Monitoring in Motion

Despite the incredible advances in heart monitoring over the past several years, most data has to be recorded in a doctor's office. That limitation is being overcome by Recom Managed Systems Inc., which is now testing a compact unit that can provide high resolution data while heart patients are performing normal daily activities.

The Greenville, SC, company is currently testing its Model 100 system, a portable unit that can be carried by heart patients to determine how their heart activity changes in response to the events they face in everyday situations. "We enable clinicians to get the same quality ECG when patients are walking as when they are supine in the office," says Marko N. Kostic, R&D systems engineer at Recom.

The firm's Model 100 provides up to 48 hours of real-time heart monitoring. That lets internists and cardiologists more accurately detect cardiac abnormalities or changes that occur during daily activities. It also lets doctors collect cardiac data over long time periods to create a base that they can compare with future cardiac tests.

The compact system is a 12-lead ambulatory recorder that provides ECG data equivalent in clinical quality to 12-lead modalities such as resting ECG and exercise stress testing.

"When you do an ECG in an ambulatory environment, most data is corrupted. There are problems with other technologies because of the noise levels from the patient and the environment," says Budimir Drakulic, CTO at Recom.

The device, which has received 510(k) clearance from the Food and Drug Administration, is now going through extensive testing at the Electrophysiology Laboratories at Cleveland Clinic Heart Center. It has also been tested at Duke University.

The company has tested the unit in other areas to make sure that the ambient environment does not create noise that can't be filtered out. "We even ran tests on race car drivers, putting a big box on their belt. There's a lot of difference in the environment when you're monitoring a driver sitting in the pit and running an ECG when he's going through a turn at 220 mph," Drakulic says.

The key to capturing heart rate information in an uncontrolled environment is to minimize noise. The body creates some noise, as does the movement of the device. That's compounded by interference from the environment, which can be harsh, particularly when the patient is near a device such as a vacuum cleaner or microwave oven.

That's compounded by the fairly low amplitude of ECG signals. "An ECG is only in the range of a couple hundred Hertz," Drakulic says.

Recom designers chose to eschew the normal way of eliminating noise.

"The whole industry in ECG amplifies the signal, then uses digital filtering to clean up the data. But when you do digital filtering afterward to remove noise, you also remove parts of data that have clinical significance," Kostic says.

Instead, they eliminate extraneous signals early in the process. "We have carefully designed the front end, with analog filtering at the beginning," Kostic says.

That approach makes it possible to best determine the difference between desirable signals and unwanted noise, something that's more difficult to do with digital processing later in the processing chain. "You get the best signal to noise ratio in the analog domain. Then we do processing of signals that are of interest to the physician," Drakulic says.

The difference for doctors making a critical diagnosis is significant. "Our data differs by up to 150 microvolts, which is the level physicians use to determine if things are normal or not," Drakulic says.

Another goal was to make the unit small enough so heart patients could carry units around for hours at a time. That requires using compact semiconductors that integrate many functions. "The Texas Instruments' MSP430 microcontroller lets us do things in a small package," Drakulic says. That microcontroller has analog to digital converters that have from 12 to 16 bit resolution, he adds.

The chip also helps extend battery life. "The MSP430 is designed for low power. It's got a wide operating voltage, from 1.8 to 3.6V," says Juan Alvarez, MSP430 marketing manager for TI. The chip is also designed so that any or all of the on-chip modules can go into sleep modes whenever possible. "It's got intelligent peripherals that can work by themselves so you can shut off power to the CPU," Alvarez says.

Drakulic notes that the technique can be extended into other types of measurements. That may occur quickly once final certification is received. Now that the company is gearing up for production, the board of directors has recently added marketing and manufacturing managers, many from Johnson & Johnson, to take the company to the next level.