Autocapture Function Research Articles

Limitations of the AutoCapture™ Pacing System in patients with cardiac stimulation devices.

AutoCapture (St Jude Medical) is a technological development that confirms ventricular capture analysing the evoked response after a pacing impulse and adjusts the energy output to changes in the stimulation threshold. Although this algorithm is aimed to assure capture minimizing energy consumption, some patients might not benefit from it. The objective of this study is to identify them. Long-term AutoCapture efficiency was assessed using the data recorded in the programmer reports of patients undergoing scheduled pacemaker check-ups during 2012 in our institution. We have evaluated 160 consecutive patients (58% men) aged 78 ± 9 years. Pacemaker stimulation mode was DDD in 116 patients (72.5%) and VVI in 44 patients (27.5%). During the scheduled visits for pacemaker check-up, 73 patients (45.6%) showed abnormalities in the long-term AutoCapture function report (high variability in the AutoCapture stimulation threshold and/or out-of-range values). After multivariate analysis, abnormal AutoCapture pattern was associated to the presence of atrial fibrillation [odds ratio (OR) 3.96 (1.59-9.82; P < 0.05)]; and a ventricular pacing ≤25% of the time [OR 4.80 (2.09-11.05; P < 0.05)]. AutoCapture abnormalities were also described in three (1.8%) patients with very low stimulation threshold. Although AutoCapture algorithm has shown both efficacy and safety, our findings suggest that some patients with atrial fibrillation or those requiring ventricular pacing ≤25% of the time may not benefit from it. Activation of the algorithm should be individualized according to the patient's characteristics and long-term AutoCapture pattern checked in the routine follow-up.

Two pacing spikes on the QRS complex in a single-chamber pacemaker

AutoCapture algorithm helps the pacemakers to automatically adjust output close to the pacing threshold. This algorithm monitors the evoked response signal of myocardial depolarization, and delivers a high output back-up pulse if there is a loss of capture. This case, with two pacemaker spikes on the QRS complexes in a patient with VVI pacemaker, simulating a sensing failure, demands clear understanding of AutoCapture function before labeling the pacemaker malfunction.

Electrical Performance and Automatic Capture Characteristics of a 3.5‐mm2 Passive Fixation Lead during 1‐Year Follow‐Up

Bipolar low polarization electrodes are recommended for a regular AutoCapture (St. Jude Medical, Inc., Sylmar, CA, USA) function in order to effectively detect the evoked response (ER) signal. The objective of this national multicenter registry was to evaluate the electrical performance and the AutoCapture characteristics of the bipolar ventricular pacing lead IsoFlex S, model 1636T or 1646T (St. Jude Medical), in combination with single- and dual-chamber pacemakers. Ventricular pacing and sensing thresholds, lead impedance, ER amplitude, and polarization signals were measured at discharge and routine follow-up visits after 1, 3, 6, 9, and 12 months. AutoCapture activation was recommended based on the results of the ER sensitivity test. Of the 252 patients initially included, 109 (43%) have completed the follow-up. The mean ventricular pacing threshold was 0.43 +/- 0.19 V at discharge and 0.68 +/- 0.32 V at 12 months postimplant. The values for the ventricular sensing threshold were between 9.51 +/- 4.12 and 9.99 +/- 4.09 mV at discharge and at the 12-month follow-up. The unipolar lead impedance decreased from 533 +/- 94 to 476 +/- 73 ohms during the follow-up. The mean ER amplitude was 16.47 +/- 6.70 mV at discharge and 17.42 +/- 7.43 mV after 12 months, and the corresponding mean polarization signals were 0.59 +/- 1.00 and 0.74 +/- 1.24 mV, respectively. AutoCapture activation was recommended in at least 95% of the patients investigated over the 12-month follow-up. The bipolar ventricular pacing lead IsoFlex S 1636/1646T shows a good electrical performance and is mostly compatible with the AutoCapture algorithm.

