Prosthetic heart valves were first introduced as a measure to combat heart disease in the 1950s. The design of prosthetic heart valves has included (a) caged-ball and caged-disc valves, (b) tilting-disc valves, (c) bi-leaflet valves, and (d) tri-leaflet valves. The materials used in manufacturing the valves include metals, polymers such as delrin or plastic silicone and pyrolytic carbon.

One of the issues in prosthetic heart valve design is the minimization of blood clotting, or thrombosis, at the prosthetic heart valve. Blood clotting is a natural process that is desirable in many circumstances. For example, when a person suffers a scrape or cut it is important that blood clots at the location of the cut or scrape. Otherwise, the loss of blood could be dangerous or even fatal.

In other situations, blood clotting is not desirable and could be dangerous. For example, it is undesirable for blood clots to form on or adjacent to a prosthetic heart valve, because such clots may affect or impede valve function. Further, there is a possibility that such clots will break away from the prosthetic heart valve and cause damage in some other part of the circulatory system.

To combat this, prosthetic heart valve designers use materials and designs that are not likely to encourage the formation of blood clots. However, for unknown reasons, these clots may still occur. To reduce the likelihood of such clotting, once a prosthetic heart valve is implanted in a patient's heart, doctors typically prescribe the use of a drug (which are called "anticoagulants"), such as sodium warfarin, (e. g., COUMADIN offered by DuPont-Merk) which slows the clotting, or coagulation, of the blood.

The proper use and timing of anticoagulant drug therapy is important. An insufficient dose of the drug may result in the undesirable formation of thrombus on or near the prosthetic heart valve (or in the circulatory system). An excessive dose may cause the patient to suffer uncontrolled bleeding from the circulatory system, including from such places as the brain, gastrointestinal tract or gums after tooth brushing.

Thus, it is important that the coagulation properties of a patient's blood be carefully controlled. Typically, physicians measure the coagulation properties of blood by testing the prothrombin time (or"Pro-Time"or"PT") of the blood. To perform this test, blood is drawn from the patient and is immediately mixed with an agent that stops the blood's inherent clotting process. Typically, the blood's red cells are then separated from the plasma and the plasma is mixed with a reagent that activates the clotting process. The PT is the time required for clots to form after the test reagent is added to the blood or plasma sample.

The PT time differs for different reagents and test conditions. Consequently, an International Normalized Ratio (or"INR") was developed which normalizes the prothrombin time for different reactivating chemicals.

Once the INR is computed, the physician has an idea of the coagulation properties of the patient's blood. With that information, the physician can adjust the dosage of anticoagulant drugs to produce the desired coagulation properties. Timely routine testing is essential to successful patient management. Diet, other drug interaction, different disease state, and lifestyle can affect a patient's INR.

In the past, monitoring of INR has been accomplished by having the patient visit a laboratory where blood is drawn and the PT and INR tests and calculations are performed. This is done on a regular and recurring basis, preferably on a monthly routine. However, using this procedure, it is well known that 40-60% of warfarin patients remain out of therapeutic range at any given time, and some suffer severe complications as a result. See Henry I. Bussey and Roger M. Lyons,"Controversies in Antithrombotic Therapy for Patients with Mechanical Heart Valves,"Pharmacotherapy 1998; 18 (3): 451-455.

Recently, devices have been developed which allow the patient to perform PT and INR tests without leaving home. The patient then visits or telephones the physician and reports the results. Based on the patient's report, the physician adjusts the anticoagulant dosage. Use of such devices increases the likelihood that the patient's anticoagulant level will be in the proper range.

Disclosure of Invention In general, in one aspect, the invention features a method of maintaining a desired level of anticoagulation in a patient's blood as a result of anticoagulant therapy. The method comprises establishing a desired range of a blood coagulation characteristic for the patient, measuring the blood coagulation characteristic of the patient, transmitting automatically to a surveillance location digital data representing the blood coagulation characteristic, comparing the

transmitted blood coagulation characteristic data to the desired range, and informing a caregiver if the transmitted blood coagulation characteristic data is outside the desired range.

