Cardiology (from Greek καρδίᾱ kardiā, "heart" and -λογία -logia, "study") is a branch of medicine dealing with disorders of the heart as well as parts of the circulatory system. The field includes medical diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology. Physicians who specialize in this field of medicine are called cardiologists, a specialty of internal medicine. Pediatric cardiologists are pediatricians who specialize in cardiology. Physicians who specialize in cardiac surgery are called cardiothoracic surgeons or cardiac surgeons, a specialty of general surgery.
Although the cardiovascular system is inextricably linked to blood, cardiology is relatively unconcerned with hematology and its diseases. Some obvious exceptions that affect the function of the heart would be blood tests (electrolyte disturbances, troponins), decreased oxygen carrying capacity (anemia, hypovolemic shock), and coagulopathies.
All cardiologists study the disorders of the heart, but the study of adult and child heart disorders are through different training pathways. Therefore, an adult cardiologist (often simply called "cardiologist") is inadequately trained to take care of children, and pediatric cardiologists are inadequately trained to take care of adults. The surgical aspects are not included in cardiology and are in the domain of cardiothoracic surgery. For example, coronary artery bypass surgery (CABG) and cardiopulmonary bypass are both surgical procedures performed by surgeons, not cardiologists. However the insertion of stents and pacemakers are performed by cardiologists.
Blood flow through the valves
As the center focus of cardiology, the heart has numerous anatomical features (e.g., atria, ventricles, heart valves) and numerous physiological features (e.g., systole, heart sounds, afterload) that have been encyclopedically documented for many centuries.
Disorders of the heart lead to heart disease and cardiovascular disease and can lead to a significant number of deaths: cardiovascular disease is the leading cause of death and caused 29.34% of all deaths in 2002.
The primary responsibility of the heart is to pump blood throughout the body. It pumps blood from the body — called the systemic circulation — through the lungs — called the pulmonary circulation — and then back out to the body. This means that the heart is connected to and affects the entirety of the body. Simplified, the heart is a circuit of the Circulation. While plenty is known about the healthy heart, the bulk of study in cardiology is in disorders of the heart and restoration, and where possible, of function.
The heart is a muscle that squeezes blood and functions like a pump. Each part of the heart is susceptible to failure or dysfunction and the heart can be divided into the mechanical and the electrical parts.
The electrical part of the heart is centered on the periodic contraction (squeezing) of the muscle cells that is caused by the cardiac pacemaker located in the sinoatrial node. The study of the electrical aspects is a sub-field of electrophysiology called cardiac electrophysiology and is epitomized with the electrocardiogram (ECG/EKG). The action potentials generated in the pacemaker propagate throughout the heart in a specific pattern. The system that carries this potential is called the electrical conduction system. Dysfunction of the electrical system manifests in many ways and may include Wolff–Parkinson–White syndrome, ventricular fibrillation, and heart block.
The mechanical part of the heart is centered on the fluidic movement of blood and the functionality of the heart as a pump. The mechanical part is ultimately the purpose of the heart and many of the disorders of the heart disrupt the ability to move blood. Failure to move sufficient blood can result in failure in other organs and may result in death if severe. Heart failure is one condition in which the mechanical properties of the heart have failed or are failing, which means insufficient blood is being circulated.
The cardiac physical exam focuses on portions of the physical exam that elucidate information about diseases and disorders outlined below. Clinical judgment, of course, should guide the physical exam but the following are pertinent things related to a general / broad cardiac exam.
Apex beat (point of maximum impulse)
Bruits: carotid, renal
Edema of the lower extremities and ascites that may indicate right heart failure
Heart sounds, heart murmurs, pericardial rub, mechanical heart valve clicking
Jugular venous distension
Retina exam with ophthalmoscope for signs of hypertension (retinal hemorrhage) and diabetic retinopathy (cotton wool spots)
Pulses: carotid, dorsalis pedis, femoral, popliteal, posterior tibial, radial, temporal, ulnar
Pulse quality: pulsus paradoxus, pulsus parvus et tardus
Respiratory sounds for crackles (edema) and other lung pathologies that can affect the heart
Rheumatic diseases can have significant cardiac findings and is too lengthy to include here
Arthritis is common amongst rheumatic diseases
Skin exam for rashes (systemic lupus erythematosus, scleroderma, dermatomyositis, vasculitis)
Endocarditis signs: Janeway lesions, Osler's nodes, splinter hemorrhages
Peripheral vascular disease
Scars indicating procedures: sternotomy, thoracotomy, pericardial window, carotid endarterectomy, thyroidectomy, etc.
Skin bulges indicating implanted devices: pacemaker, ICD, implantable loop recorder, vagus nerve stimulation
Xanthomas & xanthelasmas
Blood pressure: hypertension, congenital heart disease manifestations
Heart rate: bradycardia & tachycardia
Respiratory rate: in distress, shortness of breath causes
Cardiology is concerned with the normal functionality of the heart and the deviation from a healthy heart. Many disorders involve the heart itself but some are outside of the heart and in the vascular system. Collectively, the two together is termed the cardiovascular system and diseases of one part tends to affect the other part. The following attempts to categorize the lengthy list of disorders & diseases of the cardiovascular system, but there is overlap and a single entity may appear in multiple areas.
Hypertension is elevated blood pressure above "normal." Blood pressure is reported as fraction of systolic blood pressure over diastolic blood pressure and typically at the brachial artery while seated and measured in mmHg. The normal blood pressure changes with age with a general trend that it increases with age. Normal pressure for newborns is around 90/60 and young adults classically being 120/80 (pronounced "120 over 80").
Hypertension has significant impact on the cardiovascular system — other systems too — and is the motivating reason for treatment. Reduction of morbidity from hypertension is the end-goal of therapy.
Types of hypertension
- Essential hypertension
Hypertension with no known cause, which is about 90-95% of people with hypertension. Often thought to be due to lifestyle. Management is through medications and blood pressure that does not respond is a red flag that it may be secondary hypertension. Due to the widespread nature of hypertension, cardiologists will end up managing or recommending treatments for essential hypertension.
- Secondary hypertension
Most causes of secondary hypertension are from kidney and endocrine disorders. Cardiovascular causes of hypertension include coarctation of aorta, atherosclerosis, and aortic stenosis.
Complications of hypertension
Increased pressure results in hypertrophy of the myocardium, particularly left ventricular hypertrophy. Pulmonary hypertension — which is separate from "hypertension" described above — can result in right ventricular hypertrophy.
Generally considered to be a systolic blood pressure over 180. If there is no organ dysfunction it is called a hypertensive urgency, but if there is (e.g., confusion, breathlessness) then it is called hypertensive emergency.
Pre-eclampsia (PreE) / Eclampsia
PreE is a disease of pregnancy that results in hypertension and proteinuria. PreE has negative consequences for both the mother and fetus/baby. Progression to eclampsia involves seizures. Currently, the only definitive treatment is delivery of the fetus.
Infarction of the brain due to internal bleeding from Charcot–Bouchard aneurysms.
Hypertensive encephalopathy, hypertensive nephropathy, hypertensive retinopathy
Damage to organs from chronic hypertension.
Ventricular fibrillation is a medical emergency
Proper function of the heart relies on a healthy Electrical conduction system of the heart and an orderly transmission of the action potentials that signal the myocardium to contract. Cardiac arrhythmias have numerous causes and have varying outcomes and complications.
Atrial fibrillation (afib or AF)
Fibrillation of the atria is fairly common and more common with increased age and overall disease of the heart. If the ventricular rate exceeds 100 then the afib is further classified as "afib with RVR" meaning rapid ventricular response.
Atrial flutter (AFL)
A re-entrant tachycardia greater than 240 beats per minute and produces a characteristic saw-tooth pattern on ECG. It often degenerates to atrial fibrillation.
A decrease in the ability of the conduction system to transmit action pulses in the orderly manner. Blockage of the signal at different areas results in different types of heart block (e.g., first-degree AV block, left bundle branch block).
Long QT syndrome
Lengthening of the QT interval can result in arrhythmias and sudden cardiac death. Specifically, it can lead to torsades de pointes than can then lead to ventricular fibrillation. It can be an inherited disorder or be acquired. Certain medications are associated with lengthening of the QT interval — drug-induced QT prolongation — and an EKG may be warranted before starting the medication to ensure a normal QT interval, but this practice is debated.
Premature atrial contractions (PACs or APCs)
Normal beats originate in the SA node and extra beats originating from the atria are called PACs. They can be found in normal hearts and be asymptomatic; symptomatic PACs can be treated with beta blockers. PACs, like PVCs, can pair up with normal beats in a pattern called bigeminy.
Premature ventricular contractions (PVCs)
Normal beats are conducted through the AV node to the ventricles resulting in a narrow QRS complex. With PVCs, the extra beat originates within the ventricles and results in a wide QRS complex. Like PACs, they can be found in healthy hearts but are more likely to be found in bigeminy than PACs.
Sick sinus syndrome, Bradycardia-tachycardia syndrome (BTS)
Disease of the SA node that results in irregular changes in heart rate and in the case of BTS the arrhythmia alternates between bradycardia and tachycardia.
Supraventricular tachycardia (SVT)
A collection of tachycardia rhythms that originate before the ventricles and include the SA node, atria, and AV node. It is a broad, encomparsing term that includes other rhythms in this list (e.g., afib with RVR) and others.
Torsades de pointes
A polymorphic arrhythmia that can be syptomatic and tends to resolve to a normal sinus rhythm. However, there is a concern
Ventricular fibrillation (vfib)
Fibrillation of the ventricles is a life-threatening arrhythmia and should be treated by defibrillation and is a medical emergency. Vfib results from uncoordinated contraction of the ventricles and defibrillation acts as a 'reset' to synchronize contraction (i.e., a normal rhythm).
Ventricular tachycardia (vtach)
Tachycardia that originates from within the ventricles. Typically, "vtach" implies monomorphology but it can be an umbrella term for both monomorphic and polymorphic (i.e., torsade de pointes). To classify a ventricular rhythm as vtach, at least 3 beats in a row must originate from the ventricles and have a rate over 100. If it lasts longer than 30 seconds, it can additionally be labelled as a sustained vtach.
Disorders of the coronary circulation
Coronary arteries labeled in red text and other landmarks in blue text.
Contrary to a basic understanding of the cardiovascular system, the heart cannot itself receive enough oxygen and nutrients from the blood it pumps and it must be supplied with blood as if it were any other organ in the body. Unlike the systemic organs the heart receives perfusion in the phase of diastole rather than systole. This circulation of blood is called the coronary circulation. The coronary circulation consists of coronary arteries and coronary veins. The two main coronary arteries — right coronary artery (RCA) and left coronary artery (LCA) — branch off of the ascending aorta and the left further branches into the left circumflex artery (LCx) and left anterior descending artery (LAD). Combined, the RCA, LCx, and LAD comprise the three main coronary arteries (e.g., "three vessel disease"). Lastly, the posterior descending artery (PDA) is supplied by the RCA and/or LCx, and this connection determines the "dominance" of the heart (e.g., if the RCA supplies the PDA then the heart is "right dominant").
Disorders of the coronary circulation can have devastating effects to the heart that results in a downward spiral of worse circulation leading to worse heart function leading to worse circulation and so on.
Acute coronary syndrome (ACS)
ACS is a medical emergency and is a broad term encompassing many acute myocardial infarction symptoms. As a syndrome, it consists of a constellation of symptoms and can have many causes. The top three causes of ACS are ST elevation myocardial infarction (STEMI, 30%), non ST elevation myocardial infarction (NSTEMI, 25%), or unstable angina (38%). The first two are myocardial infarctions which are more commonly known as "heart attacks."
Angina pectoris literally means "chest pain" that refers to pain caused by ischemia of the heart. The main cause of angina is coronary artery disease, but can result from other non-atherosclerotic causes such as anemia and heart failure. Stable angina results if the angina resolves with rest or nitroglycerin, but can progress to unstable angina which is a form of acute coronary syndrome.
Atherosclerosis is the condition in which an artery wall thickens as the result of a build-up of fatty materials (e.g., cholesterol) and white blood cells ("foam cells"). Atherosclerosis of a coronary artery leads to coronary artery disease (CAD). Atherosclerosis is a broad term referring to loss of elasticity of arteries and more specific terms exist — arteriosclerosis and arteriolosclerosis — to narrow which arteries are diseased and can easily be confused due to similar spelling. Overall, atherosclerosis tends to affect the arteries of highest pressure: aorta, coronary, renal, femoral, cerebral, and carotid.
Coronary artery disease (CAD)
Coronary artery disease is a general term for any reduction in coronary circulation. One such cause is atherosclerosis. CAD can lead to ischemia (angina pectoris) or infarction (myocardial infarction). Treatment of CAD includes angioplasty, stenting, and coronary artery bypass surgery (CABG).
Myocardial infarction (a.k.a. heart attack)
A myocardial infarction is the death of a part of the heart which is typically caused by a blockage of the coronary circulation but can be caused by other insufficiency such as cardiogenic shock.
Recurrence of stenosis after being treated (e.g., stenting).
A rhythm strip showing a couple beats of normal sinus rhythm followed by an atrial beat and asystole ("flatline").