Role of ventricular autocapture function in increasing longevity of DDDR pacemakers: a prospective study

Autocapture is an algorithm for automatic adaptation of ventricular output to capture threshold. The aim of this prospective study was to estimate the effects of ventricular Autocapture algorithm on DDD-DDDR pacemaker longevity. Eighty-three patients implanted with a DDD-DDDR pacemaker (Affinity or Entity; St Jude Medical, USA) were enrolled and the Autocapture function was activated pre-discharge. Ventricular pulse duration was randomly programmed at 0.3 or 0.4 ms, with a cross-over at 8-12 weeks and again at 13-14 months. Diagnostic data were retrieved from device memory and by calculating battery current drain from long-term threshold recordings; device longevity was estimated at the following settings: Autocapture with a pulse duration of 0.3 and 0.4 ms, respectively, standard output (3.5 V, 0.4 ms) and conventional low output programming (2.5 V, 0.4 ms). According to a series of assumptions, Autocapture was associated with a 55-60% increase in estimated device longevity compared with standard output programming and a 6-7% increase in longevity compared with low output programming. No significant differences were found between Autocapture programmed with a pulse duration of 0.3 or 0.4 ms. In projections to a 10-year follow-up, use of the Autocapture function resulted in a 42% reduction in pacing-related estimated costs compared with standard output programming at 3.5 V, 0.4 ms. Pacing with constant adaptation of ventricular output in dual-chamber devices has the potential to increase generator longevity and to reduce sizeably pacing-related costs compared with standard programming.

Long-term results of endocardial pacing with Autocapture™ threshold tracking pacemakers in children

We aimed to evaluate the long-term results of endocardial pacing with Autocapture threshold tracking pacemakers in children. Implantation and follow-up data of 20 children with these pacemakers were retrospectively evaluated. The pacemakers were implanted subpectorally in five and subcutaneously in 15 patients. The indication for pacing was high-grade atrioventricular block in 18 cases. The mean age at implantation was 7+/-4.8 years. Four patients were pacemaker dependant (heart rate < 30 bpm). At implantation, the mean pacing threshold was 0.5 V at 0.5 ms. The mean evoked response (ER) signal was 8.5+/-3.6 mV, and the polarisation signal (PS) was <1 mV in 15 patients and 1-2 mV in five patients. During the mean follow-up period of 60 months, mean ER signal decreased significantly to 7.7+/-6.3 mV at 24 months and 6.5+/-2.5 mV at 60 months (P < 0.05). In four of 15 patients (26.6%), with a predischarge PS value of <1 mV, it increased between 1 and 2 mV over time. During follow-up, autocapture function was deactivated in six (30%) patients; due to inappropriate ER/PS values in four and due to severe muscle twitching in two with subpectoral implants. These problems occurred during a median period of 21 months after implantation. Generators were replaced in three patients with Microny pacemakers because of battery depletion at 54, 66 and 78 months. In two of them autocapture function had been working since implantation. In seven of 10 patients, who completed > or = 60 months of follow-up, battery impedances were still at the predischarge level. Autocapture function works well in most children at implantation. Mean ER signal significantly decreases over time despite stable pacing parameters. Autocapture function may become nonoperational due to decreased ER signal in some patients. Muscle twitching may be an important problem that may result in discontinuation of autocapture function in children with subpectoral implants.

The influence of mental and physical stress on the autocapture function in children.

