Actual pacemaker longevity: the benefit of stimulation by automatic capture verification

Self-powered cardiovascular electronic devices and systems

Cardiovascular electronic devices have enormous benefits for health and quality of life but the long-term operation of these implantable and wearable devices remains a huge challenge owing to the limited life of batteries, which increases the risk of device failure and causes uncertainty among patients. A possible approach to overcoming the challenge of limited battery life is to harvest energy from the body and its ambient environment, including biomechanical, solar, thermal and biochemical energy, so that the devices can be self-powered. This strategy could allow the development of advanced features for cardiovascular electronic devices, such as extended life, miniaturization to improve comfort and conformability, and functions that integrate with real-time data transmission, mobile data processing and smart power utilization. In this Review, we present an update on self-powered cardiovascular implantable electronic devices and wearable active sensors. We summarize the existing self-powered technologies and their fundamental features. We then review the current applications of self-powered electronic devices in the cardiovascular field, which have two main goals. The first is to harvest energy from the body as a sustainable power source for cardiovascular electronic devices, such as cardiac pacemakers. The second is to use self-powered devices with low power consumption and high performance as active sensors to monitor physiological signals (for example, for active endocardial monitoring). Finally, we present the current challenges and future perspectives for the field.

A review of specialized and automated features in implantable cardiac devices

Automated features available in cardiac implantable electronic devices continue to increase in number and complexity. These features are frequently confused with device malfunction and often result in unnecessary clinical attention. This review will serve as an update to some of the more commonly-encountered features discussed in terms of the behavior they exhibit.

Long-term performance of right ventricular pacing leads: risk factors associated with permanent right ventricular pacing threshold increase

Purpose

Right ventricular pacing threshold (RVPT) may rise over time accompanied by the increased use of implantable cardiac pacemakers. However, risk factors for permanent RVPT increase are not fully clarified in patients without definite lead fracture and dislodgment. We aimed to evaluate the long-term performance of RV pacing leads and identify risk factors associated with the occurrence of permanent RVPT increase in this population.

Methods

Patients with first implantation of cardiac pacemakers from January 2008 to June 2016 were consecutively enrolled. Follow-up for RVPT increase was until December 2017. The clinical data, specific data on the pacemaker implantation, and routine follow-up were retrieved.

Results

During a follow-up duration of 5.4 ± 2.1 years, permanent RVPT increase (except lead fracture and dislodgment) was found in 8.4% (87/1033) patients. Patients with permanent RVPT increase had higher prevalence of myocardial infarction (MI), diabetes, and the use of amiodarone. The risk factors independently associated with permanent RVPT increase were MI (HR = 1.094, 95% CI 1.014–1.180, p = 0.031), diabetes (HR = 2.804, 95% CI 1.064–3.775, p = 0.003). MI patients with RVPT increase had higher prevalence of multivessel disease and atrioventricular block. Diabetic patients with RVPT increase exhibited higher serum fasting blood glucose (FBG) and hemoglobin A1c (HbA1c) levels, which were correlated with the maximum RVPT (p < 0.001).

Conclusions

Our data showed that permanent RVPT increases (except lead fracture and dislodgement) during long-term follow-up after pacemaker implantation. The likely risk factors predisposing to chronic permanent RVPT increase are MI and diabetes with higher FBG and HbA1c levels.

Impact of pacemaker longevity on expected device replacement rates: Results from computer simulations based on a multicenter registry (ESSENTIAL)

BACKGROUND

The rate of device replacement in pacemaker recipients has not been investigated in detail.

HYPOTHESIS

Current pacemakers with automatic management of atrial and ventricular pacing output provide sufficient longevity to minimize replacement rate.

METHODS

We considered a cohort of 542 pacemaker patients (age 78 ± 9 years, 60% male, 71% de-novo implants) and combined 1-month projected device longevity with survival data and late complication rate in a 3-state Markov model tested in several Monte Carlo computer simulations. Predetermined subgroups were: age < or ≥ 70; gender; primary indication to cardiac pacing.

RESULTS

At the 1-month follow-up the reported projected device longevity was 153 ± 45 months. With these values the proportion of patients expected to undergo a device replacement due to battery depletion was higher in patients aged <70 (49.9%, range 32.1%-61.9%) than in age ≥70 (24.5%, range 19.9%-28.8%); in women (39.9%, range 30.8%-48.1%) than in men (32.0%, range 24.7%-37.5%); in sinus node dysfunction (41.5%, range 30.2%-53.0%) than in atrio-ventricular block (33.5%, range 27.1-38.8%) or atrial fibrillation with bradycardia (27.9%, range 18.5%-37.0%). The expected replacement rate was inversely related to the assumed device longevity and depended on age class: a 50% increase in battery longevity implied a 5% reduction of replacement rates in patients aged ≥80.

