Zapping The Heart Back Into Rhythm
Posted on June 8, 2005, 10:43 a.m. in Cardio-Vascular
If the electrical system in your house was going haywire, you'd call an electrician right away to fix it.
For 2.3 million Americans whose hearts beat too fast or don't keep a regular rhythm, the answer is usually medicines and occasional electric shocks. But these can cause serious side effects and lose their power over time. That leaves many patients with an irregular heartbeat that saps their strength and raises their risk of having a stroke.
Now, a new option offered at the University of Michigan Cardiovascular Center and a handful of other centers nationwide is proving to be a true, lasting cure for the vast majority of people who receive it.
Called catheter ablation, the approach has cured more than 1,000 U-M patients who have the most common form of irregular heart rhythm, called atrial fibrillation or AF, and allowed them to return to an active life. U-M doctors have cured 85 percent of patients with the kind of AF that comes and goes on its own. And even patients whose hearts beat irregularly all the time can be cured about 75 percent of the time.
Just like a house's electrical wires, the heart has a system of nerves that use a constant flow of electricity to control the pumping action of the heart's muscular walls. Normally, this keeps the heartbeat regular. But in atrial fibrillation, it goes haywire &emdash; often because of other heart problems, but sometimes for no apparent reason. Patients can feel weak or short of breath, and lose their strength.
Now, just like an electrician looks inside a house's walls to find the wires that are causing a problem, U-M heart specialists can look into the heart's walls and find the source of a rhythm problem. Then, they “zap” tiny areas of the heart muscle with intense radio waves, blocking the flow of electricity and restoring a normal rhythm.
The catheter ablation technique doesn't involve surgery, but rather a system of tiny wires that are fed into the heart through a major blood vessel. Patients only need a mild sedative, and go home from the hospital the next day.
U-M doctors are considered world leaders in catheter ablation for AF, with more successfully treated patients than most centers. U-M doctors have also performed research that shows how well the technique works and how it can be improved.
Fred Morady, M.D., leads the U-M catheter ablation team. “There are many patients who don't respond to medications or can't tolerate them. In the last few years, we've had the option of catheter ablation to cure their atrial fibrillation,” he says.
Morady is the McKay Professor of Cardiovascular Diseases and directs the Clinical Electrophysiology Service at the U-M Health System. He and other U-M cardiologists have trained many other doctors to perform the technique so it can be available to even more patients.
There's a great need for more doctors who can perform catheter ablation, Morady says. Atrial fibrillation is diagnosed in 160,000 more Americans each year, and the number of people living with the condition is expected to double in the next few decades as the Baby Boomer generation ages.
As people age, Morady explains, many factors can cause the heart's electrical system to go on the fritz and cause a rapid or irregular heartbeat. “Atrial fibrillation is often a result of some other type of heart problem, such as high blood pressure, problems with the mitral valve, and sometimes excessive thyroid hormone levels,” he says. “There are also a fair number of patients who develop it as purely an electrical problem with the heart, without any other evidence of structural problems with the heart.” People who are overweight, or who have breathing problems when they sleep are also at higher risk of developing atrial fibrillation.
No matter what the cause, AF can make a person's life miserable, keeping them from participating in activities or working because of weakness, dizziness, shortness of breath and less endurance. Then again, some people with AF have a mild form of the condition and don't know it.
Unlike other less common heart rhythm problems, AF doesn't pose a risk of killing a person directly. But because it keeps the heart from pumping blood efficiently, blood clots can form in the chambers of the heart and travel to the brain, causing a stroke that can kill or cause permanent disability. In fact, as many as 15 percent of all strokes occur in people with AF.
In addition to disability and stroke, AF can lead to heart failure, because a heart that beats too fast for many months without being controlled can become weakened and enlarged.
Drugs that keep the heart's rhythm steady, or keep it from beating too fast when its rhythm gets out off kilter, can help decrease symptoms. Blood-thinning drugs can prevent blood clots from forming. And cardioversion, or an electric shock to the chest, can “re-set” the heart rate. But many patients get less and less relief, and more and more side effects, from the various drugs as time goes on. And cardioversion's effects may only last a few months.