The Autocapture function detects the evoked response signal (ERS) to verify beat-to-beat capture, and optimizes the output of ventricular pulse amplitude automatically. We had experience concerning the instability of the Autocapture recommendation in some patients. Evoked response is subject to variation as it is a biological event. However, the present knowledge about the Autocapture function lability is very limited. The purpose of this study was to evaluate whether mental stress, body positions or exercise influence the ERS and PS in children. Study was performed in 15 consecutive patients [13.4 +/- 4.1 (5-20) year] with VVIR (n = 10) and DDD/VDD pacemakers with the Autocapture function (n = 5), had received ventricular leads including Membrane-E-1450T (n = 6), Membrane-EX-1470T (n = 2), Tendrill-DX-1388T (n = 3), Tendrill-SDX-1488T (n = 1), AV-Plus-DX-1368 (n = 1), Accufix-II-DEC (n = 1) and Vitatron (n = 1), and followed more than six months. Autocapture functions were measured during arithmetic mental stress test (MST), in different body positions, and during symptom-limited treadmill exercise. MST was applied in all except two (5 and 8 year old) who didn't have ability to perform. Activating autocapture was not recommended in only one with Accufix-II-DEC due to high PS. ERS was 10.5 +/- 6.3 mV during supine and increased to 11.9 +/- 7.5 mV during sitting (p = 0.017) and standing 12.1 +/- 7.2 (p = 0.002). However, ERS remained stable before, during and after both exercise and MST, which were 12.6 +/- 7.2 mV, 12.8 +/- 7.8 mV, 13.6 +/- 9.4 mV (p > 0.05) and 10.5 +/- 5.5 mV, 10.9 +/- 6.7 mV, 10.4 +/- 5.5 mV (p > 0.05) respectively. In addition, PS and recommendation about the Autocapture remained unchanged during the study. In conclusion, MST, different body positions and exercise do not have any clinically important influence on the Autocapture function in children.

Compatibility of automatic threshold tracking pacemakers with previously implanted pacing leads in children.

The Autocapture function controls and optimizes the amplitude of the pacing pulse and saves energy. The manufacturer recommends using a special low polarization, low threshold bipolar Pacesetter lead for the Autocapture function. The purpose of this study was to evaluate the compatibility of Autocapture with previously implanted pacing leads. The study included 15 patients (mean age 13.6 +/- 3.4 years) who needed pulse generator replacement and received the VVIR pacemaker Regency SR+ or the DDDR pacemakers Affinity DR or Integrity DR with the Autocapture function. The new pulse generators connected to previously implanted ventricular leads. At the time of implantation the pacing threshold was 1.0 +/- 0.35 V at 0.5 ms, the lead impedance was 580 +/- 80 omega, and the spontaneous R wave amplitude was 7.89 +/- 4.89 mV. The polarization signal (PS) was 3.8 +/- 3.04 mV, and evoked response (ER) was 8.15 +/- 4.57 mV at the predischarge testing. Follow-up telemetry was done at months 1, 3, 6, 12, and 18. The follow-up duration was 9.4 +/- 5 months (range 1-18 months). If the results of PS and ER measurements were acceptable for autocapture, it turned on at the 1-month visit. In six (40%) patients the results were found acceptable for autocapture function. Age, lead impedance, pacing threshold, intrinsic R wave measurement, lead age, fixation mechanism, and ER measurements were not statistically different in Autocapture suitable and not suitable groups. The main reason not to activate Autocapture had been increased PS. Any significant fluctuations were not observed in pacing threshold, lead impedance, ER, and PS during follow-up. In conclusion, previously implanted pacing leads may be compatible with the Autocapture function.

High-impedance steroid-eluting lead with automatic ventricular capture verification

There have been few reports of clinical studies on automatic ventricular capture verification with high-impedance steroid-eluting leads. Six patients were implanted with Medtronic 5554-45 leads in the atrium and Medtronic 5054-45 leads in the ventricle. A significant difference was observed (P = 0.0032) between the mean atrial evoked response (ER) (3.99 ± 1.53 mV) and the mean ventricular ER (15.21 ± 6.97 mV), although no significant difference was observed (P = 0.4637) between the mean lead polarization signals (PS) in the atrium (1.86 ± 1.53 mV) and in the ventricle (1.37 ± 0.33 mV). In all patients, the effect of autocapture was satisfactory in the ventricle; however, this function did not work properly in the atrium in four of six patients, indicating that the use of autocapture function in the atrium is not recommended. In a separate case, clinical application of the autocapture function was performed for a 73-year-old woman with bradycardia and atrial fibrillation. A Medtronic 5054-52 ventricular lead and a St. Jude Medical 5130L pulse generator were implanted. At implantation the ER was 19.15 mV, the PS was 1.96 mV, and the unipolar pacing threshold was 0.375 V (at 0.4 ms pulse width). These data seemed acceptable for proper autocapture function. At 6 months postoperatively, the ER was 16.25 mV, the PS was 1.96 mV, and the unipolar pacing threshold was 0.5 V (at 0.4 ms pulse width). The autocapture function worked properly.

