IMPLANTABLE MEDICAL DEVICE WITH ELECTROMECHANICAL DELAY

MEASU REMENT FOR LEAB POSITION AN D VENTRICULA R

DYSSYNCl !RONY ASSESSMENT

BACKGROUND OF THE INVCNTlON

The present [m ention relates generally to implantable medical deuces I IMDs) and cardiac rhythm management systems In particular, the present invention i elates to measurement of electromechanical deia\ s, which can be used to detect lead displacement or migration of electrical leads, or to assess ventricular d> ss> nchrony

IMDs. such as pacemakers, implantable cardio\ erter defibrillators and implantable hemod> namic monitors, are used to monitor cardiac conditions and del H er therapy when appiopriate The IM Ds t>picali> include electrical leads that carry elecUodes for pacing, cardioverting, defibriUating, sensing and monitoring functions The leads may also include a physiologic sensor, such as a pressure sensor, oxygen sensor, temperature sensor, flow sensor, or acceieromeier

Dϊsiodgerneru or migration of leads can compromise the benefits of cardiac therapy or monitoring by shifting the location of the electrodes (as well as any pin sioiogic sensor carried by the leads) Detection of dislodgement or displacement of leads automatically by an IMD can provide a physician an opportunity to take correctiv e action to reposition or replace dislodged lead

Implantable cardiac res\ nchronizaiion therapy (CRT) systems using biv entricular pacing have been introduced to treat patients with heart failure More than twent> million people w orldwide suffer from heart failure, with about two million new cases diagnosed each year With some patients, heart failure disease affects the synchronous beating action of the left ventricle and right \ cntnclc until the left ventricle cannot pump blood efficiently to supply the bod\ with oxj gen and nutrients These patients tend to tire easih , have a poor quality of life, and can deteriorate rapidlv toward the need of a heart transplant or death Cardiac ^synchronization therapy helps to coordinate the left ventricle and right ventricle of the heart in patients with moderate to severe heart failure It helps to improve the pumping power of the heart, can make the patients feel better, increase their energ\ levels _* , and improve their exorcise capacity

Cardiac resynchronizatioπ therapy (CRT) systems typically include a right atria! lead, a right ventricular lead, and a left ventricular lead introduced via the coronary sinus into the coronary venous, system to provide stimulation to lϊie left ventricle Some CRT systems also include a pressure sensor carried by one of the leads to measure pressure in the right ventricle. The measured pressure provides feedback for delivery of CRT pacing.

The C ¹ RT system receives sensed signals from the electrodes and provides pacing pulses so that depolarization of the left ventricle is synchronized with depolarization of the right ventricle. By synchronizing the left and right ventricles, stroke volume of the heart can be enhanced. The extent of ventricular dyssynchrony can change over time as a result of physiologic changes, and may require adjustment of timing of the CRT pacing

BRIEF SUMMARY OF THE INVENTION

An implantable medical device measures time delays between sensed electrical activity and sensed mechanical activity of the heart The measured time delays can be used to detect sensor movement indicating dislodgement or migration of a lead. It can also be used to provide an assessment of ventricular dyssynchrony, to determine timing parameters for cardiac ^synchronization therapy, and to detect dyssynchrony requiring an adjustment of CRT timing parameters.

BfUEF- DESCRIPTION OF THE DRAWINCSS

FIG. 1 depicts an example of a cardiac ^synchronization therapy (CRT) system in which the present invention may be implemented.

FIG. 2 shows waveforms representing sensed cardiac mechanical and electrical activity FIG. 3 is a block diagram of an implantable pulse generator used in the CRT system of FIG 1.

FIG. 4 is a flow chart that shows a method of detecting sensor movement with electromechanical delay measurements.

FiG, 5 is a block diagram that shows a method of assessing ventricular dyssynchrony with electromechanical delay measurements for use in determining CRT timing parameters.

FIG. 6 is a flow chart showing the use of electromechanical delay measurements for detection of ventricular dvssvncfuony.

