Powering the Body Electric

Half of all failed hearts stop suddenly due to electrical problems. A new device sets the pace by mimicking nature’s power grid.


Biventricular pacemakers

"The device doesn't change the underlying nature of the problem, but it can be quite successful in treating the disruptive symptoms of heart failure and is much less risky and invasive than something like an LVAS or a cardiac transplant."




ROUGHLY 5 MILLION AMERICANS suffer from congestive heart failure–their hearts cannot sufficiently supply the body with blood. This mechanical malfunction can result for a number of reasons, but for patients as sick as Keith Norris, the cause is largely irrelevant–he needed a new heart or a device that would act like a new heart to take over for his old one. On the other end of the spectrum, patients with less severe heart failure often can control their conditions using medications.

But there are thousands of patients who are not quite as sick as Norris who still have trouble breathing in spite of the best possible drug regimen. According to Mitchell N. Faddis, MD, PhD, assistant professor of medicine, the key to treating this mechanical malfunction may be to target a different element of the heart–the electrical system. He and colleagues at the School of Medicine are part of two nationwide trials to test a new type of implantable device, the biventricular pacemaker.

The two systems of the heart, mechanical and electrical, work together to effectively supply the body with blood.
In the electrical system, an internal "pacemaker" called the sinus node sends an electric signal to the lower chambers of the heart through a single electrical connection called the atrioventricular node. This connection immediately divides into three sub-branches–one relays the signal to the right lower chamber of the heart; the other two diverge to opposite sides of the left lower chamber. The branches’ purpose is to simultaneously deliver the electric message to both sides of the heart, allowing coordinated contractions (the mechanical function). This coordinated effort forms the healthy "lubb DUPP" heartbeat.

In some patients, the electrical system is completely askew, but the mechanical system is relatively healthy. These individuals benefit from a traditional pacemaker, which serves as a surrogate for the malfunctioning component of the electrical system, either the sinus node or the atrioventricular node.

Mitchell N. Faddis, MD, PhD, and Gregory A. Ewald, MD, display biventricular pacemakers.

In roughly one-third of patients with congestive heart failure, the sinus and atrioventricular nodes are functioning well, but two of the three sub-branches are effectively broken. As a result, the electric signal fails to reach the right and left lower chambers at the same time. When the left side contracts, the right side is relaxed and vice versa. Blood then sloshes back and forth, rather than being forced outward by a two-sided, synchronized effort.

A weakened heart only has a small amount of mechanical energy left to contract the heart muscles. If the same patient also experiences a time delay between contraction of the right and left sides of the heart, the limited mechanical energy left over is used up before enough blood can be pumped out.

Unlike a left-ventricular assist system, which uses the heart’s natural electric signal to supplement its mechanical pumping action, the biventricular pacemaker adjusts the electric signal itself. Traditional pacemakers supply two wires to the heart: one to the upper right chamber; one to the lower right chamber. The biventricular pacemaker adds a third wire, which connects to the lower left chamber. With this third wire, the pumping action of the heart’s right and left lower chambers are re-coordinated.

"The device doesn’t change the underlying nature of the problem, but it can be quite successful in treating the disruptive symptoms of heart failure and is much less risky and invasive than something like an LVAS or a cardiac transplant," says Gregory A. Ewald, MD, assistant professor of medicine.

He, Faddis and Joseph G. Rogers, MD, associate professor of medicine, are participating in two national trials to test this type of device. Participants are eligible only if a strict, advanced drug regimen does not alleviate their symptoms. Patients continue their medical routine after implantation with a device.

The Miracle InSync ICD trial, sponsored by Medtronic, is a secondary prevention trial that uses a combination biventricular pacemaker/defibrillator in heart failure patients who need a defibrillator due to life-threatening heart rhythm problems. This study will examine whether patients’ symptoms and quality of life improve. Medtronic’s InSync biventricular pacemaker (without the defibrillator) received FDA approval in August 2001.

In contrast, Guidant’s Companion trial is a primary prevention trial with respect to life-threatening heart rhythm abnormalities. Nearly half of all heart failure-related deaths are sudden, implicating an anomaly in cardiac rhythm.

"Even if a heart failure patient hasn’t had any heartbeat irregularities, he is at a high risk from dying of an arrhythmia," says Faddis.

That’s why the Companion trial is examining whether biventricular pacing can improve patients’ quality of life and help prevent sudden death in heart failure patients who have not experienced rhythm abnormalities, but who still have trouble breathing, despite medical treatment.

In this trial, participants who meet the entry criteria may remain on heart failure medications or be randomly assigned to receive one of two devices: a biventricular pacemaker or a biventricular pacemaker/ defibrillator. With more than 2,000 projected participants nationwide, Companion is the largest device study to date, and it is the first to examine whether either type of device reduces mortality.

"We already have implanted biventricular pacemakers in about 50 patients. Some have had a dramatically positive response, many have had an improvement in symptoms," says Ewald. "In some patients, it may even remove the need for more drastic procedures in the future, such as heart transplant or implantation of a ventricular assist device. These clinical trials will allow us to determine which patients will benefit most so that we can further target the therapy."