CD&D National Editors
Let's compare the measurement of blood pressure (BP) to photography.
Basically, it's usually just a single picture, says Phil Shaltis, PhD, and frequently not a very accurate one.
This measurement is most usually taken in the doctor's office, a place where, he notes, it can be especially inaccurate, since the appearance of a white coat or other caregiver in uniform isn't particularly relaxing and thus not producing a normal reading.
And Shaltis says that BP measurement even over short periods provides less than a complete picture about the heart's function and general patient health, but rather only an intermittent sort of record.
"We're trying to fill that gap," Shaltis, president of developmental firm CardioSign (Cambridge, Massachusetts), told Cardiovascular Devices & Drugs.
Potentially filling that gap – and producing what would essentially be more of a documentary record of heart function, and hopefully able to pick up signals of future impending problems, heart attack or stroke – is the company's BP sensing system that can be worn continuously, 24/7. The device is designed to offer accurate readings by making constant calculations that account for the wearer's movements and body positions.
Supporting the value of this continuous monitoring approach, Shaltis cites every-15-minute BP monitoring over a 24-hour period as a better predictor of heart problems, as well as response to medications.
But filling that gap means removal of the traditional cuff, its labor-intensive use – and its potential inaccuracies.
Shaltis earned his doctorate at the Massachusetts Institute of Technology (Cambridge), where he was a student working with Harry Asada, PhD, the Ford Professor of Engineering and director of MIT's d'Arbeloff Laboratory for Information Systems and Technology, that lab perhaps best known for its work in robotics.
With Asada and Andrew Reisner, MD, of Massachusetts General Hospital (Boston), Shaltis formed CardioSign last year to refine the prototype sensor and move it to commercialization.
The new monitor doesn't use the traditional BP cuff. Instead it uses elements that wrap around the wrist and attach to the finger.
It employs a method called pulse wave velocity, which allows blood pressure to be calculated, Shaltis explained, by measuring the pulse at two points along an artery.
In early models, the researchers used the heart as one of the points, with a heart monitor measuring the EKG. However, EKGs also aren't always accurate, and a heart monitor can be uncomfortable, so the researchers decided to use two points on the hand instead.
That posed a challenge.
The BP in the hand varies, depending on its position: If the arm is raised above the heart, the pressure will be higher than if it is below the heart. The researchers solved that problem by incorporating a sensor that measures acceleration in three dimensions, allowing the hand position to be calculated at any time. This compensates for the error resulting from height changes and also allows calibration of the sensor for more accurate calculation of blood pressure.
So, as the wearer raises the hand up or down, the hydrostatic pressure changes at the sensor. Correlating the change of pulse wave velocity to the hydrostatic pressure change, the system can automatically calibrate its measurement.
Shaltis told CD&D that pulse wave velocity measurement has been available since the 1960s, but without full exploitation of its value in studying the heart because of the difficulties of calibration that adjust to a person's everyday movements.
"The idea is that the speed at which a pressure wave propagates down the arterial tree is related to blood pressure like a fire hose," he says.
Asada adds: "The human body is so complex, but the cuff gives only snapshot data. If you get signals all of the time you can see the trends and capture the physical condition quite well."
The new calibration method is a way of doing that.
This wearable approach was born from a collaboration called the Home Automation and Healthcare Consortium, which launched in 1995 at MIT and included several faculty members and about 20 companies.
The group's first project was a ring that measures pulse rate and the amount of oxygen present in the blood.
After developing the ring, Asada decided to move on to blood pressure sensing, which he saw as offering even more valuable information about a patient's health.
Shaltis told CD&D that the sensor system has been tested in healthy volunteers and that the company is now working on enhancements to the laboratory device which, he acknowledges, is rather bulky and needs to be made more "user-friendly." The enhancements, he says, will include making it smaller and developing other aesthetic improvements, and, importantly, making it cheaper to manufacture.
Another potential use he points to is in evaluation of sleep apnea and other sleep difficulties.
He says that the monitor could be available to patients within five years, though he declined specifying the internal timeline for its commercialization.
While it might be something first doctor-prescribed, an ideal configuration for the device, and the company, would be a product available on the drugstore shelf, beside the traditional blood pressure cuff system, and also enhanced to provide alerts concerning potential problems, Shaltis notes.
Once the blood pressure information is gathered, the data could be transmitted via radio signals or wireless Internet. The device runs on a tiny battery, about the same size as the ones that power watches.
The project was funded by the National Institutes of Health, National Science Foundation (Washington) and Sharp (Mahwah, New Jersey/Osaka, Japan).
The most recent prototype was developed in collaboration with Sharp, and the development of clinical applications and human testing was led by Reisner at Mass General.
Elsewhere in the product pipeline:
• Abbott Laboratories (Abbott Park, Illinois) reported the launch of two new products for the treatment of peripheral artery disease (PAD), a condition that occurs when the vessels supplying blood to the legs, arms, stomach or kidneys become narrowed or blocked by plaque, restricting normal blood flow. The FoxCross PTA catheter is a next-generation .035 balloon dilatation catheter, and the HI-TORQUE Versacore .035 Guide Wire is a peripheral guide wire for delivery of catheters, balloons and stents. The FoxCross PTA is available in a wide variety of diameters (3 mm to 14 mm), balloon lengths (20 mm to 120 mm), and catheter lengths (50 cm, 80 cm and 135 cm) on an over-the-wire delivery platform. The HI-TORQUE features a soft, shapeable tip to provide safe access to peripheral lesions and enhanced visibility under fluoroscopy.
