Defibrillator/Pacemaker Advances Treatment of Heart Failure

A device that combines an internal defibrillator with pacemaker functions for both ventricles - the lower two chambers of the heart - is now coming into widespread use, offering new hope for thousands of patients with serious cardiac problems.

The pacing/defibrillating system was developed after years of research and clinical trials at several institutions nationwide, including the Medical College of Wisconsin. Like a standard pacemaker, the instrument is smaller than a package of cigarettes.

"It's a little larger than a pacemaker, but it has five ports in it (like the ports for small plugs on electrical equipment)", said Marilyn D. Ezri, MD, FACC, Medical College Associate Professor of Medicine. "Two of the ports are for the two coils for the defibrillation function; one is for the top chamber of the heart, called the atrium, and one each to plug in the right and left ventricles. So, this is a biventricular pacing/defibrillator system. It does everything." Both "mechanical" and "electrical" heart problems are treated by the pacemaker/defibrillator.

Most Patients Improve with Biventricular Pacing
New technology and advances in surgical techniques have made biventricular pacing possible. This breakthrough has improved patient outcomes and quality of life, in many cases, beyond what could be achieved without the enhanced capacity to synchronize the two ventricles.

"It's called CRT, cardiac resynchronization therapy, to resynchronize the right and the left ventricular activation," said Dr. Ezri. "CRT was developed about five years ago. It's designed to help people with very symptomatic heart failure who already have optimal medical therapy in terms of medications and diuretics but still are totally without energy, exercise tolerance, and still have persistent symptoms of heart failure.

"By pacing both ventricles simultaneously, one can electrically resynchronize the cardiac output of the heart, increasing blood flow out of the heart. It definitely is to be used as an adjuvant to medical therapy, and improves most, but not all, patients with heart failure. About 30% of patients will have little or no improvement, and we're learning more about the non-responders and who should probably not have the system implanted."

"The system is highly programmable, by means of a special computer that can be used to change the settings non-invasively. After the device is implanted, the various timing intervals can be easily adjusted, so even after the implant, many changes can be made to tailor the function of the device to the individual patient's needs. It has been a major advance in the treatment of heart failure. Patients feel better, and are requiring fewer re-hospitalizations."

Among the options for implanted devices for heart patients, regular pacemakers are appropriate and very effective for many patients and cost the least. The biventricular pacing systems are for more seriously ill patients and the cost is higher. A biventricular pacemaker that also has a defibrillator is the most expensive.

Defibrillators Play a Growing Role
Because studies are showing that people in need of biventricular pacing do better with implanted defibrillators even if they haven't had a serious, life-threatening arrhythmia, Dr. Ezri said, it is likely that the future "market" for biventricular pacing alone (for heart failure patients) will be very small. Deciding who gets which device is important in terms of both patient outcomes and cost control.

"There are two separate issues," said Dr. Ezri. "One is, which patients can benefit from biventricular pacing. Those are people who have very severe heart failure, who can perform only the most minimal of physical tasks, such as making a bed or walking to the bathroom, without getting severely winded or fatigued. They can do very few things comfortably, despite our best cardiology medications, and they can become quite depressed, both psychologically and physically. If the doctor sees an electrocardiogram that shows a delay in electrical activation between the two sides of the heart (called bundle branch block), there is a good likelihood that biventricular pacing, by electrically resynchronizing the heart, will help that patient.

"When one ventricle is activated, but after a few milliseconds, the other ventricle is activated, there is mechanical inefficiency of the heart as a coordinating pump. An electrical delay (seen on the ECG) in a patient with heart failure aggravates the problem of mechanical inefficiency. Not everyone with poor electrical timing has heart failure, but the presence of the ECG abnormality and heart failure identifies the people that we need to see."

"The second issue, which actually has nothing to do with heart failure, is implanting defibrillators in people who have never had a life-threatening arrhythmia. Many studies have shown that certain subgroups of people with heart disease are at high risk for having serious arrhythmias in the future, and implanting the device dramatically reduces the risk of dying suddenly. We know that pacemakers alone do nothing to alter the incidence of sudden death in these high-risk categories. New studies have shown that the combination of a pacemaker (to treat the heart failure) and back-up defibrillator (to treat the possibility of sudden collapse from arrhythmia), provides the best treatment for the heart failure patients, not just in heart attack patients, but in patients that have heart failure because of other reasons."

Procedure Is More Costly, More Difficult
Dr. Ezri said that with the much higher cost of the biventricular defibrillator/pacing device and leads, we must do much more research in deciding which patients are the most likely to improve with the system. "This is predominantly a Medicare population, and it is not acceptable to have 20% to 30% of our patients not improve with the implant, because of the expense, and more importantly, because of the risks involved of having the implant."

About 75 to 80 of the devices have been implanted at Froedtert Hospital; Associate Professor of Medicine Dr. James Roth was one of the investigators in the clinical trials prior to the device introduced to the market. Many thousands are now implanted in patients nationwide.

The surgical procedure for implanting the newer device is more difficult and time-consuming, Dr. Ezri noted, but the operation is still technically performed as an outpatient admission.

"There's quite a bit of a learning curve involved," said Dr. Ezri. "The companies are always trying to improve on the leads and the tools needed to place them in the heart. My average time per procedure now is about two to three hours, about twice as long as implanting a standard pacemaker with just the two right-sided leads. The patient comes in one day and goes home the next day after we've checked everything and made sure that there were no complications."

Dan Ullrich
HealthLink Contributing Writer

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.