, and it can develop severe damage to the heart muscle that may weaken its function. Heart rhythm disorders are divided into two large groups. One is bradycardia which represents the slow heart rate <60 bpm (beats per minute) while the other one is called tachycardia, and that is a fast heartbeat>100 bpm. The most important complications are a heart attack, a stroke or a heart failure.

Heart failure

Heart failure is a special heart condition whereas the heart muscle is weakened, and had lost its function to supply the whole organism with oxygen and nutrition rich blood. Various reasons can lead to this but most of them are preventable. An acute form is much more dangerous than the chronic one, and it has a larger mortality rate. Sometimes this condition is mistaken with respiratory diseases because its main symptoms are related to lungs. Shortness of breath, troubled breathing at night, and coughing are induced by stagnation of fluids in lungs. Heart failure is classified into four stages divided by physical ability.

Pulmonary heart disease

Pulmonary heart disease is a type of heart failure where the right ventricle is enlarged in response to high blood pressure or other stenoses in the lungs. It affects the circulatory system back into the systemic venous system causing jaundice, enlargement of the liver, high kidney blood pressure, cyanosis or swelling of abdomen, legs, and feet. Also known as cor pulmonale it is treated by diuretics and vasodilators used to decrease a strain on the heart muscle, and anticoagulants if embolism is presented.

Heart valve abnormalities

These type of abnormalities include one or more heart valves which cause the disturbance in their vent function (a backflow or disrupted blood passing). Because the heart is strained extensively, the damage on valves is increasing, and after some time the heart enlarges and develops heart failure. Heart valve abnormalities may be due to stenosis (valve narrowing) or insufficiency/regurgitation. This condition may evolve through the time or is genetically inherited. The most common cause is rheumatic acute fever, tumors, endocarditis or autoimmune diseases.

Cardiomyopathy

Cardiomyopathy is any structural or functional heart disease of idiopathic (unsure) origin which isn’t preceded by autoimmune, infectious or inflammatory heart disease. People with this condition are often candidates for transplantation. A most common classification is the structural one, divided into 4 divisions (dilated, hypertrophic, restrictive, and arrhythmogenic right ventricular dysplasia). The pump function is restricted, and the body is affected similarly to heart failure. Main complications are heart failure, arrhythmia, sudden death, thrombosis or embolism.

Congenital heart disease

Congenital heart diseases are inborn heart anomalies developed during the embryonic stage in 1 of 120 live-born children which are sometimes trivial and spontaneously cured. Thanks to the progress in medicine they can be treated in approximately 90% times if the operation is done at the right time. In most cases, the cure is guaranteed as well as the normal life. These conditions are often divided into abnormalities without cyanosis (a purplish discoloration of the skin) when the blood is overflowing from arteries to veins and abnormalities with cyanosis which decreases the saturation of arterial blood.

Rheumatic heart disease

Rheumatic heart disease is the most serious consequence of rheumatic fever which is a disease that develops after 2– 4 weeks after a streptococcal throat infection. It could affect all 3 layers of the heart (endocardium, myocardium, pericardium), and then is called pancarditis. Endocarditis includes heart valves which are being filled with fibrin and denied from their function. Myocarditis is an acute inflammation of the heart muscle. Pericarditis, the heart membrane infection is characterized by chest pain.

Heart inflammation

While all of the heart layers could be affected it is mostly localized in the myocardium. Infectious agents attack the heart muscle and damage it with the myocardial invasion, synthesis of myocardial toxins or by triggering the immune mechanisms. Along the infectious agents (virus, bacteria, protozoa) some pharmacological agents, chemicals, and radiation can be responsible for this infection. Still, most common causes are Coxsackie virus and adenoviruses.