Atrial Fibrillation Glossary
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Ablate — Eliminate tissue around the pulmonary veins or at other sources of erratic electrical signals that cause the irregular heartbeat.
Ablation — A procedure that eliminates tissue around the pulmonary veins or at other sources of erratic electrical signals that cause the irregular heartbeat.
Antiarrhythmic drugs — Medication used to convert from atrial fibrillation to normal sinus rhythm, and to maintain it. Also called rhythm control medications. For more information, see Rhythm Control Medication for Atrial Fibrillation.
Anticoagulant — A medication, such as Coumadin (warfarin) or Pradaxa (dabigatran), that is used to decrease the risk of blood clots that cause strokes. Also informally referred to as a "blood thinner".
Anterior — The front of the heart.
Antrum — The base of the pulmonary veins, which includes the posterior (back) wall of the left atrium and extends to the anterior (front) of the right pulmonary veins. In essence, it is a wide perimeter around the pulmonary veins. This area became the target for ablations because of issues with ablating the ostia.
Antrum Pulmonary Vein Ablation — A type of catheter ablation where lesion lines are placed in the antrum (base) of the pulmonary veins, which includes the posterior (back) wall of the left atrium and extends to the anterior (front) of the right pulmonary veins. Doctors do not confirm conduction block in this ablation. For a procedure where conduction block is confirmed, see pulmonary vein isolation.
Arrhythmia — See cardiac arrhythmia.
Asymptomatic — Afib episodes that the patient does not feel or for which there were no symptoms.
Atrial remodeling — Changes in the deeper layers of heart tissue (substrate) or the way electricity is conducted within the heart, which can occur when atrial fibrillation is untreated and/or when afib progresses to persistent or longstanding persistent atrial fibrillation. This is also known as substrate modification. It is more difficult to treat afib once atrial remodeling has occurred and means that pulmonary vein isolation by itself is unlikely to stop atrial fibrillation. More extensive ablation techniques are typically needed and procedure success may be lower.
Atrial volume — A measure of how much blood fills the left atrium during the cardiac cycle.
Atrioventricular (AV) node — The part of the heart that sends electrical signals from the upper to the lower chambers of the heart. See it in this diagram of the heart.
AV junctional ablation — See AV node ablation.
AV node ablation — A procedure in which the AV (atrioventricular) node is frozen or cauterized to stop electrical signals from being transmitted and a permanent pacemaker is implanted to control the heart's electrical system. This procedure doesn't stop the afib, and while some patients no longer feel their afib, many still do, and patients may still feel tired. The patient must remain on an anticoagulant due to the risk of stroke. This is usually a procedure of last resort for those elderly who are too frail for other procedures, or for those for whom all options have been exhausted. Also called AV junctional ablation.
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Balloon catheter — This type of catheter is inserted into the left atrium and the electrophysiologist inflates the balloon at the tip of the catheter. Balloon catheters can ablate a larger area of tissue than single point radiofrequency catheters, which enhances the prospects that lesions will be contiguous (without gaps) and could shorten procedure times. There are balloon catheters using cryothermy, laser energy, and even radiofrequency energy.
Bipolar radiofrequency energy — Bipolar simply means that the radiofrequency energy is transmitted from two places to a single target. Bipolar radiofrequency energy generates lower power and creates lesions that are less deep than unipolar, but since bipolar radiofrequency energy is sent to different sides of the tissue (top and bottom), high temperatures aren’t needed. This is sometimes called "phased RF".
Blanking period — The three-month period of time following an atrial fibrillation procedure in which atrial fibrillation episodes can occur as part of the body’s healing response. Any afib activity during that blanking period is not counted in a study’s results and is not used in determining success or failure of the procedure.
Blocked — See conduction block.
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Cardiac arrhythmia — An abnormal heart rhythm. There are many types, but atrial fibrillation is the most common cardiac arrhythmia.
