Cardiac Arrhythmias

 

What Is It?

A cardiac arrhythmia is any abnormal heart rate or rhythm.

In normal adults, the heart beats regularly at a rate of 60 to 100 times per minute, and the pulse (felt at the wrist, neck or elsewhere) matches the contractions of the heart’s ventricles (the heart’s two powerful lower chambers). The heart’s atria (two upper chambers) also contract to help fill the ventricles, but this milder contraction occurs just before the ventricles contract, and it is not reflected in the pulse. Under normal circumstances, the signal for a heartbeat comes from the heart’s sinus node, the natural pacemaker located in the upper portion of the right atrium. From the sinus node, the heartbeat signal travels to the atrioventricular node, or “A-V node,” (located between the atria) and through the bundle of His (pronounced HISS — a series of modified heart muscle fibers located between the ventricles) to the muscles of the ventricles. This triggers a contraction of the ventricles and produces a heartbeat.

Cardiac arrhythmias sometimes are classified according to their origin as either ventricular arrhythmias (originating in the ventricles) or supraventricular arrhythmias (originating in heart areas above the ventricles, typically the atria). They also can be classified according to their effect on the heart rate, with bradycardia indicating a heart rate of less than 60 beats per minute and tachycardia indicating a heart rate of more than 100 beats per minute.

Some common types of cardiac arrhythmias include:

  • Sinus-node dysfunction — This usually produces a bradycardia (slow heart rate), with a heat rate of 50 beats per minute or less. The most common cause is replacement of the sinus node by scar tissue. Why this happens is not known. Sinus-node dysfunction also can be caused by coronary artery disease, hypothyroidism, severe liver disease, hypothermia, typhoid fever or other conditions. It also can be the result of vasovagal hypertonia, an unusually active vagus nerve.


  • The supraventricular tachyarrhythmias — This diverse family of cardiac arrhythmias produces tachycardias (rapid heartbeats) that originate in parts of the heart above the ventricles. In most cases, the underlying problem is either an abnormality in the A-V node or the presence of an abnormal pathway that bypasses the typical route for heartbeat signals.


  • Atrial fibrillation — This is a supraventricular arrhythmia that produces a rapid and irregular heartbeat, during which the atria quiver or “fibrillate” instead of beating normally. During atrial fibrillation, heartbeat signals originate in many different foci in the atria rather than in the sinus node. Although these abnormal foci manage to trigger 300 to 500 contractions per minute within the atria, the extraordinarily high number of heartbeat signals overwhelms the A-V node. As a result, the A-V node sends sporadic, irregular signals to the ventricles, causing an irregular and rapid heartbeat of 80 to 160 beats per minute. The disordered heartbeat of atrial fibrillation cannot pump blood out of the heart efficiently. This causes a pooling of blood in the heart chambers, and increases the risk of a blood clot forming inside the heart. The major risk factors for atrial fibrillation are age, coronary artery disease, rheumatic heart disease (caused by rheumatic fever), hypertension, diabetes and thyrotoxicosis (an excess of thyroid hormones).


  • A-V block or heart block — In this family of arrhythmias, there is some problem in conducting the heartbeat signal from the sinus node to the ventricles. There are three degrees of A-V block: first-degree A-V block, where the signal gets through, but may take longer than normal to travel from the sinus node to the ventricles; second-degree A-V block, in which some heartbeat signals are lost between the atria and ventricles; and third-degree A-V block, in which no signals reach the ventricles, so the ventricles beat slowly on their own with no direction from above. Some common causes of A-V block include coronary artery disease, myocardial infarction (heart attack) or an overdose of the heart medication digitalis.


  • Ventricular tachycardia (VT) — This is abnormal heart rhythm that begins in either the right or left ventricle. It may last for a few seconds (non-sustained VT) or for many minutes or even hours (sustained VT). Sustained VT is a dangerous rhythm and, untreated, often progresses to ventricular fibrillation.


  • ventricular fibrillation — In this arrhythmia, the ventricles quiver ineffectively, producing no real heartbeat. The result is unconsciousness, with brain damage and death within minutes. ventricular fibrillation is a cardiac emergency. ventricular fibrillation can be caused by myocardial infarction, an electrical accident, a lightning strike or drowning.

Symptoms

Symptoms of specific arrhythmias include:

  • Sinus-node dysfunction — There may be no symptoms, or it may cause dizziness, fainting and extreme fatigue.


  • Supraventricular tachyarrhythmias — These can cause palpitations (awareness of a rapid heartbeat), low blood pressure and fainting.


  • Atrial fibrillation — This can cause no symptoms, palpitations, fainting, dizziness, weakness, shortness of breath and angina, chest pain caused by a reduced blood supply to the heart muscle. Some people with atrial fibrillation alternate between the irregular heartbeat and long periods of completely normal heartbeats.


  • A-V block or “heart block” — First-degree A-V block does not produce any symptoms. Second-degree A-V block causes an irregular pulse and/or slow pulse. Third-degree A-V block can cause a very slow heartbeat, dizziness and fainting.


  • Ventricular tachycardia (VT) — Non-sustained ventricular tachycardia may have no symptoms or cause a mild fluttering in the chest. Sustained VT usually causes lightheadedness, loss of consciousness, and can be lethal.


  • ventricular fibrillation — This produces absent pulse, unconsciousness and death.

Diagnosis

Your doctor will ask about your family history of coronary artery disease, cardiac arrhythmias, fainting spells or sudden death from heart problems. Your doctor also will review your personal medical history, including any possible risk factors for cardiac arrhythmias (coronary artery disease, rheumatic fever, thyroid disorders, certain medications). You will be asked to describe your specific cardiac symptoms, including any possible triggers for those symptoms.