DETAIIi: D DILSC RIPT ION

FlG. ! shows cardiac resynchronization therapy (CRT) system 10, which restores ventricular synchronization in heart H by delivering pacing pulses to one or more chambers of heart H. ϊn FIG. 1, heart H is shown in a partially cutaway view illustrating right allium RA, left atriurn LA, right ventricle RV ₅ left ventricle LV, coronary sinus CS, and coronary venous system CVS.

CRT system I O includes implantable pulse generator (IPG) 12, right atria! (RA) lead 14, right ventricular (RV) lead 16, and left ventricular (LV) lead 18. As shown in FϊG 1 , IPG 12 includes housing or canister 20, header 22 and can electrode 24. The circuitry and power source of IPG 12 are located within housing 20. The circuitry communicates with leads 14, 16, and 18 through electrical connectors within header 22. Can electrode 24 is formed on or is a part of the outer surface of housing 20, and acts as a remote indifferent electrode with respect to one or more of the electrodes carried by leads 14. 16, and 18.

As shown in FlG 1, RA lead 14 is a bipolar endocardial lead that is passed through a vein into right atrium RA of heart H. RA lead 14 includes lead body 30, connector 32, distal tip attachment mechanism 34, distal tip RA electrode 36, and proximal ring RA electrode 38. Lead body 30 contains a pair υf electrically insulated conductors which extend from connector 32 to electrodes 36 and 38. Connector 32 is inserted into a connection bore within header 22 to provide an electrical connection between electrodes 36 and 38 and the circuitry within IPG housing 20. The distal end of RA lead 14 is attached to the wall of right atrium RA by attachment mechanism 34, which may be, for example, a screw or lined fastener. RV lead 16 is a bipolar endocardial lead that is passed through right atrium RA and into right ventricle RV. RV lead 16 includes lead body 40, connector 42. distal tip attachment mechanism 44, distal tip KV electrode 46, proximal ring RV electrode 48, and pressure sensor 49, (typically placed in the right ventricular outflow tract RVOT) Lead body 40 of RV lead 16 contains a pair of electrically insulated conductors which extend from connector 42 to electrodes 46 and 48 and pressure sensor 49. Connector 42 is at the proximal end of RV lead 16, and is inserted into a connection bore of header 22 to provide an electrical connection between the circuitry within housing 20 and electrodes 46 and 48

and pressure sensor 49 Distal tip electrode 46 is placed in contact with the apex of light ventricle RV and is fixed in place by attachment mechanism 44

LV lead 18 includes lead body 50, connector 52 and LV electrode 54. Lead body

50 contains an electrically insulated conductor which extends from connector 52 at the proximal end of lead 18 to electrode 54 at the distal end of lead 18 Connector 52 is inserted into a bore within header 22 to preside electrical connection between LV electrode 54 and the circuitry within housing 20

In this embodiment, LV lead 18 is passed through right atrium RA into coronary sinus CS and then into a cardiac vein of coronary venous system CVS. LV lead 18 is shown as a unipolar lead, so that sensing of electrogram (EGM) signals and application of pacing pulses through LV electrode 54 is performed with respect to one of the other electrodes 24, 36, 38, 46, or 48 of CRT system 10 Alternatively, LV lead 18 can carry more than one electrode- and perform as a bipolar lead.

LV lead 18 is configured so that LV electrode 54 will lodge within a cardiac vein and will remain in position despite having no attachment mechanism comparable to attachment mechanism 34 of RA lead 14 or attachment mechanism 44 of RV lead 16 LV electrode 54 is positioned within the cardiac vein during implantation to achieve desired synchronous pacing performance.

CRT system 10 makes use of the ability to sense both electrical activity and mechanical activity to detect lead dislodgement, and to assess ventricular dyssynchrony

CRT system 10 uses sensed electrical activity as a trigger for measuring a time delay between electrical activity and a corresponding mechanical activity.

