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Causes of abnormal heart rhythms



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Causes of abnormal heart rhythms

What’s behind it all?

There are many possible reasons for an abnormal electrical impulse to occur. The heart muscle may be “irritable;” that is, it may be overly sensitive to changes in the amounts of natural substances in the body such as adrenaline and oxygen or minerals such as potassium and magnesium. These substances may be either overabundant or in short supply as a result of general health problems. The imbalances may result in damage to the heart muscle, with areas of injury or scar causing overactivity or underactivity of the impulse-producing cells. This is why abnormal heart rhythms and rates are so common during a heart attack.

Although “arrhythmia” always means that there is an irregularity of the heart rhythm, the presence of arrhythmia does not always mean that heart disease or damage has occurred, nor does arrhythmia mean that the heart’s pumping function or blood supply is impaired. In many cases the overall pumping function of the heart is unchanged and the heart is found through testing to have a normal structure and function despite the presence of an arrhythmia. In these instances, if a cause can be found and corrected, the arrhythmia may be totally eliminated.
The absence of heart damage is a very important finding. It may allow discovery of a cause such as stress, mineral deficiency or excessive intake of caffeine or alcohol that can be eliminated, and often allows the physician to reassure the patient that the anticipated consequences of the arrhythmia are minor.


  • Common causes




    • Physical stress (exercise)




    • Emotional stress




    • Heart diseases (heart attack, abnormal heart valves, enlarged heart, heart failure)





    • Lung diseases (emphysema, chronic bronchitis and other smoking-related disorders)





    • Other diseases (overactive or underactive thyroid, disorders involving vomiting or diarrhea that cause loss of potassium or magnesium)





    • Medications (diuretics, some asthma drugs and cold remedies, diet pills, “stay awake” pills, stimulants)



    • Dietary (low potassium, low magnesium; “fad diets,” often with inadequate mineral intake or supplementation)




    • Toxins (such as alcohol or nicotine)




    • Stimulants (caffeine, amphetamines, cocaine)




Tests to help diagnose the type of arrhythmia

In evaluating the condition of your heart, tests that do not require inserting wires, tubes or devices into the body are called noninvasive, and are preferred since they carry little risk and cause little discomfort.


Invasive tests, on the other hand, involve the insertion of wires or tubes and the use of x-ray dye or devices. They are usually done in laboratories or operating rooms equipped to deal with the risks of bleeding, infection and blood vessel blockage. Invasive tests almost always require you to sign a “consent form,” indicating that you understand the test, its benefits and any potential risks.

No one is likely to need all these tests. Your doctor will select the easiest and clearest route to arrive at your diagnosis. If you have questions about any test ordered for you, be sure to ask you doctor.

In patients with arrhythmia, testing the heart has two main purposes:


    • diagnosing the specific type of arrhythmia.

    • determining whether the heart has other problems that will ffect the importance of arrhythmia.




  • Standard Tests


Chest x-ray.

This test lets your doctor look at your lungs, the size of your heart and some of your major blood vessels. When compared to a previous x-ray it can reveal changes that may have occurred. If heart disease is present, your heart may be enlarged or there may be fluid around your heart or in or around your lungs. Some types of heart valve disease result in calcium deposits in the valves that can be seen on x-ray. Knowledge of structural abnormalities is extremely helpful to your physician since different structural problems often cause specific types of arrhythmia problems.



Electrocardiogram. The ECG, or EKG, shows your doctor how the electrical impulses travel through the top (atria), middle (junction) and bottom (ventricles) of your heart. You don’t feel this test at all. Wires with tiny pads or suction cups, placed at 10 points on your arms, chest and legs, are connected to a machine that records the exact rate and rhythm of the heart’s electrical activity and displays the way it spreads through the heart muscle.

The ECG may reveal whether the electrical impulse is starting from the right location and traveling along the normal electrical pathways. It can show that you had a heart attack, indicate thickened heart walls or suggest enlarged heart chambers. This is by far the most important test to obtain at the actual time an arrhythmia or palpitation is occurring, since it provides the doctor with a specific diagnosis. It is with this accurate and important information, the diagnosis, that all decisions about treatment begin.


