US007894900B2 (12) United States Patent (10) Patent No.: US 7,894,900 B2 Kink et al. (45) Date of Patent: Feb. 22, 2011 (54) DEVICE AND METHOD FORMONITORING 2006/0100539 A1 5.2006 Minet al. CARDAC PACING RATE 2006/01491.52 A1* 7/2006 AmitZur et al. ............. 600,485 2006/0184060 A1* 8, 2006 Belalcazar et al. .......... 600,547 (75) Inventors: Andres Kink, Kiili (EE); Mart Minn, Tallinn (EE); Toomas Parve, Tallinn (EE); Indrek Rätsep, Keila (EE) OTHER PUBLICATIONS Webster, J.G., “Design of Cardiac Pacemakers”, IEEE Press, 1995, (73) Assignee: Smartimplant OU, Tallinn (EE) Piscataway, NJ. Ericsson, A.B., "Cardioplegia and Cardiac Function Evaluated by (*) Notice: Subject to any disclaimer, the term of this Left Ventricular Pressure-Volume Relations', 2000, pp. 1-76, patent is extended or adjusted under 35 Karolinska Institutet, Stockholm, Sweden. U.S.C. 154(b) by 719 days. Soderqvist, E., "Left Ventricular Conductance Volumetry Technique Applied to a Pressure Guide Wire'. Licentiate Thesis, 2002, pp. 1-47, (21) Appl. No.: 11/847,430 Royal Institute of Technology, Stockholm, Sweden. (22) Filed: Aug. 30, 2007 (Continued) O O Primary Examiner Carl H Layno (65) Prior Publication Data Assistant Examiner Natasha N Patel US 2008/OO58882 A1 Mar. 6, 2008 (74) Attorney, Agent, or Firm Vern Maine & Associates Related U.S. Application Data (57) ABSTRACT (60) Provisional application No. 60/823,965, filed on Aug. 30, 2006. A device for monitoring cardiac pacing rate having a measur ing unit for receiving an electrical signal representing the (51) Int. Cl. patient’s cardiac demand, and a computing unit for determin A6 IB5/08 (2006.01) ing the myocardial energy balance by calculating energy con A6 IN I/08 (2006.01) sumed by the myocardium for both an external dynamic work A6IN I/365 (2006.01) for pumping blood into a vascular system, and an internal (52) U.S. Cl. ........................... 607/17, 607/24; 600/481; static work of the myocardium. Volume and time based mea 600/482; 600/483; 600/484; 600/485 Surements are used, and in one embodiment, Volumes are (58) Field of Classification Search ......... 600/481-485: estimated and Volume ratios are calculated from Volume esti 607 24 mates. In another embodiment, Volumes are estimated from See application file for complete search history. bioimpedance measurements. A further aspect is a rate adap tive pacemaker, wherein the maximum pacing rate is deter (56) References Cited mined from the myocardial energy balance Such that the energy Supplied to the myocardium approximately equals the U.S. PATENT DOCUMENTS energy consumed by the myocardium for both an external 5,046,502 A * 9/1991 Kunig ........................ 600,483 dynamic work for pumping blood into a vascular system and 6,885,892 B1 * 4/2005 Minet al. ..................... 607 24 an internal static work of the myocardium. 6,975,903 B1 12/2005 Minet al. 7,614,998 B2 * 1 1/2009 Gross et al. ................... 600/17 23 Claims, 6 Drawing Sheets O2 Pacemakers Pacing Rate PR - - Minute Wolume ings MV = RR x TV Respiration Rate Tidal Volume Cardiac output CO = PR × SV Scheletal Muscles Pacing Rate Stroke Wolume and other tissues US 7,894.900 B2 Page 2 OTHER PUBLICATIONS lent Distance Extrapolation'. International Journal of Bioelectromagnetism, 2003, pp. 1-3, vol. 5, No. 1. Denslow, S., “Relationship Between PVA and Myocardial Oxygen Salo, R. et al., “The Use of Intracardiac Impedance-Based Indicators Consumption Can Be Derived From Thermodynamics'. The Ameri to Optimize Pacing Rate'. In Critical Cardiac-Pacing, 1995, pp. can Physiological Society, 1996, pp. H730-H740, vol. 270, Issue 2. 234-249, W.B. Saunders Co., Philadelphia, PA. Salo, R., "Application of Impedance Volume Measurement to Salo, R. “The Theoretical Basis of a Computational Model for the Implantable Devices', International Journal of Determination of Volume by Impedance'. Automedica, 1989, pp. Bioelectromagnetism, 2003, pp. 1-5, vol. 5, No. 1. 299-309, vol. 11. Salo, R., "Accuracy of Conductance Catheter Measurements in a Realistic Numerical Heart Model: Validation of Reciprocal Equiva * cited by examiner U.S. Patent Feb. 22, 2011 Sheet 1 of 6 US 7,894,900 B2 Pacemaker O2 Pacing Rate PR :S 2 Minute Volume lungs MV = RRx TV Activity%3 - \ Acceleration & Respiration Rate Tidal Volume Minute Volume MV CardiaC oup N m CO = PR X S/ - \ $Ws Scheletal MuScles Pacing Rate Stroke Volume Ssssss and Other tissues FIG.1 U.S. Patent Feb. 22, 2011 Sheet 2 of 6 US 7,894,900 B2 t cycle 'S SV, ml A A Over filling of A v under paced A heart A 15 A. S v - Sisk & y &isi's A / wa Under filling of s Ny Over paced f^ heart 1 S i 60 1 i. s. ---- ---- tsyst + tdiast & PR fbeat y 0.5 O 60 120 18O PR, bpm Rest COW 4{}{} Body work, W FIG 2 U.S. Patent Feb. 22, 2011 Sheet 3 of 6 US 7,894,900 B2 Pressure P (a) Pressure. P (b) Arterial pressure Pas N P Pad FIG 3 U.S. Patent Feb. 22, 2011 Sheet 4 of 6 US 7,894,900 B2 Pressure, P P Volume, V FIG. 4 U.S. Patent Feb. 22, 2011 Sheet 5 of 6 US 7,894,900 B2 O 0.5 1 15 2 Relative Stroke Volume SW/Ves FIG. 5 U.S. Patent Feb. 22, 2011 Sheet 6 of 6 US 7,894,900 B2 Arteria Subclavia ZA1 Bio-impedance Measurement Unit, Cardiac Monitor, and Pacing Rate Controller excitation Currents F.G. 6 US 7,894,900 B2 1. 