FIG. 2 shows waveforms illustrating one example of sensed electrical and mechanical activity RV Pressure waveform represents right ventricular sensed by pressure sensor 49. The RV dP-'dt waveform represents the first derivative of the RV

Pressure waveform. The A Sense waveform represents sensed P -waves (atrial depolarizations) sensed by RA electrodes 36 and 38. The RV Sense waveform represents

R-vvaves (ventricular depolarizations) sensed by RV electrodes 46 and 48. The LV Sense waveform represents R -waves sensed by LV electrode 54, FIG. 2 also illustrates three time intervals A-C based upon delays between sensed electrical and mechanical activity. Interval A represents the time from an A Sense event to maximum change in pressure (RV dP/dt max). Interval B represents the time from an

-V

RY Sense event to RY dP.'dt max interval C represents the time from an LY Sense event to RV dP/dt max

Electromechanical time delay measurements, such as intervals A-C, representing the time from an electrical event sensed by an electrical sensor to a mechanical event sensed by a mechanical sensor can be used to estimate distance between the electrical sensor, and the mechanical sensor. Pathophysiologic electromechanical remodeling does not take place in a short time period. By sampling the electromechanical delay frequently, a sudden change in one or more of intervals A-C may mean a change in lead positions representing a lead dislodgernent or migration In CRT system 10, intervals A-C can be measured using the right atrial electrical sensor (formed by electrodes 3t> and 38), the right ventricular electrical sensor {formed by electrodes 46 and 48), or the left ventricular sensor (formed by electrode 54) as the trigger for measuring time delay The electromechanical delay measurement will depend upon the physical distance of the RA, RV, or LV sensor with respect to pressure sensor 49 The measurement can be triggered using either sensed or paced activity. One interval or a combination of intervals A-C, can be used by IPG 12 to assess lead position changes When there is a sudden change in one of the delay measurements, other measurements, using the other electrical sensors, can be e\ aluated to see whether the change occurred due to a movement of pressure sensor 49, or whether il occurred due to a movement of one of the electrodes. If only one of the intervals changed, this indicates movement of an electrode. However, if intervals triggered by more than one electrodes with respect to pressure sensor 49 have changed, the changes are likely due to a movement of pressure sensor 49.

Electromechanical delay measurements can also be used to assess the dyssynchrony between two areas of the heart. This is particularly useful in CRT therapy to assess dyssynchrony between right ventricle RV and left ventricle LV. Using measured intervals A-C at different AV or VV timing intervals, the degree of ventricular dyssynchrony can be determined. The electromechanical delay indicates the time between electrical activation at a particular site to mechanical activation at pressure sensor 49 This information can be used to adjust AV or VV timing parameters in order to synchronize the right and left ventricles during initialization of CRT system 10. By continuing to monitor intervals B and C over time, physiological changes resulting in dyssynchrony can be detected, and used to guide adjustment of AV or VV timing

parameters. In addition, the delay measurements can be used to assess effective electrical stimulation levels, and the loss of effective stimulation when no changes in electromechanical delays, are delected despite changes in AV or VY timing from one of the electrical sensor locations. Intervals A-C are only one example of electromechanical delays that can be used

Rather than RV dP/dt max, the marker derived from the mechanical signal (RY Pressure) can be maximum pressure (P max), minimum pressure (P røin) or minimum first derivative of pressure (dP'dt min). In addition, pressure can be sensed in locations other than the RVOT. (e.g the coronary sinus vein). Other types of mechanical activity sensors cars also be used. For example, an acceterometer can be used to provide a marker representing peak endocardial acceleration, which is associated with valve opening and closing. The accelerometer may, for example, be carried on LV lead S 8 and positioned in the coronary sinus (CS) \ein.

In another embodiment, the mechanical activity is a physical dimension or volume measurement representative of changing dimension or volume of a chamber of the heart

The measurement may be, for example, intracardiac impedance (Z), and the marker may be Z max or dZ/dt max.