Long-term follow-up of pacemakers with an Autocapture pacing system.

The aim of this study was to evaluate the safety and performance of the Autocapture pacing system during a 5-year follow-up period. The study was conducted retrospectively between May 1996 and May 2001. Sixty consecutive patients who had undergone VVI pacemaker implantation using an Autocapture program with leads 1402T (n: 31) and 1452T (n: 29) were included in the study. Intraoperative measurements including a ventricular stimulation threshold test, sensing of intrinsic R wave (mV), and lead impedance (W) were done by a standard pacing system analyzer. Evoked responses (ER, mV) and polarization signals (PS, mV) were measured after the pocket was closed. Pacing thresholds by Autocapture (AC thrd, V) and Vario (Vario thrd, V), battery current (mA), and battery impedance (kW) were also repeated during predischarge and 1, 6, 12, 18, 24, 30, 40, 50, and 60 months after discharge. According to the ER and PS values an Autocapture algorithm could be activated in 49 patients (88%). The Autocapture algorithm remained active during the follow-up in all of these patients. In patients with inappropriate ER and PS values (11 patients, 12%), pacemakers were programmed to a VVIR pacing mode and Autocapture algorithm was inactivated. ER and PS values did not reach appropriate values to activate the Autocapture algorithm in any of these patients in consecutive follow-ups. Twenty-four-hour Holter monitoring could be conducted in 32 patients (53%). In all recordings, when the loss of capture occurred, it was confirmed that back-up pacing continued. When the first measurements recorded during implantation were compared to approximately the 5th year measurements; ER (9.2 mV vs 9.6 mV), PS signal (1.13 +/- 0.30 mV vs 1.15 +/- 0.72 mV), AC thrd (0.4 V vs 1.2 V), Vario thrd (0.7 V vs 1.3 V), and lead impedance (502 ohm vs 620 ohm) were not changed significantly. Battery impedance increased 1 kOhm between 30-40 months of the implantation. Seven deaths occurred during follow-up. Three patients had fatal myocardial infarction, one died due to a non-cardiac event, and the remaining three died due to progressive heart failure. ER, R wave amplitude, and PS, which are the main parameters for the continuation of Autocapture function, did not change significantly during long-term follow-up. High output back up pacing provided additional safety for sudden rises in threshold. The Autocapture pacing algorithm was found to be effective and reliable during long-term follow-up.

Membrane EX lead compatibility with autocapture function in affinity pulse generator

Membrane EX lead compatibility with autocapture function in affinity pulse generator

Membrane EX lead compatibility with autocapture function in affinity pulse generator

Membrane EX lead compatibility with autocapture function in affinity pulse generator

Improved differentiation of the ventricular evoked response from polarization by modification of the pacemaker impulse.