Cardiac cycle — Describes the process of de-oxygenated blood flowing into the right atrium, which contracts and pushes the blood to the right ventricle. When the right ventricle contracts, blood is pumped through the right pulmonary artery to the lungs, where it receives oxygen. Blood is then pushed to the pulmonary veins, which bring the blood to the left atrium. When the left atrium contracts, blood is pumped into the left ventricle. When the left ventricle contracts, blood is pumped into the aorta, and then oxygenated blood goes to the rest of the body. The completion of this process is called the cardiac cycle. The heart, which is a muscle, relies on electrical impulses within the heart, such as those that emanate from the sino-atrial node, to tell muscles when they should contract and relax. Learn more at About the Heart.
Cardiac perforation — A rip or tear in the heart that can lead to cardiac tamponade.
Cardiac tamponade — A potential complication of catheter ablation wherein fluid builds up in the pericardium, the "sac" surrounding the heart, and compromises the heart’s ability to pump. This can be fatal if fluid is not drained.
Cardiac tissue — The tissue that makes up the heart.
Catheter — A thin flexible tube that is inserted through a small puncture in the groin, arm, or neck area and threaded to the heart to ablate tissue around the pulmonary veins or at other sources of the erratic electrical signals that cause the irregular heartbeat. In some cases, a balloon catheter is used for atrial fibrillation ablation — see balloon catheter.
Catheter ablation — An atrial fibrillation treatment that is done by a specialized cardiologist, called an electrophysiologist (EP), who deals with irregular heartbeats (arrhythmias). It is a minimally-invasive procedure that is generally less invasive than surgery. It is most successful in treating paroxysmal atrial fibrillation, but much progress has been made in treating persistent and longstanding persistent atrial fibrillation. It is done on a beating heart in a closed chest. Small punctures are made in the groin, arm, or neck area and thin, flexible tubes, called catheters, are inserted and threaded to the heart. Once there, the catheter's tip is threaded through a tiny incision in the wall between the left and right atria (septal wall), and is positioned to ablate tissue around the pulmonary veins or at other sources of erratic electrical signals that cause the irregular heartbeat. In some cases, a balloon catheter is used for atrial fibrillation ablation. The catheter uses an energy source, such as radiofrequency, intense cold, or laser, to create a lesion of scar tissue, called a conduction block, that stops the erratic electrical signals from traveling through the heart.
Catheter ablation risks — See Catheter Ablation Risks.
Catheter ablation success rates — See Catheter Ablation Success Rates.
Cauterized — Burned
Cerebral emboli — Blood clots that can block the flow of blood and oxygen into the brain.
CHADS2 — A scoring system that may be used to determine if someone with afib should be on an anticoagulant. To learn more, see New Stroke Risk Factors for Those with Atrial Fibrillation (AF): Female Gender, Heart Disease, and Age.
CHA2DS2-VASc — A scoring system that may be used to determine if someone with afib should be on an anticoagulant. To learn more, see New Stroke Risk Factors for Those with Atrial Fibrillation (AF): Female Gender, Heart Disease, and Age.
Char formation — During catheter ablation, high temperatures can lead to blood and tissue accumulating on the catheter tip. When charring occurs, only the outer layer of tissue may be ablated, which means the lesion isn’t transmural. In addition, if tissue that has been charred breaks off, it can enter the blood stream and result in a stroke.
Charring — See char formation.
Circumferential ablation — A type of catheter ablation that involves lesions encircling the pulmonary veins. Some electrophysiologists also make an ablation line that connects the pulmonary veins on the posterior (back) wall of the left atrium or ablate tissue from the pulmonary veins to the mitral valve. A mapping catheter is used to identify potentials, which are areas that could serve as a trigger or a macro re-entry site for atrial fibrillation. There isn’t a single endpoint, so some doctors confirm conduction block whereas others look for elimination of potentials or a reduction in electrical activity.
Closed chest procedure — A procedure where the chest isn't opened by splitting the sternum (called a sternotomy), but instead the procedure is done through small incisions or ports.
Complex fractionated atrial electrograms (CFAE, pronounced cafe) — A site where there is an unusual electrical pattern, which could be due to the length of the electrical wave (long or short), the frequency of electrical activity (a lot or a little), or the speed of conduction (fast or slow). Complex fractionated atrial electrograms appear to represent macro re-entry sites for atrial fibrillation. Ablation of complex fractionated atrial electrograms is sometimes performed to treat persistent and longstanding persistent afib.