FlG. 3 is an electrical block diagram of ϊPG 12 that prov ides delivery of resynchronizarion therapy through leads 14. 16 and 18 shown in F1G 1 As shown in FIG. 3, IPG 12 includes microcomputer-based control system 60, input signal processing circuit

62, therapy deliver)' system 64, batten ¹ 66, power supply/power on reset (POR) 68, crystal oscillator 70, system clock 72. telemetry- transceiver 74, antenna 76, switch 78, and magnetic switch circuit SO Also shown in FlG 3 are external programmer 90 and antenna 02 (which communicate with ϊPG 12 through antenna 76 and transceiver 74), and magnet 94 (which interacts with pacemaker 12 through switch 78 and magnetic switch circuit 80).

Control system 60 controls the functions of IPG 12 by executing firmware and program software algorithms stored in associated RAM and ROM Control system 60 may also include additional circuitry including a watchdog circuit, a DMA controller, a block mover/reader, a CRC calculator, and other specific logic circuitry coupled together by an on-chip data bus, address bus, power, clock, and control signal lines. Control and timing functions can also be accomplished in whole or in part with dedicated circuit hardware or state machine logic rather than a programmed microcomputer.

Input signal processing ciicuit 62 receives signals from RA lead 14 RV lead 16, LV lead 18 and can electrode 24 The outputs of input signal processing circuit 62 include digitized EGM \\a\ efoπiis, P -wave and R-wave sensed event signals, and pressure signals deriv ed from leads 14, 16, and 18 Input signal processing circuit o2 includes a plurality of channels for sensing and processing cardiac signals from electrodes earned b\ leads 14. 16. and 18 Fach channel typically includes a sense amplifier circuit for detecting specific cardiac exents and an HGIVl amplifier circuit for providing the KJM waveform signal to control system 60, where the EOM waveform is sampled, digitized and stored Therapy delivery system 64 delivers cardiac pacing pulses to leads 14. 16, and 18 to contiol the patient's heart shytlnn and to resynehsonize heait chambei actuation Delivery of the cardiac pacing pulses by therapy deliver) system 64 is under the control of control system 60 DeIh εry of pacing pulses to two or more heart chambers is controlled in part by the selection of programmable pacing intervals, which can include atrial-atrial (AA), a»ial-\ entiicular (AV) and \ enUicular-vcntricuiar (VV) inter\ als

Therapy delivery sy stem 64 can optionally be configured to include αrcuitrv, for delivering caidioveision deflbi illation theiapy in addition to cardiac pacing pulses for controlling a patient ^' s heart rhythm λccordingh . leads 14, 16, and 18 can additionally include high \ ullage caidiove-i&ion oi defibrillation shock eiectiυdes Electrical energ\ for IPCJ 12 is supplied from batten, 66 through, power supply/power on reset (POR) circuit 68 This includes power to operate the ciicuitry controlling operation of IPG 12, as well as electrical stimulation energy for delivery' to heart H, and power for telemetry signal transmissions Power supply/ PO K circuit 68 provides low voltage power VKx power on reset (POfI) signal, reference \ oltage VIlHK elective replacement indicator signal ERl and high voltage power VM (if CRT system SO also has cardkn ersion /defibrillation capabilities)

Clock signals for operation of the digital logic within IPG 12 ate prov ided by crystal oscillator 70 and system clock 72 Uplink and downlink telemetry capabilities arc provided through telemetry transceiver 74 and antenna 76 Hxternal programmer 90 can receive stored FGM data, as ^■ well as realtime generated physiologic data and nonphysiologic data from control system 60 hi addition, programming data can be supplied from external programmer 90 to control system 60

Magnetic field aeiisitive switch 78 and magnetic, switch circuit SO. issue a switch closed (SC) signai to control system 60 when magnet 94 is positioned over subcutaneously implanted IPG 12. Magnet 94 may be used by the patient to prompt control system 60 to deliver therapy or to store physiologic data Alternatively, the long-range telemetry without a magnet can be used to provide a prompt to control system 60.

FICJ. 4 is a block diagram showing the use of electromechanical delay measurements to measure relative distance between RV, LV. and RA electrodes and pressure sensor 49 to detect lead position features As shown in FIG 4, interval B is measured using the RV Sense signal from electrodes 4b and 48 as the trigger to start the time delay measurement (step 100). Interval B represents the time delay from an RV

Sense event (either a sensed R-wave or an RV pacing pulse) to the maximum dp/dt from sensor 49.