Implementations of the invention may include one or more of the following. The method may include adjusting the anticoagulant therapy to urge the blood coagulation characteristic toward the desired range. The method may include informing the caregiver if the measuring does not occur within a predetermined period. The method may include informing the patient if the measuring does not occur within a predetermined period. Measuring may comprise using a fingerstick blood coagulation characteristic tester. Measuring may comprise measuring the prothrombin time of the patient's blood or the international normalized ratio of the patient's blood. The method made comprise building a database of said data from each patient. The method may comprise repeatedly establishing, measuring, comparing, and informing for multiple patients, and compiling a database of blood coagulation characteristics.

In general, in another aspect, the invention features a database of multiple patient blood coagulation characteristics resulting from the method just described.

In general, in another aspect, the invention features a system for monitoring a blood coagulation characteristic for a patient after the patient has undergone prosthetic heart valve implant surgery and is undergoing an anticoagulation therapy. The system comprises a blood coagulation characteristic tester configured to electronically report a coagulant characteristic, and a surveillance process configured to receive and analyze the coagulant characteristic and to notify a caregiver if the coagulant characteristic is outside a desired range, the desired range chosen to reduce the likelihood of formation of thrombus or clotting in a patient after heart valve implant surgery. The system also comprises a communications medium configured to allow the caregiver to contact the patient to adjust the anticoagulation therapy to urge the coagulant characteristic toward the desired range.

Implementations of the invention may include one or more of the following. The communications medium may be additionally configured to notify the patient and the caregiver if the surveillance process is not completed within a predetermined time. The blood coagulation characteristic tester may electronically report the coagulation characteristic telephonically. The blood coagulation characteristic tester may electronically report the coagulation characteristic by radio, by satellite link or over a network.

In general, in another aspect, the invention features a kit for monitoring a blood coagulation characteristic of a patient after the patient has undergone prosthetic heart valve implant surgery. The kit comprises a prosthetic heart valve, a blood coagulation characteristic

tester configured to electronically report a coagulant characteristic, and a surveillance process configured to receive and analyze the coagulant characteristic.

Implementations of the invention may include one or more of the following. The surveillance process may be configured to notify a caregiver if the coagulant characteristic is outside a desired range, the desired range chosen to reduce the likelihood of formation of thrombus or clotting in the patient after the heart valve implant surgery. The surveillance process may comprise means to notify the patient and the caregiver if the tester malfunctions or fails to report within a predetermined period. The surveillance process may be configured to provide a first level of notification to the caregiver if the coagulant characteristic is outside the desired range by a first amount and a second level of notification to the caregiver if the coagulant characteristic is outside the desired range by a second amount.

Brief Description of Drawings Fig. 1 is a perspective view of a portion of a system according to the present invention.

Fig. 2 is a block diagram of a system according to the present invention.

Fig. 3 is a flow chart.

Best Mode for Carrying Out the Invention The invention improves the monitoring and adjustment of blood coagulation properties by automatically reporting the results of a patient-administered blood coagulation test to a surveillance system. The surveillance system determines whether the blood coagulation properties are within a preselected range and decides whether it is necessary to alert a caregiver if the property is outside that range. In one aspect, the invention includes a kit, comprising a heart valve prosthesis, a blood coagulation characteristic test device, and a surveillance process.

This kit may be provided to a caregiver prior to heart valve implant surgery. After surgery the patient and caregiver use the blood coagulation property test device and the surveillance process, as described below.

The patient 100, who may have a prosthetic heart valve (not shown), draws blood 102 by pricking or incising his or her finger, as shown in Fig. 1. The drop of blood 102 is dropped into an analysis chamber 104 of a blood coagulation characteristic test device 106. The blood coagulation characteristic test device 106 tests the blood 102 for a blood coagulation property.

For example, the coagulation test device may administer a PT test and then compute the INR and the blood coagulation property could be the PT or the INR. The PRO TIME Microcoagulation System by International Technidyne Corporation, a number of devices manufactured and sold by Boehringer Mannheim Corporation, and a device manufactured and sold by Avocet Medical, Inc., all perform this function. All of these devices are fingerstick blood coagulation

characteristic testers, in that they require the patient to prick or incise his or her finger in order to draw blood for analysis.