Computed tomography (CT) — A non-invasive diagnostic test that uses X-rays to take pictures of organs and tissue.
Conduction block — Confirmation that a lesion of scar tissue stops the erratic electrical signals from traveling through the heart.
Contact force — A measurement (in grams) of how much force the doctor applies to create lesions during catheter ablation. Contact force is one of the variables that affects transmurality. Contact force sensing catheters measure the amount of force applied.
Contact force sensing radiofrequency catheters — Contact force sensing catheters measure the amount of contact force applied to the tissue during catheter ablation as contact force can affect transmurality. With too little pressure, the lesion doesn't fully penetrate the tissue, but with too much pressure, complications can occur. To learn more, see Contact Force Sensing RF Catheters.
Contiguous lesions — Lesion lines without any gaps.
Coronary sinus — The vessel between the left atrium and the left ventricle.
Coumadin — A brand of anticoagulant, also called a Vitamin K antagonist. Warfarin is the generic name. Informally referred to as a blood thinner.
Cryothermy — Intense cold (freezing) that is used to ablate by creating a lesion of scar tissue to stop the erratic electrical signals from traveling through the heart.
Cycle — To circulate, propagate, or perpetuate atrial fibrillation.
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Dabigatran — An anticoagulant or anticlotting medication. It is a direct thrombin inhibitor, which works on a different stage of the clotting process than Coumadin (warfarin). Pradaxa is the brand name, and dabigatran is the generic name. Informally referred to as a blood thinner.
Duty-cycled RF — Where catheters cycle the radiofrequency energy on and off to allow tissue to cool and prevent char formation during catheter ablation.
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Echocardiogram — A non-invasive diagnostic test that uses ultrasound waves to create an image of the heart. A gel is often applied to the patient’s chest, and a technician moves a hand-held scanner (transducer) over the patient’s heart.
Efficacy — A medical term for effectiveness.
Ejection fraction — The measurement of how much blood is pumped from the ventricles to the atria during the cardiac cycle.
Electrical conduction — The way electricity is conducted within the heart.
Electroanatomic mapping system — A system that allows doctors to visualize structures in 3D and create appropriate lesions, particularly with the incorporation of previously-acquired magnetic resonance (MR) or computed tomography (CT) images. It also reduces fluoroscopy exposure to doctors and patients. Also called multi-modality mapping or image integration systems. To learn more, see Electroanatomic Mapping Systems.
Electrocardiogram (ECG or EKG) — A non-invasive diagnostic test during which electrodes are connected to a patient’s torso and electrical activity in the heart is recorded. It is painless and takes only a few minutes as you lie down for the test to be administered. You must be undergoing an episode of afib at the time of the EKG in order for it to be seen on the readout, which works best for patients in persistent or longstanding persistent atrial fibrillation. If afib episodes are intermittent, as with paroxysmal atrial fibrillation, then they most likely will not be recorded on the ECG and wearing a Holter monitor may be necessary to detect afib.
Electrodes — Small discs that transmit radiofrequency energy to tissue. Electrodes are used on some new ablation catheters.
Electrophysiologist (EP) — A specialized cardiologist who focuses on the electrical system of the heart and deals with irregular heartbeats (arrhythmias) such as atrial fibrillation. Catheter ablations are done by electrophysiologists.
Electrophysiology (EP) lab — Similar to an operating room for a surgeon, an EP lab is where an electrophysiologist performs procedures, such as atrial fibrillation ablation. The sterile room has a patient bed and typically has many monitors, as electrophysiologists use many imaging software systems during procedures.
Energy source — The energy used to create a lesion of scar tissue that stops the erratic electrical signals from traveling through the heart. Some typical energy sources used for atrial fibrillation procedures include radiofrequency energy, cryothermy, and laser energy.
Endoscope — A miniature camera that allows visualizing of the area to be ablated.
Endpoint — A goal of a procedure or a target result in a clinical trial.
Esophagus — The esophagus is the organ that begins at the top of the throat and extends to the stomach. It is the conduit through which food and beverages reach the stomach after swallowing. It is located behind the heart in the chest cavity.
