Pacemaker power: All in a heartbeat

Medical Tribune December 2008 P8
David Brill

Pacemakers could one day be powered by the beating of the heart, allowing for the development of more advanced features without the need for larger batteries, a British study suggests.

The team at Southampton University Hospital demonstrated that a prototype device, implanted into a pig, was able to successfully generate electricity solely from the contractions of the cardiac chambers.

At present the energy produced is just 17 percent of that needed to power a contemporary pacemaker but refinements of the model could increase this output to 100 percent, the researchers say.

“This study has proved the concept that it’s possible to harvest the energy of cardiac motion using a device that could be part of a standard pacemaker or ICD lead,” said Dr. Paul Roberts, a consultant electrophysiologist who led the study.

“We think that this study may represent a major advance in pacemaker and ICD technology. We don’t envisage that this would be a stand-alone device – we think that it would … augment current pacemaker and ICD batteries so in effect the heart would be continuing to charge the pacemaker battery.

“This may therefore allow for the development of additional device functions that had previously been limited by power constraints,” he said.

The so-called self-energizing implantable medical microsystem (SIMM) is presently hampered by the size of the lead, which has a maximum diameter of around 6mm. The researchers are now looking to bring this into line with current pacemakers by reducing the diameter to around 2 or 3 mm, Roberts said.

He added that it is likely to be several years before the device could be ready for use in humans.

The prototype, which has already attracted commercial interest and UK government funding, was inserted using the standard techniques for pacemaker implantation. The procedure was uneventful and took around 2 or 3 minutes, Roberts said.

The SIMM comprises two pressure-sensitive bladders placed in the right atrium and ventricle. As the heart contracts and relaxes the pressure pushes a magnet back and forth through the connecting lead, thereby generating electricity from a series of coils embedded in the lead.

At rest the system produced 4.3 μJ of energy and a voltage of 0.2 per heartbeat. The energy output increased to 9.6 μJ/beat during pharmacologically-induced tachycardia and dropped to 3.0 and 1.5 μJ/beat during bradycardia and atrial fibrillation, respectively.

Exercise beneficial for heart failure patients, experts say

Medical Tribune December 2008 P9
David Brill

Exercise training is safe and of great benefit to patients with heart failure (HF), experts concluded following the recent presentation of a new study.

HF-ACTION*, the largest-ever randomized trial to assess the effects of exercise in HF patients, was greeted as a success despite failing to meet its primary endpoint.

Participation in a structured exercise program produced a modest reduction in all-cause mortality or hospitalization, which only achieved significance after adjustment for prognostic factors (adjusted hazard ratio 0.89; P=0.03).

Exercise training also improved quality of life among HF patients, a substudy of the trial showed.

Discussing the findings of HF-ACTION, which involved 2,331 patients with an average age of 59, Professor Philip Poole-Wilson of Imperial College, London, UK, said that the data were "compelling" and had wide implications.

"They missed their primary endpoint and there are those who would say ‘well that’s the end of it, let’s go home.’ I think that would be a very wrong interpretation," he said.

"I think that this trial does support the use of exercise and will strengthen the guidelines for both primary care and for the treatment of HF.

"The one thing this trial does not show is what type of exercise to advocate, and I think we’re going to see a lot more studies in that area," he added.

HF-ACTION was conducted at 82 sites in Europe, Canada and the US, with patients followed up for an average of 2.5 years.

A 15 percent reduction in the risk of cardiovascular mortality and HF hospitalization – a secondary endpoint of the study – was also seen after adjustment (adjusted hazard ratio 0.85; P=0.03).

"The HF-ACTION study results support a structured exercise training program for patients with reduced left ventricular function and HF symptoms in addition to evidence-based therapy," said Professor Christopher O’Connor, the study’s principal investigator who presented the findings to the media.

He added that the additional benefits of exercise in HF-ACTION came on a background of excellent medical and device therapy – superior to that seen in any previous HF clinical trial population. More than 90 percent of the patients were on optimal medical therapy and around 40 percent had implantable cardioverter defibrillators, he said.

The exercise program comprised 36 supervised sessions, after which patients were given an exercise bike or treadmill for use at home and encouraged to undertake five weekly sessions of 40 minutes each.

After 3 months, 52 percent of patients were completing at least three such sessions per week. At one-year follow-up, just 25 percent of patients were completing the full five sessions each week.

O’Connor, director of the Heart Center at Duke University Medical Center, US, stressed that adherence is much harder to achieve in lifestyle intervention trials than drug trials, noting that by the conclusion of the study most patients were exercising for just 50 or 60 minutes per week.
Professor Mariell Jessup, a HF specialist from the University of Pennsylvania, said that for many years it was thought that the best treatment for HF was to go to bed and avoid exertion.

"Exercise in HF-ACTION was safe and it improved outcomes so it’s a very encouraging and positive trial. Now when patients come into the office you can say that you need to exercise and it’s perfectly safe for you to do so."


*HF-ACTION: Heart Failure – A Randomized Controlled Trial Investigating Outcomes of Exercise Training.