Understanding Atrial Fibrillation
Presented by: Stanford Cardiac Arrhythmia Service and Cardiac Electrophysiology Laboratory
Stanford University Medical Center
September 10, 2009
Lecture Overview:
- Atrial fibrillation is a heart rhythm problem of the upper chambers in which the electrical signals are extremely rapid and irregular
- Risk factors include age (over 60), heart disease, high blood pressure, and chronic conditions like sleep apnea and thyroid problems, as well as external triggers like alcohol or stress.
- Atrial fibrillation accounts for about 15 percent of strokes in the U.S., and more than one-third of a-fib patients may have a stroke during their lifetime.
- Catheter-based procedures are being created to close off the left atrial appendage occlusion, a structure associated with clots in atrial fibrillation.
The heart’s electrical system controls the speed and rhythm of the heart. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As it travels, the electrical signal causes the heart to contract and pump blood. The process repeats with each heartbeat.
An arrhythmia is an abnormal heart rhythm, occurring when the heart beats too slowly, too fast, or in an irregular manner. During atrial fibrillation, the heart’s two upper chambers (the atria) beat rapidly and irregularly. Atrial fibrillation, or a-fib, may cause symptoms of heart palpitations, shortness of breath, and weakness.
Episodes of atrial fibrillation can come and go, or can be chronic. Although the condition itself is not usually life-threatening, it can cause fatigue and discomfort, and can sometimes lead to stroke or other serious circulatory complications.
“The condition is caused by chaotic electrical firing in the upper heart chambers,” said Paul Wang, director of the Stanford Cardiac Arrhythmia Service and Cardiac Electrophysiology Laboratory, who introduced a presentation by arrhythmia specialists at a lecture sponsored by the Stanford Hospital Health Library. “The heartbeat is irregular, and the electrical signals move around the atria like a sandstorm.”
More than 2.3 million Americans are affected by a-fib, mostly people between ages 60 and 80, and an aging population means the number of people at risk will grow. Other risk factors, besides age, include heart disease, high blood pressure, and chronic conditions like sleep apnea and thyroid problems. A-fib may also be triggered by external factors like alcohol.
Rate and Rhythm Control
“There’s a difference between controlling heart rhythm and controlling heart rate,” said Henry Hsia, MD, a noted electrophysiologist and the associate director of the Stanford Cardiac Arrhythmia Service. “Some drugs can control heart rate and others prevent recurrence of a-fib by acting on the heart cells. But long-term efficacy for controlling atrial fibrillation may be limited.”
Drugs currently available that restore sinus rhythm (normal heartbeat) tend to show modest results and may reduce the rate of occurrence but may have possible side effects. Drugs that control heart rate appear to be easier to implement and are less likely to be associated with rare proarrythmias (medication-induced arrhythmias) but do prevent the occurrence of atrial fibrillation.
Since both methods show equal survival rates, with all these plusses and minuses, which approach is better? Studies are looking at the effectiveness of existing drugs and assessing new medications, and guidelines to maintain sinus rhythm have been established by the American College of Cardiology and the American Heart Association.
“Drugs are the No. 1 strategy to treat atrial fibrillation,” said Dr. Hsia. “The goal is to achieve sinus rhythm without side effects.”
Catheter ablation is recommended for patients who do not respond to medication.
Managing Stroke Risk
Atrial fibrillation accounts for about 15 percent of strokes in the U.S., and more than one-third of a-fib patients may have a stroke during their lifetime. Because blood is not pumped completely out of the heart’s upper chambers, the blood may pool, starting the clotting cascade. About 95 percent of atrial clots start in a structure known as a left atrial appendage.
Physicians have developed a point system of risk factors called CHADS2 to help establish guidelines in treating a-fib patients, said Paul Zei, MD, PhD, who specializes in catheter ablation of arrhythmias. The acronym stands for Congestive heart failure, Hypertension, Age, Diabetes, and Stroke history. “With each point, the risk of stroke increases,” he said.
For people with a CHADS2 score of 2 or more, the first line of defense is medication, such as aspirin or a blood thinner like warfarin or Coumadin.
Further studies are needed to examine whether surgically removing the left atrial appendage will reduce the risk of stroke. Catheter-based techniques are being developed to occlude the left atrial appendage without the need for heart surgery
“Reducing the risk of stroke in atrial fibrillation is one of our most important goals,” Dr. Zei said.
Ablation and Surgery
More than 20 years ago, heart specialists found that scar lines were electrically inert in the heart and could be used to terminate the chaotic electrical impulses that cause atrial fibrillation. Though effective, the Maze procedure required open-heart surgery and so was best combined with other surgeries. Another, less invasive approach was needed.
Then in 1998, cardiologists discovered pulmonary vein triggers: When they cauterized the areas of heart tissue responsible for the triggers, the recurrence of atrial fibrillation decreased significantly.
“Studies showed that most atrial fibrillation patients no longer needed drugs after the catheter ablation procedure,” said Amin Al-Ahmad, MD, associate director of the Stanford Arrhythmia Service. “However because there can be complications, medications are usually tried first.”
New techniques are being developed: Stanford is one of only 10 centers in the United States involved in testing a freezing technique known as cryoablation to treat the pulmonary veins.
“New technologies are making ablation more effective,” said Dr. Al-Ahmad. “Atrial fibrillation ablation is becoming an important option for symptomatic patients.”
More Options
Research is introducing novel techniques and technologies to treat arrhythmias more effectively, said Dr. Wang. Today’s single-point ablation is being refined, and balloon technology may hold promise for the future. Technological innovations, like robotic controls and new ablation devices are making more procedures possible, with better outcomes.
“Research is an important part of our work and part of our philosophy of staying at the cutting edge of the field,” Dr. Wang concluded.
About the Stanford Arrhythmia Service
The Stanford Arrhythmia Service and Cardiac Electrophysiology Laboratory offers both evaluation and treatment of arrhythmias. The team works closely with patients and their referring physicians to evaluate symptoms and determine the best treatment. Treatments range from medications, such as anti-arrhythmic agents, to novel ablation procedures.
For More Information:
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Stanford Cardiac Arrhythmia Services
http://stanfordhospital.org/clinicsmedServices/COE/heart/DiseasesConditions/arrhythmia/