At step 102, interval C time delay measurement is made using an LV Sense event from electrode 54 as the trigger. Next, an interval A measurement is made using an A Sense event (or a sensed P-vvave pacing pulse) at RA electrodes 36 and 38 as the trigger

{step 104).

Control system 60 then compares each of the measured electromechanical delays to a corresponding previous measurement (step 106). If two or more of the measurements differ significantly (e g. by greater than an allowed en or range) from a corresponding earlier measurement, control system 60 determines that pressure sensor 40 has moved

(step 108). This likely represents a dislodgement of RV lead 16.

Control system 60 also determines if only one of the electromechanical delay measurements differed significantly from its corresponding previous measurement (step 110). If none of the delay measurements differed significantly from the previous measurements, control system 60 returns to step 100 to repeat the measurement process at a scheduled future time If one of the delay measurements departed significantly from its previous measurement, control system 60 identifies the particular electrical sensor that triggered the measurement as having moved. Upon recognition of a change indicating a dislodgement or migration of RA, RV or LV electrodes (or of pressure sensor 49), an annunciating response is produced. This response can be a warning sound that indicates to the patient that the patient should visit a physician. Alternatively, the annunciating response can be in the form of uplink patient data supplied through telemetry transceiver 74 to externa! programmer 90, or automatic long-range telemetry communication can

-Q-

deliver the communicating response to a home monitor which, in turn, transmits data to a central server.

Although FlG. 4 shows a process in which electromechanical delays, (intervals A- C) are measured using RA ₅ RV, and LV triggering during each measurement cycle, other alternatives are possible For example, one of the electromechanical delays can be measured routinely, and the other delay measurements can be made only when there is a change detected in the one delay measurement that is made routinely Electromechanical delay measurement can also be used to assess dyssynchrony between tvvo areas of the heart, such as the right and left ventricles. FIG. 5 shows a flow diagram showing the use of electromechanical delay measurements in determining timing parameters to be used for CRT therapy.

In FlG 5, interval C (LV sense to dP/dt max electromechanical delay) is measured without right ventricular (RV) pacing taking place (step 120), Next, interval B (RV Sense to dP/dt max electromechanical delay) is measured without left ventricular (LV) pacing (step 122)

Using LV electrical activity as a trigger, interval C is then measured with various VV liming intervals between RV and LV pacing In the example shown, the intervals may be VV - 0, LV - RV = 20ms, LV - RV = 40ms, and so on. at increments of 20 milliseconds each. Next, interval B is measured using RV electrical activity as the trigger (step 126)

As in step 124, various VV liming intervals are used, such as VV ^::: 0, LV - RV ^:::: -20ms, LV - RV - -40ms. etc.

Hie electromechanical delay measurements are stored by control system 60. The stored delay measurements are used together w ith other measured parameters to determine base line or optimal timing parameters to be used for CRT therapy (step 128).

FIG. 6 is a flow diagram showing the use of electromechanical delay measurements over time to detect ventricular dyssynchrony. Periodically, both interval B and interval C are measured (step 130,). The measurements are stored, and the data is analyzed periodically (step 132) A determination is made whether a change in the data has occurred which exceeds a threshold value (step 134) If not, the periodic measurement of electromechanical delays continues If a change greater than a threshold has been detected, an indication that dyssynchrony has been detected is provided by control system 60 (step 136)

The presence of a mechanical physiologic sensor (such as a pressure sensor, an accelerometer. or an intracardiac impedance sensor) provides additional functionality when used in conjunction with electrical sensors. Electromechanical delay measurements can be made that represent a delay between a sensed electrical event and a subsequent related mechanical activity of the heart. The electromechanical delay measurements provide useful information for detecting dislodgement or migration of sensors or leads, determining timing parameters for CR T therapy, and detection of ventricular dyssynchrony as a result of physiological changes over time Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention