PACING
Acute performance evaluation of a new ventricular automatic capture algorithm
Kerckhoff-Klinik GmbH, Department of Cardiology and Electrophysiology Benekestrasse 2-8, D-61231 Bad Nauheim Germany ; Cardioangiologisches Centrum Bethanien Im Prüfling 23, D-60389 Frankfurt Germany ; Johannes Gutenberg-Universität Mainz Klinikum, Langenbeckstrasse 1, D-55101 Mainz Germany ; Guidant Corporation 4100 Hamline Avenue North, St Paul, MN 55112-5798 USA ; Guidant Europe, Clinical Research Department Park Lane, Culliganlaan 2B, 1831 Diegem Belgium ; Universitätsklinikum des Saarlandes D-66421 Homburg/Saar Germany
Manuscript submitted 4 February 2005. Accepted after revision 14 August 2005.
Corresponding author. Tel: +49 6032 996 0; fax: +49 6032 996 3236. E-mail address: j.sperzel{at}kerckhoff-klinik.de
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Abstract |
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Aims This study evaluated the acute clinical performance of a new ventricular automatic capture algorithm developed to work with all lead types and pacing vectors.
Methods and results During regular pacemaker implant or replacement, AutoThreshold and manual threshold tests were performed in ventricular unipolar (UP) and bipolar (BP, if applicable) pacing using a customized external prototype INSIGNIATM pacemaker. The success rate and accuracy of two different modes (commanded and ambulatory) of the automatic capture algorithm were used to evaluate the performance. Loss-of-capture events (two consecutive non-captured beats without backup pacing) were used to assess safety. Data of 53 patients (33 DDD/20 VVI) from four medical centres were analysed. Tested leads included 43 BP and 10 UP from nine manufacturers, and seven had electrodes with low polarization. The rate of successful commanded and ambulatory AutoThreshold tests was 96 and 94%, respectively, with an average absolute threshold difference compared with manual threshold of <0.1 V at 0.4 ms (commanded 0.07±0.07 V and ambulatory 0.08±0.07 V). There was no significant difference in performance between UP/BP pacing, polarization, and lead type. No loss-of-capture event was observed.
Conclusion When successful, the ventricular automatic capture algorithm accurately determined pacing thresholds in either a UP or BP pacing configuration among all leads tested.
Key Words: Pacemaker, Automatic capture verification, Pacing artifact, Polarization, Pacing threshold
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Introduction |
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Variations in pacing thresholds due to pharmacological factors, changes in pathological and physiological state, electrode–tissue interface maturation, and fibrosis have resulted in the programming of safety margins two to three times the measured pacing threshold to ensure constant myocardial stimulation.1
–4 The concept of a threshold tracking or automatic capture verification pacemaker to account for threshold fluctuations has been a major goal of the pacemaker industry since the 1970s.5–11 Automatic capture verification technology offers several advantages over traditional manual pacemaker programming, including improved patient safety through beat-by-beat capture verification,12,13 reduced clinician burden, and physician follow-up time through automatic threshold testing.14 In addition, the reduction in pacing amplitude may prolong device longevity.15
The primary obstacle in implementing automatic capture verification has been the detection of myocardial depolarization or evoked response (ER) in the presence of the large pacing artifact (ART) induced by the pacing stimulus. ART, the residual voltage on the tissue/lead interface following a stimulation pulse, is an additive signal that can mask the ER. A number of approaches for detecting ER has been developed, including the development of low-polarization leads,16 and reduction of the output coupling capacitor in the pacing circuitry.11,17 Some automatic capture verification algorithms based on these approaches have shown reduced performance when used with certain lead types, including non-low-polarization leads18 and are restricted in the pacing and sensing vectors.
Reduction of the coupling capacitor reduces the effective total discharge capacitance of the pacing circuitry and results in an increased pulse droop and increased rate of decay of the ART.11 The ART decay characteristic is determined by the time constant formed by the device electronics and the load impedance, a combination of the electrode/tissue interface and myocardial impedance. The reduced coupling capacitor technology has been shown to be effective in reducing ART, allowing for a shortening of the blanking period, thereby enabling the reliable detection of ER with a wide range of pacing lead models using both unipolar (UP) and bipolar (BP) pacing configurations.11 Evaluation of the performance of the reduced coupling capacitor technology within an automated threshold search algorithm has not been previously conducted.
