New device’s goal is to deliver synchrony

Paces at two sites and coordinates contraction

The Minneapolis-based Medtronic’s InSync ICD was developed to detect and treat potentially lethal heart rates and, at the same time, deliver cardiac resynchronization therapy to both sides of the heart. That restores left and right ventricular synchrony by simultaneously pacing both ventricles, improving the heart’s pumping efficiency. Due to its size, 4-French in diameter, the Attain lead also made by Medtronic can be easily and quickly positioned into the left ventricle. (See photos, above and p. 7.)

"The small size of the new lead allowed me to position it precisely where I wanted," says Angel Leon, MD, of Emory Health Care/Crawford Long Hospital in Atlanta and a Medtronic consultant.

"Since no two patients present similar cardiac venous anatomies, one lead option may not be sufficient," adds Steve Mahle, president of Medtronic’s cardiac rhythm management department. His company produces a number of left-heart leads in varying configurations, but all of them have a distal curved shape allowing steer-ability in small cardiac veins and include the familiar stylet delivery techniques used for placement of all pacing leads today.

Investigators at the Mayo Clinic in Rochester, MN, have also had experience with the InSync pacemaker-defibrillator as Mayo is one of the MIRACLE trial centers. (See related article on the study, p. 1.) "The device delivers small electrical impulses to the left and right chambers of the heart to better synchronize contractions," says Paul Friedman, MD, a cardiologist and study investigator at Mayo. He says the pacemaker-defibrillator device is the size of a small pager and is implanted under the skin in the chest area. It can deliver up to 34 joules of defibrillation energy. Three thin lead wires are run through veins from the device to the left and right chambers of the heart. Only a small incision is required to implant the device. The procedure takes two to three hours to perform and requires patients to stay in the hospital at least overnight.

"The trial at Mayo is just starting up, but we hope to be implanting InSync within a few weeks. It’s a matter of appropriate patient selection," he says. "The ideal patient is someone who has depressed ventricular function and is at high risk for sudden death for arrhythmia." The device stays in the patient’s chest until death or until the battery runs out. Then minor surgery is involved to replace the battery.

"The device sits under the skin below the collarbone like any pacemaker or defibrillator," he says. "Change-out surgery is done under local or twilight anesthesia." If defibrillator testing is necessary, general anesthesia is administered because arrhythmia testing involves giving painful shocks to the heart to induce and terminate rhythms. Friedman provides the following distinction between pacemaker and defibrillator technology:

1. "Pacemakers deliver very low energy [impulses] that cannot be felt by the patient. They are for people whose heart pump function is uncoordinated. This new device provides pacing at two sites in the ventricle resulting in a more coordinated ventricular contraction. That’s what’s unique about the system. The goal is to improve mechanical pump function by improving the electrical activation."

2. "The role of the defibrillator in preventing sudden death is well established. It’s for people who have weak heart muscles and who are at risk for developing abnormal rhythms. The defibrillator function of this device is similar to other approved defibs. What’s being tested is whether, by improving electrical coordination, mechanical coordination can be improved as well so people will be able to walk farther, have fewer symptoms of shortness of breath, and have less fatigue [i.e.], whether they will have less heart failure."