Cardiac arrest refers to the cessation of normal systemic circulation due to failure in proper contraction of the heart. There are several conditions that can cause cardiac arrest. Treatment of cardiac arrest includes cardiopulmonary resuscitation (CPR), defibrillation, and advanced cardiac life support (ACLS), and treatment of the underlying cause of arrest.
Asystole refers to the absence of electrical activity of the heart and is sometimes referred to as a "flatline" because the electrocardiogram shows a solid line due to the absence of electrical activity. This flatline is commonly used in television and movies to signal death. There are numerous causes of asystole that may be reversible if determined quickly enough, however, survival is very unlikely (~2% if not in a hospital). In contrast, asystole is desired and induced during cardiopulmonary bypass through a cardioplegia solution containing very high amounts of potassium. One additional example is the use of high potassium in lethal injection that results in asystole, cardiac arrest, and then death.
Pulseless electrical activity (PEA)
Pulseless electrical activity is when the electrocardiogram shows a rhythm that should produce a pulse but it does not. PEA is commonly caused by the 6 H's and 6 T's (see PEA article) and results in decreased cardiac output and insufficient oxygen delivery to the body.
Pulseless ventricular tachycardia
Pulseless ventricular tachycardia (VT) Is one classification of VT such that no pulse is felt because of an ineffective cardiac output which causes cardiac arrest, which also results in insufficient oxygen delivery to the body.
Sudden cardiac death (SCD)
Sudden cardiac death is a concept of natural death rather than a specific medical condition. There are several causes of sudden cardiac death and it is distinct from cardiac arrest. The leading cause of SCD in young athletes is hypertrophic cardiomyopathy but can also result from commotio cordis that is often sustained during athletic activity.
Ventricular fibrillation is fibrillation of the ventricles of the heart. Rhythmic contraction is necessary for efficient movement of blood, and fibrillation disrupts this rhythm sufficiently to cause cardiac arrest.
Disorders of the myocardium
The diagram shows a healthy heart (left) and one suffering from right ventricular hypertrophy (right).
A man with congestive heart failure and marked jugular venous distension. External jugular vein marked by an arrow.
The layer of the heart responsible for mechanical function is the myocardium. The myocardium is sandwiched between two thin layers — the epicardium & endocardium — and is composed of a special type of muscle cell called cardiomyocytes. Disorders of these cells results in dysfunction of the structure and function of the heart.
Cardiomyopathy is a deterioration of the myocardium. Several classifications have been used to categorize cardiomyopathies with the most common being primary vs. secondary, and dilated vs. restrictive vs. hypertrophic (presented below).
Cardiomyopathy causing ischemia of the heart due to coronary artery disease.
Cardiomyopathy caused by something other than ischemia.
Cardiomyopathy caused by amyloidosis.
Hypertrophic cardiomyopathy (HCM)
Cardiomyopathy caused by hypertrophy of the heart and is the leading cause of sudden cardiac death in young adults.
Hypertrophic obstructive cardiomyopathy (HOCM) (Idiopathic hypertrophic subaortic stenosis (IHSS))
Dilated cardiomyopathy (DCM)
Cardiomyopathy caused by dilation of the heart, typically caused by "drugs and bugs." It is the most common form of non-ischemic cardiomyopathy and the dilitation of the heart results in larger chamber volumes & thinner myocardial walls, both of which decrease the ability to pump. Specific kinds of dilated cardiomyopathy are listed below, and other causes include Chagas disease, chemotherapeutic agents (e.g., doxorubicin), tuberculosis, and pregnancy.
A type of dilated cardiomyopathy caused by chronic abuse of alcohol and results from direct toxicity of ethanol on the myocardium.
Tachycardia induced cardiomyopathy
A type of dilated cardiomyopathy caused by chronic tachycardia. A common arrhythmia that can lead to this form of cardiomyopathy is the common atrial fibrillation.
Takotsubo cardiomyopathy (Transient apical ballooning, stress-induced cardiomyopathy)
A type of dilated cardiomyopathy caused by a sudden temporary weakening of the myocardium, which can include emotional stress (i.e., broken-heart syndrome). It presents as sudden heart failure with ECG changes similarly found in myocardial infarction and typically is found in post-menopausal women.
Arrhythmogenic right ventricular dysplasia (Arrhythmogenic right ventricular cardiomyopathy)
Cardiomyopathy caused by a genetic mutation of the desmosomes that connect myocytes.
