Articles on Medical Diseases and Conditions

Category: Arrhythmias

  • Surgical Treatments for Arrhythmias

    In  addition  to  drugs  and  nonsurgical  procedures,  several types  of surgery can restore  your heart’s rhythm.  Implantation of a pacemaker can treat bradycardia (slow heartbeat);  an internal  cardioverter- de?brillator can correct more serious arrhythmias; or a procedure called maze surgery can be performed  on some people with atrial ?brillation.

    Pacemakers

    A pacemaker  is a battery-powered unit  that  regulates  your  heart’s rhythm.  Most  pacemakers  are  implanted  in people  whose sinoatrial node  is firing  too  slowly as a result  of age, heart  disease, or  heart medications; the pacemaker takes over for the sinoatrial node if it fails to start.  In a person  with heart  block, the  device replaces a blocked pathway. Today pacemakers  not  only “pace” your heart’s rhythm  but also have a “demand” sensor that can speed up or slow down your heart rate in response to your activity level, just as your heart would naturally.

    The  device itself, which is about the size of a man’s watch, contains a battery and an electronic pulse generator, with either one or two leads that  are threaded  into your heart.  The  device is programmed to read whether  your heart  rate is within an acceptable  range for you. If it is not, the pacemaker generates an electrical impulse to stimulate a heart beat at an appropriate rate. A single-chamber pacemaker has one lead that is positioned in one heart chamber, the right atrium or ventricle; a dual-chamber unit has two leads that are threaded  into both the right atrium and the right ventricle. The  pacemaker can remain in place for several years before the batteries require replacement.

    For people with heart failure or with certain physical characteristics, a third lead may be placed in the back of the heart through a side vein. This is called biventricular pacing. While more complicated to perform than the usual insertion of a pacemaker, this procedure can make some people with heart failure feel much better by coordinating the heart’s contractions.

    How a Pacemaker Is Implanted

    To have a pacemaker implanted,  you will need only a mild sedative and a local anesthetic  in the  area  of your  upper  chest.  First  the  doctor makes  a small incision  in the  skin under  the  collarbone.  The  thin, coated leads are threaded through a blood vessel under your collarbone and positioned  in your heart under X-ray. Then they connect the leads to the pacemaker unit and slip it under your skin, also just under your collarbone.  You will notice  only a small bump at the site. The  proce- dure will be over in 1 to 2 hours, and complications are rare. Serious or life-threatening complications  occur  in less than  1 percent  of cases. Infection of the pacemaker is rare but generally requires that the pace- maker  be removed.  Sometimes  less serious  complications  can occur such as bleeding, collapse of a lung, or the pacemaker’s leads may need repositioning.

    You will probably be able to return to your routine activities in a few days. Your doctor may tell you to avoid heavy lifting or vigorous move- ment of your arm on the side of the pacemaker.

    Living with Your Pacemaker

    You will need to have regular checkups. The  checkups are more frequent  until the pacemaker site heals com- pletely; then they occur about every 3 to 6 months, for monitoring. Your doctor will evaluate your pacemaker by moving an electronic  programmer over the device. The  programmer relays information about pacemaker function  and  the  life of the  battery,  and  it can also change  the programming (pacing instructions)  of the device if necessary. In addition  to the of?ce checkups,

    your doctor may also give you instructions  for how to have some monthly evaluations done by telephone.

    When  the battery begins to wear down, your pace- maker will slow down somewhat, but it won’t stop sud- denly.  Your  doctor  will be  able  to  detect  the  first warnings that the battery  is running  down before you have  any  sensation  of it.  When  the  battery  needs replacing,  you will need  surgery  to  implant  a new device. This  procedure  requires  local anesthetic,  but because the leads usually do not need replacement, the procedure  is somewhat simpler than the original implantation.

    Your  doctor  will also give you  an  identification card  that  provides  specific  information about  the device you have. It is important to show this card to health-care professionals  and to airport  security  staff

    Once  your pacemaker  is in place and the  implant site has healed, you most likely can participate  in all of your usual activities. You and your doctor  can review any possible restrictions—such as full-contact sports— that  might  apply to you. Always feel free to ask your doctor about any questions you have about appliances, medical procedures, or other  considerations that  you

    think might affect your pacemaker. In general, it’s a good idea to be aware of your surroundings and alert for any circumstances  that might interfere  with the electronic  circuitry in your pacemaker.

    Although your pacemaker is not likely to restrict your life in signif- icant ways, it is important to remember that  there  are many things your pacemaker cannot do. It cannot protect  you, for instance, from a heart  attack  caused  by blocked  arteries.  It  also cannot  necessarily replace your need for medications, including  heart-related drugs for conditions  such as high blood pressure, angina, or even other forms of arrhythmia.

    Implantable Cardioverter-Defibrillators

    The internal cardioverter-de?brillator (ICD) is a battery-operated unit, only slightly larger than a pacemaker, that is implanted under your skin to monitor  and correct your heart’s rhythm. All current ICDs also func- tion as pacemakers. An ICD  is usually placed in a person with a dam- aged heart  (as from a heart  attack) who has had or is at high risk of having life-threatening heart  rhythms,  such as ventricular  tachycardia or ventricular  ?brillation.  It may also be used for some people  with severe atrial ?brillation.

