A tiny new implantable heart pump transmits speed, power consumption, and blood flow data directly to the cardiac center
Heart failure affects over 5 million Americans with an additional 670,000 cases diagnosed each year. Most are effectively treated conservatively with medication. But thousands each year progress to the point of needing more, such as surgery.
Although heart transplantation is the desired therapy for patients with end-stage cardiac failure, the limited availability of donors (2,322 last year) has created a need for a nonbiologic left-ventricular-cardiac-assist device (LVAD).
The Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial demonstrated a dramatic 48 percent reduction in death for end-stage congestive heart failure patients when an LVAD was used compared to matched controls undergoing optimal medical management.
The first device, a pulsatile-acting pump, was approved for patient use by the FDA in October 1994. Since then, new developments have focused on continuous-flow devices that use either a centrifugal pump or an axial flow impeller. These designs can be made much more compact and have better reliability. Of interest, the patients may not actually have a pulse, something that is key to evaluation of an unconscious patient. This means that a patient without a pulse may still be alive.
Although some patients, notably those with a cardiomyopathy, may need temporary assistance until their heart heals, most fall into two categories: destination therapy — when the patient is not a candidate for a transplant and the LVAD is the only option — and bridge therapy — where the patient is placed on an LVAD in anticipation of a transplant. Overall outcomes are positive.
One study of 281 patients determined that 79 percent of patients received a transplant, recovered cardiac function, and had the device removed, or remained alive with on-going LVAD support at the end of the 18-month study. The median time to transplantation was 118 days (range 10–545). Of those who remained on an LVAD, 82 percent were alive at 6 months, 73 percent at one year, and 72 percent at 18 months, clearly demonstrating the durability of LVAD therapy.
Although the pumps are typically used for a year or two until death or transplant, one notable patient, Peter Houghton, survived and actually thrived on an LVAD for seven years. During this time, he completed a 91–mile charity walk, hiked widely in the American West and Europe, published two books, and flew in an ultralight airplane.
Initially, all LVAD patients were managed in the hospital. This changed rapidly, and now most patients are managed as outpatients, a cumbersome ordeal for patients who live far from the cardiac centers (126 hospitals in the United States performed heart transplants last year) that specialize in this management.
Obviously the follow-up care of these patients is complex. In addition to receiving anticoagulation, each patient must practice strict aseptic technique, as LVADs are not totally implantable since they must be connected to power sources. It is also necessary to monitor several flow parameters of the device.
Most patients are seen every other week or monthly. Given that some heart centers have more than 200 patients on an LVAD, a large clinical staff is needed. Routine distance monitoring of the speed of the device and its power consumption — surrogates for the patient’s overall cardiac function — is routine for all LVADs. An echocardiogram is needed to obtain an accurate measurement of blood flow, a key clinical measure. But this may all soon change!
The latest generation of LVAD, the Micromed Heart Assist 5, has a miniature ultrasonic flow probe incorporated in the actual pump. This allows it not only to monitor and report speed and power consumption, but also to report the actual flow of blood, a remarkable improvement in overall function of the device and something that will inevitably allow for better care of these patients. It weighs a mere 92 grams.
Already approved in Europe, it is under review by the FDA. And at the risk of sounding like a late-night infomercial, I can say, “But that’s not all!”
An important development in the overall care of LVAD patients is on the horizon in the United States and has already started in Europe. Micromed has joined with Numerex to provide a scalable web- and cellular-based monitoring system unlike any other. Numerex brought its machine-to-machine remote communication and management expertise to complement Micromed’s health care technology strengths.
This partnership will allow automated nondelayed remote monitoring of the three key parameters — speed, power consumption and blood flow — that will alert the cardiac center to abnormalities via the Internet. These measurements will also be able to be plotted over periods of 4 hours, 7 days, and 30 days.
Continuous monitoring without the need to travel to a center will result in considerable improvement in the patient’s quality of life and is likely to improve their overall satisfaction. It is also likely to lead to much more efficient management, allowing for fewer cardiac specialists at the cardiac centers.
LVAD use will probably expand as pump technology and follow-up management are further improved.
Although a fully implantable pump with power supply and controller is still a goal, the Micromed Heart Assist 5 is worthy of being highlighted as Tomorrow’s Medicine.