As soon as the test is completed and the blood coagulation property has been measured and computed, the blood coagulation characteristic test device 106 communicates data representing the blood coagulation property to a communication device 108 via cable 110. The communication device 108 may be incorporated into the blood coagulation characteristic test device 106. The communication device 108 formats and conditions the data representing the blood coagulation property for transmission via cable 112. The equipment illustrated in Fig. 1 is part of the patient-location equipment 114.

The patient-location equipment 114 is at a patient location 202, as shown in Fig. 2. The patient-location equipment 114 communicates the data representing the blood coagulation property to a surveillance location 204. The communication can be through uplink antenna 206 to satellite 208 to downlink antenna 209. Alternatively, the communication can be through a radio transmitter 210 to a radio receiver 212 at a communications media transfer point 214. The communications media transfer point may transmit the data to the surveillance location via uplink antenna 216 to satellite 208 to downlink antenna 209. Alternatively, the data could be transferred from the patient location 202 to the communications media transfer point 214 over a telephone system 218. Similarly, the data could be transferred to the surveillance location 204 from the communications media transfer point 214 over a telephone system 220. Transfer over the telephone system may include transfer over a network, such as the Internet. Alternatively, a network, such as the Internet, could use the broadcast cable system as a communications media.

Further, any combination of these communication approaches is within the scope of the invention as long as the data is transferred from the patient location 202 to the surveillance location 204, ultimately allowing the patient's caregiver to review the data so that the caregiver can adjust the anticoagulation therapy to urge the coagulation characteristic toward the desired range.

Once the data arrives at the surveillance location 204, it must be analyzed to determine if it falls within a range established by the caregiver in accordance with the patient's needs. For example, a physician may prescribe that a patient's INR should fall within the range 2.8 through 3.4. The surveillance location will compare the INR reported from the patient location to see if it is greater than 2.8 and less than 3.4.

The analysis at the surveillance location is illustrated in Fig. 3, and may be accomplished by computer 221 at the surveillance location, shown in Fig. 2. The analysis begins 302 by determining if the blood coagulation property is within the desired range 304. If it is, the

analysis ends 306, and is stored in a database for an undetermined time, and made available to the patient's physician.

If the blood coagulation property is outside the desired range the appropriate response must be determined. The more the blood coagulation property deviates from the desired range the more extreme the response will have to be. For example, if the blood coagulation level is less than X outside the desired range (which is determined by test 308), an alert procedure 310 is followed. Under this procedure, for example, the patient is contacted and advised to consult with his or her caregiver.

If the blood coagulation level is more than X but less than Y outside the desired range (which is determined by test 312), an extreme alert procedure 314 is followed. Under this procedure, for example, the patient's caregiver is called during working hours to inform him or her of the test results.

If the blood coagulation property is more than Y outside the desired range, an emergency procedure 316 is followed. Under this procedure, for example, the patient's physician is called as soon as the emergency condition is detected, even if it is outside normal working hours.

Through the use of this process, an INR database can be created using data from multiple monitored patients. This database can be available to caregivers to provide historical data for patient management decisions both by specific patient, by subset of patients, and by global data of all patients.

Further, the database can provide an indication of when data from a particular patient has not been received for a predetermined period of time. The failure to receive data could be due to a variety of reasons, including a malfunction of the blood characteristic tester or of any of the communications equipment in the system. The failure could also be due to the patient neglecting to administer the test. In any of these cases, the caregiver can contact the patient and determine why data has not been received from that patient.

A number of companies provide the surveillance service required at the surveillance location. For example, Raytel Cardiac Services, Inc. provides a pacemaker monitoring service which could be modified to provide the required service.

Returning to Fig. 2, the surveillance location 204 can communicate with the caregiver at the caregiver location 222 via antenna 209, through satellite 208 and downlink antenna 224.

Alternatively, the communication could be via telephone system 226.

Similarly, the communication between the caregiver location 222 and the patient location 202 could be by telephone system 228 or by any of the other communication media discussed above.

The foregoing describes preferred embodiments of the invention and is given by way of example only. The invention is not limited to any of the specific features described herein, but includes all variations thereof within the scope of the appended claim.