The aim of the study was to investigate the performance of the reduced coupling capacitor technology implemented within the INSIGNIATM (Guidant, St Paul, MN, USA) ventricular automatic capture (VAC) algorithm during AutoThreshold (automated pacing threshold measurement) and capture verification (automatic beat-to-beat capture verification) in the acute clinical environment.
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Methods |
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Study design and patient selection
Patients with a class I or II indication for permanent pacemaker therapy, either new implantation or replacement, were eligible for this prospective, non-randomized study. Patients with a history of system-related infections, chronic leads with unknown manufacturer, and model or permanent atrial fibrillation were excluded. All patients were at least 18 years old and gave written informed consent before entry in the study. The study was approved by respective ethics committees and conducted at four centres in accordance with applicable European guidelines and in compliance with the Declaration of Helsinki.
Fifty-five patients were enrolled in the study of which 53 patients (30 males, 23 females; ages 37–91 years, mean age 72.6±12.0 years) were included in the data set. Two patients were excluded due to a technical error in the study device and an unknown ventricular lead model. Patient indications were typical of the general pacemaker population and 47 (88.7%) of the implants were right-sided. Ventricular leads from nine manufacturers were tested in the study. The number of different types and manufacturers of leads were not pre-defined, but chosen by the physician for each patient. Details of lead characteristics are shown in Table 1. The mean implant duration of the 13 chronic leads was 100.3±46.1 months (range from 34–215 months) at the time of the study.
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Study procedure
After new lead implantation or chronic lead exposure using standard operative techniques, routine measurements including pacing threshold, R-wave amplitude, and impedance were performed using a standard pacing system analyzer (PSA) to verify adequate lead placement. The leads were then connected to the INSIGNIAAC Acute Study System, a custom-made external version of the INSIGNIA Ultra pacemaker. An empty can was also placed in the pacemaker pocket to emulate an implanted device. Surface electrocardiogram (ECG), intracardiac electrogram (EGM) signals, and event markers from the Acute Study System were recorded on a DAT tape during the procedure for off-line analysis. Following completion of the protocol, the Acute Study System was disconnected, the empty can removed, and a pacemaker implanted.
Pacemaker algorithm
The VAC algorithm declares capture if the positive peak of the ER signal following a pace exceeds the capture detection threshold within the ER measurement window. The VAC threshold test algorithm can operate in three modes: commanded threshold test, ambulatory threshold test, or beat-to-beat mode. The commanded threshold test, initiated through the programmer in clinic by a medical practitioner, aids in the visual identification of captured and non-captured beats by only delivering a backup stimulus following a confirmed loss-of-capture (normally the second loss-of-capture beat at the same pacing level). The delivery of a backup stimulus following a confirmed loss-of-capture was designed for safety reasons, ensuring that the patient would not have two consecutive loss-of-capture beats.
The ambulatory threshold test, designed to work automatically when the patient is away from clinic or hospital, delivers a backup pulse within 100 ms following every test stimulus. The delivery of backup stimulus following every test stimulus was designed such that no loss-of-capture beats occur during the threshold test. Both the commanded and ambulatory threshold tests follow a similar threshold search strategy. When initiated, the algorithm assesses the ER at a fixed output to evaluate the signal amplitude and signal variability. If the signal amplitude is <2 mV, if the signal to artifact ratio is <2, too much noise or if there is a large amount of signal variability, the threshold test exits and in the case of the ambulatory threshold test, reschedules the test after 1 h. If the ER signal characteristics are appropriate, the algorithm then starts a step-down threshold test with three pacing pulses delivered at each pacing voltage. The step size is 0.2 V at pacing voltages >1.0 and 0.1 V at pacing voltage <1.0 V. Upon detection of the pacing threshold, the pacing output is then set at 0.5 V above the measured threshold.
