August 8, 1997

New device combines pacemaker, defibrillator

New device combines pacemaker, defibrillator

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Dr. Jeffrey Rottman (second from right) monitors patient John Lyons' recently implanted pacemaker/defibrillator unit. Assiting were (from left) Nancy Conners, R.N., Cathy Sistrunk and Dr. Mark Anderson. (Photo by Donna Marie Jones).

Cardiologists at Vanderbilt University Medical Center are the first in the region to begin using a new device that offers the benefits of a sophisticated two-chamber pacemaker and a defibrillator rolled into one implantable unit.

The device is a significant advance in technology for patients with dangerous arrhythmias, said Dr. Jeffrey N. Rottman, associate professor of Medicine. These abnormal heart rhythms are a major cause of death in patients with heart disease.

"The absence of sophisticated pacing technology has been a real problem with these devices in the past, and has often led to very complex situations where we need to put in both a pacemaker and a defibrillator," Rottman said.

"That involves two separate procedures, with a possibility of inappropriate interactions between the two devices as well as increased risks associated with having to undergo two procedures.

"This new pacemaker-defibrillator combination represents the first of what will no doubt be many devices that adds the two-chamber pacing capability to the defibrillator."

The device received approval from the U.S. Food and Drug Administration and went on the market July 21. Two days later, two of the devices were implanted by Rottman and Dr. Mark E. Anderson, assistant professor of Medicine.

Like standard defibrillators and pacemakers, the new combination unit is implanted under the skin and attached to the heart with leads. Electrical impulses are then used to correct the arrhythmia or arrhythmias.

The heart is essentially two pumps – the upper chambers called the atria and the lower chambers called the ventricles. Pumping of the heart is controlled by electrical impulses from the sinus node, a group of cells in the right atrium.

If something goes wrong with the functioning of the sinus node and normal pacing of the heart is disrupted, a number of arrhythmias may develop. Some are too fast, others too slow. Still others are irregular or out of proper sequence.

Defibrillators monitor the heart's rhythm and when an excessively rapid rhythm occurs, it delivers a shock to correct it. Pacemakers are typically used to prevent a slow rhythm or ensure that the chambers beat in the proper sequence (atrium then ventricle).

Many patients who require an implantable defibrillator to correct a dangerously fast heart rhythm also experience slow or out-of-sequence rhythms, Rottman said.

"Often, we have to add medication to suppress the frequency of the fast heart rhythms, even when we can prevent the lethal consequences with the defibrillators," he said. "We want to avoid using the shock of the defibrillator whenever possible because it's often uncomfortable for patients.

"About half of patients with implantable defibrillators also receive additional anti-arrhythmia medication to decrease the frequency of spontaneous arrhythmia episodes."

In addition, many patients who require an implantable defibrillator have congestive heart failure, he said. "In heart failure, it's very important to maximize the residual pumping function of the heart and see to it that it contracts in the usual sequence."

Devices that combine ventricular defibrillation with ventricular pacing became available about eight years ago, but the pacing ability was inadequate for many patients, he said.

Unlike the earlier devices, the new combination unit provides pacing of both the atrium and ventricle, as well as ventricular defibrillation.

Like other defibrillators, the device records and stores data about the heart's electrical activity in the form of electrocardiogram (EKG) readings that the physician can access. However, the new combination unit takes that feature a step further with electrical information from the atrium as well as the ventricles.

"The device itself is much more sophisticated, which allows the physician taking care of the patient to be more sophisticated in terms of correct diagnoses from the stored EKGs," Rottman said.

"One of the most vexing problems has been that patients can have either an atrial arrhythmia or a ventricular arrhythmia, and sometimes it's difficult to tell them apart. They will both result in an excessively rapid heart rhythm and maybe eventually a shock from the defibrillator, but the treatment for the two should be different."

The physician – and even the device itself in limited circumstances – can make the distinction using the additional electrical input, he said.

"For example, atrial fibrillation often slows very quickly after it starts," he said. "The device might wait slightly longer to deliver a shock if it thinks the arrhythmia is related to atrial fibrillation. Simply by waiting a few seconds, we may be able to avoid an inappropriate shock."

While the device is expensive – about $1,500 more than a standard defibrillator – it costs less than both a defibrillator and a pacemaker.

"In circumstances where we had to implant both a defibrillator and a pacemaker," Rottman said, "there would be savings in the cost of the device as well as reductions in the length of hospital stay, the complexity of the hospital procedures and, we hope, the complexity of the follow-up care as well."