Restrictive cardiomyopathy (RCM)
Cardiomyopathy caused by excessive rigidity of the heart that prevents effective contraction and pumping. In comparison to DCM, RCM is often secondarily caused by other diseases such as amyloidosis, scleroderma, hemachromatosis (iron overload), and Churg-Strauss syndrome. As such, the treatment for RCM is to treat the disease causing the RCM.
Heart failure is failure of the heart to produce sufficient blood flow to meet metabolic demands of the body, or to do so at higher filling pressures. The hallmark signs of heart failure include shortness of breath (especially on exertion, at night, or while lying down) and leg swelling. Chest pain is rarely a feature of heart failure, which would point a diagnosis more toward angina pectoris or myocardial infarction. Perhaps confusingly, heart failure can be caused by coronary artery disease (CAD) and myocardial infarction (MI) that result in a deficiency in pumping that then leads to heart failure. Treatment of heart failure, like most secondary disorders, depends upon treatment of the primary cause which includes CAD & MI but also valvular problems like aortic stenosis and hypertension.
Untreated cor pulmonale can cause right heart failure from chronic pulmonary hypertrophy.
Hypertrophy of the ventricle. Thickening of the myocardium (i.e., hypertrophy) can be physiological (a normal response) or pathological. An example of physiological hypertrophy is the result of significant athletic training (athletic heart syndrome).
Left ventricular hypertrophy (LVH)
Hypertrophy of the left ventricle is more common than in the right and typically due to increased afterload on the heart such as from hypertension and aortic stenosis, but also from long standing mitral valve regurgitation. It can be diagnosed by echocardiography or ECG.
Right ventricular hypertrophy (RVH)
Hypertrophy of the right ventricle and, it too, can be physiological from athletic training. Other causes include pulmonary hypertension and COPD as well as several congenital heart defects like ventricular septal defect, tetralogy of Fallot, and hypoplastic left heart syndrome.
Cancer of the heart is very rare and those cancers tend to be benign.
Most common tumor of the heart. It is a benign tumor most commonly found in the left atrium and can be associated with Carney syndrome.
Myocardial rupture and ventricular aneurysm
Rupture is a gross structural failure of the heart. Commonly a result of myocardial infarction that weakens the wall sufficiently to result in frank rupture and is typically seen 7–10 days after infarction. If not significant enough, the wall can develop into a ventricular aneurysm.
Infection and inflammation of the myocardium is myocarditis. Most causes are infectious (parvovirus B19, Lyme disease, Chagas disease), toxic (ethanol, anthracyclines, clozipine), or immunologic (systemic lupus erythematosus, sarcoidosis, and some of the vasculitidies (see below)). Definitive diagnosis requires a biopsy.
A congenital heart defect in which the right ventricular myocardium is too thin or absent. It is a very rare disorder.
Disorders of the pericardium
Posterior wall of the pericardial sac.
The pericardium is a double-walled sac — fibrous pericardium and serous pericardium — that contains the heart. The serous pericardium — like other similar structures (e.g., pulmonary pleurae, synovium, bursae) — contains a thin layer of fluid that reduces friction from movement. The fibrous pericardium fixes the heart in the mediastinum.
Inflammation of the pericardium that is typically idiopathic or infectious in nature. Treatment of viral & idiopathic pericarditis is NSAIDs or aspirin.
Pericarditis that constricts the expansion of the heart and inhibits heart function. Causes include infections (tuberculosis, fungus, parasites) and surgery. Definitive surgery is a pericardiectomy.
A form of pericarditis that develops 2-3 weeks after myocardial infarction and is accompanied by fever, pleuritic chest pain, and symptoms of pericarditis.
The serous pericardium normally contains fluid that reduces friction, but an abnormal accumulation of fluid in the pericardium is called a pericardial effusion. The list of causes is lengthy but includes pericarditis, rheumatic diseases (e.g., systemic lupus erythematosus), trauma, and blood from myocardial rupture. If an effusion worsens then the fluid can inhibit heart function and symptoms of cardiac tamponade appear. Treatment includes pericardiocentesis to drain the fluid, if necessary, and treatment of the underlying cause.
Tamponade is a medical emergency resulting from accumulation of fluid in the pericardium that inhibits heart function. Tamponade is a consequence of the fibrous pericardium being too inelastic to permit adequate heart expansion during diastole. The classic finding is pulsus paradoxus as well as Beck's triad (low arterial blood pressure, distended neck veins, & soft heart sounds). Treatment is supportive until in a hospital where pericardiocentesis or a pericardial window can be performed to drain the fluid.