Intraoperative study of polarization and evoked response signals in different endocardial electrode designs

Proarrhythmic effect of automatic threshold testing algorithm in dual chamber devices

BACKGROUND

Operation of auto-threshold testing (ATT) algorithm in current dual chamber cardiac devices require temporary shortening of atrio-ventricular (AV) delay to accurately measure evoked potential (capture) after a pacing pulse. Near simultaneous AV pacing causes atrial pressure elevation and may be associated with atrial arrhythmias.

OBJECTIVE

We evaluated the prevalence of atrial arrhythmias induced by ATT in Abbott devices.

METHODS

Device clinic records were reviewed at a single center for patients with dual chamber Abbott pacemaker/ICD. ATT-induced atrial fibrillation (AF) cases were defined as new appropriate mode switch episodes while the ATT was operating. The auto-capture test trends were defined as unstable if there were deviations >1 V in capture threshold trend events that did not correlate with routine in-office testing.

RESULTS

One hundred and seventy patients were programmed in dual chamber pacing mode. The ventricular ATT was active in 118 patients and of these 78 had true mode switch episodes. Six patients developed AF during ventricular ATT. Three patients had most recorded atrial arrhythmias in close association with ATT (63%, 66%, 100% vs 2%,9%, 33% in other patients with known prior AF). An unstable auto-capture trend curve was seen in 33 patients (6 showing ATT-induced AF) versus 85 patients with stable auto-capture curve and no ATT-induced AF (P = .0001, the χ² test).

CONCLUSION

Ventricular auto-capture algorithm use is associated with induction of AF in dual chamber Abbott devices with a prevalence of over 5%. AF occur more frequently (18%) in patients with erratic ventricular ATT trend results.

Hemodynamic Surveillance of Ventricular Pacing Effectiveness with the Transvalvular Impedance Sensor

The Transvalvular Impedance (TVI) is derived between atrial and ventricular pacing electrodes. A sharp TVI increase in systole is an ejection marker, allowing the hemodynamic surveillance of ventricular stimulation effectiveness in pacemaker patients. At routine follow-up checks, the ventricular threshold test was managed by the stimulator with the supervision of a physician, who monitored the surface ECG. When the energy scan resulted in capture loss, the TVI system must detect the failure and increase the output voltage. A TVI signal suitable to this purpose was present in 85% of the tested patients. A total of 230 capture failures, induced in 115 patients in both supine and sitting upright positions, were all promptly recognized by real-time TVI analysis (100% sensitivity). The procedure was never interrupted by the physician, as the automatic energy regulation ensured full patient's safety. The pulse energy was then set at 4 times the threshold to test the alarm specificity during daily activity (sitting, standing up, and walking). The median prevalence of false alarms was 0.336%. The study shows that TVI-based ejection assessment is a valuable approach to the verification of pacing reliability and the autoregulation of ventricular stimulation energy.

Electrical performance and automatic capture characteristics of a 3.5-mm(2) passive fixation lead during 1-year follow-up

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSION

The bipolar ventricular pacing lead IsoFlex S 1636/1646T shows a good electrical performance and is mostly compatible with the AutoCapture algorithm.

Long-term experience with AutoCapture-controlled epicardial pacing in children

AIMS

To examine the feasibility and safety of AutoCapture (AC)-controlled pacing with epicardial leads in children, and study the effects on device longevity.

METHODS

A total of 62 children were prospectively enrolled. Pre-discharge testing precluded AC function in six children. In 56 (90%) children, devices with AC-controlled pacing were followed up to 9years. Calculated battery life in AC-controlled pacing was compared with theoretical calculations, using a two-fold stimulation output of measured thresholds.

RESULTS

In 53 of 56 children, no differences were observed for evoked response signals (13.3 vs. 11.5mV, P = 0.20) or lead polarization safety margins (5.5 vs. 4.1, P = 0.25) at 6-month and 4-year follow-up. A crossover to conventional pacing was required in 3 of 56 children. AC-controlled pacing prolonged the calculated battery life up to 15% for the identity and integrity devices with 0.95A h capacity, compared with theoretical conventional settings (P = 0.008). In patients with ventricular pacing thresholds >1.5V at 0.5ms, battery life was increased by 30% compared with theoretical conventional settings (P < 0.001).