    An ICD  can deliver  the  same sort  of low-energy,  imperceptible pulses that a pacemaker does. Furthermore, the ICD monitors the heart using the same technology.  De?brillators are different from pacemak- ers in that they also monitor  for very fast heart rates as well as for bradycardia. The  ICD  can also deliver higher-energy pulses (shocks) to the heart  when  it detects  more  serious  or  sustained  rapid  arrhythmias. These  stronger  impulses are called de?brillation shocks, and they are often life-saving.

    A person  with an ICD  can feel these stronger  impulses—usually a single  shock,  but  sometimes  a series of them—and  they  are  often described as feeling like a quick thump or kick in the chest. Depending on the level of consciousness you have at the time of the shock, it may be painful (if you are not sedated) or may not be painful (if you have received sedatives).

    Like a pacemaker, an ICD  has two parts: a pulse generator, including a battery  and  electronic  circuitry,  and  a system of coated  leads tipped with electrodes. Newer devices are as small as a pager. They are also designed to provide a controlled  burst of impulses, called overdrive pacing,  at the  first sign of ventricular  tachycardia.  If that  does  not restore  normal  heart rhythms,  the device delivers de?brillation shock.

    The  devices make decisions on what type of therapy to give based on how fast the heart  rate is. The  devices are also equipped  to regulate bradycardia (slow heartbeat) if that occurs. They also have a memory to record  arrhythmic episodes  and do some internal  electrophysiologic testing.

    In a person who has experienced prolonged ventricular  arrhythmia, the  ICD  is more  effective  than  antiarrhythmic drugs  at preventing sudden death. The device may also similarly prevent cardiac arrest in a person who is considered  at high risk of developing such arrhythmias. Before you are considered as a candidate for an ICD, your doctor must rule out other causes of the arrhythmia, such as a heart attack, myocar- dial ischemia  (inadequate  blood  ?ow to the  heart;  see page 161), or chemical imbalance and drug reactions,  which can be treated  in other ways.

    How an ICD Is Implanted

    The procedure for placing an ICD is very similar to that for a pacemaker (see page 273). At the hospital, you will be given a sedative and then a local anesthetic. The cardiologist or surgeon will make an incision in the skin and then tunnel the leads through blood vessels into your heart, or onto its surface. Then  he or she will tuck the ICD into a pouch of skin under the collarbone or somewhere above the waistline. The leads will be attached to the pulse generator. Electrophysiologic testing will be done to check out the device. The entire procedure  takes about 2 hours.

    You will probably  stay in the hospital  overnight.  You may be prescribed some antiarrhythmic medications, too. These drugs may lessen the need for high-energy shocks from your ICD.  The  recovery time, the pain after the procedure,  and risks of the procedure  are very similar to those of a pacemaker.

    After Implantation

    After your ICD is installed, you will need to return to the doctor’s of?ce for monitoring every 1 to 3 months. Your doctor can evaluate the ICD function  electronically  by moving  a programming wand  over  your chest. By this means, he or she can determine what kinds of impulses have been delivered, whether  they worked, whether  they need modi?- cation, and how much energy is left in the battery.  When  the energy level in the battery is down to a predetermined level, you will be scheduled  for replacement  surgery.  The  battery  usually lasts from  3 to  5 years, depending on how many shocks it delivers. Usually, replacement surgery is somewhat simpler than the original implantation because the leads do not need to be replaced. Some ICDs can also be checked periodically by telephone.

    Many people feel some apprehension about the possibility of receiv- ing unexpected de?brillation shocks. You may need to continue to take antiarrhythmia medications  to reduce the risk of needing a shock from the implanted  device. Some shocks are small, and some people don’t notice them. When  you do receive a stronger  shock, it may feel like a jolt, thump, or blow to the chest. Some people black out during periods of ?brillation,  so they don’t feel the shock; see “Living with an ICD,” next section, on driving if you have an implanted  ICD.  If someone  is touching you during the shock, he or she may feel a tremor, but will not be harmed by it in any way.

    You and your doctor  can discuss what to do if your ICD  delivers a shock. Your doctor may tell you to call him or her if you feel a shock, or if you feel ill after the shock.

    Apart from the discomfort of a sudden de?brillation shock, possible side effects of ICD placement include some sensitivity at the site of the implant,  especially in very slender  people;  very rare  problems  with infection;  and  some  cosmetic  issues (the  device is visible under  the skin). If you feel apprehension about the shocks or concern about your need for an ICD, ask your doctor about a support group, where you can talk with other ICD “users” and medical staff.

    You will also be given an identi?cation card that  provides speci?c information about your ICD. Carry it with you at all times, and show it to health-care professionals and airport security.

    Living with an ICD

    As with a pacemaker, your ICD  can interact  with some devices in your environment with electromagnetic or radiofrequency ?elds. Review the interactions  with implantable  devices (see page 276), and talk to your doctor in detail about how devices in your environment, medical proce- dures, or your activities might affect your ICD.

