Congenital Heart Defects
A congenital heart defect is a defect in the structure of the heart and great vessels that is present at birth.
Describe congenital heart defects and their causes
- Many types of heart defects exist, most of which either obstruct blood flow in the heart or vessels near it, or cause blood to flow through the heart in an abnormal pattern. Other defects, such as long QT syndrome, affect the heart’s rhythm.
- Heart defects are among the most common birth defects and are the leading cause of birth defect-related deaths.
- There is a complex sequence of events that result in a well formed heart at birth and disruption of any portion may result in a defect: the orderly timing of cell growth, cell migration, and programmed cell death (apoptosis).
- The cause of congenital heart disease may be either genetic or environmental, but is usually a combination of both.
- Ventricular septal defects are collectively the most common type of congenital defect, although approximately 30% of adults have a type of atrial septal defect called probe patent foramen ovale.
- Some children with congenital heart defects have no signs while others may exhibit shortness of breath, cyanosis, syncope, heart murmur, under-developing of limbs and muscles, poor feeding or growth, or respiratory infections.
- hypoplasia: Underdevelopment or incomplete development of a tissue or organ, especially when caused by an inadequate or below-normal number of cells.
- cyanosis: A blue discoloration of the skin due to the circulation of blood low in oxygen.
- long QT syndrome: A heart disease in which there is an abnormally long delay between the electrical excitation (or depolarization) and relaxation (repolarization) of the ventricles of the heart.
A congenital heart defect is a defect in the structure of the heart and great vessels that is present at birth. Many types of heart defects exist, most of which either obstruct blood flow in the heart or vessels near it or cause blood to flow through the heart in an abnormal pattern. Other defects, such as long QT syndrome, affect the heart’s rhythm. Heart defects are among the most common birth defects and are the leading cause of birth defect-related deaths. Approximately nine people in 1,000 are born with a congenital heart defect. Many defects do not require treatment, but some complex congenital heart defects require medication or surgery.
Signs and Symptoms
Signs and symptoms are related to the type and severity of the heart defect. Some children have no signs while others may exhibit shortness of breath, cyanosis, syncope, heart murmur, under-developing of limbs and muscles, poor feeding or growth, or respiratory infections. Congenital heart defects cause abnormal heart structure resulting in production of certain sounds called heart murmur. These can sometimes be detected by auscultation; however, not all heart murmurs are caused by congenital heart defects.
Causes of Heart Defects
There is a complex sequence of events that result in a well formed heart at birth and disruption of any portion may result in a defect. The orderly timing of cell growth, cell migration, and programmed cell death (apoptosis) has been studied extensively and the genes that control the process are being elucidated. In the fetus, the lungs are unexpanded and cannot accommodate the full circulatory volume. Cells in part of the septum primum die creating a hole while muscle cells, the septum secundum, grow along the right atrial side the septum primum, except for one region, leaving a gap, the foramen ovale, through which blood can pass from the right artium to the left atrium, circumventing the pulmonary circuit. A small vessel, the ductus arteriosus allows blood from the pulmonary artery to pass to the aorta. Defects in any of these structures are associated with an increased incidence of other symptoms, together referred to as VACTERL association: V – Vertebral anomalies, A – Anal atresia, C – Cardiovascular anomalies, T – Tracheoesophageal fistula, E – Esophageal atresia, R – Renal (Kidney), and/or radial anomalies, L – Limb defects.
Most of the known causes of congenital heart disease are sporadic genetic changes, either focal mutations or deletion or addition of segments of DNA. Small chromosomal abnormalities also frequently lead to congenital heart disease. The genes regulating the complex developmental sequence have only been partly elucidated. Some genes are associated with specific defects. Mutations of a heart muscle protein, α-myosin heavy chain (MYH6) are associated with atrial and septal defects. Several proteins that interact with MYH6 are also associated with cardiac defects. Another factor, the homeobox (developmental) gene, NKX2-5 also interacts with MYH6. Mutations of all these proteins are associated with both atrial and ventricular septal defects.
Known antenatal environmental factors that may lead to congenital heart defects include maternal infections (Rubella), drugs (alcohol, hydantoin, lithium, and thalidomide), and maternal illness (diabetes mellitus, phenylketonuria, and systemic lupus erythematosus). As noted in several studies following similar body mass index (BMI) ranges, prepregnant and gestating women, who were obese (BMI ≥ 30), carried a statistically significant risk of birthing children with congenital heart defects (CHD) compared to normal-weight women (BMI = 19-24.9). Although there are minor conflicting reports, there was significant support for the risk of fetal CHD development in overweight mothers (BMI = 25-29.9).
