Improving the beat for heart failure

(This article was first printed in the June 2005 issue of the Harvard Heart Letter. For more information or to order, please go to www.health.harvard.edu/heart.)

Adding a special pacemaker that coordinates the beat of the heart’s lower chambers to state-of-the-art drug therapy helps some people with heart failure live longer and better.

The first artificial pacemaker was a boxy device too big to be implanted in the chest. It ran on AC power, which tethered its user to an extension cord and prayers against power failures. Today’s pacemakers, some the size of a silver dollar, fit neatly in the chest and run on their embedded batteries for years.

Pacemakers have changed in other ways as well. Modern ones are safer, better protected against microwaves and other stray electromagnetic radiation, and smarter. While early pacemakers delivered tiny “beat now” shocks to just one chamber of the heart, some now come close to mimicking the complex electrical system of the heart.

One of these is the biventricular pacemaker. Its signals help the heart’s two lower chambers beat in perfect unison. This is called cardiac resynchronization therapy. Although it sounds like a small thing, resynchronization can help some people with heart failure stay out of the hospital and live longer. It may even strengthen a failing heart.

Results from a large trial of this device, called the Cardiac Resynchronization–Heart Failure (CARE-HF) trial, were so positive they had the director of the trial talking about “remission” for a condition that has long been considered as manageable but ultimately unstoppable.

Out of sync

Damage from a heart attack, high blood pressure, a malfunctioning heart valve, too much alcohol, and even some viral infections can lead to heart failure. This doesn’t mean the heart is about to shut down. Instead, it’s the failure of the heart to meet the body’s incessant need for oxygen-rich blood. The heart, brain, kidneys, and other organs strive valiantly to compensate. Eventually, though, they can’t, and the tissues’ demand for oxygen slowly begins to exceed the supply.

Lack of oxygenated blood causes tiredness, shortness of breath, difficulty walking, and trouble sleeping. Fluid can back up into the lungs and cause swelling in the legs. The strain on the heart can also disrupt the flow of electrical signals through the heart’s chambers, especially the left ventricle.

About one in three people with heart failure develops what doctors call ventricular dyssynchrony. In plain language, this means the two lower chambers aren’t contracting together. Instead, the right ventricle beats a fraction of a second before the left one.

Like two people trying to lift a heavy sofa at different moments, the loss of coordination costs the heart some of its pumping power. This sets the stage for a gradual downward spiral. Less power means less blood ejected with each beat, which forces the heart to work harder. The extra work leads to harmful changes in the size and shape of the heart, which can lead to even more damaging disruptions in the heart’s electrical pathways. Out-of-sync contractions can also throw the mitral valve out of alignment, making the left ventricle work even harder.

Restoring a coordinated beat helps the heart pump more efficiently. Results from the Cardiac Resynchronization trial show it can also do much more.

Reasons to CARE

The trial included 813 men and women with moderate to severe heart failure and some evidence of out-of-sync ventricles. All received state-of-the-art drug therapy; half also received cardiac resynchronization therapy in the form of a biventricular pacemaker. After two and a half years, 39% of those aided by cardiac resynchronization had died or been hospitalized for heart failure, significantly less than the 55% of those on drug therapy alone. Quality of life also improved more in the resynchronization group than in the drugs-only group.

One-third of the heart-related deaths were sudden deaths. These are often caused by the fast, uncoordinated heartbeat known as ventricular fibrillation. Combining a biventricular pacemaker with a cardioverter/defibrillator that can shock the heart back into a normal rhythm could further improve survival.

Perhaps most surprising, by the end of the trial about 20% of the volunteers who received a resynchronizing pacemaker had better left ventricular ejection fraction, a measure of how much blood remains in the chamber after a contraction. In some, it had jumped above 40%, the level often used as a cutoff for defining heart failure.

According to Dr. John G.F. Cleland, a British cardiologist who led the CARE-HF trial, the combination of state-of-the-art medical therapy and biventricular resynchronization could lead to remission of heart failure in some people.

What resynchronization won’t do

Despite its promise, cardiac resynchronization therapy isn’t a miracle cure. In the CARE-HF trial, 2 in 10 people who had a biventricular pacemaker implanted died during the course of the 30-month trial. While that’s better than the 3-in-10 death rate with medical therapy only, it is still a sobering reminder of the destructive power of heart failure.

Cardiac resynchronization doesn’t work on its own. “This isn’t a replacement for medical therapy. It won’t get you off any pills or eliminate the lifestyle changes that are so important in managing heart failure,” says Dr. Michael O. Sweeney, who directs the cardiac pacing and implantable device unit at Harvard-affiliated Brigham and Women’s Hospital.

Finally, cardiac resynchronization isn’t for everyone. Some people benefit from this type of pacemaker, some don’t, and some may actually be harmed by it. Success depends on careful assessment of the heartbeat and precise pacemaker placement.

It isn’t easy to spot out-of-sync ventricles. Many doctors use an electrocardiogram (ECG). It can spot an electrical delay through the left bundle branch, which provides the contraction signal for the left ventricle.

Unfortunately, ECGs sometimes miss people who have out-of-sync ventricles and identify ventricular dyssynchrony in people who don’t have it. The most accurate way to tell if your ventricles beat together is with a special echocardiogram that translates sound waves into motion of the heart’s wall. Right now, though, the expensive machines needed to create these images are available in only a few large medical centers.

Some people who are excellent candidates for resynchronization therapy aren’t helped by it because the device isn’t properly implanted. One of the pacemaker’s wires must stimulate a special spot in a vein on the outside of the left ventricle. Putting it there involves some tricky maneuvering. This is best done by a team with plenty of experience implanting biventricular pacemakers.

Going forward

The positive results from the CARE-HF trial will probably vault resynchronization into the front line of heart failure therapy. That’s a good thing, because a properly placed biventricular pacemaker can help someone with heart failure and out-of-sync ventricles be more active, have fewer symptoms such as shortness of breath or swollen legs, avoid hospitalization for heart failure, and live longer.

But there’s a downside to more widespread use of this expensive therapy. In the CARE-HF trial, pacemaker implantation caused serious problems in about 1 of 10 recipients. These included severe infections, pacemaker wires slipping out of place, tears in the heart muscle, and erosion of the pocket where the pacemaker sits in the chest.

Cost is another issue. A biventricular pacemaker costs at least $20,000, more if it comes with a defibrillator. Doctors earn more money by implanting a biventricular pacemaker-defibrillator than by managing an individual’s heart failure with drug therapy. This means there are what policy makers politely call “financial incentives” driving the use of the devices.

Cardiac resynchronization is new enough that not all doctors know about it. If you have heart failure, and your doctor hasn’t mentioned resynchronization therapy as an option for you, bring it up with him or her. If it looks like it is right for you, try to find a team with strong experience diagnosing out-of-sync ventricles and implanting biventricular pacemakers.

(This article was first printed in the June 2005 issue of the Harvard Heart Letter. For more information or to order, please go to www.health.harvard.edu/heart.)

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