CONCLUSIONS

With current device technology 1/4 of pacemaker recipients aged ≥70 are expected to receive a second device in their life. Replacement rate depends on age, gender, and primary indication owing to differences in patients' survival expectancy. Additional improvements in device service time may modestly impact expected replacement rates especially in patients ≥80 years.

Next-generation pacemakers: from small devices to biological pacemakers

Electrogenesis in the heart begins in the sinoatrial node and proceeds down the conduction system to originate the heartbeat. Conduction system disorders lead to slow heart rates that are insufficient to support the circulation, necessitating implantation of electronic pacemakers. The typical electronic pacemaker consists of a subcutaneous generator and battery module attached to one or more endocardial leads. New leadless pacemakers can be implanted directly into the right ventricular apex, providing single-chamber pacing without a subcutaneous generator. Modern pacemakers are generally reliable, and their programmability provides options for different pacing modes tailored to specific clinical needs. Advances in device technology will probably include alternative energy sources and dual-chamber leadless pacing in the not-too-distant future. Although effective, current electronic devices have limitations related to lead or generator malfunction, lack of autonomic responsiveness, undesirable interactions with strong magnetic fields, and device-related infections. Biological pacemakers, generated by somatic gene transfer, cell fusion, or cell transplantation, provide an alternative to electronic devices. Somatic reprogramming strategies, which involve transfer of genes encoding transcription factors to transform working myocardium into a surrogate sinoatrial node, are furthest along in the translational pipeline. Even as electronic pacemakers become smaller and less invasive, biological pacemakers might expand the therapeutic armamentarium for conduction system disorders.

Clinically guided pacemaker choice and setting: pacemaker expert programming study

Aim

The aim of this multicentre, observational, transversal study was to evaluate pacemaker (PM) choice and setting in a large number of patients, in order to understand their relationship with the patients' clinical characteristics.

Methods and results

The study enrolled a total of 1858 patients (71 ± 14 years, 54% male), consecutively evaluated during scheduled PM follow-up visits in 7 Italian cardiac arrhythmia centres. To evaluate the appropriateness of PM choice in relation to the patients' clinical characteristics, we analysed their rhythm disorders at the time of device implantation and the characteristics of the devices implanted. To evaluate the appropriateness of device setting, current rhythm disorders and device setting at the time of enrolment were analysed. In the overall study population, 64.3% of the patients received a PM with all of the features required for their rhythm disorder [80.8% in persistent atrioventricular (AV) block, 76.5% in atrial fibrillation needing pacing, 71.0% in sinus node disease, 58.7% in non-persistent atrioventricular block (AVB), 52.7% in neuro-mediated syncope]. The most frequent cause of inappropriate PM choice was the lack of an algorithm to promote intrinsic AV conduction in non-persistent AVB patients (38.1%). In 76.2% of the patients with an appropriate PM (n = 1301), the PM was optimally set for their rhythm disorder.

Conclusions

In the present 'real-world' registry, a large number of patients (35.7%) did not receive an optimal PM for their rhythm disorders. Moreover, one-fourth of appropriate PMs were not programmed according to the patients' clinical characteristics.

Using an elastic magnifier to increase power output and performance of heart-beat harvesters

Embedded piezoelectric energy harvesting (PEH) systems in medical pacemakers have been a growing and innovative research area. The goal of these systems, at present, is to remove the pacemaker battery, which makes up 60%-80% of the unit, and replace it with a sustainable power source. This requires that energy harvesting systems provide sufficient power, 1-3 μW, for operating a pacemaker. The goal of this work is to develop, test, and simulate cantilevered energy harvesters with a linear elastic magnifier (LEM). This research hopes to provide insight into the interaction between pacemaker energy harvesters and the heart. By introducing the elastic magnifier into linear and nonlinear systems oscillations of the tip are encouraged into high energy orbits and large tip deflections. A continuous nonlinear model is presented for the bistable piezoelectric energy harvesting (BPEH) system and a one-degree-of-freedom linear mass-spring-damper model is presented for the elastic magnifier. The elastic magnifier will not consider the damping negligible, unlike most models. A physical model was created for the bistable structure and formed to an elastic magnifier. A hydrogel was designed for the experimental model for the LEM. Experimental results show that the BPEH coupled with a LEM (BPEH + LEM) produces more power at certain input frequencies and operates a larger bandwidth than a PEH, BPEH, and a standard piezoelectric energy harvester with the elastic magnifier (PEH + LEM). Numerical simulations are consistent with these results. It was observed that the system enters high-energy and high orbit oscillations and that, ultimately, BPEH systems implemented in medical pacemakers can, if designed properly, have enhanced performance if positioned over the heart.