Esophageal fistula — A rare but often fatal complication of catheter ablation. Since the esophagus is located behind the heart, heat used to ablate heart tissue can inadvertently heat the esophagus, creating a fistula (or opening) in the esophagus. Whether an esophageal fistula has been inadvertently created is typically unknown at the completion of the procedure. Symptoms may not appear for two to four weeks after the procedure. If untreated, esophageal fistula can lead to septic shock and death.
Event monitor — A small portable recorder that the patient normally wears attached to a belt or around the neck that records mobile electrocardiograms to detect the heart's electrical activity. The patient presses a button, or the device activates itself, when an afib episode begins. If afib episodes are so sporadic or infrequent that they are not captured on an EKG or Holter monitor, then an event monitor may be used to confirm atrial fibrillation.
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Feasibility study — In the United States, before a large trial can be conducted to evaluate the effectiveness of a drug or device, manufacturers must first prove that the drug or device is safe. Feasibility studies typically enroll 50 or fewer people. If results suggest that the treatment is safe, the drug or device would then proceed to a pivotal trial.
Fluoroscopy — An imaging technology that uses X-rays to provide real-time video of the heart during closed-chest procedures. It is the most frequently used imaging technology to help guide catheter ablation procedures. The images are two dimensional (flat) and are in black and white. During fluoroscopy, a catheter is inserted in the groin and threaded through the vessels to reach the heart.
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Ganglionated (or ganglionic) plexi (GPs) — These are "fat pads" in the heart that contain nerves that control automatic functions, such as breathing. These nerves also initiate electrical activity at various places in the heart, and when one ganglionated plexus (singular version of plexi) is activated, it is thought that another nearby will also be activated.
Ganglionated plexi ablation — Ablating the ganglionated plexi is an advanced strategy for stopping afib. Some doctors use mapping catheters with high frequency electrodes to identify ganglionated plexi, while others simply ablate the four primary ganglionated plexi in the left atrium. Ablation of the ganglionated plexi has not been widely adopted by electrophysiologists, which may be because there is little research data available.
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Holter monitor — A small portable recorder that the patient normally wears attached to a belt or around the neck that records mobile electrocardiograms to detect the heart's electrical activity. They can typically record for 24-hours, 48-hours, or seven days, and patients normally wear Holter monitors for 24–48 hours. If afib episodes are so sporadic or infrequent that it's unlikely that they will be captured on an EKG or Holter monitor, then an event monitor, which you activate or that activates by itself when an episode occurs, may be used to confirm atrial fibrillation.
Hybrid ablation — A procedure done as a collaboration between electrophysiologists and surgeons that combines in the same operation the best of catheter ablation, done on the inside the heart, and the mini maze procedure, done on the outside of the heart. This treatment, which is typically for patients with persistent and longstanding persistent afib, improves the chances of the ablation lines being transmural. Though not yet proven, higher success rates and fewer complications could be possible because each specialty ablates areas of the heart best suited to their different approaches.
Hybrid procedure — See hybrid ablation.
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Implantable cardiac defibrillator (ICD) — An implantable cardiac defibrillator is implanted in patients who are at risk for Sudden Cardiac Death.
Image integration systems — See electroanatomic mapping systems.
Implantable loop recorder — A small device implanted under the skin in the chest area to record the heart's electrical rhythms.
International Normalized Ratio (INR) — Tests that determine if warfarin or Coumadin are working correctly. A normal INR for someone in afib is 2.0–3.0, though those with mechanical valves should follow doctor instructions as to the appropriate INR for them. INR tests are sometimes called Prothrombin Time (PT) tests.
Intracardiac echocardiography (ICE) — A procedure that provides real time ultrasound images of the anatomy to facilitate the transseptal puncture (from the right atrium to the left atrium) and to guide catheter ablation.
Irrigated radiofrequency energy catheters (cooled RF) — A single point catheter with tiny holes at the tip that spread cooled water, usually a saline solution, to the ablation area to allow the electrophysiologist to deliver high levels of radiofrequency energy while moderating the temperature where the catheter connects with heart tissue.
