Heart Rhythm Central - Nicholas Tullo, MD, FACC, FHRS

|A| |B| |C| |D| |E| |F| |G| |H| |I| |J| |K| |L| |M| |N| |O| |P| |Q| |R| |S| |T| |U| |V| |W| |X| |Y| |Z|


Angiotensin Converting Enzyme (ACE) Inhibitors

Angiotensin Converting Enzyme (ACE) is a substance found in the lungs that is part of the blood pressure control system in the body. ACE converts a precursor substance Angiotensin I into Angiotensin II, which is a potent vasoconstrictor that causes blood vessels to squeeze down. Angiotensin II is used to prevent low blood pressure, but some patients with hypertension may have too much Angiotensin II in their system. ACE inhibitors are a group of medications help relax blood vessels by blocking that enzyme, reducing the amount of Angiotensin II. They are used to treat high blood pressure and heart failure. For people with heart failure, ACE inhibitors have been shown to prolong life and reduce symptoms. This class of medications is frequently used to preserve kidney function in patients with diabetes.

Antitachycardia Pacing

Tachycardia refers to an abnormally rapid heartbeat. Some pacemakers and all defibrillators are able to rapidly stimulate the heart (faster than the tachycardia is going) in order to break up the short circuit and stop the rapid beat. Antitachycardia pacing is useful in treating ventricular tachycardia (a rapid heartbeat in the bottom chambers) by stimulating the heart with a series of rapid electrical pulses, reestablishing a normal heartbeat.


The aorta is the main artery in the body. It comes off of the left ventricle and carries blood to every part of the body except the lungs.

Aortic Stenosis

This is a valve condition where the aortic valve, which normally opens to allow the blood to exit the left ventricle and be pumped into the aorta, is narrowed. The leaflets that normally open freely are generally thickened, stiff, and calcified, which results in a decreased opening for the blood to flow out of the heart.


Heart rhythm abnormalities are known as arrhythmias. Arrhythmias are electrical problems that can arise because of disturbances in the cardiac conduction system. They can also arise from a short circuit in the atrial or the ventricular heart muscle.


Asynchrony is a lack of proper timing between various parts of the heart. There should be proper timing between the top and bottom of the heart (atrioventricular synchrony) and also between the left and right sides of the heart. Conditions that disturb the normal timing result in Asynchrony.


Atherosclerosis refers to the condition whereby plaque is deposited within the inner layers of artery walls, causing them to become thick and irregular due to excessive amounts of fat, cholesterol and other substances. As the inner walls of arteries become thickened with these deposits, the arteries become narrowed, and the flow of blood through them may become reduced.

Atrial Fibrillation (AF or AFib)

AF is the most common arrhythmia affecting adults. Somewhere between 2 and 6 million people in the United States suffer from atrial fibrillation. AF occurs when the electrical signals in the upper chambers of the heart becomes rapid and disorganized, causing the heart to beat irregularly, usually at a rapid rate. Although it isn’t life threatening, AF can lead to symptoms such as palpitations, shortness of breath, weakness, exercise intolerance and other more serious problems like chronic fatigue and congestive heart failure. The risk of having a stroke is five times higher for those with AF. There are a number of effective treatments to control AF to reduce the symptoms and minimize the risk of more serious cardiovascular problems. Read more about Atrial Fibrillation here.

Atrial Flutter (AFL)

Atrial flutter is a rapid rhythm problem that arises from the top chambers. Similar to Atrial Fibrillation, it can cause symptoms of palpitations, shortness of breath, lightheadedness, and tachycardia. Instead of many disorganized signals, however, atrial flutter is caused by a single electrical short circuit that causes the electrical signal in the top chamber to chase its own tail around and around in a circle. Atrial rates vary between 220 and 350 beats per minute during atrial flutter, leading to a very fast, occasionally steady racing of the heart at about half that rate (110 to 170 bpm).

Atrioventricular (AV) Node

The atrioventricular (AV) node is the main connecting “wire” that bridges the top and bottom chambers of the heart. It is located in the wall between the right and left atria, just above the ventricles. This part of the heart’s conduction system carries signals from the atria to the ventricles.