Study protocol
The study protocol was designed to evaluate the performance of the automatic capture technology when compared with manual ventricular threshold tests. To eliminate competition with intrinsic rhythms, thereby reducing the occurrence of fusion beats, the heart was overdrive paced at 10 b.p.m. above intrinsic rhythm or paced at an atrioventricular (AV) interval of 60 ms in the case of VVI(R) and DDD(R) implants, respectively. The protocol required that all patients have a ventricular pacing threshold 
3.5 V at 0.4 ms and an R-wave amplitude >5.0 mV to confirm adequate lead positioning. The manual UP step-down threshold tests were conducted with three pacing pulses delivered at each pacing voltage. Manual threshold tests were terminated following observed loss-of-capture and the pacing threshold recorded. A commanded UP AutoThreshold test using the ventricular automatic capture technology was then conducted. The performance of the ambulatory AutoThreshold test, meant to simulate the feature's ambulatory performance, was then evaluated in a subset of patients. In patients implanted with a BP lead, the pacing vector was changed to BP and the protocol was repeated.
Performance analysis
Recording of surface ECG, EGM, pacing stimulus markers, and other customized event markers were made during the testing for off-line evaluation of the ventricular automatic capture technology performance. Each primary paced pulse was manually classified as a capture, loss-of-capture, or fusion event and then compared with the classification performed by the ventricular automatic capture algorithm. The correct pacing threshold measurement, determined by the detection of sub-threshold pacing resulting in a confirmed loss-of-capture event, was defined as a successful test, if the difference between manual and automatic threshold was 0.2 V for a threshold 1 or 0.3 V for a threshold >1 V. Confirmed loss-of-capture events were signified by two loss-of-capture beats occurring within the previous four cardiac cycles. Threshold tests in which the ventricular automatic capture algorithm did not start the step-down threshold test portion of the algorithm due to inappropriate ER characteristics or in which the ventricular automatic capture algorithm did not detect a loss-of-capture event were defined as unsuccessful.
Statistical analysis
All values are expressed as mean±SD. Pacing thresholds were evaluated by comparing the difference between the manual and commanded threshold tests. The two-sided Fisher's exact test was conducted to compare the effect of lead fixation, lead polarization, and lead implant duration on the automatic capture success rate. A P-value <0.05 was considered significant.
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Results |
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Lead measurements
UP and BP ventricular lead measurements using a PSA are shown in Table 2.
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Performance of commanded automatic capture technology
The commanded automatic capture algorithm was successful in 92 of 96 (96%) attempted commanded threshold tests. All confirmed loss-of-capture events were captured by a high-output backup safety pace. All unsuccessful tests (n=4) were due to inappropriate ER characteristics during the threshold test initialization phase. The average absolute difference between the manual and commanded threshold test results for both UP and BP pacing configuration was assessed for UP 0.07±0.07 V and for BP 0.06±0.08 V. In a majority of patients, the difference between the manual and commanded threshold test results was
0.1 V, in both UP (44 of 50 patients) and BP (37 of 42 patients) pacing configurations (Figure 1) and all were 0.3 V. There was no significant difference in the success rates when comparing lead polarization, implant duration in both UP and BP commanded threshold tests (Table 3).
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Performance of ambulatory automatic capture technology
Ambulatory threshold tests were performed in 43 patients in a UP and in 42 patients in a BP pacing configuration. The automatic capture algorithm was successful in 80 of 85 (94%) attempted ambulatory threshold tests with backup pacing following all loss-of-capture beats. All unsuccessful tests (n=5) were due to inappropriate ER characteristics during the threshold test initialization phase. The average absolute difference between the manual and ambulatory threshold test results for both UP and BP pacing configuration was assessed for UP 0.06±0.06 V and for BP 0.08±0.07 V. For 89% of patients, the absolute difference between the manual and ambulatory threshold tests was
0.1 V in UP and BP pacing configurations (Figure 1) and was not significantly different from the difference observed between manual and commanded threshold tests for both UP and BP pacing configurations. There was no significant difference in the success rate between UP and BP pacing configurations, low-polarization and normal polarization leads, or acute and chronically implanted leads (Table 3). However, there was a difference in the success rates when comparing passive with active fixation leads, though a significant difference was only observed during BP ambulatory threshold tests. |
Discussion |
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This study describes the acute performance of a new automatic capture verification algorithm, which implements a reduced coupling capacitor design to minimize pacing artifact. The commanded and ambulatory modes of the automatic capture algorithm were able to reliably and accurately detect ventricular pacing thresholds in both UP and BP pacing configurations. Some AutoThreshold tests were unsuccessful; however, it should be noted that an unsuccessful test does not necessarily indicate a failure of the automatic capture algorithm. By design, the algorithm will enter the Retry mode if a test is unsuccessful due to signal quality. In addition, the ability of the automatic capture technology to determine the pacing threshold was minimally affected by pacing lead models, fixation mechanisms, polarization types, and lead chronicity.
