Placed under the skin of the chest, the vagus nerve stimulator monitors heart activity via a sensory lead and, when indicated, stimulates the vagus nerve in the neck. Image courtesy of BioControl, Yehud, Israel.
“We have become much better at treating systolic heart failure,” says Michael R. Gold, M.D., PhD, Director of the Division of Adult Cardiology and Michael E. Assey Chair of Cardiology at MUSC, noting that two-year mortality rates for patients with severe heart failure (HF) have decreased from 50% to 20%. However, that success has created a new challenge, according to Dr. Gold: “We now have a large population of chronic patients who are kept alive by medications and implantable cardioverter-defibrillators (ICDs), but they continue to have poorly functioning hearts.” Improving heart function and quality of life in this growing pool of patients and reducing hospital admissions, which have doubled in the past five to ten years, will require radical new therapies.
Innovative treatments for HF have been in somewhat short supply. No new classes of medications have been introduced in more than a decade. Cardiac resynchronization therapy improves heart function by coordinating the contraction of the ventricles but is indicated only in HF patients with electrocardiographic (ECG) evidence of bundle branch block. For patients without this ECG abnormality, devices are limited to those, such as the ICD, that detect and correct dangerous arrhythmias but do not improve heart function.
Vagus nerve stimulation (VNS) offers a new treatment approach that is, in principle, applicable to HF of any etiology and is intended for use in conjunction with available therapies. It is used clinically for the treatment of epilepsy and depression, has shown efficacy in improving heart function in animal studies, and has been proven safe in pilot human studies.
Like beta blockers, VNS acts on the autonomic nervous system. Adrenaline released via the sympathetic pathway speeds up heart rate and increases the force of contraction, whereas stimulation of the parasympathetic pathway slows down heart rate and prevents inflammation. In a patient with HF, whose heart cannot meet the circulatory demands of the body, the sympathetic system compensates by releasing adrenaline, forcing the heart to beat faster but also eventually leading to more heart damage. Beta blockers directly suppress this stress response triggered by the sympathetic system, whereas VNS provides a necessary counterbalance by strengthening the parasympathetic response through stimulation of the vagus nerve.
INOVATE-HF (NCT01303718), an international, multicenter clinical trial co-directed by Dr. Gold (projected enrollment: 650 patients), is currently assessing whether VNS is effective at improving heart function and reducing HF-related mortality and readmissions. Jennifer L. Cook, M.D., the local principal investigator for the trial, is excited by the potential of this new technology: “It is the first therapy of its kind, and it could dramatically improve the quality of life for patients with HF.”
Inclusion criteria include New York Heart Association class III HF, an ejection fraction of less than 40%, and continued systolic HF despite optimal medical therapy. To learn more about the trial, call MEDULINE at 800-922-5750 and ask for Deborah Adams.