Heart Conditions in Adults - Atrial Fibrillation
The electrical heart conduction pathway must be followed to ensure the heart pumps properly.
The heartbeat starts in the right atrium when a special group of cells (the sinus node or "pacemaker" of the heart) sends an electrical signal.
The signal spreads throughout the atria and to the atrioventricular (A-V) node.
The A-V node connects to a group of fibers in the ventricles that conduct the electric signal.
The impulse travels down these specialized fibers to all parts of the ventricles.
Arrhythmias (or dysrhythmias) are abnormal rhythms of the heart which cause the heart to pump less effectively.
Normally, as the electrical impulse moves through the heart, the heart contracts–about 60 to 100 times a minute in adults. Each contraction represents one heartbeat. The atria (the upper chambers of the heart) contract a fraction of a second before the ventricles (the lower chambers of the heart) so their blood empties into the ventricles before the ventricles contract.
Under some conditions almost all heart tissue is capable of starting a heartbeat, or becoming the pacemaker. An arrhythmia occurs when:
- The heart's natural pacemaker develops an abnormal rate or rhythm.
- The normal conduction pathway is interrupted.
- Another part of the heart takes over as pacemaker.
The electrical activity of the heart is measured by an electrocardiogram (ECG or EKG). By placing electrodes at specific locations on the body (chest, arms, and legs), a graphic representation, or tracing, of the electrical activity can be obtained. Changes in an ECG from the normal tracing can indicate arrhythmias, as well as other heart-related conditions.
Almost everyone knows what a basic ECG tracing looks like. But what does it mean?
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- The first little upward notch of the ECG tracing is called the "P wave." The P wave indicates that the atria (the two upper chambers of the heart) are electrically stimulated to pump blood to the ventricles.
- The next part of the tracing is a short downward section connected to a tall upward section. This spike-like section is called the "QRS complex." This part indicates that the ventricles (the two lower chambers of the heart) are electrically stimulated ("depolarization") to pump out blood.
- The next short flat segment is called the "ST segment." The ST segment indicates the amount of time from the end of the electrical signal for the contraction of the ventricles to the beginning of the "T wave".
- The next upward curve is the T wave. The T wave indicates the electrical recovery period ("repolarization") of the ventricles.
When your doctor studies your ECG, he or she looks at the size and length of each part of the ECG. Variations in size and length of the different parts of the tracing may be significant. The tracing for each lead of a 12-lead ECG will look different, but will have the same basic components as described above. Each lead of the 12-lead is "looking" at a specific part of the heart, so variations in a lead may indicate a problem with the part of the heart associated with that lead.
Atrial fibrillation is a type of arrhythmia. With atrial fibrillation, the electrical signals in the atria (the two upper chambers of the heart) are fired in a very fast and uncontrolled manner. The atria quiver instead of contracting normally. The electrical signals then arrive in the ventricles in an irregular fashion. When the atria do not contract effectively, the blood may pool and/or clot. If a blood clot becomes lodged in an artery in the brain, a stroke (brain attack) may occur. About 15 percent of strokes occur in persons with atrial fibrillation. Aspirin, warfarin, and other cardiac medications may be used to treat atrial fibrillation.
Current guidelines recommend a patient-specific approach to treating atrial fibrillation. A rate control (allowing the patient to remain in atrial fibrillation, ensuring the heart rate is controlled) or rhythm control (using specific medications or procedures to restore normal rhythm) strategy may be adopted. Your doctor will decide which treatment approach is most appropriate for you.
Medications are usually used with the rate control strategy, commonly including beta-blocker medication, such as atenolol or metoprolol, or calcium-channel blockers, such as diltiazem or verapamil, to slow down the heart rate.
The rhythm control strategy may include the use of medications (anti-arrhythmics) or electrical cardioversion to restore normal rhythm. Catheter ablation (a catheter is guided through a blood vessel to the heart and energy is sent through the catheter to destroy small areas of heart tissue that may cause the arrhythmia) is a nonsurgical procedure that is commonly used when medications are not working to control the heart rhythm. Your doctor may also recommend a surgical treatment approach, although this is less common.
Patients with atrial fibrillation should also be evaluated for their stroke risk and receive appropriate blood thinners, such as aspirin, clopidogral, warfarin, dabigatran, or rivaroxaban to prevent stroke. Some patients may have a condition (such as alcoholism with frequent falls) that would make blood-thinning medications dangerous and, subsequently, they may not be used. Your doctor will have a detailed discussion with you about which blood-thinning medications are most appropriate for you.
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