Pacing lead polarization and coating
The implementation of automatic capture verification technology in implantable devices has focused on reduction of the artifact mainly through optimization of the lead design. The artifact voltage results from ionic charge accumulation on the electrode/tissue interface following a pacing stimulus. Optimizing lead design to maximize the effective surface area, thereby increasing the surface area of the electrode/tissue interface and distributing the charge accumulation, can reduce the ART voltage and allow for ER sensing. This principle has been applied in the development of low-polarization leads, in which the tip electrode is coated with either titanium nitride (TiN) or iridium oxide (IROX) to increase the electrochemically active surface area. The TiN- or IROX-coated lead electrodes have significantly lower ART amplitudes16 and have been shown to be able to support automatic capture verification in the ventricle.12,19,20 The performance of non-low-polarization leads which include bare platinum helix and high-impedance leads with automatic capture systems has been investigated with both positive16,21 and negative16,18 results. Consistent with previous literature,11 the reduced coupling capacitor technology implemented in the Guidant automatic capture system was capable of determining an accurate pacing threshold in all leads tested, irrespective of the polarization classification.
Fixation mechanism
A lower success rate was observed in the automatic capture threshold test with acute active fixation leads when compared with passive fixation leads during UP and BP pacing in both commanded and ambulatory threshold test modes. In one active fixation lead, all tests failed when measured shortly after electrode fixation, whereas measurements taken 20 min later were all successful. Acute changes to the ER suggest that the acute performance of the automatic capture algorithm may improve over time, due to resolution of injury currents, and warrants further investigation.
Study limitations
This study was performed during pacemaker implant or replacement and all testing was done in quiet supine patients. In addition, due to the acute nature of the study, the effects of activity and lead maturation or the performance of the algorithm in a beat-to-beat mode could not be evaluated. Further evaluation of the technology in an implanted system is ongoing.
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Acknowledgement |
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Financial support for this study was provided by Guidant/CRM, 55112 St Paul, MN, USA.
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References |
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[1] Stokes K and Bornzin G. The electrode-biointerface: stimulation. In Barold SS (Ed.). Modern Cardiac Pacing 1985; Mount Kisco, NY Futura Publishing Co pp. 33–77.