The Autocapture feature, implemented in the Microny and Regency pacemakers of St. Jude Medical, continuously controls the effectiveness of ventricular stimulation by detection of the evoked response. Proper sensing of this signal depends on the magnitude of the polarization, which should be minimal. Therefore, the conjunctive use of low polarization electrodes is recommended. Further, the pacing impulse of these pacemakers has a biphasic waveform consisting of a stimulus followed by a fast discharge pulse. This study compares polarization of a modified pacing impulse with the default pacing impulse, and its effect on the ability to activate the Autocapture function when used with different types of electrodes. In 45 patients, acute measurements of the polarization and the evoked response were performed at random on the modified pacing impulses of a custom designed Regency and on the default stimuli of a standard Regency. The following bipolar leads were used: 20 Medtronic 4024 CapSure, 12 Pacesetter 1450T, and 13 Pacesetter 1470T. Using the default pacing impulse, polarization and evoked response were significantly larger with the Medtronic 4024 CapSure compared to the low polarization leads. The polarization to evoked response ratio was more frequently acceptable for activation of the Autocapture with the Pacesetter leads. In all leads the modified pacing impulse was characterized by significantly smaller polarization with the most prominent reduction in the Medtronic 4024 CapSure. The differences in the pacing impulse did not affect the evoked response. With the programmability of the fast discharge pulse, the requirements to activate the Autocapture function were fulfilled in 29 (94%) of 31 patients with the modified pacing impulse, compared to 22 (71%) of 31 patients with the standard pacing impulse. The modified pacing impulse decreased the "polarization to evoked response" ratio, and by that improved the conditions for activation of the Autocapture function.

A Cardiac Evoked Response Algorithm Providing Threshold Tracking: A North American Multicenter Study

The purpose of this study was to evaluate a pacing system using the recognition of cardiac evoked response for the automatic adjustment of pacing output. Patients were prospectively followed after primary implantation of VVIR pacemakers using AutoCapture (St. Jude Medical CRMD). Sensing and pacing thresholds, polarization signal, evoked response, and AutoCapture performance were evaluated with serial visits and 24-hour Holter monitoring. Three hundred ninety-eight patients (mean age 71 +/- 15 years) were followed for an average duration of 1 year (3 days-1.75 years) with the algorithm functional in > 90% of patients. Backup pacing in the event of exit block was confirmed in all patients. Pacing thresholds remained stable at 0.89 +/- 0.34 V with a pulse width of 0.31 ms (with chronic output autoset at 0.3 V above the actual threshold). Evoked response exhibited a small but statistically significant increase with time (8.92 mV at implant, 9.60 mV at 12 months), however, this finding did not result in any change in AutoCapture function during our follow-up period. The polarization signal remained stable with minimal variation (1.12 mV at implant, 1.18 at 12 months). No clinical adverse events were observed using the AutoCapture algorithm. In this initial experience with the AutoCapture algorithm the evoked response and polarization measurements remained adequate, allowing the system to function in the majority of patients with safe, low output pacing. High energy backup pacing provided an added safety feature over fixed output devices in cases of unexpected threshold rises. Longer follow-up is required for continued long-term validation of the algorithm.

Effects of body position and exercise on evoked response signal for automatic threshold activation.

The Autocapture function controls and optimizes the output of the ventricular pulse amplitude automatically. For this reason an automatic test has to be performed during follow-up to measure the evoked response signal and lead polarization for the calculation of the appropriate evoked response sensitivity setting. The aim of the study was to assess whether body position and exercise influence the evoked response and polarization. Both parameters were determined in the supine and upright position and subsequently during supine and upright symptom-limited ergometry. The study included 14 patients with the VVIR pacemaker Regency SR+ who had received the ventricular pacing leads Membrane E 1450 T (n = 8), CapSure Z 5034 (n = 4), or SX 60 (n = 2). The evoked response signal was 7.4 +/- 3.3 mV during supine and increased to 9.7 +/- 5.6 mV (+35%) during upright position (P < 0.05). The exercise tests were terminated at 105 +/- 36 W (supine) and 110 +/- 34 W (upright). There was a gradual insignificant decrease of the evoked response during each exercise test with a mean decrease of -1.1 +/- 0.9 mV (-15%; supine) and -1.6 +/- 2.1 mV (-16%; upright). The evoked response increased within 5 minutes during recovery to the initial values. Polarization remained unchanged during both tests. The pacemaker did not recommend activating autocapture in four patients who all had received high-ohmic pacing leads. In conclusions, the measurement of the evoked response in supine position seems to represent the worst case. Physical activities did not effect autocapture function in patients with the recommended lead, but the pacemaker did not always recommend Autocapture activation in some patients with high-ohmic pacing leads.