Glossary of Pacing Terms

This is a glossary of terms that you may hear your doctor or nurses use about pacemakers and related devices. If healthcare professionals use terms you don’t understand, you should always feel the liberty to ask them what they mean or ask them to express it again in plain language. But this will get you started:

ablate-and-pace. A nickname for AV nodal ablation for permanent atrial fibrillation. In this procedure, a small area inside the heart is ablated (destroyed surgically) and a pacemaker is implanted.

AF. The abbreviation for atrial fibrillation, sometimes called A-fib or AFib.

A-Fib. Another term for atrial fibrillation, more common in speech than writing.

asystole. (Pronounce this a-sis-toe-lee.) This is what is happening in the heart when an EKG “flat lines.” Systole refers to the heart’s contraction or squeezing together to pump out blood. A-systole means “without systole,” or a heart that is not pumping. While asystole is observed in dead people, a person can go into asystole (“flat line”) and be resuscitated, that is, brought back to life, providing the person is rescued in a short period of time.

AT. Atrial tachycardia. Sometimes called A-tach or A-Tach.

A-Tach. Another term for atrial tachycardia, more common in speech than in writing.

atria. The plural of atrium, the upper chambers of the heart. A healthy heart has two atria, a right atrium and a left atrium.

atrial arrhythmia. Any abnormal heart rhythm that originates in the upper chambers of the heart. An atrial arrhythmia may affect both chambers of the heart, but it takes its name from the place where the rhythm problem is thought to originate. This is a general terms that includes atrial tachycardia, atrial tachyarrhythmia, and atrial fibrillation. Note that if the atrial rhythm disorder involves a rhythm that is too slow, it is not called “atrial bradycardia” or “atrial bradyarrhythmia.” A too-slow rhythm that originates in the heart’s upper chambers is called “sinus node dysfunction” or “sick sinus syndrome.” Similar stuff: atrial fibrillation, atrial tachyarrhythmia, atrial tachycardia, supraventricular tachycardia (SVT),

 atrial contribution to ventricular filling.The healthy heart beat or cardiac cycle has four parts: rest, atrial contraction, rest, and ventricular contraction. The atrial part occurs before the ventricular beat so that the atria can feed maximum blood into the ventricles prior to pumping. That’s why this phase (the atrial contraction) is called the atrial contribution to ventricular filling.

atrial fibrillation. Atrial refers to a rhythm disorder which originates in the atria or upper chambers of the heart; fibrillation refers to the most extreme form of a too-fast rhythm. Although experts may disagree on what rate exactly is the “starting point” for atrial fibrillation, typical AF episodes can involve the heart’s upper chambers beating at rates of 250 to 300 beats a minute. Although AF originates in the atria, it does not stop there. As the atria beat rapidly, the heart tries to conduct this activity to the ventricles, which often results in a very rapid and uncomfortable ventricular rate—which can produce symptoms. In fact, most symptoms of AF are caused by the ventricular response to AF. But this is not to say that AF is safe. AF is associated with many other disorders, most notably the increased risk of stroke. People with AF are five times more likely to have a stroke than those without AF. AF occurs in three stages known to doctors as paroxysmal, persistent and permanent. AF is called a “progressive disorder,” meaning that it starts in a mild form but can progress to worse forms over time.

atrial flutter. A very specific type of rhythm disorder that originates in the heart’s upper chambers (atria) and is characterized an EKG with a shark-fin or “saw-tooth” pattern. Atrial flutter is not as severe as atrial fibrillation.

atrial tachyarrhythmia. This is the broad general term for any too-fast rhythm that originates in the heart’s upper chambers or atrial. This would include atrial tachycardias (slower) and atrial flutter (faster) and atrial fibrillation (fastest).

atrial tachycardia. An abnormal and too-fast heart rhythm that originates in the atria. The term “atrial” tachycardia does not indicate a rhythm disorder that occurs or only affects the atria, it refers to a rhythm disorder which originates in the atria. AT, as it is abbreviated, can occur at a variety of different rates with the fastest—and most dangerous—being atrial fibrillation (AF). But even slower forms of atrial tachycardias can be dangerous and uncomfortable. With AT, the upper chambers of the heart beat too quickly. This can cause the person to experience palpitations, the sensation of a “racing heart,” or sensations of a pounding chest. Sometimes people may experience tiredness or shortness of breath, but these symptoms are so vague that they may or may not be directly related to an episode of AT. As the atrial beat quickly, the activity may conduct down to the heart’s lower chambers and cause the ventricles to beat too quickly. This can worsen the above symptoms. AT at lower rates may not cause any symptoms at all. In fact, some people experience AT and never know it. AT may occur in short spells or episodes which start without warning and end on their own, without medical help. However, AT can progress to states where spells last longer and longer and sometimes may not go away without special medical treatment.