Isolated — A state where the pulmonary veins no longer conduct the erratic electrical signals through the heart.
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Laser energy — Light waves that are converted to heat energy to ablate, or create a lesion of scar tissue, to stop the erratic electrical signals from traveling through the heart.
Learning curve — Refers to the "learning" that doctors acquire as they perform procedures. In general, the more procedures that a doctor performs, the better the outcomes (in terms of safety and efficacy) and the faster the procedure, as the doctor learns from earlier procedures what to do and what not to do. In medical devices, the learning curve is measured in terms of how many cases or procedures a doctor needs to perform in order to become proficient with the device or technology.
Left ventricular dysfunction — Refers to when the left ventricle doesn’t work properly. Left ventricular dysfunction is a component of heart failure.
Longstanding persistent atrial fibrillation — Persistent atrial fibrillation that has lasted beyond one year. This classification was used in the AHA 2006 Guidelines for the Management of Patients with Atrial Fibrillation and adopted by the HRS Expert Consensus Statement on Catheter and Surgical Ablation of Atrial Fibrillation.
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Macro re-entry sites — These are new pathways that are created that can allow afib to cycle in the heart. Macro re-entry sites are different for each patient.
Magnetic resonance imaging (MRI) — A non-invasive diagnostic test that uses a magnetic field and radiofrequency waves to create images of organs and vessels. MRI provides more detailed images than Computed Tomography (CT), but is more expensive. Patients with pacemakers or implantable cardiac defibrillators (ICDs) may not be permitted to have MRI scans.
Mapping catheter — Catheter used to determine whether there is electrical activity, called "potentials," around the pulmonary veins. These are areas that could serve as a trigger or macro re-entry site for atrial fibrillation.
Mini maze procedure — A minimally-invasive surgical ablation that uses an energy source to scar the tissue. It doesn't require opening the chest, so it has a shorter recovery time. It is less invasive than the other surgery options, and is slightly more invasive than catheter ablation. To learn more, see Mini Maze Procedure.
Mitral isthmus — The area where the mitral valve and the left inferior pulmonary vein meet.
Mitral valve — The heart valve connecting the left atrium and the left ventricle. When the left atrium contracts, the mitral valve opens and allows blood to flow into the left ventricle. When the left atrium relaxes, the mitral valve closes.
Multielectrode circumferential mapping catheter — Catheter used to verify that the pulmonary veins are electrically isolated during catheter ablation.
Multielectrode radiofrequency catheters — These ablation catheters have several electrodes, each of which can transmit radiofrequency energy, and can ablate a larger area of tissue than single point radiofrequency energy catheters. They can enable the use of bipolar radiofrequency energy, which may reduce complications that are seen with unipolar radiofrequency energy.
Multi-modality mapping — See electroanatomic mapping systems.
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Neurological deficits — Problems with normal activities, such as speech or walking, often due to a stroke or transient ischemic attack (TIA).
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Ostia — The openings of the pulmonary veins. The singular form is ostium.
Ostial Pulmonary Vein Isolation — See Segmental Pulmonary Vein Isolation.
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Pace — The process of placing probes, which emit electricity, against cardiac tissue to stimulate nerves and/or electrical impulses.
Pacemaker — A medical device implanted under the skin in the chest area. A wire lead is connected from the pacemaker to the patient’s heart. A pacemaker is sometimes necessary if the electrical impulses in a patient’s heart are too slow. Pacemakers do not treat atrial fibrillation. However, some patients after having afib surgery may require a permanent pacemaker.
Paroxysmal atrial fibrillation — Atrial fibrillation episodes that come and go, but generally resolve themselves within seven days. This is sometimes referred to as intermittent afib. This classification was used in the AHA 2006 Guidelines for the Management of Patients with Atrial Fibrillation and adopted by the HRS Expert Consensus Statement on Catheter and Surgical Ablation of Atrial Fibrillation.
Permanent atrial fibrillation — Persistent or longstanding persistent atrial fibrillation in which a decision has been made not to try to restore normal sinus rhythm by any means, including catheter or surgical ablation. This classification was used in the AHA 2006 Guidelines for the Management of Patients with Atrial Fibrillation and adopted by the HRS Expert Consensus Statement on Catheter and Surgical Ablation of Atrial Fibrillation.
