Heart failure often is associated with hearts that have become enlarged and pump less efficiently, but cardiac resynchronization helps return many of these hearts to a more normal size and pumping efficiency. Based on the experience of heart failure patients who received this therapy from an implantable device called the Medtronic InSync system, their enlarged hearts had shrunk by more than 10 percent compared to patients who received heart failure drug therapy alone.
This shrinkage was enough to make the difference between extreme fatigue felt by many patients and their ability to accomplish everyday activities. Because the smaller, trimmer hearts pumped blood more efficiently throughout the body, most patients in the treatment group exercised more than those in the control group and reported an improvement in quality of life.
The results were reported in an article titled "The Effect of Cardiac Resynchronization Therapy on Left Ventricular Size and Function in Chronic Heart Failure", authored by Dr. Martin St. John-Sutton, Professor of Medicine and Director of Cardiac Imaging at the University of Pennsylvania Medical Center in Philadelphia.
"A 10 percent decrease in heart size is significant, not subtle", stated Dr. St. John-Sutton. "The implication of reverse remodelling and volume reduction also predicts a decrease in adverse cardiovascular events over longer-term follow up. The bottom line is that as the heart gets smaller, its function gets better and these patients feel better."
Doppler echocardiograms were obtained from 323 patients enrolled in the landmark MIRACLE study, a large, randomised clinical trial that led to the United States Food and Drug Administration approval of the InSync device for cardiac resynchronization therapy (CRT) in August 2001. Patients were measured at baseline, three months and six months. Those randomised to the treatment arm showed significant reductions in left ventricle mass and volume compared to the control group, which did not receive CRT therapy. The left ventricle is the heart's main pumping chamber.
Additionally, patients in the cardiac resynchronization group showed substantial improvements in their heart's ejection fraction - the amount of blood pumped from the chambers with each beat - as well as significant decreases in mitral valve regurgitation, a term that describes the back flow of blood from the left ventricle back into the heart's left atrium instead of to the body.
"Patients are responding exactly the way we had hoped they would with cardiac resynchronization therapy", stated article co-author William Abraham, M.D., Professor of Medicine and Chief of the Division of Cardiology at the Ohio State University Heart Center. "What is really exciting is that it doesn't appear to be a temporary phenomenon. The benefits are being sustained, over and above what these patients are receiving from standard drug therapy, from follow-up period to follow-up period."
When the heart has to work too hard to maintain adequate blood output, it can begin to change shape, with the left ventricle often growing larger, less flexible and weaker. Prolonged compensation for these impairments can change both the heart structure and its function. This combination is known as remodelling of the heart, characterised by ventricular dilatation or stretching and deteriorating pumping function. However, reverse remodelling occurs when the heart, particularly the left ventricle, begins to change back in shape, often shrinking in size and regaining at least some of its original strength.
Heart failure affects nearly 5 million Americans and is a progressive, debilitating disease, with more than 550.000 new cases diagnosed each year and an incidence that is expected to double within five years. It is the most costly cardiovascular illness in the United States, with an estimated $40 billion spent on managing heart failure each year.
However, cardiac resynchronization therapy has gained rapid acceptance in the United States medical community since Medtronic introduced it in 2001. Not only are patients feeling better, but they spend fewer days in the hospital for heart failure, the health care system's most costly reason for hospitalisation.
"There are still many patients who can benefit from cardiac resynchronization therapy", stated Ursula Gebhardt, vice president and general manager of Medtronic's heart failure business. "We've only scratched the surface of how to help these patients regain their energy, their independence and normal lifestyle."
Heart failure patients who are eligible for cardiac resynchronization therapy typically fall into two categories: those who are at high risk for sudden cardiac arrest and need the protection of an implantable cardioverter-defibrillator (ICD), and those who require resynchronization therapy but do not need ICD protection. Medtronic is the only company to offer CRT devices for these two distinct patient populations in the United States. The FDA approved the original Medtronic InSync system in August 2001, and the InSync III system with advanced programming options and sequential bi-ventricular pacing was approved in February 2003.
Both of these devices are indicated for patients who need cardiac resynchronization therapy but aren't at risk for dangerous ventricular arrhythmias. For patients who need CRT plus the protection of a defibrillator, Medtronic offers the InSync ICD device, approved in June 2002, and the InSync Marquis system, which was approved in March 2003. A fifth-generation device, the InSync III Marquis, is in clinical trials.