atrium. One of two upper chambers of the heart (plural: atria). The atria sit on top of the large pumping chambers called ventricles. Although we usually think of the heartbeat as one unit, in actual fact, there is first an atrial beat, then a short pause, followed by a ventricular beat. The ventricular beat is the thing a doctor hears through a stethoscope. However, the atrial beat plays a very important role in getting blood circulated through the body. Before every ventricular heart beat, the ventricles fill with blood. But in the first phase of the heart beat, the valve between the atrium and ventricle on each side of the heart (right and left) closes and the atria fills with blood as well. Then the valve opens and the atria pumps out all of its blood into the already-filled ventricles. The result is that the ventricles are filled even beyond the “full point” with blood; in fact, the ventricles have to stretch out a bit to take in all of this blood. This stretching action—called “contractility”—actually helps the heart pump better. Think of a rubber band, which snaps back very vigorously when it’s stretched. The same thing happens to the muscle fibers in the ventricle. By adding an extra measure of blood and stretching the ventricular muscle fibers, the ventricle pumps out a greater volume of blood more forcefully. This function is sometimes called “the atrial contribution to ventricular filling,” and it’s one reason that atrial activity is so important to the body.

arrhythmia. Although this word’s roots means “without a rhythm,” this word is commonly used by doctors to refer to any sort of abnormal heart rhythm but particularly one that needs treatment. There are two main types of arrhythmias—those where the heart beats too quickly (tachyarrhythmias or tachycardias) and those where the heart beats too slowly (bradyarrhythmias or bradycardia). Not all arrhythmias require treatment. It is possible for an arrhythmia to occur suddenly and to go away suddenly.Synonyms: dysrhythmia, rhythm disorder

asymptomatic. What a doctor or nurse would say about a physical condition or disease that the does not cause a person to notice or complain about anything unusual. Many heart conditions are “asymptomatic” in that people may not be aware there is anything wrong with them. An “asymptomatic bradycardia” means that the doctor has seen the person’s heart is beating too slowly, but this has not caused the person any noticeable problems.

AV block. A specific form of conduction disorder and one that affects about half of the people who have a pacemaker. People with AV block may have atria (upper chambers) that work normally and ventricles (lower chambers) that work normally, but the heart’s problem is electrical. The conduction pathway or route that electricity takes as it goes from the upper chambers down to the lower chambers gets delayed or blocked along the way. The result is a heart that cannot beat in synchrony (one atrial beat followed quickly by one ventricular beat). There are three degrees of AV block, with first degree the least severe and third degree the most severe. People with first-degree AV block experience a conduction delay, but may not have symptoms. Even if they have symptoms, they are likely to be mild. In many cases, people with first-degree AV block do not get pacemakers or medication. Second-degree AV block means the electricity is delayed to the point that the heart starts to loose its ability to beat in AV synchrony (one atrial beat to each ventricular beat). Symptoms are not unusual in these people, and many will get pacemakers. Third-degree AV block is sometimes called “complete AV block” or “complete heart block” because the electricity that starts at the top of the heart is completely blocked and does not make it down to the lower chambers. Such people almost always require medical intervention, typically in the form of a pacemaker.

AV nodal ablation. A surgery for certain people with permanent atrial fibrillation in which a portion of the heart (the AV node) is surgically destroyed (usually by radio-frequency energy, heat or cold). The destruction (ablation) of a portion of the AV node severs the conduction pathway from atria (upper chambers) to ventricles (lower chamber). For people with permanent atrial fibrillation, this means that the upper chambers will not drive the lower chambers to beat too quickly and cause symptoms and other problems. AV nodal ablation does not cure AF; the AF continues, but the electricity has nowhere to go. People who have an AV nodal ablation typically require the implantation of a permanent pacemaker (or CRT pacemaker) to keep the ventricles beating at the right rate. This procedure is sometimes nicknamed “ablate-and-pace.”