    Driving  is a major  consideration for a person  with an ICD.  Your ICD may take an interval of 5 to 15 seconds or longer to detect arrhythmias and deliver treatments, during which you might feel dizzy or even faint. Therefore, you are usually advised to avoid driving,  and other activities, such as piloting or scuba diving, that would put you and others at risk if you were  to  lose consciousness.  In  some  states,  these restrictions  are law. Review this issue with your doctor carefully. Some people who go for long periods without shock or symptoms are allowed to return  to driving, but only with the advice of a doctor.

    Maze Surgery

    In some people with chronic atrial ?brillation,  an operation  called the maze procedure  involves making a series of incision  lines within  the heart to create a maze that blocks electrical pathways through the heart muscle. This surgery is done in a person for whom medications, a pace- maker, or other  treatments have not been effective. A likely candidate might  be a person  with uncontrolled atrial ?brillation,  for whom the chief danger is that blood will pool in the upper chambers of the heart (the  atria); this pooling  increases  the  tendency  of the  blood  to clot, which could lead to a stroke. The  surgery may be performed  with cer- tain other  types of heart surgery to prevent atrial ?brillation  after the operation.

    The procedure is major surgery, done with the patient under general anesthesia. The  surgeon must split the breastbone  to expose the heart and  transfer  the  functions  of the  heart  and  lungs  to  a heart-lung machine during the procedure.

    The  surgeon makes a number  of small incisions in both the left and right  atria. These  incisions form a pattern  that  will direct  the heart’s electrical impulses into the ventricles and block extra impulses. As the incisions heal, scar tissue forms that cannot conduct electrical impulses,

    so the new pathways are permanently  established.  The  surgery  takes about 3 hours. Sometimes a pacemaker is implanted,  too.

    Recovery from maze surgery requires about 1 week in the hospital. You may need diuretics to prevent ?uid accumulation,  and antiplatelet medication  such as aspirin to prevent blood clots. You may experience pain from the chest incision, and fatigue for 2 to 3 months after surgery. Most people can go back to normal activities, including work, in about 3 months.

    The  maze procedure  has been adapted to a less invasive technique, similar to a catheter-based ablation technique for atrial ?brillation. The technique allows the radiofrequency to be directed to the outside of the heart. This technique  is complementary to less-invasive catheter-based ways to perform ablation of atrial ?brillation  through the veins.

  • Nonsurgical Treatments for Arrhythmias

    Great  advances have been made in nonsurgical  treatments for certain types of arrhythmias. These techniques,  including ablation and electrical cardioversion,  may restore  normal heart rhythms,  reduce or elimi- nate symptoms,  and reduce  or eliminate  the need for medications  or surgical procedures (such as implantation of a pacemaker or an internal cardioverter-de?brillator).

    Catheter Ablation

    Catheter ablation is now widely used to treat many types of tachycardia (rapid heartbeat),  including  atrial ?brillation,  atrial ?utter,  and atrial tachycardia,  as well as some  ventricular  tachycardias.  To perform catheter  ablation, a doctor specializing in the treatment of arrhythmias (an electrophysiologist) threads one or more electrode-tipped catheters into the heart chambers and uses some form of energy—usually radiofrequency—to destroy (ablate) abnormal  tissue that is generating extra impulses. The area of tissue that is eliminated is very small (about one-?fth  of an inch across) and is not signi?cant to overall heart func- tion. A small, harmless scar forms at the site, and normal heart rhythm resumes.

    The  procedure  has a high success rate and a low risk of complications, and requires only mild sedation and local anesthetic. It causes little or no discomfort, and most people can return to their daily activities in a few days. Many people are cured of their  tachycardia,  so they no longer need to take antiarrhythmic medication.

    How Ablation Is Done

    If you have ablation  done,  your doctor  will probably  tell you to stop taking  any antiarrhythmic medications  for  several days before  the

    procedure.  At the hospital, you will be given a mild sedative and a local anesthetic.  The  doctor will make one or more small punctures  in your groin and in one side of your neck, your elbow, or just under your collarbone. He or she will thread  catheters through your veins or arteries and into the heart. The procedure is done with X-ray guidance via ?uo- roscopy in real time, so the doctor can see the progress of the catheter.

    Then  the doctor  often  needs to start  an episode of tachycardia  in order to determine exactly where the arrhythmia is coming from. Using recordings  of electrical activity from inside the heart, he or she “maps” the tissue to locate the problem area. Once the site is identi?ed and the ablation catheter  is positioned,  the radiofrequency energy is turned  on and the abnormal tissue is destroyed. To ensure that all abnormal tissue has been eliminated, the doctor may test you with medications or elec- trical stimulation to see if the tachycardia can be induced again. If it can be, he or she repeats the ablation procedure.  When the tachycardia can no longer be initiated, the catheters are removed. The entire procedure lasts from 2 to 4 hours.