The SAECG (Signal-Averaged ECG) is a new type of recording to evaluate electrical activity from the bottom of the heart. It is obtained like the standard ECG discussed above except that you have to remain as motion-free as possible for 10 to 20 minutes to permit reliable information to be collected. This test shows the doctor the “average” electrical impulse created by the heart and allows further analysis to help identify which patients are at risk of certain important arrhythmias.


Holter Recording (or 24-hour Ambulatory Electrocardiogram).












By wearing a small portable electrocardiogram recorder with a few thin wires pasted to your skin, you can provide your doctor with a record of your heart rhythm over a 24-hour period at home, at work and wherever you go. During the same period you keep a diary of your symptoms and activities. Your doctor can then determine whether your heart rhythm and rate are responsible for your symptoms by comparing the Holter recording and your diary entries at corresponding times. This can be extremely helpful in proving that disturbances of the heart’s rhythm are NOT the cause of certain symptoms or problems.

When 24 or 48 hours are not enough because symptoms do not occur on a daily basis, a 30-day Event Recorder may be helpful. This unit is very similar to the Holter Recorder, but it can be disconnected from the body for bathing or other purposes. It may be carried, unconnected, until a symptom develops, and then hooked up rapidly in order to detect the heart’s rhythm at the time. Merely touching it to the chest or to the wrist permits recording of the heart rhythm by the unit. This record of the heart’s rhythm, at the time a symptom is noted, can prove or disprove an association between them.

Exercise Testing



Exercise testing can help determine whether the heart muscle is receiving adequate amounts of blood from the coronary arteries. An abnormal test result usually means that coronary artery disease is present and the patient is at risk for chest pain (angina) or for a heart attack. In patients with arrhythmia, the test can help determine whether exercise is the cause of arrhythmia or makes it worse, or even at times improves it.

The test is designed to monitor the heart’s response to increased work performed by the patient in the form of exercise such as walking at different speeds, generally uphill. Of course, fatigue, shortness of breath and a rise in heart rate and blood pressure are to be expected whenever we exercise more vigorously than we used to. Even some mild forms of arrhythmia occurring after strenuous exercise can be considered part of a “normal” response.

If, however, chest pain, a fall in blood pressure, faintness or serious arrhythmia occur, it may indicate that a coronary artery is narrowed or closed, or that a structural or electrical problem with your heart requires treatment. Performing this test in a supervised setting provides a safe environment in which to diagnose such a problem.

To perform the routine exercise test, you simply walk on a treadmill or pedal a bicycle for five to fifteen minutes while your symptoms are noted and your blood pressure and heart rate and rhythm are monitored.




  • For the test, it is recommended that you:

    • Wear comfortable clothes and shoes.

    • Eat lightly or not at all prior to the test.

    • Check with your doctor about medications you are taking. In some cases the patient is asked to suspend all medications that might alter test results. In others, the test will be performed while the patient is taking medications in order to test the effects of treatment.

    • Have a copy of the test results sent to each of your physicians.

To help make sure that an abnormal test really indicates a problem and that a normal test means a normal patient, the routine exercise test can be combined with others. When exercise and an ultrasound image of the heart are combined it is called an Echocardiographic Stress Test and when we add a nuclear scan of blood flow to the heart it is called either a Thallium Stress Test or Sestamibi Stress Test depending on which medication is used.


In the Echocardiographic Stress Test, the heart’s function at rest and in response to exercise are compared. When a narrowed coronary artery reduces blood flow to the heart muscle, the strength of contraction is decreased and this can be seen in the echocardiogram, thereby confirming the diagnosis.