AV node. A small area of tissue located at the point within the heart where the lower portions of the right and left atria and the upper portions of the right and left ventricles meet. This small specialized section of tissue has electrical properties that slows the electricity as it passes through the heart, allowing the atria to beat first and relax before the ventricles beat. The AV node is the portion of the heart’s electrical system that allows the atria (upper chambers) to communicate with the ventricles (lower chambers).

AV synchrony. A medical term for the proper timing of the heart’s upper chambers (atria) with the lower chambers (ventricles). A normal heartbeat actually consists of two contractions or beats: the upper chambers (atria) followed by the lower chambers (ventricles). The upper chambers beat first, then there is a short pause, followed by a ventricular beat. In a healthy heart, there is what doctors call one-to-one (1:1) AV synchrony. This means for every atrial beat, there follows a corresponding ventricular beat. Some rhythm disorders change 1:1 AV synchrony. It is believed that loss of 1:1 AV synchrony can cause symptoms. Dual-chamber pacemakers are designed to promote 1:1 AV synchrony because they pace the upper chambers and then the lower chambers.

bradyarrhythmia. Although not used as frequently as its synonym, “bradycardia” refers to any type of rhythm disorder in which the heart beats too slowly. There is no general agreement on what “slow” is, since athletes and people in peak physical condition have heart rates that are much slower than normal and babies and small children have heart rates that are higher than adults. Bradyarrhythmias may or may not have symptoms. When the symptoms are severe, the bradyarrhythmia may require treatment. One of the most typical ways to treat a bradyarrhythmia is with a pacemaker.

bradycardia. A type of rhythm disorder in which the heart beats too slowly. There is no general agreement on what “slow” is, since athletes and people in peak physical condition have heart rates that are much slower than normal and babies and small children have heart rates that are much higher than the rates of adults. Bradycardia may or may not have symptoms. When the symptoms are severe, the bradycardia may require treatment. One of the most typical ways to treat a bradycardia is with a pacemaker.

cardiac cycle. The medical term for the various things that happen in what we would call “one heartbeat.” The heartbeat consists of four distinct stages. In the first stage, the heart’s upper chambers (atria) beat. This is followed by a very short rest (usually measured in thousandths of a second). Then the heart’s much-larger lower chambers (ventricles) contract. This makes the sound that we typically associate with the heart beat and it’s the main noise that a stethoscope would pick up. This is followed by a short moment of relaxation. Then the cycle repeats itself. The period of contraction (beating) is sometimes called systole while the period of resting or relaxation is called diastole.

cardiac output. A measurement to help tell how efficient the heart is at pumping blood. It refers to how much blood (in liters) the heart can pump in one cardiac cycle or one heart beat. Cardiac output is essential to life in that the heart pumps oxygen-rich blood that fuels the body.

cardiac resynchronization therapy. Cardiac resynchronization therapy (CRT) requires an implanted device (like a pacemaker or ICD) which uses at least three wires or leads. One of these leads goes into the right upper chamber (right atrium), another goes into the right lower chamber (right ventricle) near the interior wall, and the other goes through one of the veins in the heart to be close to the left lower chamber (left ventricle). CRT is used to treat people with specific kinds of heart problems because it works to synchronize the heart’s pumping action. A common misconception (even in the medical world) holds that CRT synchronizes the right side of the heart with the left side. Actually, CRT works to synchronize the heart’s large left ventricle with itself! The left ventricle is the large chamber in the heart that pumps oxygen-rich blood out into the body; it’s the main “pump” of the heart. Some people develop a heart disease (LV dysfunction) which causes the left ventricle to beat in segments rather than all at once. The left ventricle tries to pump, but it contracts on one side first, then the other side. The result is that blood swirls around inside the heart without being pumped outward. A CRT device uses electrical energy to force the left ventricle to beat as one unit. It does this by sending electrical energy to the wall between right and left ventricles at the same time it sends energy to the left ventricle. The result is that the left ventricle contracts at one time, making it a better pump.