Hypoplasia can affect the heart, typically resulting in the underdevelopment of the right ventricle or the left ventricle. This results in only one side of the heart capable of pumping blood to the body and lungs effectively. Hypoplasia of the heart is rare, but is the most serious form of CHD. It is called hypoplastic left heart syndrome when it affects the left side of the heart and hypoplastic right heart syndrome when it affects the right side of the heart. In both conditions, emergency heart surgery will permit blood to circulate to the body (or lungs, depending on which side of the heart is defective). Hypoplasia of the heart is generally a cyanotic heart defect.
Sometimes CHD improves without treatment. Other defects are so small that they do not require any treatment. Most of the time, CHD is serious and requires surgery and/or medications. Medications include diuretics, which aid the body in eliminating water, salts, and digoxin for strengthening the contraction of the heart. This slows the heartbeat and removes some fluid from tissues. Interventional cardiology now offers patients minimally invasive alternatives to surgery. Most patients require life-long specialized cardiac care, first with a pediatric cardiologist and later with and adult congenital cardiologist. There are more than 1.8 million adults living with congenital heart defects.
Myocarditis and Endocarditis
Endocarditis and myocarditis are driven by inflammation of the heart.
Distinguish between myocarditis and endocarditis and their effects on the heart
- Inflammation of the inner layer of the heart wall, the endocardium, often including the heart valves, is called endocarditis.
- Endocarditis may be infective or non-infective. Diagnosis of endocarditis includes clinical identification of the vegetation, echocardiogram, and blood cultures to demonstrate the infective microorganisms involved in infective endocarditis.
- In subacute infective endocarditis, the vegetation may include granulomatous tissue which can become fibrotic or calcify.
- In non-infective endocarditis such as nonbacterial thrombic endocarditis (NBTE), also called marantic endocarditis, vegetations are typically small and sterile (do not contain microorganisms) and typically do not engender an inflammatory response.
- Inflammation of the myocardium, the heart muscle, is called myocarditis, typically characterized by infection of the heart, an inflammatory infiltrate, and heart muscle damage with or without necrosis (tissue death).
- Myocarditis most commonly has an infectious cause, such as the parovirus B19, lyme disease, or other viral and nonviral pathogens, but may also be an autoimmune reaction.
- inflammation: A condition of any part of the body, consisting in congestion of the blood vessels, with obstruction of the blood current, and growth of morbid tissue. It is manifested outwardly by redness and swelling, attended with heat and pain.
Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves (native or prosthetic valves). Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or even on intracardiac devices.
Endocarditis is characterized by a prototypic lesion, the vegetation, which is a mass of platelets, fibrin, microcolonies of microorganisms, and scant inﬂammatory cells. In the subacute form of infective endocarditis, the vegetation may also include a center of granulomatous tissue, which may fibrose or calcify.
Classification and Diagnosis
There are multiple ways to classify endocarditis. The simplest classification is based on etiology: either infective or non-infective, depending on whether a microorganism is the source of the inflammation or not. Regardless, diagnosis of endocarditis is based on the clinical features, investigations such as echocardiogram, as well as any blood cultures demonstrating the presence of endocarditis-causing microorganisms.
Since the valves of the heart do not receive any dedicated blood supply, defensive immune mechanisms (such as white blood cells) cannot directly reach the valves via the bloodstream. If an organism (such as bacteria) attaches to a valve surface and forms a vegetation, the host immune response is blunted. The lack of blood supply to the valves also has implications on treatment, since drugs also have difficulty reaching the infected valve. Normally, blood flows smoothly through these valves. If they have been damaged (from rheumatic fever, for example) the risk of bacteria attachment is increased.
Types of Endocarditis
Nonbacterial thrombic endocarditis (NBTE) or marantic endocarditis is most commonly found on previously undamaged valves. As opposed to infective endocarditis, the vegetations in NBTE are small, sterile, and tend to aggregate along the edges of the valve or the cusps. Also unlike infective endocarditis, NBTE does not cause an inflammation response from the body. NBTE usually occurs during a hypercoagulable state such as system wide bacterial infection, or pregnancy, though it is also sometimes seen in patients with venous catheters.