In the Thallium (or Sestamibi) Stress Test a small plastic tube is inserted into a vein in your hand or forearm prior to exercise. Following exercise, a small non-allergenic dose of radioactive salt is injected into your circulation; some is deposited in your heart, allowing a scanner to take pictures of your heart muscle. Using a heart scan at rest and a follow-up scan after exercise, your doctor can often determine whether your heart muscle has a normal blood supply and whether a heart attack has occurred in the past.

For patients who cannot perform treadmill or bicycle exercise, various medications can be given intravenously (IV) while the patient is lying comfortably at rest in order to obtain the same information about blood flow to the heart muscle. These medications increase the blood flow to the heart muscle by temporarily enlarging the coronary arteries, just like exercise! While these medications are generally well tolerated, possible side effects of these so-called Pharmacologic Stress Tests include:


    • chest pain (angina) that may indicate a blocked or narrowed artery to the heart

    • nausea

    • headache, dizziness or flushing

    • palpitations

    • asthma (wheezing)


These tests are not recommended for certain patients:


    • Patients who are having frequent pain of increasing severity or duration

    • Those taking certain medications for breathing problems

    • Pregnant women and mothers who are nursing, since the tests involve the use of radioactivity

As with all medications or tests, a discussion with the doctor will be most helpful in answering your specific questions. Be sure to ask!




  • Common Blood Tests

Tests of Mineral Levels (sodium, potassium, chloride and magnesium) are extremely important in evaluating the function of your heart muscle and its electrical system. Low blood levels of potassium and magnesium are especially common causes of irregular heart rhythms. Normal blood levels of potassium and magnesium have a stabilizing influence on the heart. The most common causes of abnormal mineral levels include poor nutritional intake, prolonged vomiting, chronic diarrhea and use of diuretic medications (so-called water pills). High blood levels may be due to poor kidney function, excessive intake of supplements or food additives, or medications that encourage retention of these minerals.

Tests of Thyroid Function show the level of thyroid hormone in the blood, since an overactive or underactive thyroid often results in changes in the heart’s rate and rhythm. An irregular heart rhythm may be the first sign of an overactive or underactive thyroid gland. Overproduction of thyroid hormone generally produces a faster heart rate; underproduction results in a slow heart rate.

Tests for Drug Levels may be done to determine whether a current dosage of medicine is correct (i.e., whether enough of a prescribed drug is being absorbed by your body). These tests may indicate a need for more or less drug and can provide evidence that the drug is responsible for observed symptoms.
A drug often tested in this way is digoxin, since small fluctuations in the blood level may affect response to the drug. Too little digoxin may result in little or no benefit and in certain patients result in an excessively fast heart rate, while too much may produce side effects such as loss of appetite, visual disturbances or a slowed heart rate. Another use of drug levels is to evaluate “drug interactions”-the effect of a second drug on one already being taken.


  • Tests to evaluate the heart’s structure and function



Echocardiogram. The “Echo,” as it is called, transmits sound waves to create images of each chamber of your heart, the contacting motion and thickness of the heart muscle, the major blood vessels connected to your heart, the heart valves, and the thin sack around your heart known as the pericardium. This is a non-invasive test. In patients with arrhythmia, the doctor is looking for evidence of structural problems that might cause an arrhythmia or affect its treatment.

If heart disease is discovered with the Echo, it can help to pinpoint the best treatment. When the heart is shown to be entirely normal by Echo, the arrhythmia problem is usually less serious and the patient can be reassured.
The test uses only sound waves (ultrasound, sonar). No X-rays or needles are used and it is not dangerous. In fact, this same test is used to look at babies inside their mothers’ wombs before they are born. All you have to do is lie down and relax. A skilled technician puts a dab of gel on your chest and passes a sound probe painlessly over it, obtaining pictures of the heart underneath. During the Echo you can watch your heart beating on the video screen. On a clear study, you can watch the muscle walls contract, the valves open and close and see the relationship of different parts to one another. The Echo at times is used to look for blood clots within the heart chambers.
In certain arrhythmia problems such as atrial fibrillation or flutter, the arrhythmia causes the heart muscle to relax or quiver rather than contract normally. Blood clots can develop along the non-moving walls and later dislodge and travel in the circulation leading to blockages of blood vessels in organs such as the brain (causing stroke) or other problems. Because these blood clots may be quite small and often are in difficult to see areas of the heart, a new technique called Transeophageal Echo or “TEE” has been developed. TEE involves passage of the Echo probe down the throat of a sedated patient to the esophagus, which lies directly behind the heart. The Echo images from a TEE are exquisitely clear and sharp because they are obtained from very close and do not have the lungs or chest wall to go through as in the standard Echo test. This test can yield information about blood clots in the heart that are otherwise difficult to view as well as infections in the heart.