2 DEVICE AND METHOD FORMONITORING and lower pacing rate limits to avoid over and underpacing of CARDAC PACING RATE the heart are determined by the implanting physician and are programmed into the pacemaker at the time of implanting the CROSS REFERENCE TO RELATED device. The actual values may be determined from exercise APPLICATIONS studies, from algorithms which take into account patients characteristics, or from clinical experience and are set for This application claims the benefit of U.S. provisional every patient individually (Webster, above). application 60/823,965, filed on Aug. 30, 2006, the subject Incorrect rate limits or rate response can have serious matter of which is herein incorporated by reference for all impact on a patient’s quality of life. For example, postural purposes. 10 hypotension, a Sudden drop in blood pressure caused by shifts in blood volume to the lower extremities due to a decrease in TECHNICAL FIELD hydraulic resistance, R., (FIG. 1), when rising from a seated or Supine posture, can lead to syncope and falling of the The invention relates to the field of cardiovascular methods patient, or worse. Neurogenic syncope is a similar problem and devices for determining the pace rate from patient's myo 15 but even more insidious because the sudden drop in blood cardial energy balance, i.e. from the demand of the patients pressure may occur minutes after the precipitating event. organism and external and internal work of the myocardium. If the normal compensatory vasoconstriction is missing or The invention can be used in various embodiments such as in remains insufficient, the condition may be ameliorated by rate-adaptive pacemakers. The energy balance can be deter increasing the heart rate. Obviously, the timing and the extent mined from Volume or Volume ratio and time measurements, of the heart rate increase are important. while electrical bioimpedance can be used to measure or to Patient’s upper rate limit is determined by the following estimate the volume or volume ratio. factors. The ability of heart to work at higher rates is corre lated with a better coronary reserve (CR), characterized with BACKGROUND OF THE INVENTION a capability to dilate coronary arteries and, therefore, to 25 reduce the hydraulic resistance Rof the myocardium (FIG.1). There are multiple approaches for controllingapacing rate Myocardium damaged during an ischemic event or by other of a rate-adaptive pacemaker to provide a heart rate adequate disease (e.g., diabetes) has limited cardiac reserve and capa to meet the metabolic demand (J. G. Webster, Design of bility to cope with the rising cardiac demand W. Cardiac Pacemaker. Piscataway, N.J.: IEEE Press, 1995.). The ability to operate at low heart rates is determined by the Different sensors have been used to assess metabolic 30 ability of the heart to Supply adequate cardiac output at rest, demands (workload of the body War), including body CO=SV-PR (FIG. 1 and FIG.2). Here the limitations acceleration and movement activity and transthoracic bio occur during ventricular filling. A compliant heart with good impedance to estimate minute volume MV (see also FIG. 1). diastolic function is able to increase end-diastolic Volume Minute ventilation, the product of breathing rate and tidal with minimal increase in filling pressure and can double volume, correlates well with workload W. An ideal rate 35 stroke Volume, and therefore cardiac output, without a rate adaptive pacing system would automatically control upper increase. This over filling phenomenon is accompanied by an and lower rate limits to prevent overpacing (M. Min, A. Kink, increase in myocardial “stretch' and wall stress (see U.S. Pat. T. Parve, “Rate adaptive pacemaker.” U.S. Pat. No. 6,885, No. 6,975,903). 892, Apr. 26, 2005.) and under pacing (M. Min, A. Kink, T. It is critical to maintain a balance between an energy Parve, "Rate adaptive pacemaker using impedance measure 40 demand W and a supply E in the heart (FIG. 1). Since insuf ments and stroke volume calculations. U.S. Pat. No. 6,975, ficient myocardial perfusion will lead to hypoxia, ischemia, 903, Dec. 13, 2005). These patents are incorporated herein by and infarct, under most circumstances the primary concern reference for all purposes.