Automatic atrial capture device control in real-life practice: A multicenter experience

Background

Device-based fully automatic pacing capture detection is useful in clinical practice and important in the era of remote care management.

The main objective of this study was to verify the effectiveness of the new ACAP Confirm® algorithm in managing atrial capture in the medium term in comparison with early post-implantation testing.

Methods

Data were collected from 318 patients (66% male; mean age, 73±10 years); 237 of these patients underwent device implantation and 81 box changes in 31 Italian hospitals. Atrial threshold measurements were taken manually and automatically at different pulse widths before discharge and during follow-up (7±2 months) examination.

Results

The algorithm worked as expected in 73% of cases, considering all performed tests. The success rate was 65% and 88% pre-discharge and during follow-up examination (p<0.001), respectively, in patients who had undergone implantation. We did not detect any difference in the performance of the algorithm as a result of the type of atrial lead used. The success rate was 70% during pre-discharge testing in patients undergoing device replacement.

Considering all examination types, manual and automatic measurements yielded threshold values of 1.07±0.47 V and 1.03±0.47 V at 0.2-ms pulse duration (p=0.37); 0.66±0.37 V and 0.67±0.36 V at 0.4 ms (p=0.42); and 0.5±0.28 V and 0.5±0.29 V at 1 ms (p=0.32).

Conclusions

The results show that the algorithm works before discharge, and its reliability increases over the medium term. The algorithm also proved accurate in detecting the atrial threshold automatically. The possibility of activating it does not seem to be influenced by the lead type used, but by the time from implantation.

Technologies for Prolonging Cardiac Implantable Electronic Device Longevity

Prolonged longevity of cardiac implantable electronic devices (CIEDs) is needed not only as a passive response to match the prolonging life expectancy of patient recipients, but will also actively prolong their life expectancy by avoiding/deferring the risks (and costs) associated with device replacement. CIEDs are still exclusively powered by nonrechargeable primary batteries, and energy exhaustion is the dominant and an inevitable cause of device replacement. The longevity of a CIED is thus determined by the attrition rate of its finite energy reserve. The energy available from a battery depends on its capacity (total amount of electric charge), chemistry (anode, cathode, and electrolyte), and internal architecture (stacked plate, folded plate, and spiral wound). The energy uses of a CIED vary and include a background current for running electronic circuitry, periodic radiofrequency telemetry, high-voltage capacitor reformation, constant ventricular pacing, and sporadic shocks for the cardiac resynchronization therapy defibrillators. The energy use by a CIED is primarily determined by the patient recipient's clinical needs, but the energy stored in the device battery is entirely under the manufacturer's control. A larger battery capacity generally results in a longer-lasting device, but improved battery chemistry and architecture may allow more space-efficient designs. Armed with the necessary technical knowledge, healthcare professionals and purchasers will be empowered to make judicious selection on device models and maximize the utilization of all their energy-saving features, to prolong device longevity for the benefits of their patients and healthcare systems.

Acute performance of a right ventricular automatic pacing threshold algorithm for implantable defibrillators

INTRODUCTION

Automatic pacing threshold (AT) testing with threshold trending and output adjustment may simplify follow-up and improve cardiac rhythm device longevity. The objective of this study was to evaluate the performance of a new right ventricular (RV) AT algorithm for implantable cardioverter defibrillators (ICDs) using RVcoil to Can evoked response sensing.

METHOD

Patients undergoing ICD, with or without cardiac resynchronization therapy device, implant, replacement, or upgrade were enrolled. A pulse generator emulator (Can) was temporarily placed in the device pocket. An external pacing system (Boston Scientific, St. Paul, MN, USA) with customized software was used for performing threshold tests and data acquisition. RV manual threshold and up to four AT tests using various pacing parameters were conducted. The threshold measurement and the capture detection performance of the RV AT tests were evaluated through comparison with visual examination of surface electrocardiogram.