That's why catheter ablation is such an exciting option, says Morady &emdash; its effects are permanent. And unlike open-heart surgical options that have been used on some AF patients in the past, catheter ablation only requires a small incision in the groin, to insert the wires (or catheter) into the blood vessel that leads to the heart.
Then, an X-ray machine takes real-time pictures as the doctor threads the catheter up to the heart, through the heart's outer muscle, and through the wall that separates the two upper chambers of the heart &emdash; the left atrium and right atrium. Patients have a sedative that allows them to remain awake but groggy, and keeps them from remembering the experience.
“We use the wires to map out the electrical circuits of the heart, and then to deliver radiofrequency energy to destroy some of the areas that are causing the atrial fibrillation,” Morady explains.
This “zapping” of small patches of heart muscle heats up an area the size of a pea, effectively burning the muscle tissue so it can't conduct electricity. “Everywhere that we find a spot, the energy heats the tissue and destroys that small area. We typically have to burn 40 to 60 spots before the AF resolves,” he says. Many of those spots are in the area where the veins that bring blood from the lungs enter the heart, but others are on the walls of the atrium itself.
The U-M team customizes the treatment to each patient's individual electrical situation, and the entire procedure takes about three hours. Sometimes, patients need to return for a second treatment, or need to receive a single cardioversion shock to permanently eliminate their AF.
In all, Morady says, there's still a need for research on how well catheter ablation compares with long-term drug therapy in reducing larger risks &emdash; and the procedure isn't yet recommended for people who are still keeping their heart rhythm under control with medication. But the importance of this new option for atrial fibrillation is growing, and is sure to grow as doctors gain more experienced and achieve higher success rates, and new doctors learn the technique.
One patient's catheter ablation success story:
Jerry Smith of Fort Wayne, Indiana had tried many medications in his three-year struggle with atrial fibrillation. The condition had first made itself known to him when he was out deer hunting in the fall of 2001, and was helping a friend carry his prize back to the truck. All of a sudden, he felt like he couldn't catch his breath and had to stop. Later that day, his wife took him to the emergency room, thinking he had had a heart attack.
“They put me on a medicine which would slow my heart down to a regular, normal heartbeat, and they also told me that in a certain amount of time my body would get immune to that and my heart would go back out of rhythm. And that's exactly what happened,” he says. Even stronger medication and cardioversion shocks didn't help.
Just as Smith was resigning himself to a life of inactivity at the age of 67, a young cardiologist who had trained at U-M heard about his case. He referred him to Morady, who agreed he was a good candidate for catheter ablation. After two procedures and one cardioversion in late 2004, he's completely symptom-free and back in action &emdash; and praising U-M's care.
“What amazed me about Dr. Morady was that he took time to walk you through each procedure,” Smith says. “He's one of the best doctors I think I've ever met.”
Facts about atrial fibrillation and catheter ablation:
- At least 2.3 million Americans have atrial fibrillation, the most common form of heart rhythm irregularity, and 160,000 more are diagnosed each year. The number of people living with AF is expected to double in the next three decades as the Baby Boomer generation ages.
- AF occurs when there are problems with the electrical system in the muscle of the heart's upper chambers, or atria. This can cause the heart to beat too fast, or in an irregular pattern.
- Although AF doesn't kill, it can cause weakness and shortness of breath because the heart can't pump blood very well. It can also cause blood clots to form and travel to the brain, causing a stroke. People with atrial fibrillation have five times the normal risk of stroke.
- Typical treatments for AF include medications to prevent problems with heart rhythm, to prevent blood clots from forming, or to slow down the heart rate of a person while their rhythm is off. Cardioversion, or electric shocks, can also be used to re-set heart rhythm. But none of these treatments is a cure, and all of them can lose effectiveness over time.
- Catheter ablation is a minimally invasive technique that can cure many AF patients who are no longer helped by medications or can't take AF medications. It delivers tiny but powerful jolts of radiofrequency energy to the wall of the heart, blocking the flow of electricity.