CONCLUSION

AC-controlled pacing with epicardial leads is feasible and safe in children during long-term follow-up. An adequate lead polarization safety margin persists in most patients. Calculated battery life was prolonged up to 15% with AC-controlled pacing. Patients with high or fluctuating pacing thresholds benefit the most.

Clinical Evaluation of Two Different Evoked Response Sensing Methods for Automatic Capture Detection in the Left Ventricle

BACKGROUND

This acute feasibility study compared two different automatic capture detection methodologies, the reduced coupling capacitor (RCC) and the independent pace/sense (IPS) methods, for the left ventricle (LV).

METHODS

LV threshold tests were performed in DDD mode, with LV-only and bi-ventricular (BiV) pacing using an external cardiac resynchronization therapy (CRT) defibrillator. Evoked response (ER) signals from LV leads were recorded using the LV(Tip) (LV(Tip)-->Can) and LV(Ring) (LV(Ring)-->Can) to empty pulse generator (Can) housing sensing vectors to evaluate the two methodologies. Pacing vector, pulse duration, atrioventricular delay, and interventricular delay were varied to assess their effects on ER. The minimum ER amplitude (ER(min)), signal-to-artifact ratio (SAR), and ER amplitude voltage dependence were evaluated. ER(min)>2 mV and SAR(min)>2 define potential automatic LV capture detection for the two methodologies.

RESULTS

Data collected from 43 patients (63.7 +/- 11.0 years) were analyzed, including unipolar and bipolar (14/29) LV leads. Neither ER sensing method was affected by changing the pacing vector. The LV(Tip)-->Can ER(min) was significantly decreased at the 1.0-ms pulse duration when compared to 0.4-ms (p < 0.05). During BiV pacing, LV(Tip)-->Can ER(min) increased at negative interventricular delays and decreased at positive interventricular delays relative to simultaneous pacing. LV(Tip)-->Can resulted in fewer patients with sufficient ER characteristics for capture detection, albeit only significantly at the extended pulse duration (79% vs 97%, p < 0.05) and at simultaneous and positive interventricular delays (81% vs 97%, p < 0.05).

CONCLUSIONS

Though LV capture detection was feasible using both investigated methods, the RCC method (LV(Tip)-->Can) sensitivity to the evaluated pacing parameters suggests the IPS method (LV(Ring)-->Can) provides a more robust performance.

Comparison of optical and electrical mapping of fibrillation

Optical recordings with transmembrane potential (Vm)-sensitive fluorescent dye, or extracellular potential (Ve) recordings are used to map spatiotemporal patterns of cardiac excitation during ventricular fibrillation (VF). While the optical and electrical methods are accepted, there has not been a test of whether they yield equivalent excitation times during VF. Times may differ since previous results indicate optical Vm interrogates deeper than Ve. We tested whether the steepest parts of the downward deflection of the Ve and upward deflection of optical Vm are synchronized during VF. We used simultaneous coepicentral optical and electrical mapping (32 spots, 4 kHz) with translucent indium tin oxide electrodes and a laser scanner on ventricular epicardium. VF was electrically induced in arterially-perfused rabbit hearts stained with di-4-ANEPPS. For both the optical and electrical deflections, maximum magnitudes of the slopes varied over a > 4 fold range, morphologies varied and spatiotemporal distributions were nonuniform. Time differences between the steepest parts of the optical and electrical deflections were typically a few ms. Standard deviations of time differences increased for the deflections that had the smaller slopes, which was only partly due to effects of recording noise as indicated by simulations. For deflections that had slopes ranging from the steepest found at each spot to 1/4 of the steepest, the optical deflections were on average 0.7-1 ms earlier than the Ve deflections. Thus, excitation times during VF measured optically and electrically differ. Considered together with our earlier results indicating that the optical Vm interrogates deeper than Ve, the results suggest that most fibrillatory excitations occur earlier in subsurface tissue than at the heart surface.

Acute performance evaluation of a new ventricular automatic capture algorithm

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 INSIGNIA 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.

Use of Automatic Threshold Tracking Function with Non-Low Polarization Leads:. Risk for Algorithm Malfunction

The AutoCapture (AC) function of new pacemakers (PM) from St Jude Medical (SJM) was originally recommended for use with low polarization (LP) ventricular leads only.However, recent reports have encouraged the use of the AC function with various leads, including those lacking a special LP design. The objective of this study was to analyze the reliability and safety of the AC algorithm application with different types of pacing leads. The study group comprised 30 consecutive patients with AC PMs connected to three different types of non-LP leads. Ten patients with SJM LP leads served as the control group. The study protocol included a complete AC function test using four different pulse widths (PW). The pacing threshold was independently assessed by a manual/semiautomatic check. Erratic behavior of polarization measurements with increasing PWs was demonstrated in 43% (n = 13) of the study group. Invalid polarization measurements resulted in erroneous algorithm recommendation to apply AC function in 17% (n = 5) of the study patients. Subsequent AC function activation lead to incorrect threshold determination due to missed noncapture in three patients. AC function should be applied with caution with non-LP leads. "Off label" use of these leads may cause erroneous polarization signal measurements which, in some cases, may result in incorrect pacing threshold determination, rendering a potential risk to dependent patients.

Clinical experience with an automatic threshold tracking algorithm study

The automatic threshold tracking pacing system algorithm developed by St. Jude Medical, verifies ventricular capture beat by beat by recognizing the evoked response (ER) following each pacemaker stimulus. The present automatic threshold tracking function requires a bipolar ventricular lead with low polarization. The aim of this study was to evaluate a new algorithm developed to use with unipolar leads with different levels of polarization. An external pacemaker with the ability to sense intrinsic R waves and measure ER signals, as well as deliver stimulus, was used. An algorithm for detecting the true ER in a unipolar sensing configuration (tip-case) was developed. Based on the assumption that the true evoked R wave amplitude is independent of the stimulation amplitude, the algorithm calculates and subtracts the polarization present at any pacing stimulus from the measured ER. The resulting signal is analyzed to verify capture. This study comprises 35 patients of which 26 were new implants and 9 had chronic leads. The automatic threshold-tracking algorithm was calibrated for each patient and pacing was performed at different pulse amplitudes and pulse duration. Capture was verified for each paced beat. The recordings were stored for later comparison with the tape-recorded intracardiac heart signals. The new algorithm correctly verified capture or loss of capture for every single analyzed beat at the different pacing outputs in every individual patient. The results from this initial study suggests that the new ER detection principle will allow automatic threshold tracking to be used not only with low polarization bipolar leads but with most leads.

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.

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.

CONCLUSION

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.

Interaction of spiral ganglion neuron processes with alloplastic materials in vitro(1)

The cochlear implant (CI) involves the introduction of alloplastic materials into the cochlea. While current implants interact with cochlear neurons at a distance, direct interactions between spiral ganglion (SG) neurites and implants could be fostered by appropriate treatment with neurotrophic factors. The interactions of fibroblasts and osteoblasts with alloplastic materials have been well studied in vitro and in vivo. However, interactions of inner ear neurons with such alloplastic materials have yet to be described. To investigate survival and growth behavior of SG neurons on different materials, SG explants from post-natal day 5 rat SG were cultured for 72 h in the presence of neurotrophin-3 (10 ng/ml) on titanium, gold, stainless steel, platinum, silicone and plastic surfaces that had been coated with laminin and poly-L-lysine. Neurite outgrowth was investigated after immunohistological staining for neurofilament, by image analysis to determine neurite extension and directional changes. Neurite morphology and adhesion to the alloplastic material were also evaluated by scanning electron microscopy (SEM). On titanium, SG neurites reached the highest extent of outgrowth, with an average length of 662 microm and a mean of 31 neurites per explant, compared to 568 microm and 21 neurites on gold, 574 microm and 24 neurites on stainless steel, 509 microm and 16 neurites on platinum, 281 microm and 12 neurites on silicone and 483 microm and 31 neurites on plastic. SEM revealed details of adhesion of neurites and interaction with non-neuronal cells. The results of this study indicate that the growth of SG neurons in vitro is strongly influenced by alloplastic materials, with titanium exhibiting the highest degree of biocompatibility with respect to neurite extension. The knowledge of neurite interaction with different alloplastic materials is of clinical interest, as development in CI technology leads to closer contact of implanted electrodes with surviving inner ear neurons.