The Doppler Echocardiogram uses a special computer to measure the speed and direction of blood flow inside the heart by bouncing sound waves off different locations. It can identify heart valves that are blocked or leaking and can reveal the location, severity and importance of many heart defects. Unfortunately, arteries are too small to “see” with the Echo. Repeat Doppler-Echo studies are used to evaluate changes in the severity of heart valve conditions. In the past this information could be obtained only by invasive tests, including heart catheterization.



 

 




  • Nuclear scans

Two major types of nuclear scans are used to evaluate the heart. The first are the Thallium or Sestamibi Scans, described earlier in connection with exercise testing. The second type evaluates how the muscle itself is working and is called by several names: gated blood pool study, MUGA Scan (multiple gated scan), or RVG (radioisotope ventriculogram). The Thallium and Sestamibi Scan may show an area of heart muscle that is not getting enough blood because of scar tissue from a previous heart attack or a narrowed or blocked coronary artery. In stress testing, it records blood flow to the heart immediately following peak exercise and compares it to a scan of blood flow several hours later when the heart is at rest.


The Gated Blood Pool Study (MUGA or RVG) measures the overall performance of the heart; that is, the amount of blood pumped out with each beat and the contribution each section of heart muscle makes to the total pumping action.
These nuclear scans have several advantages:
They are safe and painless (except for the small injection of radioactive medication in a vein of your hand or arm).
They take only about 20 to 60 minutes for each scan.
They are analyzed with the help of computers that make these some of the most accurate cardiac tests performed.
They require no special preparation by the patient except a 6-hour fast (and awareness of any medications you may be taking).
Caution! Because of exposure to radiation these tests should not be done if you are pregnant or breast feeding.

Cardiac Catheterization


Cardiac Catheterization, or “heart cath,” is a test in which a small tube (catheter) placed in the bloodstream provides the means whereby pressures are measured, blood samples are taken and dye is injected so that x-ray pictures can be made. Sometimes the term “heart catheterization” is used to mean “coronary angiogram” (described below) because these tests are routinely done together. The detailed information derived from this important procedure usually includes measuring pressures (catheterization) looking at the arteries (angiogram), and observing the muscle contraction (ventriculogram).
The procedure is done in a laboratory, often located in a hospital, that is specially designed for studying the heart. The test may indicate heart problems of various types including valve malfunctioning (blockage or leakage), muscle damage, or abnormal pathways for blood as a result of disease or birth defects.

By recommending a “heart cath,” your doctor has determined that the benefits of the test outweigh the risks. Since the risk of a major complication varies and depends on many factors, the risk for the individual patient may be discussed with the doctor.


The Coronary Angiogram, or arteriogram, is a special type of “heart cath” (see above) that produces a motion-picture x-ray of the blood vessels to the heart and pinpoints the location and severity of any blockages as well as variations in the size of coronary arteries.
A Ventriculogram shows the location and extent of heart muscle damage. It begins with an injection of dye into the left ventricle, the main pumping chamber of the heart. It is usually done during a coronary angiogram to show the function of the heart muscle and to see if any previous damage has occurred.


