There is an electrical current running through Sophia Gabbidon, but it comes as no shock to the 30-year-old Hartford, Conn., woman. It's just a tiny trickle of juice. She can't feel it, but it's enough to tell the medical staff at St. Francis Hospital and Medical Center how well her heart is pumping.
"I think it's great," said Gabbidon, who was diagnosed in July with congestive heart failure, a condition in which the heart pumps inefficiently. "They don't have to go inside you to see what's going on."
Gabbidon is being treated by Dr. Rick Soucier, a cardiologist who directs the congestive heart failure service at St. Francis. The machine she's wired to -- with a lead stuck to either side of her neck and another pair on each side of her lower chest -- is the BioZ impedance cardiography monitor. In a matter of minutes, it can provide data on how well Gabbidon's heart is working.
The BioZ is but one more step in medicine's march toward noninvasive diagnostic and treatment procedures. By measuring electrical resistance within Gabbidon's chest, it can provide information on the mechanical function of her heart. The only other way to get this information is to insert a catheter into the heart's pulmonary artery -- a procedure that usually involves a hospital stay, has potential risks and is far costlier.
"This allows us to look at how effective the heart is with each beat," Soucier said. And that, with other diagnostic data, allows the St. Francis crew to fine-tune Gabbidon's drug regimen so that she can feel her best and her disease can be slowed.
The BioZ monitor, manufactured by CardioDynamics of San Diego, is the market leader among new-generation impedance cardiography medical devices. Although the technology is rooted in devices NASA used to monitor the hearts of astronauts in flight, it has improved dramatically with advances in software, algorithms and digital technology.
The leads on the patient send out a small current and measure the impedance -- the resistance to the current -- in the chest. The amount and movement of liquid in the chest alters the resistance to the current, and the brain of the monitor converts the resistance to information on the heart's output and the amount of liquid in the chest.
In congestive heart failure, the heart is unable to return to the body all of the blood it is receiving. But the reasons for this inefficiency vary widely. In some cases, the heart muscle has become weak because of injury or infection. In others, the body's blood vessels are constricted and make the heart's job tougher. Often both ends of the circulatory system are involved, which can result in a buildup of body fluid that further taxes the heart.
Soucier noted that simply knowing the patient's blood pressure doesn't provide the whole picture. The BioZ and similar devices help clinicians better pinpoint the effects of heart failure on blood flow and target drugs in the correct dosage to address the specific problems.
Dr. Andre Ghantous, director of the cardiology clinic at the Hospital of St. Raphael in New Haven, Conn., said the BioZ has been in use there about a year. He said that because it can provide information about chest fluid, it can be helpful in the treatment of patients with high blood pressure or kidney failure in addition to those with congestive heart failure. He said the catheterization procedure is still the gold standard for information on the heart's mechanical performance, but the noninvasive monitor is very helpful. "It's a tool that helps the physician in making a decision," he said.
Michael Perry, chief executive of CardioDynamics, said there are about 3,000 BioZ units worldwide, most in the United States. Each unit costs just under $40,000. He said sales have grown tenfold in the last four years. He noted that most of the devices are in physicians' offices, where catheterization is typically not an option. They also are being used in hospital emergency rooms, intensive care units, operating rooms and step-down units.
Not all physicians are that impressed by the BioZ monitor.
"It's not at all a miracle device that is changing the face of cardiology," said Dr. Jeffrey Walden, whose Hartford practice, Consulting Cardiologists, bought a monitor a few months back. Walden said the device has limitations and that its accuracy declines when it is used on very large or very small people. "The margin of error seems to get worse on the extremes," he said. "I tend to use it as a helping tool for managing medications."
Irene Paigah, a spokeswoman for CardioDynamics, said the monitor is not used for people who are shorter than 4 feet or weigh less than 67 pounds or more than 341 pounds. She said it meets most adult ranges and that the company is looking into research on the use of the BioZ for children.
There have been more than 100 studies on impedance cardiography, according to Paigah. A study sponsored by CardioDynamics was reported in October at an assembly of the American College of Emergency Physicians in Boston. Researchers used the BioZ to evaluate 55 emergency room patients at Cleveland Clinic and the University of Mississippi who were older than 65 and complaining of shortness of breath. The inclusion of monitor data after the initial emergency room diagnosis and treatment plan resulted in a change in medication in nearly a quarter of the cases and a change in diagnosis in three patients.
"Those are pretty impressive numbers for a test that takes 10 or 15 minutes," said Dr. W. Frank Peacock, director of clinical operations for the emergency department at the Cleveland Clinic and one of the study's authors. He said the monitor works well for most body types, and some doctors are not enthusiastic because previous generations of these machines weren't very accurate.
"With the advent of microcomputers," he said, "this has become excellent."