Keeping Up the Pace

by Bethany Steichen

Few would argue that technology has changed considerably since the 1980's. Cell phones are a quarter of the size, computer graphics open up new fantasy worlds for games and movies, and gene therapy has the potential to treat conditions whose nature wasn't even understood in the 80's. Some things, however, have remained the same despite technological progress. For example, the leading cause of death in the United States in 2002 according to the Center for Disease Control was heart failure, just as it was in 1980. Over three million Americans are currently living with heart failure and an additional 400,000 are diagnosed each year. Worldwide, approximately 15 million people are diagnosed annually. Researchers and medical practitioners hope that a new treatment, Cardiac Resynchronization Therapy (CRT) could help solve to this problem.

What is Heart Failure?

Contrary to popular belief, heart failure is neither a sudden nor a single disease. Rather it is the heart's gradual loss of pumping ability. This process could take several years and can result from several causes including arteriosclerosis, congenital heart disease or heart attack.

There are two major types of heart failure: 1) Systolic and 2) Diastolic. In systolic heart failure, the heart loses its ability to contract and is therefore unable to force enough blood into circulation. Diastolic heart failure occurs when the heart cannot relax properly. The heart does not completely fill with blood and the cardiac muscle stiffens. Both types can occur in varying severity. Mild cases may be scarcely noticeable to the patient whereas severe cases can impact daily activities and prove fatal.

Size Does Matter

Smaller hearts are better equipped to pump efficiently. Just as working out with heavy weights can increase the size of biceps, hearts that are forced to work hard to pump blood swell up, sometimes to the size of a tetherball, and develop thick, muscular walls. While this may be desirable in skeletal muscle, cardiac muscle that becomes too thick loses its flexibility.

Electrical signaling is also disrupted by the additional time it takes to move through the enlarged heart and the ventricles no longer contract in unison. Instead, the left ventricle contracts, forcing blood into the right ventricle which then contracts, sending the blood back to the left ventricle rather than into the right atrium.

Standard pace makers cannot correct this problem as they are implanted in the right atrium and right ventricle. This is where CRT differs from traditional pacing. Synchronous pacing uses three small wires known (leads) that are connected to a battery to send simultaneous electrical signals to both sides of the heart, stimulating it to work in unison.

Synchronous Pacing

In CRT, leads are implanted in the right atrium and ventricle, and a third lead is placed in the left ventricle. The challenge in doing this is finding a pathway into the left ventricle. Veins are used to implant leads because they are low pressure conduits to the heart. The normal flow of the blood in veins is to the right side of the heart and if small blood clots form, they will go to the lungs rather than the brain.

The left side of the heart presents technical difficulties to implantation as it is attached to the aorta, the artery that supplies blood to most of the body. The pressure of the blood leaving the heart would be too much to safely implant a lead. An alternate route was needed for CRT to be possible.

The Heart is its Own Source of Blood

Cardiac tissue, just like every other tissue in the body requires the oxygen and nutrients supplied by the blood. Therefore, one of the arteries that branches off the aorta leads directly back to the heart. Then a vein takes blood from the left side of the heart to the right atrium through a small hole called the os of the coronary sinus. This vein provides a means to implant a lead in the left ventricle.

Implanting

During an operation, leads are fed through the subclavian vein into the right atrium. To implant in the left ventricle, the lead must be run against the low pressure flow of a vein from the right atrium to the left ventricle. It is then imbedded at the base of the ventricle using a hook-like head. Leads are also implanted at the base of the right ventricle and in the right atrium. Programming of the pacemaker allows for control over electrical stimulation in all three chambers so that the ventricles contract simultaneously followed by contraction of the atrium.

The blood then returns to a normal circulation pattern rather than sloshing between the ventricles.

CRT-D

While the biventricular synchronization improves the pumping ability of the heart, patients are also at risk of sudden cardiac death. In this condition, the electrical impulses in the heart become irregular. They can speed up (tachycardia), slow down drastically (bradycardia), or signal erratically (arrhythmia). The heart will then suddenly stop beating with brain damage and death resulting in a matter of minutes.