  • Specialized tests

The Electrophysiologic Study (EPS) is designed to evaluate the electrical system of the heart and is perhaps the most common and specific test for evaluating abnormal heart rhythms (arrhythmia). The EPS is of proven value in the diagnosis of serious arrhythmias and is used to assess the severity of rhythm problems and to guide the physician to the best drug or medical device for treatment, if needed. It is done most often to help diagnose and treat excessively fast (tachycardia) or slow (bradycardia) rhythms of the heart, especially when these abnormal rhythms have been associated with important symptoms such as dizziness, lightheadedness, fainting or collapse.

The test is conducted in a specialized hospital laboratory similar to that used for cardiac catheterization. The patient lies on an x-ray table and one or more fine, flexible wires are placed in an arm or leg vein, much like a needle for intravenous fluids, which is also utilized. The wire is then floated through the bloodstream to the interior of the heart chambers, where the heart’s electrical impulses are measured and recorded.
An ECG (electrocardiogram) and heart rhythm are recorded at the same time. The heart may then be challenged by electrical impulses from a pacemaker-like device. The heart’s response discloses whether the electrical system is healthy or whether it is at risk for certain types of abnormal rhythms.
The EPS is done frequently and without complications in laboratories with experienced staff. The complications for any individual vary, depending on what is to be done. The benefits and risks should be discussed with the doctor recommending the test as well as with the doctor performing the test.
During an EPS, the pathways traveled by electrical impulses in the heart can be identified and abnormal rhythms of the heart “mapped.” After identifying the specific pathway, the wire catheter is placed next to it and a small burst of radiofrequency energy is sent through the wire to permanently inactivate the pathway and interrupt the abnormal rhythm-like placing a “road block” across traffic. This procedure, called ablation, can in successful cases eliminate the need for medication entirely.

How much rest and exercise are good for me?
REST



EXERCISE





  • Is rest best?

Some patients who get palpitations with exertion assume it’s the exercise that’s the problem, and all that’s needed is to cut back on the physical exertion. Nothing could be further from the truth. By severely restricting physical activity, you can get “out of shape” and reduce your stamina so that even a short walk may seem like a chore. In short, it’s better to stay active. By exercising regularly and keeping your body in condition, you’ll feel better while accomplishing all exercises more comfortably.

Regular activity is essential for every healthy person, and we should be able to engage in the routines of daily living free of troubling symptoms if we’re going to be truly comfortable. For most of us, maintaining a regular level of exercise is something we do without thinking-we notice a problem only when we “overdo it.”
During exercise, the heart is particularly sensitive to our needs. It increases its rate and pumping action in response to the physical stress. When we are “out of shape” this rapid and forceful heart beat is exaggerated. This is because of the increased stress placed on the heart from doing “more than it’s used to.” High adrenaline levels play an important role and can sometimes trigger abnormal heart rhythms (arrhythmia) in the process.
The awareness of a rapid and forceful heart beat (palpitations) triggered by exercise can be quite troubling, especially if the rhythm seems irregular as well as fast. One of the best ways to prevent these situations is to stay physically conditioned (“in good shape”) by doing some form of regular exercise. Then our everyday physical requirements will be less likely to “exceed our capacity” and trigger excessively fast heart rates or irregular rhythms.
Under your physician’s guidance, a carefully planned exercise program can improve the way you feel and help reduce palpitations. Exercise doesn’t have to be strenuous to be valuable. Overall, exercise should be guided by common sense. As your level of fitness improves, you’ll “feel better,” your heart will have greater capacity without high pulse rates, and the lowered stress on your body will be less likely to trigger irregular heart rhythms.

Age is not an excuse for not exercising. At first, it may be difficult, tiring, and even boring. It may produce headache, shortness of breath, shakiness and excessive sweating, but with time it usually gets easier and more enjoyable. Most people continue exercising because it makes them feel better and makes daily activities easier.



  • Always consult your doctor first!

It’s best to discuss an exercise program with your doctor first, since in some cases a supervised exercise or stress test may be necessary before you start. Also, the doctor may feel that a specific exercise is not advisable because of a particular condition or problem that exists. If any new symptoms occur with your exercise program, be sure to tell your doctor.




  • General exercise guidelines





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