    You will stay in the hospital for at least a few hours,  while doctors watch for recurring  symptoms, rhythm  disturbances,  or bleeding from the catheterization sites. You may be able to go home after this obser- vation period, or you may need to stay overnight.

    You can probably be moderately active, walking and climbing stairs, almost immediately.  Many people go back to work or school in a few days. Your doctor may recommend that you take aspirin for 2 to 4 weeks to thin your blood so that clots do not form at the ablation sites in your heart. You will probably return  for a follow-up visit to the electrophys- iologist in a few weeks.

    Complications from ablation are rare but can be serious. Depending on the type of arrhythmia treated, and where in your heart the ablation is done, you could develop heart block (requiring a pacemaker) or expe- rience bleeding around the heart. However, the chance of heart attack, stroke, or death from ablation is quite rare.

    In people with supraventricular arrhythmia and no other  heart dis- ease, a complete  cure of tachycardia is achieved by ablation more than

    95 percent of the time. In people with ventricular arrhythmia, the cure rate is also high.

    In people with other heart problems, such as a previous heart attack resulting in heart muscle damage or in heart muscle problems, an inter- nal defibrillator  is almost  always implanted  as well (see page  275).

    Rather     than     curing     the     tachycardia entirely, catheter ablation helps reduce the number  of times  the  de?brillator  is acti- vated. Sometimes to achieve a cure, though,  more than one session of ablation is needed.

    Cardioversion

    Cardioversion  is the medical term for restoration of your heart’s normal rhythm.

    Cardioversion  can be done  either  chemi-

    cally (with drugs) or electrically (with shock). Atrial fibrillation, ventricular tachycardia, and ventricular ?brillation are the  types of arrhythmia most  commonly

    treated  with  cardioversion.  Ventricular  ?brillation,  the  most  serious type of arrhythmia, can only be treated  with electrical shock.

    If your doctor  chooses to treat  your atrial ?brillation  with antiar- rhythmic  drugs,  he or  she may give you the  medications  to  take at home. But ?rst you take blood thinners  for several weeks. Or the doc- tor may admit you to the hospital to give you the antiarrhythmia drugs either intravenously or by mouth, where hospital staff can check to see how you respond to treatment, and equipment  can be used to monitor your heart rate and rhythm.  Your symptoms, the medication your doc- tor is giving you, and the presence of other heart conditions (if any) will be factors in this decision.

    If your  doctor  recommends electrical  cardioversion  (sometimes called direct-current or DC cardioversion), the procedure  will be done in a hospital.  It involves delivering  a synchronized  electrical  current through paddles that  touch  your chest wall and allow the  current  to travel to your heart. The shock causes all of your heart cells to contract simultaneously,  which  stops  the  abnormal  electrical  signals without damage to the heart. Then  the heart returns  to a normal heartbeat.

    How Electrical Cardioversion Is Done

    Before you have a cardioversion  done, your doctor  will probably pre- scribe blood thinners  such as warfarin for 3 to 4 weeks to reduce your

    risk of blood clots. If you take other medications, you should take them as usual unless you are told otherwise. On the day of the procedure,  do not eat after midnight.  Also, do not use any skin lotions on your back and chest, because they could interfere with the cardioversion apparatus.

    In the hospital, you will be given an intravenous sedative, possibly by an anesthesiologist.  The  doctor  will place cardioversion  pads (or paddles) on your chest and back, on either side of your heart. The pads are connected  to an external de?brillator  so that your heart rhythms can be monitored and regulated.  Once you are asleep, the doctor  will deliver the shock so that the current  ?ows across your heart. If the ?rst shock does  not  restore  your  normal  heart  rhythm,  the  doctor  can deliver gradually increased levels of current.

    After the procedure,  you will probably awaken quickly without  any memory of the experience. You may have some minor chest discomfort or skin irritation where the pads were placed. You will probably be able to go home  within  an hour  after  the  procedure.  Have  someone  else drive you home, and do not drive or try to make any important deci- sions for the rest of the day, until the effects of the sedative are entirely gone. You will need to continue  taking warfarin until  your physician tells you to stop; periodic blood tests will check your clotting time.

    Electrical cardioversion restores normal heart rhythms about 90 per- cent  of the  time.  About  half of the  people  who have the  procedure relapse within a year; if so, the procedure  can be repeated.

  • Antiarrhythmic medications

    Antiarrhythmic medications  slow down rapid heartbeats  and regulate irregular or premature heartbeats. Generally, these drugs work by block- ing chemical reactions that promote  electrical conduction.  They act to either suppress abnormal electrical impulses or slow down transmission of impulses as they are conducted through  heart tissue. As a result, your heart beats more rhythmically and you experience fewer symptoms.

    You may be given these medications  intravenously  during an emergency situation, or they may be prescribed for you to take orally for an inde?nite  period.  Certain  antiarrhythmics, such as amiodarone,  cause side effects such as increased sensitivity to sunlight. This drug may also affect your vision, the thyroid, or the lungs. Many people are surprised to learn that an antiarrhythmic drug can in fact cause an arrhythmia or make an existing one more frequent or more severe.