Automatic External Defibrillator (AED)

Defibrillators deliver a brief, high-energy shock to a patient’s chest wall through paddles or electrode patches applied to the skin. Most defibrillators are found in hospitals, in doctors’offices, or on ambulances. An Automatic External Defibrillator is designed for non-professional in an emergency to potentially save someone from cardiac arrest. They are frequently found in major businesses, shopping malls, or in schools and stadiums. The display on an AED gives simple instructions to rescuers – and has a built-in safeguard to avoid delivering a shock unless absolutely necessary.



Beta-blockers are prescription medications that are designed to block the effects of adrenaline on the heart. Adrenaline increases the heart rate, constricts blood vessels, and causes the heart to beat more vigorously. Thus, beta blockers reduce heart rate and blood pressure. They are used to treat abnormal heart rhythm problems (tachycardia), can help with hypertension, and reduce the oxygen needs of the heart in patients who have coronary artery blockages.


Bradycardia refers to a slow heartbeat. A normal heart contracts about 100,000 times each day, at a rate of 60 to 80 times a minute at rest. Any time the heart rate falls below 60 bpm, bradycardia is present. Bradycardia is not always abnormal, but it can indicate problems with the electrical system of the heart, including conditions such as heart block (or AV Block) and Sick Sinus Syndrome.


Cardiac Resynchronization Therapy (CRT)

When a normal heart contracts, the left and right ventricles should squeeze at the same time. Some patients have a problem with their electrical system that results in delay of the electrical signal to one side or another, resulting in “dyssynchrony” or loss of the proper timing between the walls of the heart, which reduces the efficiency of the heart’s contraction. Cardiac resynchronization therapy uses a special pacemaker system to correct the electrical imbalance and re-establish the proper timing between the heart chambers. The pacemaker wires (leads) electrically stimulate the heart muscle on both sides to synchronize the contractions of the ventricles.


Cardiomyopathy is a condition in which the heart muscle is diseased for one reason or another and cannot pump blood efficiently. Diseased heart function can cause the heart muscle to become weak or the heart muscle can become stiff and have difficulty filling. Reduced pumping of the heart can result in congestive heart failure and can also lead to electrical problems (arrhythmias).

Catheter Ablation

Catheter ablation is an invasive electrophysiology (EP) procedure in which one or more flexible thin wires (catheters) are guided via x-ray into the blood vessels to the heart chambers.  Once the catheter is positioned in the proper location, electrical (radiofrequency) energy is used to destroy very small areas of heart tissue that may be causing rapid heart rhythms (arrhythmias).

Coronary Artery Disease (CAD)

Coronary artery disease occurs when the blood vessels that feed the heart become clogged, usually from atherosclerosis. This condition is also called coronary heart disease or ischemic heart disease.



Defibrillation refers to the procedure whereby a strong electrical shock is delivered to the heart to stop a fast, erratic, and often fatal heart rhythm disturbance (ventricular fibrillation). The shock is administered through electrodes placed on the chest wall (external defibrillation) or in the heart chamber (internal defibrillation).


Dyspnea (DIS-nee-uh) is a word that refers to shortness of breath. It includes difficult or labored respiration, and can indicate either a lung problem or possibly a heart problem.


Echocardiogram (Echo)

An echocardiogram is a non-invasive test that uses ultrasonic waves to record an image of the inside of the heart. It allows us to see the heart valves and measure the size and function of the walls of the heart, including a measurement of the left ventricular ejection fraction (LVEF).


Edema is the build-up of fluid in body tissues. As fluid oozes out of the microscopic blood vessels (capillaries), it accumulates in the spaces between cells and is characterized by swelling, usually in the lower (or gravity-dependent) parts of the body like feet and legs. Edema can be a sign of heart failure, vascular problems, or it may be a sign of fluid overload.

Ejection Fraction (EF)

The ejection fraction (EF) is a measure of the portion of blood that is squeezed out of the bottom chambers with each contraction of the heart. Most often, the number refers to the left ventricular function, which should be about 55 percent or more. An ejection fraction below 50 percent indicates that the heart muscle is weakened.