Defibrillation, an electrical shock to the heart, acts like a restart button and jolts the heart back into a steady rhythm. Each minute that passes without defibrillation decreases a person's chance of survival by seven to ten percent, so immediate treatment is critical.

To meet this need, defibrillators can be implanted along with a pacemaker. The implanted device is slightly larger than a regular pacemaker, but it is able to sense when any arrhythmia occurs and will take over with defibrillation therapy in addition to standard pacing when it occurs.

By combining the pacemaker and defibrillator, the patient has immediate treatment for heart rhythm problems and the damage is minimized. The CRT pacemaker too can be, and usually is, combined with a defibrillator. This is then known as CRT-D.

CRT and CRT-D Candidates

The expense and the high level of treatment involved in CRT makes it suitable for treating only very severe cases of heart disease. Heart efficiency is measured as a percentage of blood ejected from a chamber. The average ejection fraction for a healthy person with no heart disease is 65%. Patients who are recommended to CRT often have ejection fractions between 15 and 20%. Even in such critical cases as these, drug therapies are tried before implanting.

The Results

Extensive clinical trials show dramatic improvements in CRT patients' health and quality of life. Death by progressive heart failure decreased by 51%, the number of hospital visits were significantly reduced, patients showed a steady increase in distance they were able to walk on a treadmill over six minute period, and an overall increase in daily activity were observed.

CRT also appears to do more than halt cardiac problems so they do not continue to deteriorate. A study done by Medtronic, a Minnesota-based company, in 2001 found that patients receiving CRT actually showed a reversal of heart failure effects. Significantly, researchers found a ten percent reduction of heart size compared with patients on drug therapy alone. A smaller heart is able to pump more efficiently and correspondingly, increased ejection fractions were observed. For patients this translates into more mobility, energy, and functionality. Fatigue decreased and an overall improvement in quality and enjoyment of life were reported.

This treatment is a breakthrough for treating heart disease and has already taken hundreds of people off of heart transplant waiting lists and several thousand have implants worldwide. With such strong data indicating CRT's ability to reverse heart disease effects, medical researchers are wondering if this could be a replacement for a 'miracle pill' in cardiac health.

One Woman's Story

Cindy Eccles was in fine shape eight years ago; she was involved in her job, taking care of her mother, spending time with her adult daughter, and a local bowling league. However, an acute case of pneumonia in both lungs put a halt to all of that. Lethargy made it difficult for her to do daily activities that most people take for granted - such as getting out of bed, laundry, and yard work. Even brushing the cat was a strenuous and exhausting task. Additionally, Cindy experienced black outs, memory lapses, and uncontrollable muscle spasms that terrified her.

For sixteen months, Cindy was in and out of the hospital being treated as a respiratory case. The condition of her heart wasn't even checked until it stopped while in the hospital. At this time she was diagnosed with cardio-myopathy congestive heart failure bundle branch blockage an immediately put on IV therapy.

Cindy received an infusion every Tuesday and felt an energy boost that dissipated throughout the week. By Sunday her energy was sapped and she slept nearly constantly until her next treatment. At this time her heart ejection rate was averaging between 15 and 20% with occasional peaks in the 30's with the expectation that her heart would continue to deteriorate.

She was given an opportunity to participate in a clinical trial by Guidant and had a biventricular defibrillator (CRT-D) implanted two years ago.

Since that time she reports a remarkable difference in her life, "It's indescribable how you feel. I just want a person I can throw my arms around and say 'Thank you!'". While full time work would be too much of a stress on her heart, Cindy has returned to many of her former activities including taking care of her mother, neighborhood youth groups, and the bowling league.

Her twitching has stopped completely, her ejection fraction is steadily above 35%, and she hasn't passed out since beginning the treatment. She noticed an immediate increase in energy as soon as she was out of surgery recovery and has found that the energy level stays high consistently. A few weeks after receiving the device she discovered she was significantly more tan, not from being outdoors, but by increased blood circulation. She's also rediscovered her freckles.