CHF. Congestive heart failure. This term is considered a bit old-fashioned in medical circles today because it is possible to have heart failure without congestion (water retention) and it is possible to have congestion without heart failure. At one time, all heart failure was termed CHF; that is less frequently the case today.

chronotropic competence. The ability of the healthy heart to automatically adjust its rate to be appropriate for the level of activity going on. For example, a chronotropically competent heart will decrease its rate when a person is sitting still and watching TV, but increase its rate when that same person goes out to play tennis.

chronotropic incompetence. The medical lingo for a condition in which the heart cannot beat fast enough to keep up with a person’s activities or needs. For example, the heart should beat more quickly when a person runs and slower when a person is sleeping. When the heart is working properly, the body automatically adjusts the heart rate to be appropriate to the activity. A person in an exercise class should experience an elevated heart rate. If the heart does not adjust the rate to be appropriate for activity or if it makes the adjustment only very slowly or incompletely, the doctor will diagnose “chronotropic incompetence.” Many pacemaker patients have some degree of chronotropic incompetence.

complete AV block. This is the same as the term “complete heart block” (below).

complete heart block. A type of heart rhythm disorder in which electrical signals from the heart’s upper chambers (atria) do not conduct down to the lower chambers (ventricles). The signals are blocked at or around the AV node (between atria and ventricles). This is also called “third-degree heart block” or “third-degree AV block” and is the most serious form of heart block. In complete heart block, the upper chambers effectively have no communication with the lower chambers. Pacemakers are used to treat people with complete heart block.

contractility. A medical word for the stretchiness of muscle fibers. Muscles are designed to be able to stretch out and contract back. The heart walls are actually made of muscle with the property of contractility. They not only can stretch out and contract, the fibers are designed so that the more they stretch, the harder they snap back. This means that a heart filled to the maximum can contract more vigorously (and pump more blood) than a heart which is not filled to the stretching point. A good example of contractility is the rubber band: if you stretch a rubber band hard, it snaps back more energetically than if you just pull it a little.

CRT. Cardiac resynchronization therapy, a type of pacing therapy in which the right and left ventricles (and usually the right atrium, too) are paced. The goal of CRT is to resynchronize both sides of the ventricles. A non-CRT device paces only the right ventricle.

CRT-D. A nickname for a CRT device with a built-in defibrillator.

CRT-P. A nickname for a CRT device that offers only pacing or low-voltage stimulation, in other words, it does not have a built-in defibrillator.

diastole. The portions of the heart beat (or “cardiac cycle”) during which the heart’s chambers relax or rest. Each cardiac cycle consists of a resting phase (diastole) followed by the contraction of the upper chambers (atrial systole), then another moment of rest (diastole) and the contraction of the lower chambers (ventricular systole). The cycle then begins again. The resting or relaxing phases are known as diastole.

diastolic blood pressure. The blood pressure reading taken during periods when the heart is at rest. Since the heart is not beating, diastolic blood pressure is lower than systolic blood pressure, which is taken during times when the blood is being pumped by the heart. In a blood pressure reading of 120/60, 120 is the systolic value and 60 is the diastolic value.

dual-chamber. A description for a cardiac device which has one lead (wire) in the right atrium and another lead in the right ventricle. A dual-chamber pacemaker always has two leads. The main purpose of a dual-chamber pacemaker is to pace the heart in a way that tries to synchronize activity in the upper portion of the heart with activity in the lower portion of the heart. The coordination of upper and lower chambers is known as AV synchrony.

dysrrhythmia. From the standpoint of the roots of the word, this is best word to use for rhythm disorder because it means a dysfunctional or poorly functioning heart rhythm. In actual fact, this word is only rarely used by medical people. It refers to any abnormal heart rhythm, but particularly one that needs treatment. There are two main types of arrhythmias—those where the heart beats too quickly (tachyarrhythmias or tachycardias) and those where the heart beats too slowly (bradyarrhythmias or bradycardia). Not all arrhythmias require treatment. It is possible for an arrhythmia to occur suddenly and to go away suddenly.

electrophysiologist. A physician who specializes in the electrical conduction system of the heart. Electrophysiologists are familiar with rhythm disorders, cardiac rhythm devices, and electrical problems of the heart. Sometimes abbreviated EP.