Electrophysiology (EP) Study

An electrophysiology study is an invasive test performed by a heart rhythm specialist (cardiac electrophysiologist). Wire catheters are inserted painlessly into a vein and guided to the heart chambers. The electrical activity of the heart is then recorded and the function of the cardiac conduction system is assessed. Extra beats are induced with the wires to observe the response and determine the functioning of the electrical system. An EP study also involves programmed stimulation (premature beats stimulated by the wire catheters) to initiate abnormal heart rhythms, determine the cause of tachycardia, and assess the risk of life threatening arrhythmias.


An embolism is a sudden obstruction of a blood vessel, most commonly by a freely circulating blood clot (embolus). Some emboli are made up of other material such as cholesterol/plaque, amniotic fluid, or even air.



Fibrillation is a rapid, chaotic contraction of the heart muscle due to an electrical disturbance, resulting in loss of effective contraction of the heart muscle. Fibrillation of the atria (top chambers) is called atrial fibrillation (AF). Ventricular fibrillation (VF) can occur in the bottom chambers. Ventricular fibrillation is typically fatal if not corrected within several minutes.


Flutter is an electrical disturbance associated with rates of electrical activation in the range of 250-350 beats per minute. It can affect the upper or lower chamber of the heart, making them beat extremely rapidly but with a regular pattern. Flutter can be due to a short circuit in the heart muscle or it can arise from a very rapidly firing focus, or small area within the heart muscle.


Heart Attack (Myocardial Infarction)

A heart attack or “MI” occurs when the coronary arteries become completely blocked such that the blood cannot carry sufficient oxygen and nutrients and a part of the heart muscle becomes damaged. The symptoms of a heart attack are variable but most often involve chest pain. Getting prompt emergency treatment can minimize the amount of damage and can dramatically improve the patient’s prognosis

Heart Block

Heart block (also referred to as “AV Block”) occurs when electrical impulses generated in the upper chambers of the heart are not properly passed down to the lower chambers. The heart may then beat too slowly, reducing the oxygen that gets to the body and brain.

Heart Failure

Congestive heart failure occurs when the heart muscle does not pump enough blood to meet the body’s needs. Heart failure can occur due toweakening of the heart muscle (systolic heart failure) or because of improper filling of the heart (diastolic heart failure). Heart failure can be treated with medications, which can improve symptoms and perhaps slow the progression of heart failure.

Hypertension (High Blood Pressure)

Hypertension is the condition whereby the blood pressure is elevated (over 140/90).  Hypertension can be “labile” (comes and goes) or can be chronic. Hypertension can lead to damage of the blood vessels and is the leading cause of stroke, heart attack, and certain arrhythmias like atrial fibrillation.

Hypotension (Low Blood Pressure)

Hypotension refers to having a low blood pressure. Hypotension can cause symptoms of weakness, lightheadedness, or exercise intolerance.


Implantable Cardioverter Defibrillator (ICD)

An implantable cardioverter-defibrillator is an electronic device that is inserted under the skin to protect patients from sudden cardiac death. ICDs function to stop life-threatening arrhythmias ventricular fibrillation or ventricular tachycardia. ICDs monitor the heart rhythm and also function as pacemakers in case the heart rate is too slow. They can deliver anti-tachycardia pacing therapies and, if necessary, deliver a life-saving shock (defibrillation) if a dangerously rapid heart rhythm is detected.

Infarct or Infarction

A myocardial infarction or “infarct” is an area of damaged tissue resulting from inadequate blood flow from an obstructed coronary artery.


Ischemia is the detrimental effect of an insufficient flow of blood to tissue, usually due to constriction or obstruction of an artery. Myocardial (or heart muscle) ischemia results from coronary insufficiency, meaning that the supply of oxygen and nutrients is insufficient to meet the demands of the heart muscle.


Left Ventricular Hypertrophy

Left ventricular hypertrophy (LVH) is a condition where the thickness of the walls of the main pumping chamber is abnormally increased. The thickening can be due to genetic abnormalities or possibly from deposits of abnormal material within the heart muscle. LVH can also occur in patients with chronic hypertension or aortic stenosis in order to compensate for the increased cardiac workload associated with these conditions.

Long QT Syndrome (LQTS)

Long QT syndrome is a disorder of the electrical activity of the heart. It can be inherited (“Congenital Long QT Syndrome”), acquired after taking certain medications (“Drug-Induced Long QT Syndrome”), or caused by a combination of both. People with LQTS are susceptible to a particular type of ventricular tachycardia known as Torsades de Pointes, which can cause fainting and may lead to ventricular fibrillation, a potentially fatal heart rhythm disturbance.