Another form of sterile endocarditis is termed Libman-Sacks endocarditis; this form occurs more often in patients with lupus erythematosus and is thought to be due to the deposition of immune complexes. Like NBTE, Libman-Sacks endocarditis involves small vegetations, while infective endocarditis is composed of large vegetations. These immune complexes precipitate an inflammation reaction, which helps to differentiate it from NBTE. Also unlike NBTE, Libman-Sacks endocarditis does not seem to have a preferred location of deposition and may form on the undersurfaces of the valves or even on the endocardium.
Myocarditis or inflammatory cardiomyopathy is inflammation of heart muscle (myocardium). Myocarditis is most often due to infection by common viruses, such as parvovirus B19, less commonly nonviral pathogens such as Borrelia burgdorferi (Lyme disease) or Trypanosoma cruzi, or as a hypersensitivity response to drugs.
Myocarditis is often an autoimmune reaction. Streptococcal M protein and coxsackievirus B have regions (epitopes) that are immunologically similar to cardiac myosin. After the virus is gone, the immune system may attack cardiac myosin.
Symptoms and Outcomes
The consequences of myocarditis thus also vary widely. It can cause a mild disease without any symptoms that resolves itself, or it may cause chest pain, heart failure, or sudden death. An acute myocardial infarction-like syndrome with normal coronary arteries has a good prognosis. Heart failure, even with dilated left ventricle, may have a good prognosis. Ventricular arrhythmias and high-degree heart block have a poor prognosis. Loss of right ventricular function is a strong predictor of death.
Symptoms in infants and toddlers tend to be more nonspecific, with generalized malaise, poor appetite, abdominal pain, and/or chronic cough. Later stages of the illness will present with respiratory symptoms with increased work of breathing and is often mistaken for asthma.
Since myocarditis is often due to a viral illness, many patients give a history of symptoms consistent with a recent viral infection, including fever, rash, diarrhea, joint pains, and easy fatigueability.
A large number of causes of myocarditis have been identified, but often a cause cannot be found. In Europe and North America, viruses are common culprits. Worldwide, however, the most common cause is Chagas’ disease, an illness endemic to Central and South America that is due to infection by the protozoan Trypanosoma cruzi.
Myocardial Ischemia and Infarction
Ischemic heart disease is caused by reduced blood flow to the heart muscle, usually due to atherosclerosis, and can lead to a heart attack.
Distinguish between the effects of myocardial ischemia and infarction on the heart
- Ischemic heart disease (IHD), or myocardial ischaemia, is a disease characterized by ischaemia, or, reduced blood supply, to the heart muscle, usually due to coronary artery disease and myocardial infarction.
- Coronary artery disease is the narrowing of the heart arteries due to atherosclerosis, the deposition of fat on the walls. If these deposits come loose, they can cause a clot that will block blood flow to the heart muscle, causing a myocardial infarction.
- Symptoms of stable ischemic heart disease include angina, which is characteristic chest pain on exertion, and decreased exercise tolerance. Symptoms of myocardial infarction include acute chest pain, shortness of breath, nausea, vomiting, palpitations, sweating, and/or anxiety.
- Treatment of IHD is dependent on the underlying disease. Stable IHD may be treated with anti-angina drugs. Treatments for myocardial infarction include coronary angioplasty, treatment with “clot buster” medications, and coronary bypass, where blocked heart blood vessels are replaced.
- The phrase “heart attack” is sometimes used incorrectly to describe sudden cardiac death, which may or may not be the result of acute myocardial infarction.
- angioplasty: The mechanical widening of a narrowed or totally obstructed blood vessel generally caused by atheroma.
- ischemia: Local disturbance in blood circulation due to mechanical obstruction of the blood supply, such as by a narrowed artery or clot.
- angiography: A medical imaging technique in which an x-ray image is taken to visualize the inside of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers.
Ischemic heart disease (IHD), or myocardial ischaemia, is a disease characterized by ischaemia, or reduced blood supply to the heart muscle, usually due to coronary artery disease and myocardial infarction. Coronary artery disease is the narrowing of the heart arteries due to atherosclerosis, the deposition of fat on the walls. If these deposits come loose, they can cause a clot that will block blood flow to the heart muscle, causing a myocardial infarction. The risk increases with age, smoking, high cholesterol levels, diabetes, and high blood pressure, and is more common in men and those who have close relatives with ischaemic heart disease and a history of myocardial infarction. It is the most common cause of death in most western countries, and a major cause of hospital admissions.