Your doctor may suspect that you have a cardiac arrhythmia based on your medical history and symptoms. During the physical examination, your doctor will check your heart rate and rhythm, together with your pulses. This is because certain cardiac arrhythmias cause a mismatch of the pulse, which reflects the activity of the ventricles, and the heart sounds. Your doctor also will check for physical signs of an enlarged heart and for heart murmurs, one sign of a heart-valve problem.

The diagnosis of a cardiac arrhythmia can sometimes be confirmed with an electrocardiogram (EKG). However, because cardiac arrhythmias may come and go, a one-time office EKG may be normal. If this is the case, ambulatory electrocardiography may be required. During ambulatory electrocardiography, the patient wears a portable EKG machine called a Holter monitor, usually for 24 hours. Alternatively, you may wear a device for much longer. You will be taught to press a button to record the EKG reading whenever you experience symptoms. This approach is especially useful if you experience infrequent symptoms of arrhythmia.

When a patient suffers from ventricular fibrillation, it is an emergency. The patient is unconscious, pulseless and not breathing. If available, electrical cardioversion must be administered as soon as possible. If not available, then Cardiopulmonary resuscitation (CPR) should be started.

Expected Duration

The duration of a cardiac arrhythmia depends on its underlying cause. For example, atrial fibrillation that is caused by an overactive thyroid may go away with treatment of the underlying disorder. However, cardiac arrhythmias that result from progressive or permanent damage to the heart tend to be long-term problems. When a heart attack causes ventricular fibrillation, death can occur within minutes.

Prevention

Cardiac arrhythmias that result from coronary artery disease can be prevented by taking the following actions to modify your risk factors:

  • Eat a heart-healthy diet, including abundant vegetables and fruits, fish and plant sources for protein, and avoiding saturated and trans fats
  • Controlling cholesterol and high blood pressure
  • Quit smoking
  • Control your weight
  • Get regular exercise

Cardiac arrhythmias related to medications can be minimized by checking with your health-care provider or pharmacist about any potential drug interactions. This may result in switching to another medication or reducing the dose of the problem medication. ventricular fibrillation resulting from Electrical shock can be prevented by following routine safety precautions around live wires and by seeking shelter during electrical storms.

Not all cardiac arrhythmias can be prevented.

Treatment

The treatment of a cardiac arrhythmia depends on its cause:

  • Sinus node dysfunction — In people with frequent, severe symptoms, the main treatment is usually a permanent pacemaker.


  • The supraventricular tachyarrhythmias — The specific treatment depends on the underlying cause of the arrhythmia. In some people, massaging the carotid sinus in the neck will stop the problem, while other people require medications such as beta-blockers, calcium channel blockers, digoxin and amiodarone. Some patients respond only to radiofrequency catheter ablation, a procedure that destroys an area of tissue in the A-V node to prevent the passage of excess electrical impulses from the atria to the ventricles.


  • Atrial fibrillation — Atrial fibrillation resulting from an overactive thyroid can be treated with medications or surgery, while fibrillation resulting from rheumatic heart disease may be treated by replacing damaged heart valves. Medications, such as beta-blockers (for example atenolol and metoprolol), digoxin (Lanoxin), amiodarone (Cordarone), diltiazem (Cardizem, Tiazac), or verapamil (Calan, Isoptin, Verelan), can be used to slow the heart rate. Other treatment options include radiofrequency catheter ablation, or electrical cardioversion, a procedure that delivers a timed Electrical shock to the heart to restore normal heart rhythm.


  • A-V block — First-degree A-V block typically does not require any treatment. People with second-degree A-V block may be monitored with frequent EKGs, especially if they do not have any symptoms and have a heart rate that is adequate for their daily activities. Some patients with more ominous patterns of second-degree heart block may require placement of permanent pacemakers. Third-degree A-V block is almost always treated with a permanent pacemaker.


  • Ventricular tachycardia — Non-sustained VT may not need any treatment if there is no underlying structural damage to the heart. Sustained VT always needs treatment, either with intravenous medication or emergency Electrical shock (similar to ventricular fibrillation, see below).


  • ventricular fibrillation (VF) is treated with defibrillation, giving the heart a measured Electrical shock to restore normal rhythm. The Electrical shock can be delivered on the skin over the heart in an emergency situation. People who have survived VF and those at high risk for VF are potential candidates for placement of an automatic implantable cardioverter defibrillator (AICD). The device is similar to a pacemaker, with wires attached to the heart that connect an energy source placed under the skin. The procedure is done in the operating room.

When To Call A Professional

Call your doctor if you have any symptoms of a cardiac arrhythmia, including palpitations, dizziness, fainting spells, fatigue, shortness of breath or chest pain. Call for emergency help immediately whenever someone in your family develops a severely irregular pulse. If you cannot feel a pulse at all, and the person is not breathing, perform Cardiopulmonary resuscitation (CPR) until emergency professionals arrive.

Prognosis

The prognosis for cardiac arrhythmias depends upon the type of rhythm disturbance and whether or not the person has coronary artery disease, congestive heart failure, or some other heart-muscle disorder. The prognosis for ventricular fibrillation is grave, and death follows quickly without emergency treatment. Most atrial arrhythmias have an excellent prognosis. Heart block, even for the most serious type third-degree A-V block, has a good prognosis. The availability of permanent pacemakers, implanted cardioversion/defibrillation devices, and effective medications has improved the prognosis for many people with serious cardiac arrhythmias.

 

Johns Hopkins patient information

Last revised: December 5, 2012
by David A. Scott, M.D.

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