Persistent atrial fibrillation — Atrial fibrillation episodes that generally last beyond seven days or require intervention to terminate, such as medication or electrical cardioversion. This is sometimes referred to as continuous afib This classification was used in the AHA 2006 Guidelines for the Management of Patients with Atrial Fibrillation and adopted by the HRS Expert Consensus Statement on Catheter and Surgical Ablation of Atrial Fibrillation.
Phased RF — Ability to automatically turn on and off radiofrequency energy to allow tissue to cool to avoid overheating and charring of tissue.
Phrenic nerve — The nerve that automatically prompts the diaphragm to expand and constrict during normal breathing. It is located near the pulmonary veins. Phrenic nerve injury is a potential complication of catheter ablation and makes normal breathing difficult.
Pivotal trial — A clinical trial that evaluates efficacy and safety of a drug or device in a large group of people, often at several centers. Results from a pivotal trial are submitted to the Food & Drug Administration (FDA) to support FDA approval for the treatment. Pivotal trials for investigative drugs are usually randomized, so that a patient may receive the experimental drug or an already-approved FDA drug or placebo. In a medical device pivotal trial, patients may or may not be randomized. In recent ablation catheter pivotal trials, patients were randomized to either receive treatment by the ablation catheter or by an antiarrhythmic medication.
Posterior — The back wall of the heart.
Potentials — Areas that could serve as a trigger or macro re-entry site for atrial fibrillation.
Pradaxa — An anticoagulant or anticlotting medication. It is a direct thrombin inhibitor, which works on a different stage of the clotting process than Coumadin (warfarin). Pradaxa is the brand name, and dabigatran is the generic name. To learn more, see FDA Approves Pradaxa as Alternative to Warfarin for Stroke Prevention in Atrial Fibrillation.
Pulmonary veins — The veins that connect the lungs to the left atrium. See them in this diagram of the heart.
Pulmonary Vein Antrum Isolation (PVAI) — This type of catheter ablation involves lesion lines in the antrum of the pulmonary veins, and doctors confirm that conduction block has been achieved. It may include additional lesion lines in the superior vena cava, roof of the atrium, or the septum, but these vary by doctor and there isn’t a standard set of lesion lines.
Pulmonary vein isolation (PVI) — Ablation of the area around the pulmonary veins to block electrical impulses that stop atrial fibrillation from perpetuating in the heart. Also called pulmonary vein antrum isolation (PVAI). The first Pulmonary Vein Isolation procedures ablated tissue in the ostia (opening) of the veins. Ostial Pulmonary Vein Isolation, also called Segmental Pulmonary Vein Isolation, led to a high incidence of pulmonary vein stenosis (narrowing of the veins). As a result, PVI or PVAI, ablation performed on the outer area of the veins, is mostly performed today.
Pulmonary vein ostium — The opening to the pulmonary veins.
Pulmonary vein stenosis — A significant narrowing of the pulmonary veins that can result from catheter ablation. This is a serious complication that can obstruct oxygenated blood from flowing from the lungs into the heart.
Pulmonary vein venography — A procedure that helps determine the location of the pulmonary vein ostia, the base of the pulmonary veins, and guides the manipulation of the catheter.
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Radiofrequency energy — Radio waves that are converted to heat energy to ablate, or create a lesion of scar tissue, to stop the erratic electrical signals from traveling through the heart.
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Segmental Pulmonary Vein Isolation — The first pulmonary vein isolation procedure, which was performed by Michel Haïssaguerre, MD, and colleagues. Ablation was performed in the ostia (opening) of the pulmonary veins. However, a high incidence of pulmonary vein stenosis (narrowing of the pulmonary vein) occurred, which led to other techniques outside and around the pulmonary veins. Also called Ostial Pulmonary Vein Isolation.
Septal wall — The wall between the left and right atria.
Sequential ablation — See stepwise ablation.
Silent brain infarcts — Areas of the brain that are cut off from blood supply and oxygen but do not result in noticeable neurocognitive impairment. Those who have silent brain infarcts have a higher risk of getting dementia or experiencing cognitive decline.