Symptoms of stable ischemic heart disease include angina, which is characteristic chest pain on exertion, and decreased exercise tolerance.
Ischaemic heart disease may be present with any of the following problems:
- Angina—chest pain on exertion, in cold weather or emotional situations
- Acute chest pain—acute coronary syndrome, unstable angina or myocardial infarction
- Heart failure—difficulty in breathing or swelling of the extremities due to weakness of the heart muscle
Ischemic heart disease is typically associated with an underlying specific heart disease.
In “stable” angina, chest pain with typical features occurs at predictable levels of exertion. Various forms of cardiac stress tests may be used to induce both symptoms and detect changes with electrocardiography (EKG), echocardiography (using ultrasound of the heart), or scintigraphy (using a radioactive marker to examine blood uptake by the heart muscle). If part of the heart seems to receive an insufficient blood supply, coronary angiography may be used to identify narrowing of the coronary arteries and suitability for angioplasty or bypass surgery.
Diagnosis of acute coronary syndrome and myocardial infarction generally take place in the emergency department when a patient presents with acute chest pain, combined with shortness of breath, nausea, vomiting, palpitations, sweating, and/or anxiety. An EKG is performed, looking for changes that are characteristic of a myocardial infarction. In the absence of these characteristic markers, heart damage is detected by cardiac markers in the blood that identify heart muscle damage. If there is no evidence of damage or infarction, a diagnosis of “unstable angina” is given. Depending on the risk assessment, stress testing or angiography may be used to identify coronary artery disease in these patients.
In patients with heart failure, stress testing or coronary angiography may be performed to identify and treat underlying coronary artery disease.
The disease process underlying most ischemic heart disease is atherosclerosis of the coronary arteries, which decreases blood flow to the heart muscle. Atherosclerosis is the thickening of the artery wall as a result of plaque formation, which is the accumulation of fatty materials such as cholesterol. Atherosclerosis reduces blood flow to the heart muscle, causing ischemia. When these plaques weaken, they can develops a tear, which forms blood clot that obstructs blood flow, causing a myocardial infarction.
Treatment of ischemic heart disease is dependent on the underlying disease process. In stable IHD, antianginal drugs may be used to reduce the rate of occurrence and severity of angina attacks. Treatments for acute coronary syndrome and myocardial infarction include coronary angioplasty, treatment with thrombolysis “clot buster” medication, and coronary bypass, where narrowed blood vessels on the heart are replaced.
Various treatments are offered in people deemed to be at high risk of coronary artery disease. These include control of cholesterol levels in those with known high cholesterol, smoking cessation, and control of high blood pressure.
Cardiac arrhythmia (irregular heartbeat) are a heterogeneous group of conditions involving abnormal electrical activity in the heart.
Describe what are cardiac arrhythmias
- Some arrhythmias are life -threatening medical emergencies that can result in cardiac arrest. Others cause symptoms such as an abnormal awareness of heart beat (palpitations), and may be merely uncomfortable.
- The term cardiac arrhythmia covers a very large number of very different conditions. The most common symptom of arrhythmia is an abnormal awareness of heartbeat, called palpitations.
- Automaticity refers to a cardiac muscle cell firing off an impulse on its own. All of the cells in the heart have the ability to initiate an action potential; however, only some are designed to routinely trigger heart beats. These cells are found in the conduction system of the heart.
- Ventricular fibrillation is imminently life-threatening. Atrial fibrillation is not typically a medical emergency.
- Arrhythmia may be classified by rate (normal, tachycardia, bradycardia) or mechanism (automaticity, reentry, fibrillation). It is also appropriate to classify by site of origin.
- Causes of SADS in young people include viral myocarditis, long QT syndrome, Brugada syndrome, Catecholaminergic polymorphic ventricular tachycardia, hypertrophic cardiomyopathy, and arrhythmogenic right ventricular dysplasia.
- automaticity: The ability of the heart muscles to contract independently of each other when separated or in unison when reattached in whole or in groups.
- supraventricular tachycardia: Any rapid heart rhythm originating at or above the atrioventricular node.
- Cardiac arrhythmia (irregular heartbeat): A large and heterogeneous group of conditions in which there is abnormal electrical activity in the heart.