EP. An abbreviation which sometimes refers to electrophysiologist (the doctor) and other times refers to electrophysiology (as in EP lab or EP test).

first-degree AV block. A type of cardiac rhythm disorder in which the electrical impulses from the heart’s upper chambers (atria) do not reliably conduct to the ventricles. First-degree AV block is not as severe as complete AV block. In first-degree AV block, some conduction impulses get through but they are not properly timed. People with first-degree AV block do not always have symptoms and may not need a pacemaker.

heart attack. A heart attack is a very specific problem with the heart that occurs when the veins on the outside of the heart get clogged to the point that oxygen-rich blood cannot get to the heart muscle. This causes portions of the heart muscle to start to die. Depending on how much of the heart is affected and how severe the blockage is, the heart attack may be fatal or it may be barely noticed. Even if a person survives a heart attack, a portion of the heart muscle (myocardium) has died and the heart may no longer function as well as it once did. A heart attack should be thought of as a “plumbing problem” causes by clogged pipes which prevents the heart from pumping effectively. It is not the same as sudden cardiac arrest which is an “electrical problem.” Synonyms: myocardial infarction, MI

heart block. A type of rhythm disorder in which impulses from the heart’s upper chambers get delayed or even blocked within the heart before they can travel down to the lower chambers. There are three main degrees of heart block (1st degree, 2nd degree and 3rd degree, with 1st degree the most mild and 3rd degree the most severe) and four different types. Depending on the type and severity of heart block, it may or may not require treatment (some forms of heart block are so mild that the doctor may not want to even treat it). Some types of heart block require a pacemaker. In fact, about half of the patients who get a pacemaker get it mainly because they have some form of heart block. Synonyms: AV block

heart failure. A syndrome (meaning it’s more of a collection of symptoms and conditions than a specific disease) in which the heart no longer pumps blood efficiently to the body. Despite its name, heart failure does not mean that the heart fails suddenly. Heart failure is a progressive syndrome, meaning it comes on gradually. Doctors classify heart failure into four main classes (I, II, III and IV) with IV the most severe. People with Class I heart failure do not even have symptoms and may be unaware they have heart failure. Typical symptoms of heart failure include fatigue, weakness, lightheadedness, and fluid retention. Heart failure is treated with drug therapy and may require the implantation of a CRT device. Learn more: heart failure drugs, CRT, congestive heart failure

HF. Heart failure.

implantable pulse generator. A small device that is implanted into the body and used to generate small amounts of electrical energy (“pulses”) to treat a number of conditions. One of the most common forms of implantable pulse generators are pacemakers. Pulse generators may also be used in the treatment of epilepsy, obesity, depression, and to manage chronic pain. (These devices are not exactly the same as pacemakers but they are based on the same pulse generator concept. Synonym: pulse generator, IPG

IPG. Abbreviation for implantable pulse generator

lead. (Pronounced leed.) The wire that goes into the heart (at one end) and plugs into the pulse generator (at the other end) to create a pacemaker. A pacing lead has one or more electrodes at the end that goes into the heart. With these electrodes, the lead can “listen” and pick up activity in the heart in a process known as “sensing.” If the pacemaker decides to send out a small amount of electrical energy, that energy (or pulse) goes out through the electrode(s). The main body of the lead is insulated and contains wires that plug into the pulse generator. Some pacemakers require one lead, others require two or more. Unlike pulse generators, a lead requires no battery or energy supply so it may last many years—even a lifetime—in the body without replacement.

LV dysfunction. The inability of the heart’s left ventricle to pump blood efficiently, often defined by a low LVEF score (see below). The left ventricle is the largest chamber of the heart and the most muscular one. Its job is to pump oxygenated blood fresh from the lungs out into the entire circulatory system. When the left ventricle is no longer able to do this well, the person may experience symptoms of weakness, fatigue, or shortness of breath. Most people with heart failure have some degree of LV dysfunction. Synonym: systolic dysfunction (systole refers to the “pumping out phase” of the cardiac cycle, which is the job of the left ventricle).

LVEF. This acronym is almost never written out, but it stands for left-ventricular ejection fraction. It defines, as a percentage, how much of the blood within the left ventricle of the heart is actually pumped out in a given left-ventricular contraction (heart beat). LVEF numbers are sometimes a bit misleading, in that nobody has an LVEF of 100%. There is no a universal agreement as to what normal or abnormal LVEF scores are, but as a general rule, an LVEF below 40% is considered low and indicated LV dysfunction. Most doctors would agree that an LVEF of 60% or above is great. The area around 50% is a bit controversial; some doctors would say this is normal, others would say it is low.