[2] Preston TA, Fletcher RD, Lucchesi BR, Judge RD. Changes in myocardial threshold: physiologic and pharmacologic factors in patients with implanted pacemakers. Am Heart J 1967; 74: 235–242.[CrossRef][Web of Science][Medline]
[3] Dohrmann ML and Goldschlager NF. Myocardial stimulation threshold in patients with cardiac pacemakers: effect of physiologic variables, pharmacologic agents, and lead electrodes. Cardiol Clin 1985; 3: 527–537.[Medline]
[4] Danilovic D and Ohm OJ. Pacing threshold trends and variability in modern tined leads assessed using high resolution automatic measurements: conversion of pulse width into voltage thresholds. Pacing Clin Electrophysiol 1999; 22: 567–587.[Medline]
[5] Kadhiresan VA, Olive A, Gornick C, Spinelli J, Villalta D. Automatic capture verification by charge-neutral sensing. Pacing Clin Electrophysiol 1999; 22: 73–78.[Medline]
[6] Kennergren C, Larsson B, Uhrenius A, Gadler F. Clinical experience with an automatic threshold tracking algorithm study. Pacing Clin Electrophysiol 2003; 26: 2219–2224.[Medline]
[7] Preston TA and Bowers DL. The automatic threshold tracking pacemaker. Med Instrum 1974; 8: 322–325.[Medline]
[8] Preston TA and Bowers DL. Clinical applications of the threshold tracking pacemaker. Am J Cardiol 1975; 36: 322–326.[Medline]
[9] Alt E, Kriegler C, Fotuhi P, Willhaus R, Combs W, Heinz M, Hayes D. Feasibility of using intracardiac impedance measurements for capture detection. Pacing Clin Electrophysiol 1992; 15: 1873–1879.[Medline]
[10] Danilovic D, Ohm OJ, Stroebel J, Breivik K, Hoff PI, Markowitz T. An algorithm for automatic measurement of stimulation thresholds: clinical performance and preliminary results. Pacing Clin Electrophysiol 1998; 21: 1058–1068.[Medline]
[11] Sperzel J, Neuzner J, Schwarz T, Zhu Q, König A, Kay GN. Reduction of pacing output coupling capacitance for sensing the evoked response. Pacing Clin Electrophysiol 2001; 24: 1377–1382.[Medline]
[12] Madrid AH, Olague J, Cercas A, del Ojo JL, Munoz F, Moro C, Sanz O. A prospective multicenter study on the safety of a pacemaker with automatic energy control: influence of the electrical factor on chronic stimulation threshold. PEACE Investigators. Pacing Clin Electrophysiol 2000; 23: 1359–1364.[CrossRef][Medline]
[13] Clarke M, Liu B, Schuller H, Binner L, Kennergren C, Guerola M, Weinmann P, Ohm OJ. Automatic adjustment of pacemaker stimulation output correlated with continuously monitored capture thresholds: a multicenter study. European Microny Study Group. Pacing Clin Electrophysiol 1998; 21: 1567–1575.[CrossRef][Medline]
[14] Lau C, Cameron DA, Nishimura SC, Ahern T, Freedman RA, Ellenbogen K, Greenberg S, Baker J, Meacham D. A cardiac evoked response algorithm providing threshold tracking: a North American multicenter study. Clinical Investigators of the Microny-Regency Clinical Evaluation Study. Pacing Clin Electrophysiol 2000; 23: 953–959.[CrossRef][Medline]
[15] Brockes C, Rahn-Schönbeck M, Duru F, Candinas R, Turina M. Impact of automatic adjustment of stimulation outputs on pacemaker longevity in a new dual-chamber pacing system. J Interv Card Electrophysiol 2003; 8: 45–48.[Medline]
[16] Lau C, Nishimura SC, Yee R, Lefeuvre C, Philippon F, Cameron DA. Intraoperative study of polarization and evoked response signals in different endocardial electrode designs. Pacing Clin Electrophysiol 2001; 24: 1055–1060.[Medline]
[17] Sperzel J, Pitschner HF, Schwarz T, König A, Zhu Q, Neuzner J. Automatic capture verification in ICD lead systems using intracardiac ventricular evoked response and reduced coupling capacitance. Europace 2003; 5: 83–89.
[18] Luria D, Gurevitz O, Lev DB, Tkach Y, Eldar M, Glikson M. Use of automatic threshold tracking function with non-low polarization leads. Pacing Clin Electrophysiol 2004; 27: 453–459.[Medline]
[19] Schuchert A, Ventura R, Meinertz T. Effects of body position and exercise on evoked response signal for automatic threshold activation. Pacing Clin Electrophysiol 1999; 22: 1476–1480.[Medline]
[20] Bolz A, Hubmann M, Hardt R, Riedmuller J, Schaldach M. Low polarization pacing lead for detecting the ventricular-evoked response. Med Prog Technol 1993; 19: 129–137.[Medline]
[21] Schuchert A, Voitk J, Liu B, Kolk R, Stammwitz E, Beiras J. Autocapture compatibility in patients with the MembraneEX lead and affinity pulse generators. Europace 2001; 3: 332–335.
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