The Myocardium is another name for the muscular tissue of the heart. It contracts to pump blood, and then relaxes to allow the heart to fill again.



Necrosis is the breakdown of tissue due to cellular death, often due to lack of oxygen (ischemia) or other forms of local injury (e.g. trauma, temperature extremes).



Cardiac pacemakers are battery-operated devices that provide a tiny electrical “pulse” that causes the heart muscle to contract. These devices prevent slow heart rates by “pacing” the heart. Permanent pacemakers are implanted under the skin along with a thin wire or wires (“leads”) that are inserted into a vein to pick up the heart’s activity and transmit the electrical pulse to the heart muscle when needed. Temporary pacemakers are located outside the body and are attached to wires that are temporarily inserted, either into a vein or onto the outside of the heart (most often after open-heart surgery). Pacemakers are most often used to treat Sick Sinus Syndrome or AV Block.


Normally, we don’t feel our heartbeat. Palpitations refer to the sensation of feeling the heart beating abnormally. Sometimes this can be a sign of arrhythmia, but palpitations can sometimes occur during a normal heart rhythm.

Peripheral Artery Disease

Peripheral artery disease or peripheral vascular disease is a clogging of the arteries in the legs or in the arms. This can result in ischemia of the fingers or toes.

Premature Contractions

Early (premature) or “skipped” beats are the most frequent cause of irregular heart rhythms. These can start in the upper or lower chambers of the heart.



Revascularization refers to restoring the normal blood flow through a diseased or narrowed artery. This can be done from inside the vessel with balloon angioplasty or by inserting a stent, or it can be done from the outside with a “bypass” graft, which is a new blood vessel that surgically “plugs into” the diseased vessel past the point of blockage to restore blood flow to the tissues downstream.


Sick Sinus Syndrome (SSS)

Sick Sinus Syndrome refers to a group of signs and symptoms that indicate that the heart’s natural electrical pacemaker, the sinus node, is not functioning properly. In SSS, the heart rate is too slow to meet the body’s needs, and symptoms of fatigue, lightheadedness, and exercise intolerance occur. Sometimes, SSS occurs in combination with rapid atrial arrhythmias like atrial fibrillation. When that happens, we can diagnose “Tachycardia-Bradycardia Syndrome.” A permanent pacemaker, sometimes in combination with medication, is the optimal treatment. SSS is more common in older patients.

Sinus Rhythm

Sinus rhythm refers to the normal rhythm of the heart, which originates from the natural pacemaker known as the sinus node or sinoatrial node. “Normal Sinus Rhythm” (NSR) is present if the rate is between 60 and 100 beats per minute.

Sinus Tachycardia

Sinus Tachycardia is present if the natural pacemaker or sinus node fires at rates above 100 beats per minute. This is a normal event in patients who are exercising, are excited, or with illness (like a fever or infection). When sinus tachycardia occurs at rest, it may be due to anemia or hyperthyroidism, which need to be treated.


Strokes are also called “brain attacks,” because the process is similar to a heart attack. Most strokes occur because a blood vessel in the brain becomes occluded, so the brain tissue fed by that vessel is robbed of oxygen and nutrients. If the vessel remains occluded, permanent damage to part of the brain occurs, causing neurologic deficits like paralysis on one side of the body, numbness, difficulties in speech, and other disabilities. A small number of strokes occur because of acute bleeding within the brain tissue. All strokes pose serious health threats. Atrial fibrillation increases the risk of stroke 5-fold.

Sudden Cardiac Death (SCD)

In SCD, the heart abruptly and unexpectedly stops pumping properly and the cardiovascular system collapses (cardiac arrest). The most common cause of SCD is an abnormal called ventricular fibrillation (VF). During VF the electrical signals in the pumping chambers are so rapid and disorganized that the heart muscle cannot pump properly. The normal contractions of the ventricles stop, and all tissues are starved of oxygen. An individual with VF will lose consciousness within seconds. Without immediate emergency help (Defibrillation), death will follow within minutes of an episode of ventricular fibrillation.