MI. Myocardial infarction (heart attack).

pacemaker. A small implantable device that is usually inserted in the upper area of the chest and connects to wires that go through a vein and into the heart. The pacemaker monitors the heart and sends out a small electrical pulse (usually just a few volts) to the heart when it senses that the heart is not beating fast enough. This electrical pulse causes the heart muscle to contract or beat. Pacemaker may describe just the implanted device (which is also called an “implantable pulse generator” or “pulse generator”) or it may include the pacemaker and the wire or wires that plug into it. The wires are called leads. Synonym for device only: implantable pulse generator, pulse generator

parameter. A type of setting for the pacemaker or defibrillator. A parameter is the type of setting (such as “rate”); clinicians can then adjust it to any number of available values called settings.  Most modern pacemakers have many different parameters and even more settings to allow for pacemaker function to be individualized for each patient.

paroxysmal. The medical term for “sudden,” this word is usually used to describe something such as a rhythm disorder that starts abruptly.

programmer. A special table-top computer which is able to communicate with an implanted device and allows the doctor or nurse to make changes in how the device is set. Programmers run on proprietary (company-specific) software. The doctor or nurse is able to use the programmer to get information from the memory of a pacemaker, to check on battery status, and to view current settings (and change them). Only the programmer made by a company can program devices made by the company. Sometimes, special devices require a special programmer. Most pacemaker clinics keep several types of programmers available.

programmer software. The software that is used to run the programmer. Manufacturers update programmer software regularly so that programmers can communicate with the latest generation of devices. Software updates are usually done by a company representative who downloads the new software from a plug-in card or insertable media.

programming wand. On the programmer, the device—which looks sort of like TV remote control unit—that must be placed over the implanted device in order for the programmer to be able to communicate. The wand is usually attached to the programmer by a wire or coiled wire but some new programmers have cordless wands. The wand is used to establish what doctors call “telemetry” (communication).

pulse generator. A small device that is implanted into the body and used to generate small amounts of electrical energy (“pulses”) to treat a number of conditions. One of the most common forms of pulse generators are pacemakers. Pulse generators may also be used in the treatment of epilepsy, obesity, depression, and to manage chronic pain. (These devices are not exactly the same as pacemakers but they are based on the same pulse generator concept.) Synonym: implantable pulse generator

rhythm disorder. An abnormal heart rhythm as defined by the rate or the sequence/timing of beats or both. There are two main types of arrhythmias—those where the heart beats too quickly (tachyarrhythmias or tachycardias) and those where the heart beats too slowly (bradyarrhythmias or bradycardia). Not all arrhythmias require treatment. It is possible for an arrhythmia to occur suddenly and to go away suddenly. Synonyms: arrhythmia, dysrhythmia

SA node. Sinoatrial node. This is a little area of tissue in the high right atrium that generates the electricity that causes the healthy heart to beat. The SA node is sometimes called the heart’s “natural pacemaker.” Synonym: sinus node

SCA. Sudden cardiac arrest. This sounds like the heart stops but actually in SCA the heart is trying to beat so rapidly it can no longer contract and relax fully and winds up quivering and not pumping. SCA is most often associated with ventricular fibrillation, where the heart tries (and fails) to beat 200, 250, even 300 beats a minute or more. SCA is the same as SCD (sudden cardiac death), but SCA is more commonly used today.

SCD. Sudden cardiac death.

second-degree AV block. A type of heart block where impulses from the upper chambers of the heart (atria) get delayed in the AV node and are not reliably conducted to the lower chambers (ventricles). In second-degree AV block, some impulses are blocked entirely and others are delayed. Some forms of second-degree AV block may require treatment with a pacemaker.

sick sinus syndrome. A general term that covers a lot of possible conditions and complaints that arise when a person’s sinoatrial or SA node is not functioning properly. The SA node’s job is to send out a small bit of electrical energy every time the heart should beat. This electricity originates from the SA node (in the right upper chamber of the heart) and then travels down through the heart causing it to beat. When something happens and the SA node does not work properly, typically by not sending out electricity often enough or rapidly enough, a rhythm disorder can result. In fact, about half of the people who get pacemakers get it for some form of sick sinus syndrome (sometimes abbreviated SSS). Synonyms: SSS, sinus node dysfunction

sinoatrial node. A tiny patch of specialized heart cells located high up on the heart’s upper right chamber. The sinoatrial node—also called the SA node—is able to generate a small amount of electricity which then travels down the heart and causes it to beat. When the SA node is working properly, it sends out electricity at exactly the right moments to keep the heart beating at the right rate. When the SA node malfunctions and sends out beats too quickly, too slowly, or in a disorganized way, a rhythm disorder can result. The SA node is sometimes called the “heart’s natural pacemaker.” Synonyms: SA node, sinus node

systole. The medical term for the portion of the cardiac cycle in which the blood is pumped out into the body.