• Biosite (San Diego) has initiated a voluntary, nationwide recall of one lot of Triage Cardiac Panel. The test is used by healthcare professionals as an aid in the diagnosis of myocardial infarction. The product has been recalled due to reports of low recovery of quality control samples containing creatine kinase MB (CK-MB), troponin I and myoglobin on the affected lot.
• Preliminary data presented at the SCAI Scientific Sessions show that 82% of patients treated with Cook Medical's (Bloomington, Indiana) Zilver PTX drug-eluting peripheral stent were free from reintervention at two-year follow up. The ongoing Zilver PTX Registry study is assessing the safety and efficacy of the Zilver PTX in treating PAD. In many cases, PAD patients who have been treated with balloon angioplasty and stenting experience restenosis, or renarrowing of the arteries, over time and must undergo more invasive treatment such as bypass surgery to restore blood flow to key arteries. The Zilver PTX self-expanding nitinol stent uses a proprietary, polymer-free technology to coat the device with paclitaxel, an antiproliferative drug that has been used successfully to reduce the risk of renarrowing of arteries following angioplasty in coronary disease patients.
• Edwards Lifesciences (Irvine, California) received FDA approval for the Carpentier-Edwards Perimount Magna Ease aortic valve, designed for easier implantation in the heart. The new valve includes a low profile and smooth commissure posts to ease insertion through small incisions or small aortic roots. "The Magna Ease valve sets a new standard for tissue valves, by combining enhanced implantability with the unsurpassed hemodynamics and long-term durability of bovine pericardial tissue," said cardiac surgeon Michael Mack, MD, a consultant to Edwards Lifesciences.
• Jubilant Organosys (Noida, India) said that its subsidiary in the U.S., Draximage, has received FDA approval for the company's Abbreviated New Drug Application (ANDA) for Draximage's generic Sestamibi. The product is found to be bioequivalent and therapeutically equivalent to reference listed drug Cardiolite. The Sestamibi is a generic kit used in the preparation of Technetium (Tc-99m) Sestamibi injection – a diagnostic cardiac imaging agent used in myocardial perfusion imaging to evaluate the flow of blood to the heart.
• Medtronic (Minneapolis) reported the implant of its Cardioblate Closure left atrial appendage occlusion device. Published literature suggests that the left atrial appendage (LAA) is the main source of clots coming from the left atrium. Patients with an arrhythmia known as atrial fibrillation (AF) have an increased risk of clot formation as a result of the uncoordinated and fast beating of the heart's upper chambers, which may lead to blood pooling in the LAA. The Cardioblate Closure device is intended to occlude the LAA permanently without the need to enter the heart and does not introduce man-made materials into the blood stream. It is designed to be pliable and atraumatic to ensure no collateral damage to surrounding structures of the heart, unlike rigid epicardial occlusion devices.
• Spectranetics (Colorado Springs, Colorado) reported initial data from the four-year, retrospective LExICon (Lead Extraction in Contemporary Settings) study demonstrating the safety and efficacy of laser assisted lead removal using the Spectranetics laser sheath. The Spectranetics laser sheath uses low temperature ultraviolet light to safely, effectively and efficiently ablate scar tissue holding problematic leads in place. A circle of fibers emit pulses of laser energy traveling over the cardiac lead towards the tip to break down scar tissue binding the lead to the vein or heart, permitting the lead to be safely removed. Spectranetics' LLD EZ Lead Locking Device technology can also be used to assist removal by creating traction on the lead while the laser sheath is advanced over it.
• St. Jude Medical (St. Paul, Minnesota) reported the U.S. launch of its Attune Flexible Adjustable Annuloplasty Ring for the repair of diseased heart valves. The Attune ring is a flexible annuloplasty ring designed to support a repair of the heart's mitral valve. The ring's flexibility allows the annulus to continue its natural movement as the valve opens and closes, thus contributing to more physiologic valve function. The ability to adjust the ring post-implant promotes ideal leaflet alignment to reduce or eliminate residual regurgitation, or small leaks after the repair. The Attune ring can be adjusted after it is sutured to the annulus - a feature that allows physicians greater control in altering its size and shape to contribute to a more refined repair specific to fit each patient's heart valve anatomy. The Attune ring is suitable for repairs performed with open chest, minimally invasive or robotic surgical approaches.
• SynCardia (Tucson, Arizona) reported that study data showed the SynCardia temporary CardioWest Total Artificial Heart has a bridge-to-transplant rate of 72% at 6 months. The company says that unlike BiVADs and LVADs which assist the heart ventricle(s), the Total Artificial Heart replaces both dying heart ventricles. This eliminates complications caused by a dying heart, including right native heart failure.
• W.L. Gore & Associates (Flgstaff, Arizona) said it has developed the GORE Adsorbent Filter, an integrated filtration solution simplifying manufacturing of medical devices without compromising product performance. The filter contains activated carbon media and Gore's expanded polytetrafluoroethylene membrane. The company says the filter delivers a combination of adsorption, high airflow, and liquid resistance.
Additionally, Gore reported availability of a 31-mm diameter version of the Gore Excluder AAA endoprosthesis, a device providing physicians with an endovascular option to treat abdominal aortic aneurysms (AAAs) in patients with aortic inner neck diameters up to 29 mm. Enhancements include a flat-top design that enables greater efficiency and a lengthening of the trunk from 7 cm to 8 cm for larger anatomies. The device, an endovascular graft/stent combination that seals off the aneurysm and creates a new path for blood flow – is inserted through a small incision in the patient's leg using a catheter-based delivery technique. Once positioned in the diseased aorta, the device self-expands using radial force, with a pair of proximal anchors to help ensure excellent fixation.