Wednesday, February 28, 2007

Heart Failure Device: Diagnose or Adios?

Tomorrow, the FDA will review the Chronicle – an implantable hemodynamic monitor (measures heart pressures) made by Medtronic, Inc. that is used for long-term measurement of patients with congestive heart failure. The device looks just like a pacemaker (in fact it uses one of their old pacemaker generator cans) but does not pace. Instead, the device measures the time, surface EKG, temperature and right ventricular heart pressures on a continuous basis. Patients can then upload this information via the internet to a central database for their doctor to review in an attempt to facilitate their management.

So why is this such a big deal?

Because it will be the first time the FDA considers an implantable device that has no therapeutic value – only diagnostic. It heralds the beginning of a development cycle for numerous other devices soon to be developed for this and other ailments by Medtronic and their competitors including pressure and chemical sensors. Importantly, it will also provide the FDA with data regarding the utility of these devices to facilitate management of complicated patients with heart failure and avoid hospitalization.

Why might such a device be needed?

Clinicians are keenly aware of their inability to reliably assess fluid status in a number of select patient groups: the obese, those with underlying lung disease, etc. Patients with recurrent admissions for congestive heart failure exacerbations might be good candidates for such a device, provided the company can convince the FDA that the benefits of the diagnostic data can outweigh the risks of implanting the device.

How Does it Work?

The Chronicle system is composed of three parts: the sensor lead, Chronicle device, and an external pressure reference device that the patient wears. The lead is implanted into the patient’s right ventricle, preferably in an area of high blood flow (to assure non-fouling of the sensor), and connected to the Chronicle device planted beneath the skin of the chest just below the collar bone. The patient also wears a device that measures ambient barometric (atmospheric) pressure throughout the day. Every so often, the patient downloads the pressure and temperature information stored on the Chronicle by first placing their external pressure reference in a base station (similar to a wireless phone’s base station) that is plugged into a phone jack and contains a wand. The wand is then placed over the person’s implanted Chronicle device and the information stored in the Chronicle (time, pressure and temperature information) are downloaded. During the download process, the Chronicle’s internal clock is synchronized with the clock on the external pressure reference to permit adjustments to measured heart pressures based on the ambient atmospheric pressure at a given time. The time, pressure, and temperature data are then uploaded via the internet for the physician’s review.


While it is uncertain where a stand-alone pressure sensor such as the Chronicle will gain approval (but I think it will be at least approved for the sickest of patients), the technology is sure to be incorporated in future devices incorporating pacing and defibrillation in the future – and this might be the best news of all for those suffering with severe heart failure.


References: Wall Street Journal (subscription)

Medtronic COMPASS-HF Study Press release summarizing the Chronicle heart failure study data.

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