Atrial Fibrillation afflicts approximately 1,000,000 per
year in the G-20 nations. Left untreated
this mildly irregular atrial rhythm progresses to a fully chaotic atrial cardiac
state over a period of 5 to 15 years.
Left untreated AF progresses from intermittent bouts of irregular rhythm
to chronic nearly continuous chaotic rhythms that dramatically increase stroke
risk. Even in the early stages, AF
creates a deteriorating quality of life due to the bouts of cardiac flutter
which degrade a patient’s ability to perform normal activities.
Treatment options include both pharmaceutical and surgical
courses. For most patients,
pharmaceutical treatment mask the symptoms but does nothing to slow the
progression of the disease. Eventually,
the disease overcomes the ability of the drugs to mask symptoms and the patient
requires surgical intervention. Surgical
interventions are effective in 60 to 80% of early stage patients. In 25% of the successful early stage surgeries,
the disease progression continues. The
result is that 300,000 patients or more are effectively left untreated every
year because no diagnostic method is available to guide the surgical treatment.
A new medical diagnostic has been developed that efficiently
maps the electrical activity of the entire atrial chamber continuously. This allows surgical interventions to treat
80% of the previously untreatable patients.
The new diagnostic uses a computationally intense inverse solution to
find the depolarization charge on the surface of atrial chamber wall.
Convergence of the inverse solution requires a precise anatomical surface and a
knowledge of location of the catheter electrodes during the recording of the
electrograms. To meet these
requirements, the system incorporates a high-resolution ultrasound system and
impedance-based localization system into a single catheter capable of recording
48 intracardiac electrograms simultaneously.
The system level engineering required to meet constraints imposed
by phase noise, bandwidth and impedance are discussed. An introduction to some
of the novel signal processing algorithms will be presented. A physical model for the impedance
Localization is developed to motivate the requirements and methods for
discussion of distortion in the body.