Cardiac arrhythmia (irregular heartbeat) is any of a large and heterogeneous group of conditions in which there is abnormal electrical activity in the heart. The heartbeat may be too fast or too slow and may be regular or irregular. Some arrhythmias are life-threatening medical emergencies that can result in cardiac arrest. Others cause symptoms such as an abnormal awareness of heartbeat (palpitations) and may be merely uncomfortable. These palpitations have also been known to be caused by atrial/ventricular fibrillation, wire faults, and other technical or mechanical issues in cardiac pacemakers/defibrillators. Still others may not be associated with any symptoms at all, but may predispose the patient to potentially life threatening stroke or embolism. SADS, or sudden arrhythmic death syndrome, is a term (as part of sudden unexpected death syndrome) used to describe sudden death due to cardiac arrest brought on by an arrhythmia in the absence of any structural heart disease on autopsy.
The Conduction System
Automaticity refers to a cardiac muscle cell firing off an impulse on its own. All of the cells in the heart have the ability to initiate an action potential; however, only some of these cells are designed to routinely trigger heart beats. These cells are found in the conduction system of the heart and include the SA node, AV node, Bundle of His, and Purkinje fibers. The sinoatrial node is a single specialized location in the atrium which has a higher automaticity (a faster pacemaker) than the rest of the heart and, therefore, is usually responsible for setting the heart rate and initiating each heart beat.
In normal electrical activity, each heart beat originates as an electrical impulse from a small area of tissue in the right atrium of the heart called the sinus node or sino-atrial node or SA node. The impulse initially causes both atria to contract, then activates the atrioventricular (or AV) node which is normally the only electrical connection between the atria and the ventricles (main pumping chambers). The impulse then spreads through both ventricles causing a synchronized contraction of the heart muscle and, thus, the pulse. In adults the normal resting heart rate ranges from 60 to 80 beats per minute. The resting heart rate in children is much faster. A slow rhythm (less than 60 beats/min), is labeled bradycardia. This may be caused by a slowed signal from the sinus node (sinus bradycardia), a pause in the normal activity of the sinus node (sinus arrest), or by blocking of the electrical impulse on its way from the atria to the ventricles (AV block or heart block). Heart block comes in varying degrees and severity. Bradycardias may be present in the normally functioning heart of endurance athletes or other well-conditioned persons.
Arrhythmia may be classified by rate (normal, tachycardia, bradycardia), or mechanism (automaticity, reentry, fibrillation). It is also appropriate to classify by site of origin. Arrhythmias with atrial origin include: Premature Atrial Contractions (PACs), Wandering Atrial Pacemaker, Atrial flutter, and Atrial fibrillation (Afib). Arrhythmias arising at the junction: Supraventricular tachycardia (SVT), Junctional rhythm, and Junctional tachycardia. Arrythmias arising from pathologies at the AV node (AV blocks): First degree heart block, which manifests as PR prolongation, Second degree heart block, and Third degree heart block, also known as complete heart block.
When an entire chamber of the heart is involved in a multiple micro-reentry circuits and, therefore, quivering with chaotic electrical impulses, it is said to be in fibrillation. Fibrillation can affect the atrium (atrial fibrillation) or the ventricle (ventricular fibrillation); ventricular fibrillation is imminently life-threatening. Atrial fibrillation affects the upper chambers of the heart, known as the atria. Atrial fibrillation may be due to serious underlying medical conditions and should be evaluated by a physician. It is not typically a medical emergency. Ventricular fibrillation occurs in the ventricles (lower chambers) of the heart; it is always a medical emergency. If left untreated, ventricular fibrillation (VF, or V-fib) can lead to death within minutes. When a heart goes into V-fib, effective pumping of the blood stops. V-fib is considered a form of cardiac arrest.
Dysrhythmias may also be treated electrically, by applying a shock across the heart—either externally to the chest wall or internally to the heart via implanted electrodes. Cardioversion is either achieved pharmacologically or via the application of a shock synchronized to the underlying heartbeat. It is used for treatment of supraventricular tachycardias. Defibrillation differs in that the shock is not synchronized. It is needed for the chaotic rhythm of ventricular fibrillation and is also used for pulseless ventricular tachycardia. Often, more electricity is required for defibrillation than for cardioversion. In most defibrillation, the recipient has lost consciousness so there is no need for sedation.