Supraventricular Tachycardia (SVT)

Any abnormal rapid rhythm that comes from above the ventricles is considered a “Supraventricular Tachyarrhythmia,” (SUPRA meaning “above”).  SVT refers to rapid, regular heart arrhythmias arising from the top chambers. There are many different electrical abnormalities that cause SVT. They can be caused by a “short circuit” that causes the electrical signal to chase itself around in a circle. They can also be caused by an abnormal spot or “focus” in the top chamber that starts to fire rapidly.

Syncope (Fainting)

Fainting, or the sudden loss of consciousness with spontaneous recovery (usually within a minute or so), is a common symptom that affects up to 50% of all people at some point in their life. It is generally caused by a sudden decrease in blood flow to the brain, either from a drop in blood pressure or possibly due to a sudden change in the heart rhythm. No matter what the cause, fainting can be dangerous simply because of the potential for injuries from falling.

Syndrome of Inappropriate Sinus Tachycardia

Sinus Tachycardia (sinus nodal rates above 100 beats per minute) is usually due to exercise, stress or excitement. When sinus tachycardia occurs at rest, it may be due to anemia or hyperthyroidism. However, rapid heart rates in the absence of any medical explanation may be due to a rare condition known as the “Syndrome of Inappropriate Sinus Tachycardia.”  This often causes symptoms of palpitations, dizziness, chest pain, and shortness of breath. It can usually be treated successfully with medications.



Any heart rate above 100 beats per minute is considered “Tachycardia.” Tachycardia can be normal (e.g. sinus tachycardia while exercising), or it can be due to an abnormally fast heart arrhythmia. Tachycardia can become dangerous if the heart rate is fast enough to interfere with the heart’s ability to contract properly. Tachycardia can cause a wide range of symptoms, from palpitations to lightheadedness and possibly even syncope (fainting). Ventricular tachycardia, which arises from the bottom chambers, can result in cardiac arrest.


Valvular Heart Disease

The heart valves function to keep the blood moving forward through the heart. Valve problems can be inherited or can develop due to age, infection, or other causes. Valvular “stenosis” means that the valve does not open widely and the blood has to squeeze through a narrow opening to pass through and out of the heart. Valvular “regurgitation” or “incompetence” means the valve leaks such that a portion of the blood goes backwards through the valve. Either condition can reduce the heart’s ability to push blood from chamber to chamber. Medication and surgery are potential treatment options.

Ventricular Fibrillation (VF)

Ventricular fibrillation is a very rapid, disorganized tachyarrhythmia that arises from the bottom chambers of the heart and results in cardiovascular collapse and often Sudden Cardiac Death. It is a serious electrical disturbance that almost always occurs in patients with a prior history of heart disease, such as a heart attack or heart failure. In a small number of cases, the VF occurs acutely as a consequence of a heart attack (myocardial infarction).  In that case, VF is triggered by the sudden lack of oxygen to the heart muscle, which disturbs the electrical signals. VF causes the heart to stop pumping effectively. The lack of oxygen throughout the body, and especially to the brain, can cause irreversible damage and death within minutes.

Ventricular Tachycardia (VT)

Characterized by a very fast heart rate arising from the bottom chambers, VT usually occurs in patients with heart muscle damage from an old heart attack or from cardiomyopathy. It causes the heart to beat so rapidly that the blood pressure becomes dangerously low. Severe symptoms such as fainting, lightheadedness, palpitations, and chest pain may occur. If the blood pressure becomes so low that the body (and the heart) suffers from ischemia, then it can lead to ventricular fibrillation and Sudden Cardiac Death. VT can be sustained or it may occur in bursts of Non-sustained VT. Rarely, it may occur in people with normal hearts. It usually requires prompt treatment to prevent cardiovascular collapse. To prevent recurrences, patients are often treated with medication. Sometimes it becomes necessary to recommend an Implantable Cardioverter-Defibrillator (ICD) to stop recurrent episodes rapidly and automatically. It may be treated with radiofrequency ablation or surgery. In the setting of underlying heart disease, it is a serious condition that requires aggressive treatment to improve patients’ survival.

Featured image: Featured image: CC A-SA 3.0 ZooFari via Wikipedia Commons.

Pin It on Pinterest

Share This