    You and your doctor  will need to carefully consider  the balance of bene?ts and risks of medication. Your doctor will also do thorough test- ing and monitoring, either with Holter monitoring, electrophysiologic studies, or both, to determine what drug works best for you. The electrophysiologic  testing  indicates  how well a medication  is controlling your symptoms, exactly how it alters your heart’s rhythm, and how well it protects your heart from an arrhythmia induced during the study.

    Apart  from  these  antiarrhythmics, medications  such  as calcium channel blockers  or beta-blockers   may be prescribed.

    If you have atrial ?brillation,  which can make you more susceptible to blood clots, you will probably  also take an anticoagulant or an antiplatelet  medication  . As with all medica- tions, drug interactions  with antiarrhythmics are always a concern;  be sure to let your doctor  know about other  medications  you are taking, including over-the-counter drugs and herbal remedies.

  • Diagnosing Arrhythmias

    Once your doctor diagnoses an arrhythmia through your symptoms or an examination, he or she will need to determine where it originates and whether it requires treatment; that is, whether it is causing symptoms or putting  you at risk for more serious problems in the future.

    The electrocardiogram  is a very important tool that  your  doctor  uses to  diagnose  and  study  your  arrhythmia. The ECG  records and measures the path and timing of your heart’s electri- cal impulses from their origin in the sinoatrial node, through the atria, through the atrioventricular node, and into and through the ventricles. However,  the  standard  ECG  can only  record  the  electrical  activity that takes place during the short time that the machine is hooked up to you.

    Ambulatory  ECG  methods  enable  your  doctor  to  study  longer periods of the heart’s activity while you go about your normal routine. Ambulatory  ECGs  are available in the form of a Holter monitor , which you wear for 24 to 48 hours  and which provides a continuous readout.  Your doctor  compares the ECG  recordings  with your account  of your activities and symptoms to see if an arrhythmia is occurring,  how often it occurs, and how it relates to the daily log of your activities. Also, the effectiveness of any antiarrhythmic medica- tions you may be taking can be monitored. However,  if your arrhyth- mia  is very infrequent, 48  hours  of Holter monitoring may  not capture  it.

    An event monitor   is another  ambulatory  ECG,  one that allows for longer  recording—as  long as 30 days. You activate the device yourself if you sense symptoms. The monitor’s recording system is “looped” to continuously  record and erase, so that when you activate it, it can retrieve data from 1 to 4 minutes prior to that time.

    Your doctor may want to order exercise stress testing  to see if an arrhythmia is brought  on by exercise. If you have had faint- ing spells, you may be asked to have a tilt-table  study  to observe how your heart responds to a change in position. This informa- tion  helps  your  doctor  determine how to  prevent  fainting  episodes. Echocardiography  may also be used to determine if there is structural  heart disease that may be causing arrhythmias.

    Electrophysiologic studies  are done in a hospital setting to more speci?cally study an arrhythmia,  test the effect of medications, and perform  some treatments  such as catheter  ablation. Electrophysio- logic studies are generally done by threading catheters through  the veins into  your heart  in order  to record  electrical signals and stimulate  the heart to induce an arrhythmia, to provide more precise information about your heart rhythms. Because the test requires that catheters are placed in your veins, it is described  as an invasive study. However,  with proper preparation,  electrophysiology studies can be performed with little or no discomfort  and are among the safest of all invasive tests. Also, impor- tantly, if possible, some arrhythmias are treated or cured at the same sit- ting during your electrophysiologic studies, with only a small risk to you.

    Electrophysiology studies  require  taking  periodic  X-rays via ?uo- roscopy during the procedure to determine where the catheter is within the heart. In some cases, transesophageal echocardiography may be used.

    Substances That Can Affect Heart Rhythm

    Thousands of substances have the potential to affect the electrical signals that stimulate your heartbeat. The impact of any one of them on you can range from harmless to severe. If you are diagnosed with a heart arrhythmia, be aware of your own exposure to some of these substances, and talk to your doc- tor about how they might be affecting your symptoms, the effects of your med- ications, or your overall heart health.
    • Caffeine in coffee, soft drinks, tea, or chocolate
    • Alcohol
    • Tobacco, including secondhand smoke
    • Diet pills
    • Some over-the-counter cough and cold remedies (especially those with pseudoephedrine)
    • Some herbal remedies (such as ephedra or ephedrine)
    • Prescription drugs (such as antianxiety, antipsychotic, or antiarrhythmic medications)
    • Bronchodilators, whether prescription or over-the-counter
    • Automobile emissions
    • Industrial pollution
    • Paint thinners
    • Propane gas
    • Hazardous substances in the workplace (such as carbon monoxide)

  • Types of Arrhythmia

    Irregularities in your heart rhythms can be described by the effect they have on the speed of your heartbeat (acceleration or deceleration) and where they occur in your heart (in the atria or in the ventricles). Another type of arrhythmia, called heart block, is a partial or complete interruption in the transmission of the electrical impulses between the upper and lower chambers of your heart.

