DALLAS, April 11 -- A new rating scale may help doctors make better medical decisions about whether a person should receive a drug or a device to fix a potentially deadly heart irregularity, according to researchers reporting in today's Circulation: Journal of the American Heart Association.
Ventricular tachycardia (VT) is a rapid heartbeat that affects the lower chambers of the heart. Ventricular fibrillation (VF) is a quivering of the heart muscle. Both conditions reduce the heart's ability to pump blood and can result in collapse, cardiac arrest and sudden death, unless prompt medical attention is given.
Robert Sheldon, M.D., Ph.D., professor of medicine at the University of Calgary, Alberta, Canada, who headed the study, says that implantable defibrillators (ICDs) are better than medication for the oldest and sickest patients with VT or VF. Medication may be a better choice for those who are younger.
Implantable defibrillators are placed underneath the skin near the collarbone. They are programmed to react when a patient's "danger" level occurs and deliver an electric shock to the heart, speeding up the heart rate and stopping the arrhythmia.
The "gold standard" for drug treatment of VT/VF is amiodarone, says Sheldon. The medication changes the chemistry that creates electrical currents in the heart and prevents many recurrences of VT or VF. However, the drug can have serious side effects, including scarring of the lungs or liver, disruption of thyroid function and tremors. This is one reason why implantable defibrillators are being studied so intensely.
Compared to medication, ICDs reduced the death rate by half among individuals with VT or VF if they were 70 years or older, had poor left ventricular function (weaker contractions) and were bedridden or easily winded.
"These findings were quite unexpected," Sheldon says. "Not only do they suggest that older, sicker patients are most likely to benefit from receiving an ICD as first-line therapy, but they suggest that younger, healthier patients with VT/VF -- which include a larger segment of the population -- would have better treatment results with medication. If confirmed, these findings may have broad implications for the provision of therapy for patients with VT/VF."
Three large international studies found that implantable defibrillators reduced the death rate by 30 percent among VT/VF patients in general, compared to amiodarone. Patients with ICDs experienced improvement of quality of life provided they only need a few interventions from the device. Once patients needed shocks from their defibrillators, a sensation described by one of Sheldon's patients as "like being kicked by a mule," they may become dissatisfied with the devices.
In the latest study of 659 patients, the researchers again compared the two treatments with roughly half of the patients receiving the drug, and the other half receiving an implantable defibrillator. But this time, the subjects were divided into four groups based on risk factors such as being age 70 or older, having significantly decreased left ventricular function (ejection fraction), and having symptoms of heart failure such as a tendency to become short of breath while sitting or lying down.
The top quarter had the highest ratings on risk factors. This group that received an implantable defibrillator had 50 percent fewer deaths, compared to the high-risk group that received the medication. In those with at least two of the risk factors, the risk of dying in the year following treatment was about 14 percent in patients with the defibrillator and 30 percent in those receiving the drug.
Conversely, the youngest VT/VF patients with the least amount of left ventricular or functional impairment derived the least benefit from an implantable defibrillator compared to those who received the drug.
In an accompanying editorial, Arthur J. Moss, M.D., of the Heart Research Follow-Up Program at the University of Rochester Medical Center in Rochester, New York, wrote that because the sickest patients apparently benefit the most from defibrillators, the technique will become "increasingly targeted for patients with more severe heart disease."
Both Sheldon and Moss agree that further study is needed to confirm the findings.
Co-authors are Stuart Connolly, M.D.; Andrew Krahn, M.D.; Robin Roberts, M.Tech; Michael Gent, D.Sc. and Martin Gardner, M.D.
For more information about ventricular tachycardia or ventricular fibrillation, visit the American Heart Association's online Heart and Stroke A-Z Guide at http://www.americanheart.org.