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Tuesday, January 20, 2009

What is new in atrial fibrillation?

Pulmonary vein isolationThe four pulmonary veins are blood vessels that carry oxygen-rich blood from the lungs to the left atrium. There is a narrow band of muscle cells that surrounds the openings of the pulmonary veins where they enter the left atrium. This band of muscle cells may begin to actively discharge electrically, and this discharge may initiate AF. During pulmonary vein isolation (PVI), the band of muscle cells is destroyed by energy applied through a catheter. This effectively blocks the electrical discharges from crossing over from the band to the left atrium and hence prevents AF.
Procedure. Before PVI, the doctor performs a history and physical examination, an EKG, a 24-hour Holter monitor, and a trans-esophageal echocardiogram to exclude blood clots in the atria, and, sometimes, a CAT scan of the chest. The doctor also may ask the patient to stop certain medications, particularly blood thinners such as aspirin, clopidogrel (Plavix), or warfarin, several days before the procedure. The doctor may check a blood prothrombin time and INR level to make sure that blood clotting is adequate for the procedure.
PVI is performed under deep conscious sedation (but not general anesthesia) in a cardiac electro-physiology laboratory and takes three to six hours. Several catheters are inserted through large veins (in the neck, arm or groin) and fed into the left atrium under x-ray (fluoroscopy) guidance. One of the catheters is equipped with an ultrasound transducer that allows the doctor to view the structures inside the heart during the procedure. The junction of the pulmonary veins with the left atrium is identified, and energy is then applied through another catheter to this area. This results in the destruction of the band of muscle cells and their replacement by a scar. This process is repeated at the opening of each of the four pulmonary veins into the left atrium.
Course post-pulmonary vein isolation. After PVI, patients remain in the hospital telemetry unit for several days so that the heart's rhythm can be monitored.
Many patients will experience AF and palpitations (irregular heart beat) while in the hospital and during the first two or three months following PVI. Therefore, they are given medications such as amiodarone to prevent episodes of AF and anticoagulation with medications such as warfarin to prevent strokes. The palpitations and episodes of AF gradually decrease. By three months after the procedure, the majority of patients will have a normal rhythm, and the doctor may stop warfarin and amiodarone.
Patients usually will have an EKG and a CAT scan of the chest three months after PVI. The CAT scan is done to make sure that there is no narrowing of the pulmonary veins (pulmonary vein stenosis) due to the scarring.
Effectiveness of pulmonary vein isolation. PVI in the U.S. is a new procedure. Most cardiologists in the U.S. have limited experience with PVI. When performed by experienced doctors, PVI can be expected to prevent AF in 70% to 80% of patients during the first year. Some patients may need additional PVI procedures to prevent further AF episodes. Because this procedure is new, it is difficult to know whether successfully-treated patients will continue in a normal rhythm for a prolonged period of time.
Risks of pulmonary vein isolation. When performed by doctors experienced in PVI, the procedure is safe. The risks of pulmonary vein isolation include cardiac tamponade (bleeding into the pericardium, the sac surrounding the heart), narrowing of the openings of the pulmonary veins, injury to the phrenic nerve that controls the function of the diaphragm, injury to peripheral blood vessels, and, in rare cases, death.
In the early years of PVI, doctors were trying to destroy the tissues inside the pulmonary veins. This led to narrowing (due to scarring) of the pulmonary veins which, in turn, led to pulmonary hypertension, a condition in which the blood pressure in the pulmonary veins and arteries increases. Pulmonary hypertension is a serious condition that can lead to heart failure and even death. Doctors no longer try to destroy tissue inside the pulmonary veins. Instead, they try to destroy the tissues only at the junction of the pulmonary veins and the atria. The current technique is not only safer but is more effective and simpler.
Candidates for pulmonary vein isolation. Generally, good candidates for PVI include:
Patients with chronic sustained AF or paroxysmal (intermittent) AF
Patients who develop recurrent AF while on medications
Patients with recurrent AF who cannot tolerate the side effects of long-term medications
Patients with recurrent AF who do not wish to continue taking long-term medications or anti-coagulation
Atrial Fibrillation At A Glance
Atrial fibrillation is an abnormal rhythm of the heart.
Atrial fibrillation is caused by abnormal electrical discharges within the atria
Atrial fibrillation reduces the ability of the atria to pump blood into the ventricles and usually causes the heart to beat too rapidly.
Symptoms of atrial fibrillation include palpitations, dizziness, fainting, weakness, fatigue, shortness of breath and chest pain although some people have no symptoms.
Complications of atrial fibrillation include heart failure and stroke.
Atrial fibrillation can be diagnosed by physical examination, electrocardiogram, Holter monitor or patient-activated event recorder.
Treatment of atrial fibrillation is directed toward controlling underlying causes, slowing the heart rate and/or converting the heart to normal rhythm, and stroke prevention using blood-thinning medications.
Medications are commonly used in the longer-term to control or prevent recurrence of atrial fibrillation, but medications may not be effective and may have intolerable side effects.
Electrical cardioversion is successful in over 95% of patients with atrial fibrillation, but 75% of patients have a recurrence of atrial fibrillation within one to two years.
Some doctors may leave patients in atrial fibrillation for the longer-term provided the heart rate is under control, blood flow is adequate, and blood is adequately thinned with medications.
Non-medication treatments of atrial fibrillation include pacemakers, AV node ablation, atrial defibrillators, and the Maze procedure.
Pulmonary vein isolation shows promise for the treatment of atrial fibrillation and has a high rate of success; however, longer-term experience is necessary.

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