Oct 18 2005
Correcting the timing of heart contractions through cardiac resynchronization therapy can be a lifesaver for people with advanced heart failure. But the procedure, as it is done today, fails in about 15 percent of patients.
Using a minimally invasive approach that may startle heart specialists, a medical-student researcher developed a technique that--at least in pigs--overcomes the procedure's main shortcomings. Steven Mickelsen, a third-year medical student at the University of New Mexico School of Medicine, performed the research during a year away from medical school as a Howard Hughes Medical Institute-National Institutes of Health research scholar at the National Heart, Lung, and Blood Institute.
Proper timing of the pumping action between the lower chambers of the heart, which send blood to the lungs and the rest of the body, is important for the heart to work effectively. When this timing goes awry in patients with heart failure, implantation of a cardiac resynchronization device can help.
A critical step in cardiac resynchronization therapy is the placing of leads--thin wires that resynchronize the beating of the left and right ventricles--onto the heart itself. The standard approach to lead placement on the left ventricle is through the blood vessel on the heart's surface, which is technically challenging in some patients and limits lead placement to where blood vessels are. A substantial number of cardiac leads fail to work because they are positioned poorly, or they become dislodged. When lead placement fails, the most common next step is open chest surgery to place the lead--an invasive procedure that requires a surgeon and general anesthesia.
Under the mentorship of Elliot McVeigh of NHLBI's Laboratory of Cardiac Energetics, Mickelsen searched for a better way to position the critical leads, testing his new technique in small pigs whose hearts are about the size of a human's. Using a catheter inserted through the pig's jugular vein, he implanted pacing leads by puncturing the upper chamber of the heart to reach the pericardium, which is the fluid-filled sac around the heart.
This is the first time researchers have purposely punctured the heart and attempted to leave something--like a catheter or pacing lead--behind. "Cardiac puncture normally is considered a major complication," Mickelsen explained. "Everyone avoids it." Perforations can lead to bleeding that basically strangles the heart so it can't pump.
But Mickelson and his colleagues found they could do it. They were able to insert a pacing lead into the pericardial space, and the puncture site healed with the lead in place.
They report on the study in the October issue of the journal Pacing and Clinical Electrophysiology.
"The method described in this paper represents a very attractive alternative for pacing lead placement," said Albert C. Lardo, director of the Image Guided Cardiotherapy Laboratory at The Johns Hopkins University School of Medicine. "Clinical and animal studies in our laboratory have shown that there is an optimal location for lead placement, but in patients with slightly abnormal coronary vein anatomy, it is often difficult or impossible to position the lead ideally. In these patients, leads must be implanted in highly invasive open chest surgery.
"This new technique allows for optimal lead placement through a minimally invasive approach," Lardo continued. "Following further testing in animals, implementation of such a method could have significant clinical implications, such as a reduction in complications, hospitalization, and recovery time compared with conventional surgical procedures."
Mickelsen inserted a catheter through the pig's jugular vein into the right side of the heart. Using x-rays to watch as he guided the catheter through the veins, he positioned the catheter just above the right atrium and threaded a long needle through the catheter. He then punctured the wall of the vein that leads into the atrium, one of the upper chambers of the heart, and inserted the needle and catheter into the pericardium, the sac that holds the heart. From there, he guided a thin wire through the hollow needle into the pericardial space. The catheter and needle were removed, leaving the wire in place. The wire was used to place the pacing lead on the outer wall of the left ventricle, or lower chamber, of the heart, which pumps blood into the arteries.
The main complication for the pigs was pericardial effusion, leaking of blood into the pericardium – which was not terribly surprising to the researchers. "No one had designed equipment for this purpose. We had to improvise with the tools that were available," Mickelsen said. "We learned from this small series how to improve the approach."
They are devising better tools, such as new pacing leads, now. "We need to reproduce the procedure without any effusion and place the pacing lead exactly where we want it," Mickelsen said. Then they need to try the procedure in a small series of animals that are on aspirin or have high blood pressure in their veins--in other words, more like people with heart failure.
"This study demonstrated the feasibility and safety of a revolutionary, minimally invasive approach to introducing an electrical lead to stimulate or pace the heart, taking advantage of heart anatomy," said Hiroshi Ashikaga, a co-author on the paper and head of cardiac electromechanics research in the McVeigh lab.
"If the patient doesn't have many veins on the heart's outer surface, or if the veins are in the wrong position, we can't give optimal therapy," explained Fred Kusumoto of the Mayo Clinic, Jacksonville, Florida, a senior author on the paper. "With this technique, if it proves fruitful, we can put the leads anywhere."
When Mickelsen first ran his idea by Kusumoto, the cardiac electrophysiologist says his initial thought was, "this is a very creative, novel method for taking care of a very difficult problem we have in electrophysiology patients."
Mickelsen was one of 38 medical students and five dental students who were HHMI-NIH research scholars during 2004-2005. They lived and worked on the NIH campus in Bethesda, Maryland. Now back at the University of New Mexico School of Medicine in Albuquerque to complete his third year of medical school, Mickelsen is planning to develop some minor modifications to the approach and equipment and try the experiment again next year.
"I want to be a researcher and a clinician," Mickelsen said. "This was the first opportunity I had to take an idea from the beginning and try to get people interested, get approvals, and make it happen."