RESULTS

Data from 43 patients were analyzed. A total of 158 AT tests were performed, in which 144 AT tests (91.1%) measured correct threshold values. No consecutive asystolic noncaptured beats were observed in any AT tests, and none of the AT tests resulted in incorrectly low threshold measurements. The difference between manual and AT measurements was -0.05 ± 0.43 V. The accuracy for detecting capture and noncaptured beats were 95% and 99%, respectively.

CONCLUSION

The RVcoil to Can evoked response sensing based RV AT algorithm can reliably measure pacing threshold for ICDs, including CRT-Ds.

Automatic adjustment of stimulation output in resynchronization therapy: impact and effectiveness in clinical practice

BACKGROUND

Algorithms for automatic pacing output adjustment have been implemented in pacemakers and implantable defibrillators (ICD) and recently in cardiac resynchronization therapy defibrillators (CRT-D). We assessed the impact and effectiveness of these automatic features.

METHOD AND RESULTS

We prospectively enrolled patients successfully implanted with the following Medtronic CRT-Ds: Concerto [with automatic left ventricular (LV) output management algorithm], Consulta [automatic management of atrial, right ventricular (RV) and LV voltage], and Sentry (only manual voltage adjustments). Patients with complete device data available for at least 12 months were included in the analysis. We analysed data from 739 patients (360 Sentry, 335 Concerto, 44 Consulta). During the first 6 months, the LV pacing amplitude underwent more frequent adjustments in Concerto (63%, P< 0.001) and Consulta (64%, P= 0.047) patients than in Sentry (48%). Similarly, RV and atrial amplitude at 6 months differed from the pre-discharge value more frequently in Consulta (61 and 50%, respectively) than in Sentry patients (33 and 28%, both P< 0.01). The LV pulse amplitude for Concerto and the voltages in the three chambers of Consulta were significantly lower than the corresponding values programmed in Sentry at 6 and 12 months. The proportion of CRT-D interrogations involving manual reprogramming was 97 ± 8% for Sentry, 79 ± 20% for Concerto, and 56 ± 16% for Consulta (all P< 0.001).

CONCLUSIONS

Algorithms for the automatic management of the pacing output reduced pacing output in comparison with the standard manual management approach, with potential optimization of battery longevity. Moreover, they reduced the need to manually reprogram CRT-Ds, suggesting the possibility to simplify CRT-D management and facilitate remote monitoring.

Long-term RV threshold behavior by automated measurements: safety is the standpoint of pacemaker longevity!

BACKGROUND

We studied long-term right ventricular (RV) pacing threshold (RVPT) behavior in patients consecutively implanted with pacemakers capable of automatic output reprogramming tracked by automatic RV threshold measurement (automatic verification of capture [AVC]).

METHODS

All the patients had state-of-the art steroid-eluting bipolar pacing leads and were RV-paced by an AVC algorithm from the three American manufacturers. Follow-up occurred twice in the first year after implantation, then yearly until approaching elective replacement indicator.

RESULTS

Three hundred and twenty-one patients aged 73 ± 12 years were observed for 49 ± 26 months on average. At implantation, RVPT was 0.54 ± 0.2 V at 0.4 ms at an average 774 ± 217 Ω impedance. Forty-one of the 321 patients (12.8%) had a permanent RVPT increase above 1.5 V at 0.4 ms: RVPT was between 1.6 and 2.5 V in 29 of 321 (9%) patients, whereas it was between 2.6 and 3.5 V in seven of 321 (2.2%) patients, and >3.5 V in five of 321 (1.5%) patients. No exit block occurred because of automatic RV output adjustment by AVC algorithms. No predictor of RVPT increase was found at multivariable analysis. The maximum RVPT increase occurred within 12 months from implantation in 19 of 321 (5.9%) patients, between the first and the second year in 12 of 321 (3.7%), between the second and the sixth year in eight of 321 (2.5%), and after the sixth year in two of 321 (0.6%).

CONCLUSION

Despite technologic improvement in lead manufacturing, long-term increase of the RVPT occurs in about 13% of patients, possibly representing a serious safety issue in 3.7% when 2.5 V at 0.4 ms is exceeded. AVC algorithms can improve patients' safety by automatic tailoring of the pacing output to threshold fluctuations, while maximizing device longevity.