    Bradycardia and Tachycardia

    An irregular heartbeat can be either too slow (bradycardia) or too fast (tachycardia). A healthy person generally has a resting heart rate of 60 to 100 beats per minute.
    Bradycardia, a heart rate of less than 60 beats per minute, may not be a medical problem. A physically active person whose heart pumps very ef?ciently may have a lower heart rate that is not at all abnormal. But a very slow heart rate can become a problem if the brain does not receive enough blood, causing symptoms such as light-headedness or fainting.
    Bradycardia most commonly affects older people because with age- related damage of the heart’s electrical system, all the impulses from the atrium may not get to the ventricle. It may be caused by damage to the sinoatrial node (where the electrical pulse begins) or to the biological “wires” that connect the upper chambers (atria) to the lower chambers (ventricles). This damage may be brought on by heart disease, aging, a genetic defect, or some drugs or medications. Medications or a tempo- rary pacemaker can speed up the heart’s contractions temporarily. A pacemaker is also a long-term treatment.
    Tachycardia, a very rapid heart rate of more

    than 100 beats per minute, can take many forms, depending on where in the heart it occurs. Fibrillation, perhaps the most serious form of tachycardia, causes the heart muscle to quiver instead of contracting rhythmically. (For symptoms, see page 258.) The heartbeat is not only too fast but uncoordinated as well. Both tachycardia and ?brillation, in various forms, can be treated with medications, surgery, or mechanical devices.

    Heart Block

    Heart   block  is a  condition in  which  the sinoatrial  node  sends  a normal  electrical impulse,   but  the  signal  does  not   travel through the  atrioventricular node  and into the ventricles  as it should. Therefore, there may be inef?cient  contraction of the ventri- cles. It usually occurs as a result of aging, or because  the  heart  is scarred  from  chronic heart disease such as coronary  artery disease or from valvular heart  disease (which a per- son may be born  with). Prior  heart  surgery may also cause scarring. Certain  medications that  slow the  electrical  conduction through the  heart—for  example, digitalis, beta-blockers, or some calcium blockers—can  worsen heart block.

    Heart  block is classi?ed into three groups, according to how severe it is. In ?rst-degree heart block, the electrical impulse moves too slowly through the  atrioventricular node.  Your doctor  may refer  to the  PR interval,  which  is a part  of an  ECG  recording that  measures  the amount  of time it takes for an impulse to get from the atria into the ventricles (see page 265). If your PR interval is longer than 0.2 seconds, you have ?rst-degree heart  block. If your heart  rate and rhythm  are normal,  there  may be nothing wrong  with your heart.  In fact, some highly conditioned athletes also have ?rst-degree heart block. Usually, you will not require treatment for a ?rst-degree heart block. If you are taking medications  such as digitalis  or beta-blockers , the drug may be causing the condition.

    If you have second-degree heart  block,  some  signals from  your sinoatrial  node  do  not  reach  your  ventricles.  In  most  people  with second-degree block, impulses  are progressively  delayed  in the  atri- oventricular  node with each heartbeat  until a full beat is skipped. This is called a Mobitz  type of block. You may have no symptoms,  or you may experience some dizziness, but the condition  is not serious. On an ECG,  the skipped beat will show up as a P wave that is not followed by a QRS wave—a tracing of a contraction in the atria that did not activate the ventricles (see page 265). In a Mobitz type II heart block, the inter- val between the P wave and the QRS wave remains constant,  but the atrioventricular node  intermittently blocks the  electrical  impulses.  A Mobitz type I block may pass on its own, but a Mobitz type II block is generally more serious and requires that you have a pacemaker implanted .

    In a person who develops third-degree or complete  heart block, no signals at all are passing from the atria into the ventricles. To compen- sate, the ventricles use their own secondary pacemaker to contract  and keep blood moving. But the heartbeats  generated  this way are slow and cannot  maintain  full heart  function.  On  an ECG,  the  relationship between  the  P wave and the  QRS  wave is completely  abnormal  (see page 266). A person with third-degree heart block may lose conscious- ness, may develop  heart  failure,  and  is at risk of cardiac  arrest.  A mechanical pacemaker must be implanted  on an emergency  basis. If it is not possible to put one in right away, a temporary  pacemaker device can be used to keep the person alive until surgery can be done.

    For all types of heart  block, the decision  of whether  to implant  a pacemaker  is based on the severity of the bradycardia  symptoms.  In some  cases, the  deciding  factor  is how  slow your  heart  rate  has become.

    Ventricular Arrhythmias

    Generally,  an arrhythmia in the ventricles is a more serious condition than one in the atria, because the ventricles perform  the heart’s essen- tial pumping  functions.  Most serious ventricular  arrhythmias occur in association with other forms of heart disease, rather than as an isolated problem.  A healthy  person  may have numerous isolated  extra heart- beats originating in the ventricle, and a person with normal heart func- tion  usually does  not  require  treatment. Ventricular tachycardia  is made up of several of these irregular  heartbeats in a row.