Single point radiofrequency catheter — An ablation catheter that emits radiofrequency energy from a single point at the catheter tip.
Steam pops — A potential complication of irrigated radiofrequency ablation catheters, which use water or a saline solution to cool the temperature of the tissue at the ablation site. The high temperature created by radiofrequency energy can cause water inside of tissue to boil. Sometimes so much steam builds up that it bursts through the tissue. Steam pops look like craters and can lead to cardiac perforation.
Stepwise ablation — This catheter ablation strategy, which is the only one with a stated goal of terminating afib, involves isolating the pulmonary veins and making additional lesion lines, such as the roof of the left atrium, the coronary sinus, or the mitral isthmus, and then checking for conduction block after each. This is sometimes called sequential ablation because the additional lesion lines are often performed in the doctor's own specified order.
Sternum — The breastbone, which is split to allow access to the heart for an open-chest procedure.
Sternotomy — An incision that splits the sternum in order to do an open-chest procedure.
Stroke — A stroke happens when an artery that carries blood to the brain gets clogged by a blood clot (ischemic stroke) or ruptures (hemorrhagic stroke), depriving the brain of oxygen. Without oxygen, the nerve cells in the brain die and cannot be restored. This causes permanent disability in the parts of the body controlled by the impacted nerve cells. For more information about strokes, see Stroke Risks from Afib.
Substrate — The deeper layers of heart tissue.
Substrate modification — See atrial remodeling.
Superior vena cava — The vessel that transports de-oxygenated blood from the body back to the right atrium of the heart. See it in this diagram of the heart.
Symptomatic — Atrial fibrillation that the patient feels or recognizes.
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Thrombus (clot) — A thrombus can form naturally within the body, such as blood that enters the left atrial appendage and is "caught" on the rough edges of the interior of the left atrial appendage. This becomes a blood cot and, if it detaches, can travel through the blood stream and reach the brain, causing a stroke. A thrombus, or clot, can also form during a procedure, such as a catheter ablation. When heat-based energy is applied to tissue, charring of blood or tissue can follow. If this charred blood or tissue detaches from the heart, it can enter the blood stream and reach the brain, causing a stroke.
Transesophogeal echocardiogram (TEE) — An invasive imaging test that uses ultrasound waves to create images of the heart. A small tube with a miniature scanner ("transducer") is inserted into the patient’s mouth and guided into the esophagus. The transducer emits sound waves toward the heart and records the sound waves that are "reflected" off the heart to create images. It is often used prior to a procedure, such as a cardioversion, catheter ablation, or surgery, to determine if there are any blood clots in the heart.
Transient ischemic attacks (TIAs) — Often called "mini-strokes", they are considered to be warning strokes as a blood clot temporarily blocks an artery. TIAs usually last no more than five minutes, and may only last for seconds. They leave no permanent damage. Those who have had a TIA are much more likely to have a stroke. One-third of those who have had a TIA will have a stroke, often within a year. For more information about TIAs and strokes, see Stroke Risks from Afib.
Transmural lesion — An ablation line that fully penetrates the inner and outer layers of cardiac tissue and prevents chaotic electrical activity from circulating in the heart.
Transmurality — When a lesion has fully penetrated the inner and outer layers of cardiac tissue it is known as transmural, which creates a conduction block that prevents afib from circulating in the heart.
Trigger — An anatomic area, such as the pulmonary veins, that emits electrical impulses that initiate atrial fibrillation. Also, as a secondary definition, there are various things that are referred to in the patient community as triggers because they start an afib episode. Foods, alcohol, stress, and many other things are commonly considered as triggers within the afib patient community.
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Unipolar radiofrequency energy — Unipolar is radiofrequency energy that is transmitted from a single point at the catheter's tip.
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Warfarin — An anticoagulant, also called a Vitamin K antagonist. Coumadin is the brand name. Informally referred to as a blood thinner.
Wavelength — The heart’s natural "electricity system" emits energy at varying lengths and speeds. Wavelength is one attribute electrophysiologists evaluate in order to diagnose and treat arrhythmias.
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