systolic blood pressure. The first number of a blood pressure reading, which reports blood pressure as the heart is pumping blood out into the system (during systole).

sinus node. Another term for the sinoatrial or SA node. Synonyms: SA node

sinus node dysfunction. Another term for sick sinus syndrome. Depending on its severity and symptoms, it may require treatment with a pacemaker.

SVT. An abbreviation for supraventricular tachycardia. This refers to any too-rapid heart rhythm that originates above the ventricles (atrial or AV-nodal). Atrial fibrillation is a type of SVT.

sudden cardiac arrest. A general medical term for any condition which causes the heart to abruptly stop working as a pump. This condition is usually caused by an electrical problem in the heart. In most (but not all) cases, sudden cardiac death (SCD) is caused by a rhythm disorder known as ventricular fibrillation or VF. It occurs when the heart’s electrical signals get mixed up to the point that the heart tries to beat at rates of 250 or 300 beats a minute or higher. The healthy heart beats about once a second. Try opening and closing your fist (that’s about the size of the heart) and you can easily keep pace with a rate of 60 beats a minute. But if you try to open and close your fist at a rate of 250 or 300 beats a minute, you’ll find you can’t really fully open or close it. The same thing happens to the heart. Instead of actually beating, it starts to quiver. It stops pumping blood. This can be fatal in minutes. One way to rescue a person experiencing SCD is to defibrillate them, that is, apply a large “jolt” of electricity to the heart. This electricity can often restore the heart’s normal rhythm.

supraventricular tachycardia. A general term for any too-fast heart rhythm that originates “above the ventricles” or “supra-ventricularly.” While supraventricular tachycardias or SVTs include atrial tachyarrhythmias, an SVT can also be a too-rapid heart rhythm that originates in the AV node.

symptomatic. The official word that describes a physical condition which causes the person who has it to complain. Symptoms are always reported by the patient. (“I feel tired,” “My chest hurts,” “I almost passed out.”) They are different than signs which are indications of an illness that the patient does not report. (For instance, a sign might be a fever that is detected at the doctor’s office or slurred speech.) Many heart conditions cause people to go to their doctor and report symptoms. If the patient has complaints (fatigue, dizziness, lightheadedness) and the doctor finds out the patient has a slow heart rate which is causing those symptoms, the doctor would name the illness “symptomatic bradycardia.”

telemetry. Literally, “remote measurement,” telemetry refers to the ability of devices to communicate with other pieces of equipment. A pacemaker implanted in the chest can communicate with the physician via a programmer through the telemetry process. During telemetry, the programming wand sends out signals through the body’s skin and tissue that are received by the pacemaker. The pacemaker “recognizes” these signals and responds. The signals from the programmer can then guide the pacemaker through a variety of steps: to share information it has stored in memory, to allow the physician to access how the device is set (and make changes) and to update the doctor or nurse on the state of the battery or other vital information. Many devices in the medical or hospital setting use telemetry.

third-degree AV block. Another term for complete heart block.

ventricular fibrillation. A too-rapid heart rhythm originating in the ventricles which is very fast and disorganized. Ventricular fibrillation causes the heart to try to beat so rapidly that it cannot truly beat but merely quivers. As a result, the heart ceases pumping. Ventricular fibrillation is often associated with sudden cardiac arrest and may cause death in a few minutes. Defibrillation can rescue a person from ventricular fibrillation.

ventricular tachycardia. A too-rapid heart rhythm originating in the ventricles which is usually organized and rapid but not as fast as ventricular fibrillation. Ventricular tachycardia is a dangerous rhythm disorder but not as dangerous as ventricular fibrillation; nevertheless, ventricular tachycardia can be fatal. At the lower end of the spectrum, ventricular tachycardia may be tolerable but will almost always provoke severe symptoms. Defibrillation can rescue a person from ventricular tachycardia.

VF. Ventricular fibrillation.

VT. Ventricular tachycardia.

 

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