    Premature Ventricular Contraction

    Premature ventricular contractions  occur when your ventricles contract too soon and interrupt the normal heartbeat. They may happen without warning,  and often  occur after you have consumed  caffeine or taken over-the-counter medications  that  contain  ephedra  or ephedrine.  By themselves, premature contractions  may be harmless and often do not require treatment. But if you have another  heart condition  such as car- diomyopathy or heart failure, premature ventricular contractions  can be a warning  of more  serious or prolonged  rhythm  disturbances  such as ventricular tachycardia or ventricular ?brillation.

    Ventricular Tachycardia

    In a person with ventricular tachycardia, a series of ventricular contrac- tions  originates  from  a spot  within  the  ventricles,  and the  heartbeat quickens—from 100 to 250 beats per minute. The  initial concern with this form of tachycardia is that the arrhythmia  may interfere  with the ability to pump blood, and the person may become dizzy or faint. But ventricular tachycardia may deteriorate  without warning into ventricu- lar ?brillation, which is life-threatening.

    Therefore, ventricular  tachycardia  is considered  a medical  emer- gency. The  goal of treatment is to stop the rapid heartbeat,  with elec- trical  shock (de?brillation)  if necessary, and then  to prevent  it from recurring. If the heart cannot return to a normal rhythm, it may go into ventricular ?brillation,  which can be fatal in minutes.

    Ventricular Fibrillation

    Ventricular fibrillation  is the  most  dangerous  form  of arrhythmia, requiring  immediate  emergency  attention. In  this  form  of extreme tachycardia, several impulses may be ?ring from different locations in the heart, and the heart contractions are in chaos. Although the heart rate may be as high as 300 beats per minute,  the heartbeats are com- pletely  ineffective  and  very little  blood  leaves the  heart.  Since  the brain is the organ most sensitive to the loss of oxygenated blood, ven- tricular  ?brillation  causes unconsciousness.  Someone  should call 911 or  emergency  medical  services immediately  and  begin  cardiopul- monary  resuscitation (CPR)  immediately  if you  are  not  breathing properly.  Electric  shock (de?brillation)  is usually essential to restore heart rhythm,  to prevent severe damage to the brain and other organs. Cardioversion (see page  271) may be used  to  deliver  the  necessary shocks. As many as 250,000 people die suddenly each year from ven- tricular  ?brillation.

    A de?brillator (sometimes called an automated external de?brilla- tor, or AED) is an electronic device that emergency medical services personnel or other  trained “?rst responders” use to deliver shock to someone  whose   heart   is  fibrillating.  These  defibrillators  are now available in many public places such as health  clubs and airports.

    Supraventricular Arrhythmias

    An arrhythmia that  occurs  in either  of the  two  atria  of your  heart, located above your ventricles, is considered a supraventricular (or atrial) arrhythmia.

    Supraventricular Tachycardia

    Supraventricular (or atrial) tachycardia is a regular but very rapid heart- beat (more than 100 beats per minute) involving the upper chambers of the heart. It can occur in several different  forms, when regions of the atria other than the sinoatrial node (the natural pacemaker) develop the ability to ?re electrical impulses repetitively. The path that these “extra” impulses take determines  what type of tachycardia you have.

    In one type (atrioventricular nodal reentrant tachycardia), electrical impulses travel in an abnormal  circular path around  the atrioventricu- lar node between the atria and the ventricles, causing the heart to beat with  each  circle.  Another  form,  called Wolff-Parkinson-White syn- drome,  occurs when there  is an extra electrical  pathway between  the atria and ventricles that causes electrical impulses to arrive at the ven- tricles too soon, resulting in a rapid heart rate. Some are caused by short circuits or extra electrically active tissue in the heart. It turns out that these “reentry circuits” are the most common mechanism.

    If you have supraventricular tachycardia, you may experience palpi- tations  or  a sense that  the  heart  is ?uttering  or  racing.  Often  these symptoms  occur  abruptly  with  little  or  no  warning.  Some  people have shortness  of breath,  chest pressure  or pain, or light-headedness. These sensations may last for a few seconds or several hours. The symp- toms can be alarming,  but usually supraventricular tachycardia  is not life-threatening. Of course, if you have these symptoms, you should have your doctor  diag- nose and treat your condition.  Treatment with drugs (see page 268) can relieve symptoms, or a cardiac ablation procedure  (see page 269) can cure the condition.

    If you have severe symptoms and go to the emergency  room,  doctors  may give medica- tions that can stop the supraventricular tachy- cardia and thus relieve your symptoms rapidly. Also, if the  type of tachycardia  you have has not  yet been  diagnosed,  an ECG  performed while you are  experiencing  the  symptoms  is very helpful in determining the best long-term treatment.

    Atrial Fibrillation

    Atrial fibrillation  (AF) is the  most  common type of arrhythmia in the United States, occurring in 5 to 10 percent  of all people over 65. People over the age of 80 are especially vulnerable, too, although it can occur in some people who are 40 or younger. In a person with AF, the electrical impulse from the sinoatrial  node accelerates as it spreads across the atria, causing these upper chambers of the heart to quiver, contracting rapidly and irregu- larly—at rates of 400 to 600 beats per minute.  A specialized structure between the atria and the ventricles, the atrioventricular node, acts as a safeguard,  stopping  one or two of every three  signals from  the  atria before they reach the ventricles. But the ventricles still beat too rapidly and irregularly.

    AF may occur without  any associated heart  disease. However,  it is commonly  linked with hypertension (high blood  pressure),  coronary artery  disease, mitral  valve disease, pericardial  disease, lung  disease, cardiomyopathy, or thyroid disease. When AF occurs, it is important to slow the ventricular rate and then look for the cause and treat that.

    Several different  forms  of AF can occur,  and  the  symptoms  can vary widely. Some people experience AF only occasionally, with symptoms  such as palpitations  that  last from  a few seconds to a few days before  subsiding  spontaneously;  this form  is called paroxysmal atrial ?brillation.  In  a person  with  persistent  AF, episodes  do not  stop  by themselves, and drugs or other treatments—such as ablation or cardioversion  are required  to restore  normal heart rhythm. Permanent AF is constant and does not respond to treatment.  In these situations  treatment focuses on heart  rate control  and prevention  of blood clots. AF can cause symptoms of fatigue or short- ness of breath  and lead to ?uid buildup. Over time the heart rate may slow to the point of causing bradycardia .

    For  many people,  the  experience  of AF is unpleasant—causing  a sensation of palpitation  and unwellness—but  not necessarily harmful. Treatment can relieve the symptoms,  and AF is generally unlikely to advance  to  a more  serious  condition. But  having  palpitations  can be frightening and worrisome.  If you experience  palpitations  for the ?rst  time,  you should  always get medical  attention to  diagnose  the problem.

    AF can cause blood to pool in the atria, which can lead to blood clots. If a clot travels from the heart into a smaller artery in the brain, it can cause a stroke. About 15 percent of strokes occur in people with AF, and among  those with AF, the rate of strokes is about 5 percent  per year. Once  AF is diagnosed,  your  doctor  may prescribe  warfarin,  a blood thinner,  which prevents blood clots from forming and reduces the risk of stroke by two thirds. Risk factors for blood clots associated with AF include  advanced  age, diabetes,  high  blood  pressure,  previous  heart damage, and a history of stroke.

    Left untreated, AF can cause a chronic increase in heart rate, which can weaken the ventricles over time and cause heart failure. But most people seek treatment before this occurs.

    Atrial Flutter

    Atrial ?utter is another  common form of arrhythmia in which the atria beats rapidly but relatively regularly. It usually occurs when electrical impulses  are trapped  in an endless loop, typically in the  lower right atrium.  Although the atria may be contracting as quickly as 300 times per minute, the atrioventricular node allows only some of those beats to pass into the ventricles. Still, the ventricles are contracting too quickly and the heart is not pumping  as ef?ciently as it needs to. Atrial ?utter or atrial ?brillation  often occurs as a consequence  of a heart attack or surgery on the heart or lungs.

  • Arrhythmias

    Every second or so, an electrical impulse originating in the right atrium of your heart travels through the heart and triggers a single heartbeat, or contraction of the heart. A group of specialized cells in the muscle tissue, called the sinoatrial (SA) node, initiates the signal, acting as your heart’s natural pacemaker. The impulse travels through the four chambers of your heart in a carefully timed sequence to stimulate the rhythmic contractions that pump blood through your body (see pages
    9–10).
    Any change or interruption in the electrical signal that throws off this rhythm is called an arrhythmia. The heart may beat too fast, too slow, or in an irregular pattern. Arrhythmias can occur in people with normal hearts or those with underlying disease. Throughout the course of your lifetime, your heart will occasionally skip a beat or palpitate slightly, and these brief variations are completely harmless. Some people have minor arrhythmias that never cause a problem. However, in some arrhythmias, the pumping action of the heart can be seriously affected, or it can cause symptoms of palpitation (awareness of the abnormal heartbeat), light-headedness, or fainting. If you have another heart condition, such as heart failure, an arrhythmia is more likely to cause a problem for you.
    Some people are born with an irregular heartbeat. Other cardiovascular conditions, such as high blood pressure, valvular disease, heart failure, or coronary artery disease can be factors; diabetes can also con- tribute (see page 105). Substances such as caffeine, tobacco, alcohol, cocaine and prescribed medication, some over-the-counter cough and cold medications, diet pills, and some herbal remedies can affect the pattern of your heartbeat (see page 267). Stress can also cause arrhythmias in some people, as the body releases adrenaline, the stress hormone. Low levels of or an imbalance of electrolytes such as low potassium levels may cause or worsen an arrhythmia. Your doctor may order a blood test to check your electrolytes, to make sure there is no correctable problem causing your arrhythmia.
    Treatment, therefore, may include lifestyle changes and control of other conditions, taking an antiarrhythmia medication, avoiding some medications, nonsurgical procedures, or surgery (for instance, implantation of a pacemaker) to restore a normal heartbeat. Your doctor may refer you to a heart rhythm specialist, called an electrophysiologist.